Apparatus and methods for micro-scale mechanical testing under flow conditions

Abstract

Embodiments of the present disclosure generally relate to apparatus and methods for micro-scale mechanical testing under flow conditions. In an embodiment, provided a nozzle assembly is provided. The nozzle assembly includes an end piece and an end cone coupled to the end piece. The nozzle assembly further includes a nozzle extending through an inner diameter of the end cone and an inner diameter of the end piece, the nozzle comprising: a plurality of ports formed in a first surface of the nozzle; and a second surface opposite the first surface. The nozzle assembly further includes a piston coupled to the second surface of the nozzle and configured to exert force on the nozzle. Core holders that include the nozzle assembly and core-flooding apparatus that include the nozzle assembly are also described. Core holders described herein may be used to investigate core samples under triaxial stress.

Description

TITLE: APPARATUS AND METHODS FOR MICRO-SCALE MECHANICALTESTING UNDER FLOW CONDITIONSFIELD

[0001] Embodiments of the present disclosure generally relate to apparatus and methods for micro-scale mechanical testing under flow conditions.DESCRIPTION OF RELATED ART

[0002] X-ray tomography technology provides opportunities to visualize and study various aspects of core flooding including three-dimensional fluid occupancies and calculating in situ fluid saturation in natural porous media. Such imaging and information enables researchers to assess formations and designs for oil recovery, CO2 sequestration, and ground subsidence. In laboratory experiments, conventional core holders include a main body made of metal materials such as aluminum, nickel alloys, or titanium. These metal materials, however, absorb significant amounts of X- rays during imaging which results in degraded X-ray image quality and resolution. Therefore, when using conventional core holders made of metal materials, image quality of the rock matrix and the contained fluids in the porous media is poor.

[0003] Conventional carbon fiber core holders, which may be used for imaging, can be used at elevated pressures and temperatures. However, such pressures and temperatures are not reflective of actual field conditions for most subsurface systems. In addition, actual conditions observed in the field include various stresses on porous media — including both radial stress and axial stress. Investigating porous media under such conditions is not possible using conventional core holders. Overall, conventional technologies have not achieved core holders having both imaging abilities and abilities to withstand actual conditions that mimic or simulate those observed in the field.

[0004] There is a need for new apparatus and methods for micro-scale mechanical testing under flow conditions.SUMMARY

[0005] Embodiments of the present disclosure generally relate to apparatus and methods for micro-scale mechanical testing under flow conditions. Unlike conventional technologies, embodiments described herein enable placing a coresample under triaxial stress conditions while flowing fluids through the pore space of the core sample. In addition, and unlike conventional technologies, embodiments described herein enable the determination of properties or characteristics of core sample — such as pore space, a redistribution of fluid(s) in the pore space, among others — while applying stress conditions to the core sample and / or flowing fluid(s) through the core sample. For example, embodiments of the present disclosure enable mapping and measuring deformation of the pore space as well as the impact of the deformation on redistribution of fluids in the pore space. In further contrast to conventional technologies, embodiments described herein allow imaging of the core sample, for example, during testing. Embodiments described herein enable investigations on a laboratory scale and then implemented in the field, thereby lowering costs.

[0006] In an embodiment, provided a nozzle assembly is provided. The nozzle assembly includes an end piece and an end cone coupled to the end piece. The nozzle assembly further includes a nozzle extending through an inner diameter of the end cone and an inner diameter of the end piece, the nozzle comprising: a plurality of ports formed in a first surface of the nozzle; and a second surface opposite the first surface. The nozzle assembly further includes a piston coupled to the second surface of the nozzle and configured to exert force on the nozzle.

[0007] In another embodiment, a high-pressure, high-temperature core holder is provided. The core holder includes a core tube defining an outside diameter of the core holder, the core tube formed of an X-ray transparent material. The core holder further includes a flexible internal sleeve in the core tube, the flexible internal sleeve comprising: an inner diameter defining an interior volume of the core holder; and an outer diameter. The core holder further includes a nozzle assembly described herein. The core holder further includes a second end piece opposite the first end piece, the second end piece: adhered to the inner diameter of the core tube with a structural adhesive; and in contact with the outer diameter of the internal sleeve. The core holder further includes a first end cap threadedly coupled to an outer diameter of the first end piece. The core holder further includes a second end cap opposite the first end cap, the second end cap threadedly coupled to an outer diameter of the second end piece. The core holder further includes a second end cone opposite the first end cone,the second end cone: coupled to the inner diameter of the flexible internal sleeve and adapted to seal the interior volume of the core holder; and coupled to an inner diameter of the second end piece.

[0008] In another embodiment, a core-flooding apparatus is provided. The coreflooding apparatus comprises a core holder described herein optically coupled to an X-ray computed tomography scanner system.

[0009] In another embodiment, a method is provided. The method includes placing a core sample in a core holder under triaxial stress conditions while flowing a fluid through a pore space, void space, fracture, or combinations thereof of the core sample, a portion of the core holder made of an X-ray transparent material, the pore space, void space, or fracture being 10 pm or larger. The method further includes performing high-resolution x-ray microtomography of the pore space, void space, fracture, or combinations thereof while the core sample is under the triaxial stress conditions.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] So that the manner in which the above recited features of the present disclosure may be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, may admit to other equally effective embodiments.

[0011] FIG. 1 is an exploded view of a core holder showing various components according to at least one embodiment of the present disclosure.

[0012] FIG. 2A is a cross-sectional view of a core holder according to at least one embodiment of the present disclosure.

[0013] FIG. 2B is a partial cross-sectional view of the core holder of FIG. 2A according to at least one embodiment of the present disclosure.

[0014] FIG. 3 A is a side perspective view of an example end piece according to at least one embodiment of the present disclosure.

[0015] FIG. 3B is a top view of the example end piece shown in FIG. 3A according to at least one embodiment of the present disclosure.

[0016] FIG. 3C is a side cross-sectional view of the example end piece shown in FIG. 3 A according to at least one embodiment of the present disclosure.

[0017] FIG. 3D is a side view of the example end piece shown in FIG. 3A according to at least one embodiment of the present disclosure.

[0018] FIG. 4A is a side view of an example end cone according to at least one embodiment of the present disclosure.

[0019] FIG. 4B is a cross-sectional view of the example end cone shown in FIG. 4A according to at least one embodiment of the present disclosure.

[0020] FIG. 5A is a side perspective view of an example nozzle according to at least one embodiment of the present disclosure.

[0021] FIG. 5B is a top view of the example nozzle shown in FIG. 5A according to at least one embodiment of the present disclosure.

[0022] FIG. 5C is a side cross-sectional view of the example nozzle shown in FIG. 5A according to at least one embodiment of the present disclosure.

[0023] FIG. 5D is a top cross-sectional view of the example nozzle shown in FIG. 5A according to at least one embodiment of the present disclosure.

[0024] FIG. 6A shows a side view of a nozzle assembly for a core holder according to at least one embodiment of the present disclosure.

[0025] FIG. 6B shows a cross-sectional side view of the nozzle assembly in FIG. 6A.

[0026] FIG. 6C shows a top perspective view of the nozzle assembly in FIG. 6A.

[0027] FIG. 7 shows a schematic diagram of the experimental setup used for investigations.

[0028] FIGS. 8 A and 8B show porosity- and saturation-based representative elementary volumes (REVs), respectively. (Swt initial water saturation; Sor. residual oil saturation).

[0029] FIG. 9 shows variations in measured porosity and computed permeability with effective stress.

[0030] FIGS. 10A-10D show grain displacement vectors during the hydrostatic compression. The average displacement magnitude in each cube is represented by the length of the arrow inside and the hatching shows different magnitudes ofdisplacement. The direction of grain displacement is indicated by the orientation of the arrows.

[0031] FIGS. 11 A-l 1C show grain movement simulation showing the track of the grain during the compression process, the grain’s final position after the compression, and area the misalignment. FIG. 11 A: Before alignment, there was an obvious deviation for the same grain at the effective stress of 100 psi and 3,000 psi, which is shown by the arrows; FIG. 11B: grains were roughly matched after the grain translation, however, there was a large area of misalignment; FIG. 11C: after the grain rotation was performed, the area of misalignment decreased, indicating an improved match.

[0032] FIGS. 12A-12C show pore maps obtained under different stress conditions (values: distance between grains; different hatching indicates grains and the pore space).

[0033] FIG. 13 shows volume-weighted pore size distributions at the effective stresses of 100 psi and 3,000 psi.

[0034] FIGS. 14A and 14B show fluid occupancies before and after the compression, respectively. The triangle shows the movement of brine-oil interfaces. The circle highlights a snap-off event triggered as throat size decreased. The rectangle shows an example of the local displacement of oil by water.

[0035] FIGS. 15A-15D show the impact of pore space contraction on oil connectivity: FIGS. 15A and 15B: completely isolated oil globules caused by snap- off; and FIGS. 15C and 15D: partially disconnected oil phase, which remains connected through neighboring throats.

[0036] FIGS. 16A and 16B show fluid occupancies at the end of the imbibition performed before and after the compression, respectively. (Triangle, square: additional displacement of oil by water; circle: facilitated snap-off).

[0037] FIG. 17 shows predicted variations in imbibition relative permeability curves after the compression based on the measured end-point saturations and computed end-point relative permeabilities. (The solid and dashed lines only show the relative positions of the relative permeability curves before and after the compression and may not represent their real values).

[0038] FIG. 18 shows segmented pore maps acquired at different effective stresses (different hatching shows the solid and pore spaces). Pore bodies and throats contracted with the increase in effective stress. Some of the throats were completely closed after the compression (the area bounded by rectangles).

[0039] FIGS. 19A and 19B show water-flooding at the effective stress of 150 psi (1 MPa) or 2,150 psi (14.8 MPa), respectively. (Different hatching shows supercritical carbon dioxide (scCCh), water, and solid; Resolution: 2.47 pm; Solid rectangles: facilitated piston-like / pore-body filling events; solid ellipses: facilitated snap-off; dashed diamonds: additional scCCh trapping caused by facilitated snap-off or saturation hysteresis).

[0040] FIGS. 20 A and 20B show variation in residual scCCh cluster during the dissolution process. (Different hatching shows scCCh, water, and solid; Resolution: 2.47 pm). As scCCh was dissolved into the brine, main terminal menisci (MTMs) moved toward the center of the large pores and snap-off occurred in throats.

[0041] FIG. 21 shows changes in scCCh volume in different pores during the dissolution steps.

[0042] FIG. 22 shows water relative permeabilities during the dissolution processes at the effective stresses of 150 psi (1 MPa) and 2,150 psi (14.8 MPa). (Solid lines: scCCh dissolution in brine; dashed lines: scCCh dissolution in 50% isopropanol and 50% methanol).

[0043] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.DETAILED DESCRIPTION

[0044] Embodiments of the present disclosure generally relate to apparatus and methods for micro-scale mechanical testing under flow conditions. Applications of embodiments described herein may include any suitable formation such as oil recovery, CCh sequestration, and ground subsidence.

[0045] Embodiments described herein are applicable to any suitable porous material, including geomaterials. Geomaterials may include consolidated and unconsolidated sand, soil, conventional rocks of sandstone and carbonate types, aswell as any other suitable geological formations that may be considered unconventional so long as the geomaterial may be characterized or mapped in three dimensions with an X-ray micro-CT scanner. The geomaterial studied is the core sample.

[0046] Accordingly, core samples may include any suitable porous material, including geomaterials. Suitable core samples may include those core sample having pores, void spaces (e.g., area between grains), or fractures that may be imaged by micro-CT. For example, suitable core samples may include those samples having pores that are 10 micron or larger. The core samples may be consolidated porous media or unconsolidated porous media. Unconsolidated porous media may include soil, sand, and sandpacks. Consolidated porous media may include conventional sandstone and carbonates. The porous media may include materials from conventional formations. Conventional formations generally refer to porous media having pore sizes, void space sizes, or fracture sizes of 10 pm or larger and permeabilities above 1 milliDarcy.

[0047] The porous media may include quartz, calcite (CaCCh), feldspar, dolomite (MgCCh), silica, illite, apatite, muscovite, rutile, gypsum, anhydrite, chamosite, clinochlore, zircon, biotite, pyrite, expansible clays, kaolinite, mica minerals, trace minerals, organic matter, or combinations thereof. The porous media may include rock. In some examples, the oil-containing porous media comprises an oil-wet porous media, a mixed-wet porous media, or a weakly water-wet porous media.

[0048] Pores of the porous media may be any suitable pore size. For example, in some embodiments, the pore size (pm) is 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000. Each of the foregoing numbers may be preceded by the word “about,” “at least about,” “less than about,” or “more than about”, and any of the foregoing numbers may be used singly to describe an open- ended range or in combination to describe a close-ended range. For example, and in some embodiments, the pore size may be from about 10 pm to about 30 pm, about 400 pm to 750 pm, less than about 300 pm, or at least about 450 pm.

[0049] As used herein, the term pore is used interchangeably with void space and fracture. For example, although methods are described with respect to pores andcharacterizing the pores, the methods are applicable to void spaces and fractures and characterizing void spaces and fractures. The size of the void space of the porous media as well as the size of the fracture may be the same or similar to that described with the pore size.

[0050] Geomechanical deformation is commonly observed in subsurface systems. However, conventional technologies cannot be used to study, e.g., the impact of pore space deformation on the frequency of different fluid displacement mechanisms at the pore level, such as piston-like advance, pore-body filling, and snap-off events. Even though core-scale experiments may be useful for quantifying the relationship between flow properties and the effective stress, due to the lack of visualization of in situ flow behavior, conventional technologies do not allow for direct monitoring of the underlying pore-scale phenomena responsible for the observed trends. As such, the state-of-the-art lacks methods or apparatus for quantifying various aspects of the pore space deformation and relating the impact of such changes on the fluid-fluid displacements.

[0051] It is challenging when employing conventional core holders made of metal materials to image and visualize rock samples (porous media) and the contained fluids during investigations as conventional core holders are made of X-ray obscuring materials. Those conventional carbon fiber core holders utilized for imaging, however, cannot be used under actual conditions. Actual conditions — those seen in the real world and observed in the field — include triaxial stress. Triaxial stress includes confining stress (radial stress) which is stress in the x and y dimensions. Triaxial stress also includes axial stress, which is stress in the z dimension. That is, conventional technologies have not achieved core holders having, for example, both imaging abilities and abilities to withstand actual conditions, including triaxial stress, that mimic or simulate those conditions observed in the field.

