Heterogeneous heat transfer structures for geothermal energy recovery

Abstract

Thermally conductive material or coated material / proppants in fracturing treatments for downhole fracturing in a wellbore whereby thermally conductive materials and heat transfer surfaces are utilized in geothermal systems to facilitate and enhance heat distribution and conductance as well as provide for identification, monitoring and location of coated particles, or a combination thereof.

Description

[0001] In the United States Patent Office

[0002] TITLE OF INVENTION

[0003] Heterogeneous Heat Transfer Structures for Geothermal Energy Recovery

[0004] INVENTORS

[0005] Christopher N Fredd, Centennial, Colorado Doug Pipchuk, Calgary, Alberta Canada John Daniels, Houston, Texas

[0006] Dmitriy Potapenko, Houston, Texas

[0007] CROSS-REFERENCE TO RELATED APPLICATIONS

[0008] Non-Applicable

[0009] FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0010] Non-Applicable SPECIFICATION

[0011] Field of the Invention

[0012] The present invention relates generally to thermally conductive materials and heat transfer surfaces in geothermal systems. Specifically, the present system utilizes thermally conductive materials in fracturing treatments to create various heat transfer structures in a subterranean formation.

[0013] Summary

[0014] The present invention relates to improving heat transfer within hydraulic fractures and / or natural fractures in an enhanced geothermal system (EGS) or from natural fractures in closed-loop geothermal systems (e.g., co-axial designs, multiple string designs, or U-shape designs). EGSs rely on hydraulic fracture(s) or reopening of existing fractures to create surface area in the subsurface, thereby increasing injectivity and heat transfer from the subsurface formation to the injected fluids. Propping agents such as sand or ceramic proppants may be pumped into the formation during the hydraulic fracturing treatment to establish hydraulic conductivity to enable flow of the injected fluids during EGS operations. Parameters such as, but not limited to, fluid injection rate, number of fractures, spacing between fractures, and surface area of fractures impact heat transfer. These parameters are commonly expressed as a thermal-type curve for the fracture system.

[0015] The present invention optimizes heat transfer processes by creating heterogeneous heattransfer structures. The term heterogeneous heat-transfer structures for the purpose of the current invention should be understood as any structures created inside the EGS hydraulic fracture system that comprise at least three spatial sections, namely A, B and C, so that spatial section B is positioned between spatial section A and spatial section C, and wherein the thermal conductivity of spatial section B is substantially lower than the thermal conductivity of spatial sections A and C. FIG 1 shows various examples of heterogeneous heat-transfer structures. Here FIGla shows an example of the heterogeneous heat-transfer structure where spatial zones A 1, B 2 and C 3 are not in contact with each other, FIGlb shows an example of the heterogeneous heat-transfer structure where spatial zones A 1 B 2 and B 2, C 2 are in contact with each other not in contact with each other, FIG 1c shows an example of the heterogeneous heat -transfer structure where the spatial zone C is located in the zone 4 with thermal conductivity K2 and spatial zones A 1 and C 3 are located in the zone 5 with heat conductivity gradually changing from KI to K3, FIG Id shows an example of the heterogeneous heat-transfer structure where spatial zones A 1 and C 2 are located in the zone 6 with heat conductivity gradually changing from KI to K3 which also encloses the spatial zone B, and FIG le shows an example of a hydraulic fracture system comprising the main fracture 7 and side fractures 8,9 with spatial zone A 1 located in the side fracture 8 in the zone 10 with thermal conductivity KI, spatial zone C 3 located in the side fracture 9 and main fracture 7 in the zone 11 with thermal conductivity K3, and spatial zone C 2 located in the main fracture 7 and the side fracture 8 in the zone with thermal conductivity K2.

[0016]

[0017] FIG I

[0018] FIG. 1 provides examples of various types of heterogeneous heat-transfer structures. 1 - spatial zone A with heat conductivity KI, 2 - spatial zone B with heat conductivity K2, 3 - spatial zone C with heat conductivity K3, 4 - zone with thermal conductivity K2, 5 - zone with conductivity varying between KI and K3, 6 - zone with conductivity varying between KI and K3 which also encloses spatial zone B, 7 - main fracture, 8 and 9 - side fractures, 10 - zone with thermal conductivity KI, 11 zone with thermal conductivity K3. Solid dashed lines represent trajectory between special zone A and Spatial zone B.