[0052] To overcome these and other challenges, the inventors have discovered new core holders that enable X-ray imaging of core samples and the ability to perform investigations (including X-ray imaging) of fluid flow through core samples under actual conditions including triaxial stress conditions. The core holders of the present disclosure may include:

[0053] (a) a core tube comprised of (or formed of) X-ray transparent material;

[0054] (b) an internal sleeve in the core tube, the internal sleeve comprised of (or formed of) a flexible material. Flexible materials may include, but are not limited to, a fluoroelastomer, such as a fluoroelastomer comprising a copolymer comprising tetrafluoroethylene and propylene;

[0055] (c) triaxial hardware that includes a nozzle assembly on one end of the core tube. The nozzle assembly enables movement of a nozzle of the nozzle assembly toward a core sample in the core holder.

[0056] The core holder configuration described herein is advantaged over conventional core holders, enabling both imaging and investigations of fluid flow through core samples under actual conditions. For example, the carbon fiber of the core tube enables X-ray imaging and maintains mechanical integrity under high stress conditions. The internal sleeve minimizes gas diffusion between the porous media of the core sample and the confining fluid chamber environment. The triaxial hardware enables studying of core samples under actual conditions including triaxial stresses.

[0057] The core holder may optionally include an adhesive (such as an epoxy resin) adhering the core tube to an end piece(s) of the core holder, and the end piece(s) are disposed between the core tube and the internal sleeve. The adhesive may be utilized to provide additional mechanical strength to the core holder by adhering the core tube and the end pieces to one another. The carbon fiber core tube, flexible internal sleeve, triaxial hardware, and optional adhesive allow studies under actual conditions: such as, for example overburden pressures (e.g., such as from about 200 psi to about 7,000 psi, such as from about 1,000 psi to about 7,000 psi, such as from about 2,000 psi to about 5,000 psi); core pressures (from about 200 psi to about 5,000 psi, such as from about 1,000 psi to 4,000 psi); and temperature (e.g., from about 70°F to about 200°F, such as from about 100°F to about 200°F, such as from about 104°F to about 200°F). As described below, the nozzle assembly of the core holder may exert axial stress in a range from about 1 psi to about 7,000 psi, such as from about 1,000 psi to about 7,000 psi, such as from about 2,000 psi to about 5,000 psi.

[0058] FIG. 1 is an exploded view of a core holder 100 showing various components according to at least one embodiment described herein. Core holders described herein include a core tube 105, a first end piece 110a, a second end piece110b, a first end cone 115a, a second end cone 115b, a first end cap 120a, a second end cap 120b, and an internal sleeve 125.

[0059] Core holders described herein may be used to investigate any suitable core sample as described above. The core sample may be cylindrical having any suitable dimensions. For example, the cylindrical core sample may have dimensions of 4 to 12 mm in diameter by 25 to 100 mm in length, though other diameters and lengths are contemplated.

[0060] FIG. 2A is a cross-sectional view of a core holder 200. The core holder 200 includes a core tube 105 that defines a portion of an outer diameter 201c of the core holder 200. The core holder 200 may include an internal sleeve 125 that defines an inner diameter of the core holder 200. Portions of end pieces 110a, 110b may be positioned between the core tube 105 and the internal sleeve 125. Portions of end cones 115a, 115b may be positioned inside an inner diameter of the internal sleeve 125. The end cones 115a, 115b and the inner diameter of the internal sleeve 125 may form an interior volume 202 of the core holder 200. The interior volume 202 may be adapted to accommodate a core sample for investigation, for example, core-flood testing. The core holder 200 may include a first end 201a and a second end 201b. Each of the two ends 201a, 201b may be defined by an end cap 120a, 120b threadedly coupled to an end piece 110a, 110b, respectively. During use, the core holder 200 may be positioned vertically such that the first end 201a is a top end of the core holder 200 and the second end 201b is a bottom end of the core holder 200.

[0061] The core tube 105 may comprise, or is formed of, an X-ray transparent material such as carbon fiber. The carbon fiber of the core tube enables X-ray imaging and maintains mechanical integrity under high stress conditions. The core tube 105 may include a first surface 105a and a second surface 105b. The first surface 105a of the core tube 105 may define an inner diameter of the core tube 105. The second surface 105b may define an outer diameter of the core tube 105 and may define at least a portion of the outer diameter 201c of the core holder 200.

[0062] The core holder 200 may further include a first end piece 110a and a second end piece 110b piece opposite the first end piece 110a. End pieces 110a, 110b (collectively, end pieces 110) may be made of any suitable material such as aluminum or a nickel alloy such as Hastelloy. Each of the end pieces 110 may include: a firstsurface I l la, 111b (collectively, first surface 111); a second surface 112a, 112b (collectively, second surface 112) opposite the first surface 111; a third surface 113a, 113b (collectively, third surface 113); a fourth surface 114a, 114b (collectively, fourth surface 114) opposite the third surface 113; a fifth surface 130a, 130b (collectively, fifth surface 130) opposite the first surface 111; and threads 131a, 131b (collectively, threads 131) defining a portion of the fifth surface 130. The first surface 111 may define an inner diameter of the end piece 110. The second surface 112 may define a first outer diameter of the end piece 110. The fifth surface 130 and threads 131 may define a second outer diameter of the end piece 110, the second outer diameter being outside (and larger than) the first outer diameter of the end piece 110.

[0063] Each end piece 110 may extend a certain length down the core tube 105 such that when the two end pieces 110 are coupled to the core tube 105. The second surface 112 of each end piece 110 may be coupled to, adhered to, or bonded to the first surface 105a of the core tube 105 by an adhesive. The adhesive may be a structural adhesive. The adhesive may be any suitable resin such as an epoxy resin. Suitable epoxy resins may include Hysol epoxy resin. Suitable Hysol epoxy resin may include Henkel Loctite Hysol EA 9394 C-2 Aero Epoxy commercially available from Krayden.

[0064] The second surface 112 of each end piece 110 may have a roughened or textured surface. The roughened / texture surface may increase the coupling, adhering, or bonding strength between the second surface 112 of each end piece 110 and the first surface 105a of the core tube 105.

[0065] FIGS. 3A-3D show different views of end piece 110 according to at least one embodiment of the present disclosure. Specifically, FIG. 3A shows a side perspective view of the end piece 110, FIG. 3B shows a top view of the end piece 110, FIG. 3C shows a side cross-sectional view taken along segment B-B of the end piece 110 shown in FIG. 3B, and FIG. 3D shows a side view of the end piece 110.

[0066] As illustrated in FIG. 3A, the end piece 110 may include interior grooves 140. An o-ring may be positioned in the grooves to seal a confining fluid. The o-ring may be made of any suitable material such as a fluoroelastomer described herein. As illustrated in FIG. 3D, the end piece 110 may include a confining fluid ports 220.Confining fluid may travel through the confining fluid ports 220 to the confining fluid chamber 225.

[0067] The internal sleeve 125 may have a first surface 125a and a second surface 125b opposite the first surface 125a. The first surface 125a of the internal sleeve 125 may define an inner diameter of the internal sleeve 125. The second surface 125b of the internal sleeve 125 may define an outer diameter of the internal sleeve 125. The inner diameter (first surface 125a) of the internal sleeve 125 may define an interior volume of the core holder 200. The interior volume of the core holder 200 may be adapted to receive a core sample for investigations, for example, core-flood testing.

[0068] The internal sleeve 125 may comprise, or may be formed of, a flexible material such as a rubber or an elastomer. The flexibility of the internal sleeve enables confining pressures to be placed on the core sample during investigations. Suitable rubbers or elastomers may include fluoroelastomers, such as those fluoroelastomers comprising a copolymer comprising tetrafluoroethylene and propylene. Examples of fluoroelastomers suitable for use as an internal sleeve may include AFLAS fluoroelastomers commercially available from Seals Eastern Inc. (New Jersey). An example AFLAS fluoroelastomer may include 90 durometer black AFLAS fluoroelastomer (compound 7182B). The fluoroelastomer may minimize gas (CO2, hydrocarbon, etc.) diffusion between the core sample and other portions of the core holder 200.

[0069] The core holder 200 may further include one or more confining fluid ports. In FIG. 2, the core holder 200 includes two confining fluid ports 220a, 220b (collectively, confining fluid ports 220) through which a confining fluid flows. The confining fluid ports 220 may be in fluid communication with a confining fluid chamber 225. The confining fluid chamber 225 may be defined by the core tube 105, the internal sleeve 125, and the two end pieces 110a, 110b. More specifically, the confining fluid chamber 225 may be defined by the first surface 105a of the core tube 105, the second surface 125b of the internal sleeve 125, and the fourth surfaces 114a, 114b of the first and second end pieces 110a, 110b, respectively.

[0070] The confining fluid chamber 225 may be adapted to accommodate a confining fluid, such as mineral oil or other suitable confining fluid, to apply confining pressure to the internal sleeve 125. During use, confining fluid may betransmitted to the confining fluid chamber 225 through the confining fluid ports 220. The internal sleeve 125 may be adapted to contact a core sample in response to a confining pressure applied to the internal sleeve 125 in the confining fluid chamber 225.

[0071] The core holder 200 may further include a first end cone 115a and a second end cone 115b opposite the first end cone 115a. The first end cone 115a and the second end cone 115b may be adapted to seal opposite ends of the interior volume 202 of the core holder 200. The end cones 115a, 115b (collectively, end cones 115) may be made, or formed, of any suitable material such as a nickel alloy, such as Hastelloy. Each end cone 115 may include: a first surface 116a, 116b (collectively, first surface 116); a second surface 117a, 117b (collectively, second surface 117) opposite the first surface 116; a third surface 118a, 118b (collectively, third surface 118); and a fourth surface 119a, 119b (collectively, fourth surface 119). The third surface 118 of the end cone 115 may define a first outer diameter of the end cone 115. The fourth surface 119 of the end cone 115 may define a second outer diameter of the end cone 115. The second outer diameter (the fourth surface 119) of the end cone 115 may be larger than the first outer diameter of the end cone 115. The first outer diameter (the third surface 118) of the end cone 115 may be coupled to, or may contact, the inner diameter (the first surface 125a) of the internal sleeve 125. The second outer diameter (the fourth surface 119) of the end cone 115 may be coupled to, or may contact, the first surface 111 (inner diameter) of the end piece 110. FIGS. 4A and 4B show a side view and a cross-sectional view, respectively, of end cone 115 according to at least one embodiment of the present disclosure. The cross-sectional view of the end cone 115 shown in FIG. 4B is taken along segment A-A of the end cone 115 shown in FIG. 4 A.

[0072] The end cones 115 and the internal sleeve 125 may define the interior volume 202 of the core holder 200. Specifically, the interior volume 202 of the core holder 200 may be defined by the first surface 116a of the first end cone 115a, the first surface 116b of the second end cone, and the first surface 125a (inner diameter) of the internal sleeve 125. The third surface 118 (first inner diameter) of the end cone 115 may be adapted to fit inside the internal sleeve 125 and may be coupled to the first surface 125a (inner diameter) of the internal sleeve 125. The fourth surface 119(second outer diameter) of the end cone 115 may be coupled to the first surface 111 (inner diameter) of the end piece 110. One or more o-rings may be located on the second outer diameter (the fourth surface 119) of the end cone 115. For example, the one or more o-rings may be located on the second outer diameter (the fourth surface 119) of the end cone 115 and may fit into an interior groove 140 of the end piece 110. The one or more o-rings may be used to prevent confining fluid from exiting the confining fluid chamber. The one or more o-rings may be made of any suitable material such as a fluoroelastomer described herein.

[0073] The core holder 200 may further include a first end cap 120a and a second end cap 120b opposite the first end cap 120a. The first end cap 120a and the second end cap 120b may define the first end 201a and the second end 201b, respectively, of the core holder 200. Each of the end caps 120a, 120b (collectively, end cap 120) may include: (i) a first surface 121a, 121b (collectively, first surface 121); (ii) a second surface 135a, 135b (collectively, second surface 135) perpendicular to the first surface 121 of the end cap 120, the second surface 135 of the end cap 120 defining an inner diameter of the end cap 120; (iii) a third surface 136a, 136b (collectively, third surface 136) perpendicular to the first surface 121 of the end cap 120, the third surface 136 of the end cap 120 defining an outer diameter of the end cap 120; and threads 122a, 122b (collectively, threads 122) defining at least a portion of the second surface 135 of the end cap 120. The first surface 121 of the end cap 120 may have a diameter that matches, or is near to, the inner diameter (second surface 135) of the end cap 120.

[0074] The end cap 120 may be secured to the end piece 110 via the threads 122 of the end cap 120 and the threads 131 of the end piece 110. The first surface 121 may trap the end piece 110 and the end cone 115 upon securing the end cap 120 to the end piece 110. The end caps 120a, 120b may further include sidewalls 123a, 123b (collectively, sidewalls 123). The sidewalls 123a, 123b of the end caps 120a, 120b may define an interior volume 124a, 124b, respectively, in which a first nozzle 205a and a second nozzle 205b may be disposed, respectively. The end cap 120 may be made of, or formed from, of any suitable material such as a nickel alloy, such as Hastelloy.

[0075] The first nozzle 205a may be part of a nozzle assembly further described below with respect to FIGS. 6A-6C. Unlike conventional core holders, the first nozzle205a is movable in the z direction in the interior volume 202 by, for example, operation of a piston (not shown). First surface 603a of the first nozzle 205a may contact a core sample positioned in the interior and apply axial stress to the core sample. A portion of the first nozzle 205a may extend into the interior volume 202 as shown in FIG. 2A.

[0076] The first nozzle 205a may be positioned opposite the second nozzle 205b. Each of the first nozzle 205a and the second nozzle 205b may include a plurality of ports 305-308 (shown in FIGS. 5A-5D), such that the first nozzle 205a comprises a first plurality of ports and the second nozzle comprises a second plurality of ports. The plurality of ports 305-308 may be in fluid communication with the interior volume 202 of the core holder 200. The plurality of ports 305-308 of the first nozzle 205 may be operable to inject (e.g., liquids and / or gases) into the interior volume 202 of the core holder 200 and into the core sample. The plurality of ports 305-308 of the second nozzle 205b may be operable to collect fluids from the interior volume 202 and / or the core sample. The outer diameter 315 of the nozzles 205a, 205b may fit into the internal diameters of the end cones 115.

[0077] FIGS. 5A-5D show various views of the nozzles 205a, 205b. Only a portion of first nozzle 205a (corresponding to nozzle 603) is shown FIGS. 5A-5D. The nozzles 205a, 205b may include the plurality of ports 305-308. The nozzles 205a, 205b may include a first end 301 and a second end 302 opposite the first end 301. Each of the plurality of ports 305-308 may include: a fluid entry 305a-308a, proximate to the first end 301 of the nozzles 205a, 205b; a fluid exit 305b-308b located on the second end 302 of the nozzles 205a, 205b; and a volume 305c-308c therebetween.

[0078] As described above, the first nozzle 205a and the second nozzle 205b may be disposed in the respective interior volumes 124a, 124b (collectively, interior volume 124) of the respective end caps 120a, 120b. During investigations, fluids (gases and / or liquids) may be injected into the core sample by flowing such fluids through the plurality of ports 305-308 of first nozzle 205a into the interior volume 202 of the core holder 200 wherein the core sample is located. The fluids may be collected from the core sample by the second plurality of ports of the second nozzle 205b.

[0079] FIG. 6A shows a nozzle assembly 600 according to at least one embodiment of the present disclosure. FIGS. 6B and 6C show different views of the nozzle assembly 600 shown in FIG. 6A. During assembly of a core holder described herein, the nozzle assembly shown in FIGS. 6A-6C may be placed at the first end 201a (top end) of the core holder 200. The nozzle assembly 600 of the core holder may exert axial stress in a range from about 1 psi to about 7,000 psi, such as from about 1,000 psi to about 7,000 psi, such as from about 2,000 psi to about 5,000 psi.

[0080] The nozzle assembly 600 may include an end piece 601 (corresponding to first end piece 110a), an end cone 602 (corresponding to first end cone 115a), a nozzle 603 (corresponding to first nozzle 205a). The nozzle 603 may extend through an inner diameter of the end cone 602 and an inner diameter of the end piece 601.

[0081] First surface 603a of the nozzle 603 may contact a core sample positioned in the interior volume 202 of the core holder 200 and apply axial stress to the core sample. The nozzle 603 may further include a second surface 603b opposite the first surface 603a of the nozzle 603. Screws 605 may be used to fasten the end piece 601 and end cone 602. Two additional screws 604 may be used to provide supporting strength between the nozzle 603 and the end cone 602.

[0082] The nozzle assembly 600 may further include a piston 607 such as a miniature piston. The piston 607 may be directly or indirectly coupled to the second surface 603b of the nozzle 603. The piston 607 may be designed to apply longitudinal (axial) pressure to a core sample positioned in the core holder 200. During use, a fluid such as mineral oil may be injected into the top of the piston 607, which forces the piston 607 to the direction of the nozzle 603. The applied pressure may be transferred to the core sample through the nozzle 603.

[0083] The piston 607 may be positioned by use of two plates 606 and 609 and two screws 608. Plate 606 may be any suitable plate such as a threaded plate. When plate 606 is a threaded plate, the plate 606 may be threadedly coupled to an outer surface of the piston. Plate 609 may be any suitable plate and coupled to nozzle 603. Plate 609 may serve to distribute force from the piston 607 onto nozzle 603. In this example, the piston 607 is indirectly coupled to the nozzle 603 via plate 609.

[0084] The core holders (e.g., core holder 100, core holder 200) described herein may be manufactured in a machine shop. Dimensions and specifications of the coreholders (e.g., core holder 100, core holder 200) may be designed or otherwise configured.

[0085] The core holder 200, as an example apparatus, described herein is useful for performing core-flood tests among other applications. During use, a core sample may be placed in the internal sleeve of the core holder 200. In some implementations, a core-flooding apparatus may include the core holder 200 and an X-ray microcomputed tomography (CT) scanner system coupled (e.g., optically) to the core holder 200. The core-flooding apparatus is adapted to perform a core-flood test. The X-ray micro-CT scanner system may include an X-ray micro-CT scanner for scanning tomography and recording X-ray micro-CT images / scans and a computer system for post-processing of the X-ray CT images. Example post-processing may include, but is not limited to, measuring and analyzing porosity, quantifying fluid saturations, monitoring front movements in the core, calculating recovery factors, or other types of analyses for evaluating effectiveness of hydrocarbon recovery techniques. The X- ray micro-CT scanner system may be used to monitor imbibition or saturation of a core sample. The X-ray micro-CT scanner is a non-destructive tool that is utilized to measure various properties of the core sample and occupancies of fluids in the porous media during core-flood testing.

[0086] In use, the core holder 200 may be assembled by the following nonlimiting procedure. The core tube 105 may be adhered to two end pieces 110 using an adhesive. The internal sleeve 125 may be positioned inside the end pieces 110. Nozzle assembly 600 may be installed on one end of the internal sleeve 125 by screwing the first end cap 120a onto the first end piece 110a (corresponding to end piece 601) via the thread 122a of the first end cap 120a and thread 131a of the first end piece 110a and then tightened using suitable equipment. Second end cone 115b may be installed on the opposite end of internal sleeve 125. An o-ring may be positioned on the outside diameter (the fourth surface 119) of the second cone and / or the outside diameter (the fourth surface 119) of first end cone 115a (corresponding to end cone 602) and in an interior groove of the respective end pieces 110. Second end cap 120b may be screwed onto the second end piece 110b via the thread 122b of the second end cap 120b and thread 131b of the second end piece 110b and then tightened using suitable equipment. A core sample may be positioned inside the internal sleeve 125. Havingthe first nozzle 205a (corresponding to nozzle 603) in place, the second nozzle 205b may be installed into the second end cap 120b.

[0087] The core holder may be positioned vertically and mineral oil may be loaded into the confining fluid chamber 225 via the confining fluid ports 220. The mineral oil applies surrounding stress (confining stress) to the core sample. Mineral oil may be loaded into the top of the piston 607 to apply axial stress to the core sample. During testing, fluids (e.g., a hydrocarbon liquid (e.g., crude petroleum), an aqueous liquid (e.g., brine), a gas (e.g., CO2 gas, N2 gas, methane gas), a supercritical fluid (e.g., supercritical CO2), or combinations thereof) may be injected through the first nozzle 205a (corresponding to nozzle 603) and into the interior volume 202 where it enters the core sample. Such fluids may be collected from the core sample via the second nozzle 205b. During testing, the core sample may be imaged using an X-ray micro-CT scanner system. For examples, pores and pore space of the core sample may be imaged, visualized, and / or characterized while applying triaxial stress to the core sample.

[0088] Embodiments of the present disclosure also relate to methods such as characterizing a pore space of a core sample using the core holder 200 and / or a coreflooding apparatus described herein. As described herein, the term pore is used interchangeably with void space (area between grains) and fracture. For example, although methods are described with respect to pores and characterizing the pores, the methods are applicable to void spaces and fractures and characterizing void spaces and fractures.

[0089] Additionally, or alternatively, methods may include performing, e.g., coreflood testing using the core holder 200 and / or a core-flooding apparatus. As described above, core-flooding apparatus includes or is otherwise coupled to an X-ray micro-CT scanner system 707 (shown in the Examples). Apparatus and methods of using apparatus described herein enable imaging and characterization of the pore space of porous media under triaxial stress conditions and enables researchers to assess formations and designs for oil recovery, CO2 sequestration, and ground subsidence. Suitable core samples used with embodiments of the present disclosure may include those core samples having pores that are 10 pm or larger. Suitable core samples are described herein.

[0090] In at least one embodiment, a method may include placing a core sample in a core holder of embodiments described herein under triaxial stress conditions. Triaxial stress conditions mimic actual conditions observed in the field. Triaxial stress includes confining stress (radial stress) which is stress in the x and y dimensions. Triaxial stress also includes axial stress, which is stress in the z dimension. Radial stress (a confining pressure) may be applied to the internal sleeve 125 the core sample by injecting a confining fluid such as mineral oil into the confining fluid chamber 225 via the confining fluid ports 220. The internal sleeve 125 imparts the radial stress on the core sample. Axial stress may be applied to the core sample by use of nozzle assembly 600. Here, a fluid may be injected into the top of piston 607, which forces the piston to the direction of the nozzle 603. The applied pressure (axial stress) is transferred to the core sample through the nozzle whereby the first surface 603 a of the nozzle 603 contacts the core sample.

[0091] The method may further include flowing one or more fluids (e.g., liquids and / or gases) into the pore space of the core sample. Here, the one or more fluids may be injected into the interior volume 202 of the core holder 200 and into the core sample through the plurality of ports 305-308 formed in the first surface 603a of the nozzle 603. The one or more fluids may enter a pore space of the core sample. Any suitable fluid may be utilized. Suitable fluids may include carbon dioxide (CO2) gas, supercritical CO2 (scCCh), liquid CO2, brine, water, a hydrocarbon (gas or liquid), a mineral oil, or combinations thereof. Fluid may include an X-ray tagging agent such as Nal or other suitable X-ray tagging agent. X-ray tagging agents may be utilized to enhance the contrast between the fluid phases in micro-CT images.

[0092] The method may further include performing high-resolution X-ray microtomography of the pore space while the core sample is under the triaxial stress conditions. Additionally, or alternatively, high-resolution X-ray microtomography of the pore space may be performed while flowing the one or more fluids into the pore space of the core sample. As described herein the core tube 105 may include, or is formed of, an X-ray transparent material such as carbon fiber. The carbon fiber of the core tube 105 enables X-ray imaging and maintains mechanical integrity of the core tube under the high stress conditions.

[0093] The method may include determining a characteristic of the pore space. Any suitable characteristics of the pore space may be determined including dimensions, deformation of the pore space, an impact of deformation on redistribution of a fluid in the pore space, or combinations thereof. Pore space deformation affects the behavior of multiphase flow through porous media including effective permeability, relative permeability, and fluid distributions. Therefore, effective permeability, relative permeability, and fluid distributions of multi-phase flow may also be determined.

[0094] Determining a characteristic of the pore space may include mapping the pore space of the core sample, mapping a deformation of the pore space of the core sample, mapping an impact of deformation on redistribution of fluid in the pore space, or combinations thereof. Additionally, or alternatively, determining a characteristic of the pore space may include measuring a pore space, measuring a deformation of the pore space, measuring an impact of deformation on redistribution of fluid in the pore space, or combinations thereof.

[0095] The method may be part of core-flood testing. As described above, the example core-flooding apparatus includes or is otherwise coupled to an X-ray micro- CT scanner system. A first set of CT images of the core sample may be collected prior to injecting fluids into the core sample. A core-flood test may then be performed on the core sample located inside the interior volume 202 of the core holder 200. A second set of CT images of the core sample may then be collected during or after the core-flood test.

[0096] The core-flood test may include a saturation test. To saturate the core sample, a confining pressure may be applied to the internal sleeve 125 by injecting a confining fluid (e.g., mineral oil) into the confining fluid chamber via the confining fluid ports 220. Confining the core sample ensures that the injected fluids (such as aqueous fluids) are passed through the core sample. Performing the core-flood test may include injecting an aqueous fluid (for example, water, brine, etc.), with or without a chemical additive (e.g., surfactant, polymer, etc.), into the core sample while the confining pressure is applied to the core sample; injecting a hydrocarbon (e.g., crude oil and / or other hydrocarbon fluid) into the core sample while the confining pressure is applied to the core sample; injecting gas (e.g., nitrogen, CO2,CH4, etc.) into the core sample while the confining pressure is applied to the core sample; or combinations thereof. This core-flood test may include collecting CT images during the saturation test. For example, the CT images may be collected during the aqueous fluid saturation phase, the hydrocarbon saturation phase, or both phases. If desired, a gas such as CO2 or a supercritical fluid such as supercritical CO2 may be injected into the core sample before the aqueous fluid is injected.

[0097] The core-flood test may include a flooding test. Performing the core-flood test may include (a) injecting a hydrocarbon (e.g., crude oil and / or other hydrocarbon fluid) into the core sample; (b) injecting an aqueous fluid (water, brine, etc.), with or without chemical additives (e.g., surfactant, polymer, etc.), into the core sample; (c) injecting a gas (e.g., nitrogen, CO2, CP , etc.) into the core sample; or (d) combinations thereof. The injection of the aqueous fluid into the core sample of operation (b) simulates a water flood, while the injection of the gas into the core sample of operation (c) simulates a gas flood. The water flood and the gas flood may include injection of different or additional injection fluids. This core-flood test may include collecting CT images during the flooding test. For example, the CT images during the fluid injection of operation (a), the water flood of operation (b), the gas flood of operation (c), and or combinations thereof may be collected and analyzed to determine fluid saturation. The CT images collected during performance of methods described herein may be used to provide, for example, a core sample saturation history during the core-flood testing. The effectiveness of oil recovery techniques (e.g., effectiveness of the surfactant flood) may be determined based on the series of CT images. Effectiveness of gas sequestration techniques may be determined based on the series of CT images.

[0098] The Examples section provides non-limiting illustrations of methods described herein.

[0099] Embodiments of the present disclosure may be further understood by the following non-limiting examples. The following non-limiting examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use embodiments of the present disclosure, and are not intended to limit the scope of embodiments of the present disclosure.EXAMPLES

[0100] The Examples show use of core holders described herein under conditions that mimic actual conditions observed in the field, including triaxial stresses on porous media. Pore space of the porous media (core sample) may be imaged, visualized, and characterized while the porous media is under triaxial stress.Example I: Core holder

[0101] A core holder was designed to work in harsh conditions that mimic or simulate actual conditions such as high pressure, high-temperature, and triaxial stress. In addition, the core holder having the core sample therein may be scanned by an X- ray computed tomography scanner during high-temperature, high-pressure coreflooding experiments. Overall, core holders described herein enable improved accuracy in characterizing three-dimensional (3D) fluid occupancies and calculating in situ fluid saturation based on computed tomography numbers during X-ray scanned investigations such as core-flooding tests.

[0102] A core holder was designed to accommodate a cylindrical-shaped core sample having a diameter of 10 mm and a length of 75 mm. The core tube was made of carbon fiber to minimize X-ray attenuation. The core holder further included two ends. Each of the two ends included an end cap and an end piece. The end cap and end piece for each of the ends were threadedly connected to one another to lock the end cap to the end piece. End caps and end pieces were made of Hastelloy TMC-276 and aluminum, respectively. A portion of the core tube was adhered to the two end pieces using an adhesive resin. An internal sleeve, which may be made of a fluoroelastomer material, was positioned inside the core tube. The internal sleeve holds the core sample. The fluoroelastomer material may be desired to minimize gas (CO2 and / or hydrocarbon) diffusion between the porous media of the core sample and a confining fluid chamber during core-flooding tests. Both ends of the internal sleeve are installed into end cones. End cones were made of Hastelloy TMC-276. The nozzles are installed into the end caps. During investigation of a pore space of porous media (a core sample), mineral oil was used as a confining fluid. Mineral oil was injected into the confining fluid chamber via confining fluid ports. Fluids (e.g., hydrocarbon liquids, aqueous fluids, and / or gases) were injected into the interior volume of the core holder via the first nozzle. Mineral oil was also injected into thepiston, which forces the piston to the direction of the nozzle. The applied pressure is transferred to the core sample through the first nozzle.

[0103] Overall, core holders described herein enable, for example, improved accuracy in characterizing pore space deformation, three-dimensional fluid occupancies and calculating in situ fluid saturation based on computed tomography numbers during X-ray scanned investigations such as core-flooding tests under triaxial stress conditions.Example II. Pore Space Deformation and Its Implications for Two-Phase Flow Through Porous Media: A Micro-Scale Experimental Investigation

[0104] Pore space deformation significantly affects the behavior of multiphase flow through porous media including effective permeability, relative permeability, and fluid distributions. However, because of the lack of fundamental studies on the mechanisms correlating pore-level fluid displacements with the pore space deformation, no compelling conclusions have been reached to account for observed effects. To explore this correlation, two-phase (oil / brine) flow experiments were performed on a miniature water-wet sandpack under various stress conditions, including triaxial stress conditions, while imaging the pore space and pore fluid configurations using high-resolution X-ray microtomography. Also investigated was: the relationship between pore space deformation and two-phase flow behavior in porous media; the impacts of pore space deformation on the frequencies of different pore-scale fluid displacement mechanisms; and the pore-scale mechanisms that lead to the changes in the relative permeabilities with the effective stress are explored. Such investigations are not possible utilizing conventional core holders.II.1. Introduction

[0105] Geomechanical deformation is commonly observed in environmental and petroleum subsurface systems. Understanding the impact of pore space deformation on multiphase flow in porous media is important for various engineering processes that involve fluid flow in the subsurface, such as hydrocarbon recovery, groundwater remediation and management, CO2 geosequestration, and hydrogen storage.

[0106] Studies have explored the variation in relative permeabilities at different stress conditions. The majority of the investigations to date measured the relative permeabilities by increasing the hydrostatic confining pressure (total stress) while thepore pressure was fixed. However, despite similar experimental procedures, the reported results have been inconsistent and inconclusive. For example, certain studies have determined that the increase in hydrostatic confining pressure caused the relative permeability of the non-wetting phase to decrease significantly, whereas that of the wetting phase remained nearly unchanged. Other studies have demonstrated different trends whereby the relative permeability of the non-wetting phase increased and that of the wetting phase decreased with the confining pressure. In addition to these conflicting observations, other studies found that neither the wetting nor the nonwetting phase relative permeabilities were sensitive to the rock deformation.

[0107] To date, a very limited number of studies have been conducted on the impact of pore space deformation on the frequency of different fluid displacement mechanisms at the pore level, such as piston-like advance, pore-body filling, and snap-off events. Even though core-scale experiments are useful for quantifying the relationship between the flow properties and the effective stress, conventional studies and apparatus do not allow for direct monitoring of the underlying pore-scale phenomena responsible for the observed trends because of the lack of visualization of in situ flow behavior.

[0108] Therefore, quantifying various aspects of the pore space deformation — for example, the pore and throat size distributions, aspect ratio, and coordination number, and relating the impact of such changes on the fluid-fluid displacements, — remain an open area of research. In addition, the results reported in previous studies are inconclusive and controversial as several key factors have been ignored. For example, the observed changes in the relative permeabilities under various stress conditions may not only be caused by the deformation of the pore space, but by other factors such as saturation history and flow rate. Moreover, when crude oil is used as a nonwetting phase during core-flooding experiments, the impact of the pore space deformation on the multiphase flow behavior may be influenced due to the wettability alteration triggered by the direct contact between the crude oil and the rock. Another source of uncertainty in the literature is that the relative permeability at different stress conditions is often determined using multiple core samples with different properties. Furthermore, because the vast majority of previous experiments were conducted on consolidated rock samples under relatively low-pressure conditions, theresults may not correctly reflect the deformation dependency of flow processes in unconsolidated porous systems.

[0109] Herein, a series of two-phase (oil / brine) core-flooding experiments were performed on a miniature sandpack under various stress conditions and the pore space and the residing fluids were imaged using a high-resolution X-ray micro-computed tomography (X-ray micro-CT) scanner. The deformation mechanisms were investigated by tracking the motion of the grains using pore maps acquired under different stress conditions. A pore network model extraction platform was utilized to quantify the deformation of pore bodies and throats, and its subsequent impact on the pore-throat aspect ratios and the coordination numbers of the medium. The effect of pore space deformation on the competition among different fluid displacement mechanisms during the flooding processes, and subsequent changes in fluid saturations and distributions, were assessed by analyzing the 3D fluid occupancy maps. Changes in in situ capillary pressure during both drainage (non-wetting phase displacing wetting phase) and imbibition (wetting phase displacing the non-wetting phase) after compression through interfacial curvature analysis were evaluated to better understand the impact of pore space deformation on fluid displacements. Variations in relative permeabilities after compression were predicted by combining end-point saturations measured from segmented fluid occupancy maps and end-point relative permeabilities computed through direct simulations using commercial software Avizo from FEI.II.2. Experimental

[0110] Core sample. A single cement-free sandpack, 10 mm in diameter and 75 mm in length, was prepared. The sandpack was composed of 17 wt%, 48 wt%, 21 wt%, 7 wt%, and 7 wt% of 60, 70, 80, 100, and 140 mesh, respectively, Northern White monocrystalline sands (100% SiCh) with high sphericity and roundness. This composition mimics an unconsolidated porous medium with a grain size distribution similar to that of the Berea sandstone. Therefore, the sorting of the sand grains in the sample was representative of that in a natural consolidated sandstone. The sand mixture was scanned by a high-resolution micro-CT scanner before subsequent sandpack construction procedures, and its grain size distribution was computed using the image processing and analysis software Avizo from FEI. Dry vibration wasutilized to pack and densify the sandpack. After 3 hours of vibration, the sample was secured by two 50-pm mesh screens and consolidated core samples at both ends. This was followed by partially saturating the sands with distilled water. The water saturation was low enough to provide sufficient space for water expansion. Next, the entire sandpack assembly was immersed in the liquid nitrogen for several hours until the sample was completely frozen. At this stage, it was transported into a core holder or a freezer for long-time preservation.

[0111] Fluids. Soltrol 170 mineral oil was used as the non-wetting phase during the two-phase core-flooding experiments. A brine solution that included 4 wt% NaCl and 7 wt% Nal was used as the wetting and phase during the two-phase core-flooding experiments. Nal (X-ray tagging agent) was added into the brine to enhance the contrast between the two phases in micro-CT images. The brine was degassed by stirring under a -11 psig vacuum until no air bubbles appeared. The Soltrol 170 mineral oil was passed through activated silica gel and alumina to remove the polar components that could potentially alter the wettability of the sample. For reference scans to obtain the pore maps of the sample, the brine solution included only 4 wt% NaCl. The brine solutions with and without the Nal are referred to as doped and nondoped brine, respectively. Selected properties, at 0 psig and 20°C, of the fluids at ambient conditions are shown in Table II-l.Table II- 1

[0112] Experimental Setup. The experimental setup 700, as shown in FIG. 7, included a high-pressure, high-temperature multiphase core-flooding system integrated with a high-resolution X-ray micro-CT scanner. The core-flooding system included a custom-built miniature triaxial core holder 705 made of carbon fiber, six pairs of Quizix™ 5,000 series dual-cylinder pumps 701, two Rosemount™ differential pressure transducers (DPTs) 711a, 711b with different ranges, andHastelloy™ and flexible PEEK tubings. The core sample (sandpack) was placed inside core holder 705. During core-flooding experiments, one pair of pumps 701a was used to inject oil (Soltrol 170) into the sandpack via line LI at a constant rate, one pair of pumps 701b was used to inject the doped brine into the sandpack via line L2 at a constant rate, and one pair of pumps 701c was used to inject non-doped brine into the sandpack via line L3 at a constant rate. Rupture disks (RD) were placed on lines coupled to the pairs of pumps 701. A pair of back pressure regulation pumps 701d received the effluent via line L4 at the outlet of the core holder at a constant pressure. A pair of pumps 701e (via line L7) and a pair of pumps 701f (via line L8) were utilized independently to apply the radial and axial stresses, respectively, to establish a hydrostatic experimental condition using a fluid such as mineral oil. The DPTs 711a, 711b were connected at both ends of the sandpack sample via effluent lines L5 and L6 to record the pressure drop during the experiments. The DPTs were also coupled to manual pump 709. An imaging system 707 is coupled (e.g., optically) to the core holder 705. The imaging system 707 was a high-resolution HeliScan X-ray micro-CT scanner (Thermo Fisher Scientific). The imaging system included an X-ray source integrated with a high-voltage power supply, a sample stage, and a large-area X-ray detector. The detector collected a series of X-ray projections of the sample at pre-defined rotation angles. The projections were then reconstructed using a supercomputer to generate 3D digital structures of the sandpack and the fluid occupancy maps during various stages of the stress and flow experiments. All components outside the micro-CT scanner were connected using corrosion-resistant Hastelloy™ tubing, whereas the flexible PEEK tubing was used inside the micro-CT scanner.Experimental Procedures

[0113] After loading the core sample (sandpack) into a core holder described herein, an initial hydrostatic confining pressure of 100 psig was applied to secure the sandpack. The core holder was vertically mounted on the stage of the micro-CT scanner and connected to the flow system using the PEEK tubing. The sandpack was allowed to thaw inside the CT scanner at ambient temperature for 4 h, and subsequently dried with N2 for an additional 2 h. The remaining N2 was purged out of the system by injecting CO2 for 30 min, and then the sample was vacuumed for 12 h.Afterward, the core sample, nozzles, and PEEK flow lines were fully saturated with the doped brine. The pore pressure and hydrostatic confining stress were then simultaneously increased to 100 psig and 200 psig, respectively, and multiple locations of the sandpack were scanned to confirm 100% brine saturation. Pressure drop values were recorded at 0.1, 0.2, 0.3, and 0.4 cc / min brine flow rates to obtain the initial permeability of the sandpack to brine. Subsequently, the doped brine was displaced with the non-doped brine and the reference scan (Refl) was recorded at a resolution of 2.39 pm. Thereafter, the non-doped brine present in the sandpack was miscibly displaced with the doped brine before the start of two-phase flow tests.

[0114] Experimental procedure for flooding tests. Two cycles of drainage and imbibition flow tests were performed under effective stresses of 100 psi and 3,000 psi. The first drainage test (PD1) was conducted by injecting the oil at a flow rate of 0.02 cc / min while the effective stress was maintained at 100 psi. This process mimics oil migration into an unconsolidated reservoir by which an initial water saturation is established. After reaching the steady-state condition, images were acquired to obtain the initial water saturation and the corresponding fluid occupancy map. The steadystate condition was established when the pressure drop stabilizes and no further changes in the fluid occupancy were observed through consecutive scans.

[0115] This step was followed by an imbibition process (Imbl) at a water flow rate of 0.02 cc / min. The low flow rates used in the drainage and imbibition processes ensured that the displacements during both tests occurred under a capillary-dominated regime (capillary numbers / VCa(Drainage) = 1.06 x 106; ACa(Imbibition) = 4.17 x 107). Micro-CT images obtained at the end of Imbl were utilized to evaluate oil recovery after waterflooding under low effective stress conditions. This step represents waterflooding processes performed at early stages of primary depletion, during which deformation of the pore space is negligible due to minimal pore pressure reduction. Afterward, the initial water saturation and fluid occupancy established at the end of PD1 were restored by a second drainage test (PD2) with the same flow rate of 0.02 cc / min.

[0116] At this point, the flow of the oil was halted, and both radial and axial stresses were gradually increased to 3,100 psig while the pore pressure was maintained at 100 psig. A purpose of stopping the oil injection was to explore theimpact of the rock compression on the oil occupancy during primary depletion. After characterizing the fluid redistribution caused by the compression, oil injection was resumed (PD3) at the same flow rate. Another scan was performed when a steadystate condition was reached, and the new image was compared with the ones obtained after PD1 and PD2 to investigate the effects of pore space contraction on the drainage process. A second imbibition (Imb2) was then conducted at the same flow rate of 0.02 cc / min. The new saturation and fluid occupancy map obtained at the end of this stage were compared with their counterparts obtained before the deformation (e.g., Imbl) to evaluate the efficacy of waterflooding at various stages of production from water-wet unconsolidated reservoirs. Next, the sample was flushed with one hundred pore volumes of methanol, followed by one hundred pore volumes of the non-doped brine, to obtain a new reference scan (Ref2). The absolute permeability of the medium after deformation was measured. A new pore map was then generated by a third reference scan (Ref3) after the effective stress was reduced to 100 psi. The new pore map was compared with its counterpart produced prior to the compression (Refl) to examine whether the sample had experienced plastic deformation.II.3. Data Acquisition and Analysis

[0117] Two types of scans were performed during the flow tests. The first was a succession of rapid survey scans to confirm whether the system had reached a steadystate condition. The second type included scans used for mapping the pore space and the fluid distributions under the steady-state conditions. Table II-2 shows selected parameters used for each scan type. The parameters utilized for each scan type were the same except for the accumulation number (the number of projections acquired at each pre-defined rotation angle), which only affects the acquisition time and the image quality. In Table II-2, FOV refers to field of view.Table 11-2

[0118] The projection images generated after each scan were reconstructed to obtain the raw 3D gray-scale images. The raw 3D images were preprocessed using commercial software, Avizo, before subsequent data analyses using the following steps: first non-local mean and median filters were applied to sharpen the interfaces and remove the internal noise in each phase. By applying the interactive threshold function to the images acquired by the reference scans, the pore maps are extracted, in which the intensities of the grain and the pore space were set to zero and one, respectively. Then, the images obtained after the drainage and imbibition tests were aligned with the ones acquired by reference scans (referred to as image registration). The intensities of the drainage and imbibition images were then multiplied by those in the pore maps so that the intensities of the grains were adjusted to zero, while those of the oil and water phases remained unchanged. Here, an objective was to eliminate segmentation errors caused by the grains and doped brine having similar X-ray intensities. This was followed by the segmentation of oil and brine using an interactive thresholding function. Then, the segmented grains, brine, and oil phases were combined into one single image, which was used for further statistical analysis.

[0119] The pore maps extracted from the reference scans were used to characterize the deformation of the sample at both the macroscale by analyzing volume strain, porosity, and tortuosity, and the microscale by analyzing grain translation and rotation, pore and throat size distributions, aspect ratio, and coordination number. From the final segmented images, quantities such as fluid saturation, pore-fluid occupancy distribution, and hydraulic conductivity to each phase were obtained. These data were subsequently used in the simulations of the oil and brine flow under different stress conditions by directly solving the Navier-Stokes equations, which yielded the corresponding changes in the velocity, pressure, and the effective permeability of each phase after compression. Additionally, the oil-brine interfaces were extracted from the segmented images to quantify local capillary pressures using the Young-Laplace equation:Pc = Pnw - Pw = OT(Eq. 1) wherein: Pcis capillary pressure or the pressure difference across the fluid-fluid interface; Pnwand Pware pressures of the non-wetting and wetting phases, respectively; <J is interfacial tension between the two fluids; and KTis total curvature of the interface, which is equal to the sum of principal curvatures K and K2(that is, KT= K1+ K2).

[0120] The image processing steps for calculating the local capillary pressures are summarized as follows: (1) The segmented image was used as an input to a curvature analysis platform by known methods. (2) The platform first extracted the fluid-fluid interfaces from the segmented images using the Marching Cubes algorithm. (3) Because the interfaces extracted from the voxelized images had stair-like topologies, they were processed using a smoothing algorithm to minimize the impact of voxelization on the curvature calculations. (4) The curvatures were determined at each vertex of every oil / water interface using a finite difference approximation of the second fundamental form of differential geometry. (5) The local capillary pressure of the considered interface was calculated from the mean of the obtained curvatures at different vertices. (6) To investigate the variations in the in situ capillary pressure at different locations of the field of view (FOV) and to more easily process the large image sizes (e.g., 2,100 x 1,700 x 1,900 voxels) captured, the images were partitioned into 16 sub-volumes of 525 x 850 x 950 voxels. (7) The average microscopic curvature for each sub-volume was then obtained using known methods.

[0121] The image segmentation step was conducted three times and averaged each parameter of interest.II.4. Non-limiting Results

[0122] Porosity and saturation values determined from the FOV were representative of those of the entire core sample (sandpack). Geomechanical deformation of the sandpack at macro and micro scales was characterized and the pore-scale fluid displacements and redistributions induced by the contraction of the pore space (under a no-flow boundary condition) was investigated. The impacts of the pore space contraction on the frequency of different pore-scale displacement mechanisms — e.g., piston-like advance, pore-body filling, and snap-off — and the resulting changes in the fluid occupancy, connectivity, velocity, and pressure duringdrainage and imbibition flow processes were also investigated. Variations in the in situ capillary pressure during drainage and imbibition were also examined to further explain the impact of compression on fluid displacement. Changes in relative permeability curves with effective stress were predicted by combining end-point saturations measured from segmented fluid occupancy maps and end-point relative permeabilities computed through direct simulation. Finally, a simplified model of porous media is proposed to help interpret the pore-scale mechanisms that lead to changes in the relative permeabilities after the compression. All such investigations are impossible using conventional core holders.

[0123] Representative Elementary Volume (REV). REV refers to the smallest volume above which the measured properties may be considered representative of the overall corresponding values of the homogeneous sample. To ensure that the brine and oil saturations and porosity measured by microtomography represented the entire core sample, the scanned FOV was larger than the porosity- and saturation-based REVs of the medium. REV was determined by plotting porosity and saturations versus the volumes of sub-samples. As shown in FIGS. 8A and 8B, the porosity- and saturation-based REVs were 0.1 mm3and 2 mm3, respectively, both of which were much smaller than the imaged FOV (e.g., 198 mm3). Variations in porosity and saturations caused by pore space deformation remained constant for sub-samples with volumes greater than 2 mm3. This indicated that the volumetric reduction in the pore space and its impact on the fluid saturation in the FOV represented changes in the entire core sample.

[0124] Geomechanical Deformation. Geomechanical deformation of the sandpack was characterized at both macro and micro scales. Table II-3 shows properties of the sample at different effective stresses.Table 11-3

[0125] At the macro scale, the strain in the sample along the radial (x and y) and axial (z) directions of the Cartesian coordinate system was evaluated by localizing the same particles under different stress conditions. After the compression, the radial strains along the x and j’ directions were 1.04% and 1.15%, respectively, and the axial strain along the z-di recti on was 0.67%. The strain anisotropy was in agreement with the permeability anisotropy found in common reservoir rocks in which the vertical permeability is smaller than the horizontal one. As a result, the volume strain of the sandpack was as large as 2.86% at the effective stress of 3,000 psi. The total pore volume of the sandpack sample decreased by -166 mm3after the compression, while the change in grains’ volume was negligible.

[0126] FIG. 9 shows variations in the porosity and permeability with changes in effective stress. As the effective stress increased from 100 psi to 3,000 psi, the imagebased porosity decreased from 30.19% to 28.17%, and the absolute permeabilities, measured by recording the pressure drops at various flow rates, decreased from 6.55 D to 5.43 D. Additionally, the local permeability of the FOV and its changes due to deformation were evaluated using the absolute permeability computation module provided with the image processing and analysis software Avizo. The module simulated single-phase flow along the z-axis (flow direction) of the sandpack with a constant input velocity and output pressure informed by the physical experiment. During the simulation, a stabilization zone, where pressure was quasistatic and the fluid could freely spread, was created in the front and rear (inlet and outlet) of the segmented pore maps. A one-voxel-wide plane of solid phase, with a no-slip condition, was added to other faces of the image to isolate the sample from the outside. After solving the Navier-Stokes equations using the finite volume method, the permeability was estimated by using Darcy’s law. As shown in FIG. 9, the computed permeabilities agreed with the measurements and decreased from 6.92 to 5.05 D due to the compression. The very small differences between the computed andmeasured permeability values before and after compression may be attributed to the sample’s heterogeneity. The decrease in the absolute permeability was attributed partly to the contraction of the pore space and partly to a slight increase in tortuosity (from 1.73 to 1.78) as the grains moved. After the sample was depressurized, neither the absolute permeability nor the porosity returned to their initial values before the compression, indicating that the sample had deformed plastically.

[0127] At the micro (i.e., pore) scale, various aspects of the geomechanical deformation were investigated, including the translation and rotation of grains, the volumetric changes of pore bodies and throats, and the distortion of pore geometry. Grain translation (changes in the position of grains) was characterized by the vector field in a 1.50 x 1.50 x 1.50 mm sub-volume cropped from the top corner of the FOV (see FIGS. 10A-10D). This sub-volume was further partitioned into 16 cubes, in which the magnitude and direction of the grain displacement were represented by the length and orientation of the arrows. Overall, the grains moved toward the center of the sandpack as it was compressed under the hydrostatic stress condition. However, the arrows in the adjacent cubes varied slightly in both length and orientation, indicating that displacement of the neighboring grains was slightly different in both magnitude and direction. Additionally, strain anisotropy was detected at the pore scale in the grain displacement vector field. As observed in both the x-z and the y-z planes, the extended arrows intersected with the z-axis instead of the origin, indicating that deformation along the radial direction was greater than that along the axial direction.

[0128] The movement of the individual grains during the compression process may be tracked by registering the same particles imaged under different stress conditions. It was observed that grains rotated while moving toward the center of the sample. FIGS 11A-11C illustrate the image registration procedure. The different hatching shows: the grain imaged before the compression and its position during the registration process; the final position of the grain acquired by the scan after the compression, which serves as the reference image during the registration; and the misalignment.

[0129] As shown by the arrows in FIG. 11 A, there was a prominent deviation between the grain’s initial and final positions before registration. After the translation was performed (FIG. 1 IB), the grain moved to its final location. However, thecorrespondence was not perfect (the misalignment) because of the slight deviation in orientation. To quantify the grain rotation, the grains were simplified as ellipsoids and two parameters that characterize their orientation were measured: the angle between the major axis of the grains and the z-axis, cp, and the angle between the projection of the major axis on the horizontal plane and x-axis, 9. By analyzing 100 random grains in the FOV, it was found that each grain rotated individually. The average variations in cp and 9 were ±0.38° and ±0.36°, respectively. This indicated that the grain rotation was insignificant as the grains moved during the compression process. After the grain rotation was conducted, the area of the misalignment decreased, suggesting that a more accurate match had been achieved (see FIG. 11C).

[0130] The deformation of the pore space was visualized directly by comparing the pore maps obtained under different stress conditions. As shown in FIGS. 12A- 12C, most throats contracted (the areas bounded by squares and triangles) or even closed (the areas bounded by circles) as the effective stress increased. However, it was also found that a small number of throats expanded after the compression as shown by the diamonds.

[0131] To quantify the deformation of the pore bodies and throats, two 4.55x4.55x4.55 mm ball-stick pore network models were extracted from the pore maps obtained at the effective stresses of 100 psi and 3,000 psi using the pore network model extraction tool (through maximal ball algorithm) provided with the commercial software PerGeos. The models were then used to compute features of the pore structure before and after the compression, such as the counts and diameters of the pores and throats, the number of throats per pore (i.e., coordination number), and pore-throat size ratio (i.e., aspect ratio). Table II-4 shows selected properties of pores and throats at different effective stresses.Table II-4

[0132] As shown in Table II-4, the sandpack used in the experiments had a larger coordination number and smaller aspect ratio than common consolidated sandstones. After the compression, 6.15% of the original throats were completely closed, resulting in a reduction in the coordination number from 10.57 to 10.19. Additionally, the average equivalent diameter (the diameter of a sphere with the same volume as the irregular pore space) of the pore bodies and throats decreased by 8.28 pm and 6.82 pm, respectively. Because of the different initial sizes, throats contracted by 12.78%, whereas pore bodies contracted by 5.26%. Consequently, the aspect ratio increased from 4.61 to 5.88 after the compression. The properties calculated at the effective stress of 3,000 psi were corrected by removing the extra pore elements that entered the sub-volume during the compression. FIG. 13 shows the volume-weighted size distributions of the pore bodies and throats at different effective stresses. As effective stress increased from 100 psi to 3,000 psi, the size distribution of both the pore body and throat shifted toward the left, indicating the volume reduction of pore bodies and throats. The pore size distribution maintained its shape as the pore diameters decreased, suggesting the deformation was uniform in all pore bodies. The contraction of the large throats was more than that of the small throats, resulting in a narrower distribution with a higher peak value.

[0133] Compression-Induced Fluid Redistribution. To investigate how the pore space contraction contributes to oil production during the primary depletion process, oil injection was stopped before the compression to ensure that fluid displacements / redistributions occurring during the compression stemmed only from the pore space contraction. Fluid occupancies before and after the compression are shown in FIGS. 14A and 14B. Under both stress conditions, oil resided in the center of the large pores, whereas brine occupied the small pores, crevices, and corners. The water tended to be held in place and therefore displaced the oil as the pore space contracted (the areas bounded by triangles and squares in FIGS. 14A and 14B). Consequently, the water saturation increased, and 19.47% (standard deviation: c = 0.8%) of the original oil in place (OOIP) was produced during the compressionprocess. It was also found that the compression process triggered numerous snap-off events in the FOV, which in turn impaired the hydraulic connectivity and conductivity of the oil phase (compare the regions bounded by circles in FIGS. 14A and 14B). Table II-5 shows saturation and volume of each phase in the FOV before and after the compression. The volumes of pores, brine, and oil were corrected by subtracting the additional volume that entered the FOV after the compression.Table II-5

[0134] As shown in Table II-5, the brine volume in the FOV increased by 2.48 mm3(standard deviation: c = 0.34 mm3) after the compression even though no brine was injected into the sample and the additional pore space that had entered the FOV during the compression was cropped out from images. The extra water in the FOV may originate from the portion of the sandpack located near its outlet or from elsewhere in the sample with higher water saturation caused by local heterogeneity.

[0135] Impact of Compression on Drainage. To explore the impact of pore space deformation on the drainage process, the flow of oil was resumed after the compression with the same rate as before (0.02 cc / min), and the new fluid occupancy map obtained at the steady state was compared with those acquired during the previous two drainage tests (i.e., PD1 and PD2) conducted before the compression. Because PD2 is a duplicate of PD1 (with similar saturation and fluid occupancies), PD1 was used to represent the drainage process before the compression in the following discussion. The drainage process conducted after the compression (PD3) established a water saturation (29.57%, standard deviation: c = 0.36%) similar to thatof PD1 (29.94%, standard deviation: o = 0.36%). However, the fluid occupancies before and after the compression were slightly different. Compared to PD1, the overall fluid saturation established by PD3 remained unchanged because of the counterbalance between the suppression and reinforcement of piston-like advance. This result indicated that oil saturation may stay constant as the pore space contracts during primary depletion when other sources of energy support continuous oil flow. Despite constant saturation, ~9% of the OOIP was produced from the sandpack due to the volumetric reduction of the pore space, suggesting that rock compression serves as a driving force for oil recovery during the primary depletion process, particularly in unconsolidated geosystems.

[0136] Impact of Compression on Imbibition. The two waterflooding tests (Imbl and Imb2) conducted at the same flow rate of 0.02 cc / min before and after the compression were compared to investigate the impact of pore space contraction on the imbibition process. Because similar initial water saturations and distributions were established by the preceding drainage tests (PD1 and PD3), differences observed between Imbl and Imb2 were considered the consequence of the pore space contraction. Among the three types of pore-scale displacement mechanisms taking place during imbibition — snap-off, piston-like advance, and pore-body filling, — the latter two, which are governed by the advance of the main terminal menisci (MTMs), are considered the main mechanisms impacting oil recovery in porous systems that are not strongly water-wet. A decrease in pore size leads to an increase in the threshold capillary pressure, meaning that the threshold water pressure above which MTMs may enter the neighboring pore elements is reduced. Hence, both piston-like advance and pore-body filling displacements were facilitated throughout the FOV during the imbibition process as the pore space contracted, resulting in a decrease in the residual oil saturation during Imb2 compared to that of Imbl (see FIGS. 16A and 16B). Snap-off also occurred more frequently as the threshold capillary pressures increased after the compression as shown by the areas bounded by circles in FIGS. 16A and 16B. Because snap-off occurred only in the pore elements where MTMs did not exist, these additional snap-off events triggered by pore space contraction during Imb2 were mainly observed in pore elements in which a large residual oil cluster wasalready trapped during Imbl, resulting in the fragmentation of the large residual oil clusters.

[0137] Variation in In Situ Capillary Pressure Due To Pore Space Contraction. In porous media, immiscible or partially miscible fluid displacements may occur only when in situ local capillary pressure reaches the threshold value of the targeted pore element (i.e., threshold capillary pressure). Therefore, investigating the variations in the in situ capillary pressure with the pore space deformation helps explain changes in fluid saturations and distributions after a change in stress conditions. The in situ local capillary pressures after each step of the experiment were computed by performing interfacial curvature analysis on the pore-fluid occupancy maps. Table II-6 shows average capillary pressure and saturation within the FOV at the end of each step. Before the compression, the two drainage tests (PD1 and PD2) had similar average capillary pressures (3,204 Pa and 3,213 Pa, respectively). The distributions of in situ capillary pressures were slightly different. This might be because PD1 was performed with an initial water saturation of 1, whereas PD2 was conducted with that being 1-Sor. During the compression process, the average in situ capillary pressure within the FOV decreased to 2,429 Pa, which was attributed to the water-to-oil displacements provoked by pore space contraction. During the subsequent PD3 process, the average in situ capillary pressure increased to 3,322 Pa and exceeded the initial values reached after PD1 and PD2 even though similar water saturation had been established. During the imbibition processes, the overall capillary pressure increased after the compression even though the residual oil saturation decreased.Table II-6

[0138] Relative Permeability Simulation. To study the impact of the pore space contraction on the relative permeability, the effective permeability of each phase were computed through direct simulations designed to solve the Navier-Stokes equations on the experimentally-acquired pore-fluid occupancy maps. This was carried out using the same function provided by the Avizo software for computing the absolute permeability. The segmented oil and water phases were utilized as the inputs to compute the effective permeability of each phase. Table II-7 shows measured endpoint saturations and computed absolute permeabilities, computed effective permeabilities, and computed end-point relative permeabilities of each phase before and after the compression. In Table II-7, “comp.” refers to computed values and “meas.” refers to measured values.Table II-7Effective Kabs, D Sw, % ko, D kw, D kro, D k,-w, DProcess stress (psi) (comp.) (meas.) (comp.) (comp.) (comp.) (comp.)100 PD1 6.92 29.94 5.41 0.00 0.78 0.00Imbl 50.58 0.00 2.77 0.00 0.403,000 PD3 5.05 29.57 4.73 0.00 0.94 0.00Imb2 57.54 0.00 2.93 0.00 0.58

[0139] After the compression, the computed effective oil permeability (ko) during drainage decreased from 5.41 D to 4.73 D due to conductivity impairment caused by the pore space contraction and local snap-off events. The end-point relative permeability of oil (kro) increased from 0.78 to 0.94 D after the compression because the decrease in the effective oil permeability (0.68 D) was less than that in the absolute permeability of the medium (1.87 D). Effective water permeability (kw) during imbibition increased from 2.77 D to 2.93 D as a result of increased water saturation. As a result, the end-point relative permeability of water krw increased from 0.40 D to 0.58 D after the compression. FIG. 17 shows the predicted imbibition relative permeability curves before and after the compression based on the measured end-point saturations and the computed end-point relative permeabilities. Both oil andwater relative permeability curves moved to the right (toward higher water saturation) after the compression, indicating that the oil relative permeability increased and water relative permeability decreased at fixed saturations.

[0140] Overall, and unlike conventional core holders, the results indicated that various investigations of core samples may be conducted under actual conditions using embodiments of the present disclosure. In Example II, pore space deformation and its effects on multiphase flow in porous media was investigated using a core holder described herein. Here, a series of two-phase (oil / brine) core-flooding experiments were performed on a miniature water-wet sandpack under various hydrostatic stress conditions. The geomechanical deformation and fluid displacements during drainage and imbibition flow processes were characterized by imaging the pore space and fluid distribution configurations using high-resolution X-ray microtomography .

[0141] The sandpack was compressed after a 29.76% initial water saturation was established by primary drainage to simulate the deformation of unconsolidated reservoirs during primary depletion processes. As the effective stress increased from 100 to 3,000 psi, the volumetric strain of the pore space reached 9.34%, whereas the volumetric strain of the grains was 0, indicating that the compaction of the sandpack was entirely due to the contraction of the pore space rather than the deformation of the solid matrix. The reduction in pore volume led to -19.47% of the OOIP being produced during the compression process when all the fluid injections were halted, while no water left the pore space due to the water-wetness of the sandpack. It was also observed that, as the grains moved during the compression process, their rotation was insignificant compared to their translation (changes in location). Consequently, pore bodies and throats contracted by similar magnitudes (8.28 and 6.82 pm, respectively). However, the deformation of throats appeared to be relatively more prominent than that of pore bodies. This meant that, in the water-wet sandpack, the hydraulic conductivity to the water residing in corners, crevices, and small pores was impaired more by pore space contraction than that to the oil phase occupying the centers of large pores provided that fluid occupancy remained unchanged. As a result, and at a given saturation, the oil relative permeability increased and the water relative permeability decreased after the compression. Comparison of the drainage before andafter the compression indicated that the pore space contraction serves as an important driving mechanism for non-wetting phase production during the primary depletion process from water-wet unconsolidated reservoirs. By comparing the two waterflooding tests performed before and after the compression, it was found that the overall in situ capillary pressure during the imbibition process increased after the compression. Consequently, additional oil was produced during the waterflooding process conducted after the compression.Example III. Micro-Scale Experimental Investigation of the Effect of Pore Space Deformation on Trapping of Supercritical Carbon Dioxide (CO2)

[0142] The impact of pore space deformation on various trapping mechanisms of supercritical CO2 (scCCh) relevant to storage of CO2 in deep saline aquifers was investigated using a core holder of the present disclosure. Here, a series of unsteadystate two-phase brine / scCCh drainage, imbibition, and dissolution tests were performed on a miniature sandpack sample under various stress conditions. High- resolution X-ray microtomography techniques were employed to acquire the pore and fluid occupancy maps at each step of the experiment. The maps were used to characterize the pore space deformation and changes in the frequencies of various pore-scale fluid displacement events. Overall, the results revealed that, during the SCCO2 injection stage, additional SCCO2 was stored in the sandpack sample after the sandpack was compressed. Capillary trapping was impaired by the pore space contraction because all the imbibition displacement mechanisms at the pore scale, including the piston-like advance and snap-off, were facilitated as a consequence of an increase in their threshold capillary pressures. The increased frequency of snap-off events caused additional trapping and displaced SCCO2 from throats by fragmenting large residual SCCO2 clusters into smaller globules. During the dissolution process, the trapped SCCO2 clusters and globules shrank in both pore bodies and throats, resulting in movement of the MTM interfaces and snap-off events, respectively. The water relative permeability during the dissolution process decreased, at a fixed saturation, with the increase in the effective stress since the small pores occupied by the water phase deformed more significantly than the large pores. Such investigations and conclusions therefrom are not possible utilizing conventional core holders.III.1. Introduction

[0143] Carbon capture and storage (CCS) technologies are utilized to mitigate CO2 emissions. CCS refers to technologies utilized for separating CO2 during different stages of industrial processes, transporting CO2 to a storage location (such as a stable geological formation), and isolating CO2 from the atmosphere. CO2 storage technologies mainly involve geological storage, ocean storage, and mineral carbonation. Of these, geological storage, which refers to the injection of CO2 into a stable geological formation, is the most economically viable. Geological storage may be further classified into three categories based on the type of geological formation: oil reservoirs; unmineable coal seams; and deep saline aquifers. Of these, deep saline aquifers are considered to have the largest storage capacity. As CO2 is injected into saline aquifers, the CO2 retains a supercritical state because of the high-pressure and high-temperature conditions caused by the depth of the geological formation. Under such conditions, the fluid has a liquid-like density that establishes the potential to efficiently utilize the underground storage space. Supercritical CO2 (SCCO2) plumes tend to migrate upward in aquifers due to buoyancy. The sealing cap at the top of the aquifer acts as a barrier that prevents it from leaking into the atmosphere. Meanwhile, imbibition occurs at the tail of the scCCh plume due to favorable pressure fields developed by the aforementioned upward movement. As a consequence, a portion of the SCCO2 becomes hydraulically disconnected due to the capillary trapping phenomenon. Because the trapped scCCh is immobile, capillary trapping is considered to be one of the most significant short-term trapping mechanisms in geological storage of scCCh.

[0144] Conventional experimental and simulation studies have been conducted to characterize multiphase flow and trapping of CO2 at macro and micro scales, finding that capillary trapping of scCCh was governed by the wettability of porous media and the displacement patterns and the amount of trapped scCCh depended on capillary and bond numbers. In addition, dissolution of scCCh in the aqueous phase was found to serve as one of the main long-term trapping mechanisms. Once SCCO2 is dissolved into the brine, it migrates with the flow of the brine and is unlikely to recover to a separate phase and be released into the atmosphere again. Dissolution of SCCO2 was often assumed to be instantaneous in numerical modeling. However, conventionalmacro- and micro-scale experimental studies have shown a prolonged depletion of residual scCCh by dissolution.

[0145] In conventional CO2 geosequestration studies, one of the factors that is ignored is the pore space expansion caused by the rising pore pressure during injection. As a consequence, not only the total pore volume of the aquifer but also the displacement threshold capillary pressures, which govern the displacement efficiency during CO2 injection and subsequent imbibition, may change. Therefore, the CO2 volume that may be stored in aquifers may be significantly different from what is expected. Moreover, the water flow behavior during the dissolution process may be affected by variations in the water hydraulic conductivity. Thus, it is useful to investigate the impact of the pore space deformation on various geological storage mechanisms during CO2 geosequestration.

[0146] To this end, and as shown herein, a series of unsteady-state two-phase (brine and supercritical CO2) drainage, imbibition, and CO2 dissolution experiments were performed on a miniature sandpack under various stress conditions using embodiments described herein. These respectively represented the fluid displacements that occur during supercritical CO2 (scCCh) injection, imbibition at the tail of the SCCO2 plume, and dissolution in deep saline aquifers. Pore and fluid occupancy maps at each step of the experiment were imaged using a high-resolution micro-CT scanner and then utilized for characterizing the deformation of the pore space and changes in the frequencies of various fluid displacement events. Variations in local fluid pressure were evaluated by direct simulation, which used a finite volume method to solve Navier-Stokes equations. Moreover, dissolution of trapped scCCh in water at the pore scale was characterized by comparing the fluid configurations imaged at different dissolution stages. The water relative permeability during dissolution under different stress conditions was also measured.III.2. Experimental

[0147] Core Sample. A cement-free sandpack with a diameter of 10 mm and a length of 75 mm was created and used in the core-flooding experiments. The sandpack was a mixture that included 17 wt%, 48 wt%, 21 wt%, 7 wt%, and 7 wt% of 60 mesh, 70 mesh, 80 mesh, 100 mesh, and 140 mesh, respectively, high-roundness and high- sphericity Northern White monocrystalline sands (100% SiCh). Thissandpack mimics the grain size distribution of the Berea sandstone and was representative of natural unconsolidated sandstones. Once the sands were well mixed, the pack was densified by vibration for three hours. Prior to placement in a miniature core holder (e.g., core holders of the present disclosure), the sandpack was partially saturated with distilled water through spontaneous imbibition and then frozen in liquid nitrogen.

[0148] Fluids. The aqueous phase used in the two-phase core-flooding experiment was a 2 wt% NaCl brine solution tagged with 4 wt% Nal. Nal was added to the brine to enhance its contrast with the CO2 in the micro-CT images. Because the brine solution’s grayscale intensity in the images appeared to be similar to that of the sand grains, it was replaced by a brine containing only 2 wt% NaCl before acquiring a reference scan to map the pore space. The brine solutions with and without Nal are labeled as doped and non-doped, respectively. The CO2 phase was maintained at a supercritical state (1250 psig and 50°C) throughout the experiments. Prior to beginning the core-flooding experiments, the doped brine and the scCCh were circulated bypassing the core holder while being supplied from a 1300 cc Hastelloy cell. Properties of the doped brine and scCCh used were estimated from the experimental data (at 1250 psig and 50°C) and are shown in Table III-l.Table III- 1

[0149] Experimental Setup. The experimental setup is a high-temperature and high-pressure core-flooding system integrated with a high-resolution X-ray micro-CT scanner were employed to conduct the flow experiments. Compared to the two-phase core-flooding system shown in FIG. 7, the apparatus included, e.g., a bypass loop and an equilibration cell utilized for equilibrating the fluids before the experiments. A compensation pump was connected to the equilibration cell to replenish the scCCh and make up for the pressure decline caused by scCCh dissolution in brine. Liquid CO2 was supplied from a cylinder and subsequently passed through a secondaryequilibration cell that contained brine before it was further pressurized and injected by the compensation pump into the primary equilibration cell. This pre-equilibration process allowed for the fluids to establish an equilibration state in a shorter amount of time.

[0150] During core-flooding experiments, the equilibrated brine and scCCh stored in the primary equilibration cell were injected into the core sample at constant flow rates by two individual Quizix pumps (with flow rate range and resolution of 0.000031 to 15 cc / min and 0.000001 cc / min, respectively). The effluent was collected at constant pressure by the back pressure regulation pump and discharged into a semienclosed glassware. The compensation pump continued its operation to make up for scCCh injection and maintain the pressure in the primary equilibration cell (with absolute pressure measurement range and accuracy of 0 to 10,000 psi and 0.1 psi, respectively). Two more pumps applied the radial and axial stresses to establish hydrostatic stress conditions. Meanwhile, pressure drops were recorded by Rosemount DPTs (with the differential pressure measurement range and accuracy of 0 to 250 inch of water (inffcO) and 0.01 inffcO, respectively). To maintain the supercritical state of CO2, all coreflooding components except for the liquid CO2 cylinder and core holder were set in an oven with a constant temperature of 50°C. The tubing and the core holder in the micro-CT scanner were heated and insulated by heating and insulation tapes. The pumps, DPTs, liquid CO2 cylinder, and equilibration cells were all connected by corrosion-resistant Hastelloy tubing, and flexible PEEK tubing was used in the micro-CT scanner. The high-resolution HeliScan X-ray micro-CT scanner manufactured by Thermo Fisher Scientific includes an X-ray source, a high-voltage power supply, a sample stage, and a large-area X-ray detector. A series of X-ray projections of the sample were collected at pre-defined rotation angles during the experiments. These projection images were further reconstructed using a supercomputer to generate 3D pore and fluid occupancy maps. Experimental Procedure

[0151] After the frozen core sample was transferred into a core holder of the present disclosure, the entire assembly was vertically mounted on the sample stage of the micro-CT scanner and connected to other core-flooding components. The core holder was left in place for several hours until it thawed completely. Gaseous CO2was then injected at 30 psig to dry the core sample and displace the air left in the pore space. The assembly was then vacuumed overnight and fully saturated with brine. Once 100% water saturation was confirmed at multiple locations by rapid scans, the pore and confining pressures were gradually increased to 1250 psig and 1400 psig, respectively. At this stage, the initial absolute permeability was measured by recording the pressure drop at various brine flow rates and calculating the imagebased porosity by performing a reference scan after displacing the doped brine with its non-doped counterpart. Finally, the non-doped brine was replaced by the doped solution before conducting the two-phase flow tests.

[0152] A series of drainage and imbibition tests were conducted under various stress conditions to investigate the impacts of pore space deformation induced by the injection of scCCh on stratigraphic and capillary trapping of the fluid in deep saline aquifers. To eliminate interference caused by changes in the fluid properties — such as density, viscosity, and interfacial tension, — the effective stress was adjusted by changing the confining pressure and maintaining the pore pressure constant. Because pore space deformation would be less prominent if the sandpack deforms plastically, the two-phase flow tests were first carried out at low and then at high effective stresses. During the experiments, 15 pore volumes (PVs) of scCCh were injected into the sandpack at a constant flow rate of 1.2 cc / min (capillary number: NCa= 5.39 / 107). Afterward, 15 PVs of chase brine were injected at a flow rate of 0.05 cc / min to mimic imbibition at the tail of the scCCh plume. The low brine flow rate allowed for the imbibition to occur under a capillary-dominated flow regime (NCa= 5.87 / 107). This was followed by a bump test, during which another 5 PVs brine was injected at 0.07 cc / min (NCa= 8.22 / 107) to examine whether additional scCCh would be produced.

[0153] At this stage, the scCCh that remained in the pore space was considered hydraulically disconnected and trapped. Subsequently, the trapped scCCh was gradually dissolved by injecting under-saturated brine while measuring the relative permeability of the aqueous phase by recording the pressure drop across the core sample at the flow rates of 0.05 to 0.2 cc / min (NCa= 5.39 / 107to 2.35 / 106). During the dissolution process, configurations of shrinking trapped globules of scCCh were imaged at multiple steps. A chemical solution including 50% isopropanol and 50%methanol, which had a much larger CO2 solubility compared with water, was injected into the sandpack sample to accelerate the scCCh dissolution. Chemical that remained in the pore space was then miscibly displaced by the doped brine. Once a 100% water saturation was confirmed by absolute permeability measurements and quick scans at multiple locations, the sandpack was compressed by gradually increasing the hydrostatic confining pressure to 3400 psig. After the compression, the drainage, imbibition, and dissolution tests were repeated with the same flow rates, and the new fluid occupancy images acquired at each step were compared with their counterparts obtained before the compression.III.3. Image Acquisition and Processing

[0154] During the core-flooding experiments, two groups of scans were conducted. Selected imaging parameters are shown in Table III-2. The first was a succession of rapid monitoring scans. Once two successive fluid occupancy maps acquired by these scans were similar, it was assumed that the sandpack sample and the fluids in the pore space had reached a steady-state condition. The second group was the main scans that were utilized for accurately mapping and quantifying the volume of each phase after the steady-state condition had been established. Based on the objectives, they could be further divided into reference scans, which were used to measure the properties of the pore space, and the two-phase scans for measuring fluid saturations and characterizing the in situ wettability and pore-scale fluid displacements. During the main scans, the detector collected 5 projection images (frame to average=5) at each pre-designed angle. These were subsequently merged into one single projection image to eliminate the noise that was randomly posed during the scans. Table III-2 shows selected parameters used for each scan type. The parameters utilized for each scan type were the same except for the accumulation number — the number of projections acquired at each pre-defined rotation angle, — which only affects the acquisition time and the image quality.Table III-2

[0155] After being reconstructed by a supercomputer, the images were preprocessed and analyzed using Avizo software. Non-local means and median filters were first applied to remove the internal noise in each phase and sharpen the fluid / fluid and fluid / solid interfaces. The images acquired by the reference scans were then segmented using the interactive thresholding function to distinguish the pore space from the solid. Because of the similar grayscale intensities, it was challenging to directly segment the sand grains and the doped brine in the fluid occupancy maps. Therefore, the fluid occupancy maps and the reference scan images were registered and then multiplied the intensities of the former by those of the segmented pore map. Using this approach, the intensity of the sand grains became zero and only the scCCh and doped brine phases remained in the images, which then could be directly segmented using the interactive thresholding function. Finally, the segmented brine, scCCh, and solid phases (as represented by different hatching in FIGS. 19A, 19B, 20A, and 20B), and combined into one image for analysis. By counting the voxels of each phase, the image-based porosity and fluid saturation could be calculated.III.4. Non-limiting Results

[0156] Pore Space Deformation. As the effective stress was increased from 150 to 2,150 psi (1 MPa to 14.8 MPa), the image-based porosity and the absolute permeability of the sandpack sample decreased from 0.32 D and 7.82 D to 0.30 D and 5.00 D, respectively. The reduction in the porosity was constant along the axial direction of the sample, indicating that the sandpack deformed uniformly. At the micro scale, as shown in FIG. 18, adjoining grain particles approached each other with negligible rotation as the effective stress increased. Consequently, the pore volume was reduced, and a portion of the throats were completely closed due to their smaller sizes as shown by the areas bounded by rectangles in FIG. 18. To quantify the pore space deformation, a series of pore space properties under different effectivestress conditions were computed by extracting ball-stick pore network models, in which balls and sticks represent pore bodies and throats, respectively, from the segmented pore maps using a maximal ball algorithm. Table III- 3 shows pore space properties determined at the different effective stresses. As shown in Table III-3, the diameters of both pore bodies and throats decreased approximately by 5 pm as the effective stress was increased from 150 psi to 2,150 psi.Table III-3

[0157] Stratigraphic Storage of scCOi at Various Stress Conditions. As scCCh is injected into deep saline aquifers, the pore space may expand due to an increase in pore pressure. Consequently, both the fluid flow behavior (e.g., velocity and pressure) and the pore-scale displacement threshold capillary pressures (the capillary pressures above / below which drainage / imbibition displacements may occur) may vary, which subsequently affect the frequency of the pore-scale fluid displacement events and hence the amount of the scCCh that could be stored. To investigate the impact of the pore space deformation on the storage capacity, the scCCh injection tests performed at the effective stresses of 150 psi and 2,150 psi were compared. Because they were performed with the same initial conditions (Swt = 1) and injection flow rates, it may be considered that differences in the fluid occupancy were triggered by the pore space deformation. The scCCh occupied the center of large pores, while the water mainly resided in small pores, throats, and comers, indicating a strongly water-wet state. This was further confirmed by the measurements of in situ contact angles. After the effective stress was increased from 150 psi to 2,150 psi, it was found that the piston-like displacements were reinforced although the threshold capillary pressure was increased. Additional water was displaced by invading MTMs from both adjoining pore bodies and throats. As a consequence, the scCCh volume increased even though the pore volume had decreased. Table III-4 shows calculated porosity, pore volume (Vp), scCCh saturation (SC02), and volume (VC02) in the sandpack sample at each step of the experiment. It was found that the impact of the pore space deformation on the storage capacity of scCCh in a brine saturated porous medium was governed by two opposing factors: the local scCCh pressure and displacement threshold capillary pressures.Table III-4

[0158] Residual Trapping Under Various Stress Conditions. As scCCh is injected into deep saline aquifers, its plume tends to migrate upward due to buoyancy until it reaches an ultra-low-permeability seal and then spreads laterally. During this process, the pressure field changes such that it becomes conducive to imbibition by chase brine (brine-to-scCCh displacements) at the tail of the plume. Consequently, a portion of the scCCh is trapped at the center of large pores. To probe the effect of pore space deformation on the residual trapping of scCCh, fluid occupancies acquired after the two chase brine injection experiments conducted at the effective stresses of 150 psi and 2,150 psi were compared. Compared to the scCCh-flooding, the frequency of the fluid displacements during the chase brine injection was affected by the threshold capillary pressure but not pressure gradient. As the effective stress was increased from 150 psi to 2,150 psi, the brine-to-scCCh displacements were facilitated due to the rising threshold capillary pressure as illustrated by the areas bounded by rectangles in FIGS. 19A and 19B. As a result, the volume of scCCh trapped by capillary forces in the pore space decreased after the compression even though additional scCCh had been stored during the preceding scCCh-flooding step. The brine-to-scCCh displacements involved piston-like and pore-body filling controlled by MTMs andsnap-off events governed by the movements of the arc menisci (AMs). Table III-5 shows volume and count of the residual scCO2 clusters / globules in the imaging FOV at different effective stresses.Table III-5

[0159] The residual scCCh in the sandpack sample was mainly comprised of a large scCCh cluster at the effective stress of 150 psi. After the compression, residual scCCh at the effective stress of 2,150 psi fragmented into multiple smaller clusters and globules. As snap-off displaced additional scCCh from throats, the total volume of the residual scCCh was reduced even though the count of the scCCh clusters / globules increased drastically. The frequency of the small scCCh cluster / globule significantly increased as the effective stress increased from 150 to 2,150 psi, whereas the size of the largest cluster reduced substantially. Overall, the capillary trapping of scCO2 was weakened as the effective stress was increased due to pore-scale displacement mechanisms being facilitated.

[0160] scCOi dissolution and water relative permeability. To mimic scCO2 dissolution in deep saline aquifers, under-saturated water was injected into the sandpack sample at the end of each chase brine injection, allowing the trapped CO2 globules to dissolve. The configuration of these disconnected clusters was monitored by imaging them at different injection steps of under-saturated brine (e.g., Dissolution 1, Dissolution 2, etc.). The information was subsequently processed and utilized to characterize the dissolution process at the micro scale. FIGS. 20A and 20B show a 3D example of the MTM movement and the snap-off caused by dissolution. Because SCCO2 dissolution was a dynamic process, the fluid occupancy acquired at different effective stresses continued to change.

[0161] To examine the relative preference of scCCh dissolution in pore elements of different sizes, the inventors evaluated variations in scCCh volume in pores with diameters smaller than 150 pm, diameters between 150 pm and 250 pm, and diameters greater than 250 pm during the dissolution process. Because the majority ofthe pores were within the range of 150 pm to 250 pm, changes in scCCh volume in these pores were much larger than those in other elements. To eliminate the skewed trend in the data, the ratio of the changes in the scCCh volumes to their initial values before the dissolution (at the end of the imbibition experiment) were utilized to evaluate dissolution in different pores. As shown in FIG. 21, 16% of the scCCh in the pores smaller than 150 pm was dissolved during the first stage of the dissolution (Dissolution 1) at the effective stress of 150 psi, while the reduction in the scCCh volume in the pores with sizes between 150 and 250 pm and greater than 250 pm was only 11% and 6%, respectively. Similar trends were also observed during the second dissolution stage at the effective stress of 150 psi and the one after the compression. The results indicated that scCCh dissolution was more favored in smaller pores. FIG. 22 shows the water relative permeability during the dissolution process. At a fixed saturation, the relative permeability measured at the effective stress of 2,150 psi was smaller than that measured at the effective stress of 150 psi. For a given fluid distribution, the effective permeability to water decreased more than the absolute permeability after the compression, resulting in a reduction in the water relative permeability. A similar trend was observed in an imbibition relative permeability study reported in Example II.

[0162] Overall, scCO2 dissolution showed certain similarities to the brine-to- scCO2 imbibition even though the mechanisms at the pore and molecular scales are different. The MTMs moved from throats and small pores to the center of large pores during the dissolution process. Snap-off occurred in throats as SCCO2 molecules were dissolved into the aqueous phase through the AMs. Furthermore, scCCh dissolution was also more favored in smaller pores. At the macro-scale, the water relative permeability during the dissolution decreased with the increase in the effective stress at a fixed saturation due to the higher stress sensitivity of the small pores occupied by the water phase.

[0163] Unlike conventional technologies, embodiments of the present disclosure enable investigation of CO2 storage that mimics actual conditions. As described, the impact of pore space deformation on various scCCh trapping mechanisms in deep saline aquifers — e.g., stratigraphic, capillary, and dissolution trapping — was investigated using a series of two-phase scCCh / brine drainage, imbibition, anddissolution experiments performed on a miniature sandpack sample at various triaxial stress conditions. A high-resolution X-ray micro-CT scanner was employed to image the pore and fluid configurations, which were subsequently used for characterizing the deformation of the pore space and changes in the scCCh volume and saturation.

[0164] As the effective stress increased from 150 to 2,150 psi, the porosity and absolute permeability of the sandpack sample decreased. The average equivalent diameters of both pore bodies and throats decreased. However, due to the different initial sizes, the contraction was relatively more prominent in throats than in pore bodies. Consequently, the aspect ratio and the coordination number increased and decreased, respectively, after the compression. By comparing the two scCCh-flooding tests performed under different stress conditions, it was found that the scCCh volume increased after the compression even though the pore volume had decreased. During the subsequent imbibition tests, piston-like advances and snap-off events were facilitated after the compression. Because the sandpack sample had a large coordination number and small aspect ratio, additional scCCh trapping was not frequently observed. On the other hand, snap-off contributed to the brine-to-scCO2 displacement by providing additional MTMs for the piston-like advances and porebody filling events and fragmenting large scCO2 clusters into smaller globules. Consequently, the amount of trapped SCCO2 decreased after the compression even though additional SCCO2 was stored in the pore space by the preceding SCCO2- flooding test. By comparing the SCCO2 configurations acquired at different stages of the dissolution process, it was found that MTMs moved from small pores and throats toward the center of large pores, resulting in a reduction in the residual scCCh volume. Meanwhile, snap-off was triggered in throats as scCCh molecules were dissolved into the aqueous phase through the AMs. Since most of the brine / scCCh interfaces were located in throats, corners, and small pores, scCCh dissolution was more favored in small pore elements. In relation to the macroscopic flow properties, the water relative permeability during the dissolution process decreased with the increase in the effective stress.EMBODIMENTS LISTING

[0165] The present disclosure provides, among others, the following embodiments, each of which may be considered as optionally including any alternate embodiments:

[0166] Clause 1. A nozzle assembly, comprising: an end piece; an end cone coupled to the end piece; a nozzle extending through an inner diameter of the end cone and an inner diameter of the end piece, the nozzle comprising: a plurality of ports formed in a first surface of the nozzle; and a second surface opposite the first surface; and a piston coupled to the second surface of the nozzle and configured to exert force on the nozzle.

[0167] Clause 2. The nozzle assembly of Clause 1, wherein: the first surface is configured to contact a core sample; and / or the plurality of ports are operable to inject fluids into the core sample.

[0168] Clause 3. The nozzle assembly of any one of Clauses 1 or 2, wherein the nozzle assembly further comprises a plate positioned between the piston and the second surface of the nozzle, the plate distributing force exerted by the piston onto the nozzle.

[0169] Clause 4. The nozzle assembly of any one of Clauses 1-3, wherein the force exerted by the piston and onto the nozzle exerts axial stress on a core sample.

[0170] Clause 5. A high-pressure, high-temperature core holder, comprising: a core tube defining an outside diameter of the core holder, the core tube formed of an X-ray transparent material; a flexible internal sleeve in the core tube, the flexible internal sleeve comprising: an inner diameter defining an interior volume of the core holder; and an outer diameter; a nozzle assembly comprising: a first end piece adhered to an inner diameter of the core tube with a structural adhesive and in contact with the outer diameter of the internal sleeve;a first end cone coupled to an inner diameter of the first end piece, the first end cone further coupled to the inner diameter of the flexible internal sleeve and adapted to seal the interior volume of the core holder; a first nozzle extending through an inner diameter of the first end cone and an inner diameter of the first end piece, the first nozzle comprising: a first plurality of ports formed in a first surface of the first nozzle, the first plurality of ports in fluid communication with the interior volume of the core holder; and a second surface opposite the first surface; and a piston coupled to the second surface of the first nozzle and configured to exert force on the nozzle; a second end piece opposite the first end piece, the second end piece: adhered to the inner diameter of the core tube with a structural adhesive; and in contact with the outer diameter of the internal sleeve; a first end cap threadedly coupled to an outer diameter of the first end piece; a second end cap opposite the first end cap, the second end cap threadedly coupled to an outer diameter of the second end piece; and a second end cone opposite the first end cone, the second end cone: coupled to the inner diameter of the flexible internal sleeve and adapted to seal the interior volume of the core holder; and coupled to an inner diameter of the second end piece.

[0171] Clause 6. The core holder of Clause 5, wherein the interior volume of the core holder accommodates a core sample.

[0172] Clause 7. The core holder of any one of Clauses 5-6, wherein the nozzle assembly is: adapted to exert axial stress on a core sample by action of the piston; and / or adapted to flow fluid into a pore space of the core sample via the first plurality of ports.

[0173] Clause 8. The core holder of any one of Clauses 5-7, wherein the nozzle assembly further comprises a plate positioned between the piston and the secondsurface of the first nozzle, the plate distributing force exerted by the piston onto the first nozzle.

[0174] Clause 9. The core holder of any one of Clauses 5-8, wherein the core holder is adapted to withstand, and operate under: an overburden pressure that is from about 1,000 psi to about 7,000 psi; a core pressure that is from about 200 psi to about 5,000 psi; a temperature that is from about 75°F to about 200°F; or combinations thereof.

[0175] Clause 10. The core holder of any one of Clauses 5-9, wherein the nozzle assembly of the core holder exerts axial stress in a range from about 1,000 psi to about 7,000 psi.

[0176] Clause 11. The core holder of any one of Clauses 5-10, further comprising: a confining fluid port adapted to receive a confining fluid; and a confining fluid chamber in fluid communication with the confining fluid port, the confining fluid chamber adapted to receive the confining fluid, the confining fluid chamber defined by: the core tube; the first and second end pieces; and the internal sleeve.

[0177] Clause 12. The core holder of Clause 11, wherein: the flexible internal sleeve is adapted to contact a core sample in response to a confining pressure applied to the internal sleeve in the confining fluid chamber.

[0178] Clause 13. The core holder of any one of Clauses 5-12, further comprising: a second nozzle opposite the first nozzle, the second nozzle comprising a second plurality of ports, the second plurality of ports in fluid communication with the interior volume of the core holder, the second plurality of ports are operable to collect fluid exiting a core sample.

[0179] Clause 14. The core holder of any one of Clauses 5-13, wherein the X-ray transparent material comprises carbon fiber.

[0180] Clause 15. A core-flooding apparatus, comprising: the core holder of any one of Clauses 5-14, the core holder optically coupled to an X-ray computed tomography scanner system.

[0181] Clause 16. The core-flooding apparatus of Clause 15, wherein the X-ray computed tomography scanner system monitors a core sample comprising porous media having pores, void spaces, or fractures that are 10 pm or greater.

[0182] Clause 17. A method comprising:placing a core sample in a core holder under triaxial stress conditions while flowing a fluid through a pore space, void space, fracture, or combinations thereof of the core sample, a portion of the core holder made of an X-ray transparent material, the pore space, void space, or fracture being 10 pm or larger; and performing high-resolution x-ray microtomography of the pore space, void space, fracture, or combinations thereof while the core sample is under the triaxial stress conditions.

[0183] Clause 18. The method of Clause 17, wherein the method further comprises: determining a characteristic of the pore space, void space, fracture, or combinations thereof.

[0184] Clause 19. The method of any one of Clauses 17 or 18, wherein the determining the characteristic of the pore space, void space, fracture, or combinations thereof comprises: mapping a deformation of the pore space, void space, fracture, or combinations thereof; mapping an impact of deformation on redistribution of a fluid in the pore space, void space, fracture, or combinations thereof; measuring a deformation of the pore space, void space, fracture, or combinations thereof; measuring an impact of deformation on redistribution of fluid in the pore space, void space, fracture, or combinations thereof; or combinations thereof.

[0185] Clause 20. The core holder of any one of Clauses 17-19, wherein the fluid comprises carbon dioxide (CO2), supercritical CO2 (scCCh), brine, water, a hydrocarbon, a mineral oil, or combinations thereof.

[0186] As is apparent from the foregoing general description and the specific embodiments, while forms of the embodiments have been illustrated and described, various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, it is not intended that the present disclosure be limited thereby. Likewise, the term “comprising” is considered synonymous with the term “including.” Likewise whenever a formulation, a composition, an element or a group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same formulation, composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “Is” preceding the recitation of the formulation, composition, element, or elements and vice versa, e.g., the terms“comprising,” “consisting essentially of,” “consisting of’ also include the product of the combinations of elements listed after the term.

[0187] References cited herein are incorporated by reference herein in their entirety to indicate the state of the art as of their publication or filing date and it is intended that this information may be employed herein, if desired, to exclude specific embodiments that are in the prior art.

[0188] For purposes of this present disclosure, and unless otherwise specified, all numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and consider experimental error and variations that would be expected by a person having ordinary skill in the art. For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

[0189] As used herein, the indefinite article “a” or “an” shall mean “at least one” unless specified to the contrary or the context clearly indicates otherwise. For example, embodiments comprising “a fluid” include embodiments comprising one, two, or more fluids, unless specified to the contrary or the context clearly indicates only one fluid is included.

[0190] While the foregoing is directed to embodiments of the present disclosure, other and further aspects of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

ClaimsWhat is claimed is:

1. A nozzle assembly, comprising: an end piece; an end cone coupled to the end piece; a nozzle extending through an inner diameter of the end cone and an inner diameter of the end piece, the nozzle comprising: a plurality of ports formed in a first surface of the nozzle; and a second surface opposite the first surface; and a piston coupled to the second surface of the nozzle and configured to exert force on the nozzle.

2. The nozzle assembly of claim 1, wherein: the first surface is configured to contact a core sample; and the plurality of ports are operable to inject fluids into the core sample.

3. The nozzle assembly of claim 1, wherein the nozzle assembly further comprises a plate positioned between the piston and the second surface of the nozzle, the plate distributing force exerted by the piston onto the nozzle.

4. The nozzle assembly of claim 1, wherein the force exerted by the piston and onto the nozzle exerts axial stress on a core sample.

5. A core holder, comprising: a core tube defining an outside diameter of the core holder, the core tube formed of an X-ray transparent material; a flexible internal sleeve in the core tube, the flexible internal sleeve comprising: an inner diameter defining an interior volume of the core holder; and an outer diameter; a nozzle assembly comprising:a first end piece adhered to an inner diameter of the core tube with an adhesive and in contact with the outer diameter of the internal sleeve; a first end cone coupled to an inner diameter of the first end piece, the first end cone: further coupled to the inner diameter of the flexible internal sleeve and adapted to seal the interior volume of the core holder; a first nozzle extending through an inner diameter of the first end cone and an inner diameter of the first end piece, the first nozzle comprising: a first plurality of ports formed in a first surface of the first nozzle, the first plurality of ports in fluid communication with the interior volume of the core holder; and a second surface opposite the first surface; and a piston coupled to the second surface of the first nozzle and configured to exert force on the nozzle; a second end piece opposite the first end piece, the second end piece: adhered to the inner diameter of the core tube with the adhesive; and in contact with the outer diameter of the internal sleeve; a first end cap threadedly coupled to an outer diameter of the first end piece; a second end cap opposite the first end cap, the second end cap threadedly coupled to an outer diameter of the second end piece; and a second end cone opposite the first end cone, the second end cone: coupled to the inner diameter of the flexible internal sleeve and adapted to seal the interior volume of the core holder; and coupled to an inner diameter of the second end piece.

6. The core holder of claim 5, wherein the interior volume of the core holder accommodates a core sample.

7. The core holder of claim 5, wherein the nozzle assembly is: adapted to exert axial stress on a core sample by action of the piston; and adapted to flow fluid into a pore space of the core sample via the first plurality of ports.

8. The core holder of claim 5, wherein the nozzle assembly further comprises a plate positioned between the piston and the second surface of the first nozzle, the plate distributing force exerted by the piston onto the first nozzle.

9. The core holder of claim 5, wherein the core holder is adapted to withstand, and operate under: an overburden pressure that is from about 1,000 psi to about 7,000 psi; a core pressure that is from about 200 psi to about 5,000 psi; a temperature that is from about 75°F to about 200°F; or combinations thereof.

10. The core holder of claim 5, wherein the nozzle assembly of the core holder exerts axial stress in a range from about 1,000 psi to about 7,000 psi.

11. The core holder of claim 5, further comprising: a confining fluid port adapted to receive a confining fluid; and a confining fluid chamber in fluid communication with the confining fluid port, the confining fluid chamber adapted to receive the confining fluid, the confining fluid chamber defined by: the core tube; the first and second end pieces; and the internal sleeve.

12. The core holder of claim 11, wherein: the flexible internal sleeve is adapted to contact a core sample in response to a confining pressure applied to the internal sleeve in the confining fluid chamber.

13. The core holder of claim 5, further comprising: a second nozzle opposite the first nozzle, the second nozzle comprising a second plurality of ports, the second plurality of ports in fluid communication with the interior volume of the core holder, the second plurality of ports are operable to collectfluid exiting a core sample.

14. The core holder of claim 5, wherein the X-ray transparent material comprises carbon fiber.

15. A core-flooding apparatus, comprising: the core holder of any one of claims 5-14, the core holder optically coupled to an X-ray computed tomography scanner system.

16. The core-flooding apparatus of claim 15, wherein the X-ray computed tomography scanner system monitors a core sample comprising porous media having pores, void spaces, or fractures that are 10 pm or greater.

17. A method comprising: placing a core sample in a core holder under triaxial stress conditions while flowing a fluid through a pore space, void space, fracture, or combinations thereof of the core sample, a portion of the core holder made of an X-ray transparent material, the pore space, void space, or fracture being 10 pm or larger; and performing high-resolution x-ray microtomography of the pore space, void space, fracture, or combinations thereof while the core sample is under the triaxial stress conditions.

18. The method of claim 17, wherein the method further comprises: determining a characteristic of the pore space, void space, fracture, or combinations thereof.

19. The method of claim 17, wherein the determining the characteristic of the pore space, void space, fracture, or combinations thereof comprises: mapping a deformation of the pore space, void space, fracture, or combinations thereof; mapping an impact of deformation on redistribution of a fluid in the pore space, void space, fracture, or combinations thereof;measuring a deformation of the pore space, void space, fracture, or combinations thereof; measuring an impact of deformation on redistribution of fluid in the pore space, void space, fracture, or combinations thereof; or combinations thereof.

20. The method of claim 17, wherein the fluid comprises carbon dioxide (CO2), supercritical CO2 (scCCh), brine, water, a hydrocarbon, a mineral oil, or combinations thereof.

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