[0019] In a specific embodiment of the present invention the characteristic size of spatial sections A and B and C in their largest dimension may be approximately 1cm, or be approximately 10 cm, or be approximately 1 m, or be approximately 10m. The term approximately for the purpose of the present invention is defined as plus or minus 20 percent (20%). The term “substantially lower” for the purpose of the current invention is defined as “at least two-fold lower”, and the term “substantially higher” means “at least two-fold higher”. The term “plurality” for the purpose of the present invention is defined as “two or more”.

[0020] In a specific embodiment of the present invention heterogeneous heat-transfer structures may comprise a) heat transfer fins and / or b) heat transfer pillars which may be pillar layers (i.e., dunes, streaks or ribbons) with any ratio of length to height, including where the length is greater than the height, within the hydraulic fractures and / or natural fractures, which can be considered analogous to adding fins to a heat exchanger or heat transfer plates to a heated floor, respectively. The length to height ratio may be 0.01 to 1 million.

[0021] The desirable heat transfer material or materials used for creating said heat heterogeneous heat transfer structures preferably have thermal conductivity equal to or greater than 5 W / m / K and lower than 10,000 W / m / K, or equal to or greater than 10 W / m / K and lower than 5,000 W / m / K, or, equal to or greater than 50 W / m / K and lower than 2,000 W / m / K, between 50 -100 W / m / K or between 100 W / m / K and 10,000 W / m / K. One impact of this invention, in the case of EGS in horizontal wells with multistage hydraulic fracturing, is that the same heat production can be accomplished with fewer hydraulic fractures and / or higher injection rate during geothermal operations, both of which improve the overall economics of the management of geothermal systems.

[0022] While strides have been made to overcome the inadequacies of heat conduction and transfer of geothermal heat from subsurface formations, it remains evident that considerable failings remain in art. It is in light of these shortcomings, inventors seeks to remediate the deficiencies of previous inadequate attempts to address the long felt need for efficient and economical transfer of heat-conductive particles into a hydraulic fracture system via any heterogeneous heat conductive particles or structures composed of said heat conductive particles via a system, apparatuses and / or methods of provision thereof, that adequately serves the need of energy transfer, collection and harvesting from subsurface formations to the terrestrial surface for energy production derived from geothermal sources. Moreover, these same systems, devices and methods do not address the facilitation of heat conductive elements of different shapes, sizes, conductivities, densities, or a combination thereof, for the proper transport of heat from within hydraulic fractured systems’ and their respective fractures, natural or man-made, to sufficiently harness subsurface energy as heat for uses as an alternative to existing means of energy production.

[0023] Too, although inventors have set forth the best mode or modes contemplated of carrying out the present invention known to the inventor such to enable a person skilled in the art to practice the present invention, the preferred embodiments are, however, not intended to be limiting, but, on the contrary, are included in a non-limiting sense apt to alterations and modifications, based primarily on several factors (provided herein), all within the scope and spirit of the provided disclosure and appended claims.

[0024] Background

[0025] Enhanced Geothermal Systems (EGS): Geothermal systems require three optimized key elements for maximum efficiency in operation: heat, heat-collecting fluid, and flow conductivity at depth. There are many areas around the world where deeply buried rocks are hot but lack proper flow for adequate conductivity and sufficient operability in traditional geothermal systems. Enhanced geothermal systems rely on the injection of fracturing fluids at high pressure into deep formations to create hydraulic fracture systems. Said fracture systems may comprise a set of interconnected hydraulic fractures and may include a main hydraulic fracture and side fractures, created, for example, by re-opening natural fractures which are connected to said main fracture.

[0026] Propping agents included in the fracturing treatments and / or continuous injection keeps these fractures open after the release or dissipation of the hydraulic pressure, thereby increasing the flow conductivity which allows the heat-collecting fluid to circulate throughout the fractured rock and to transport heat to the surface where this heat can be used or transformed to other forms of energy such as mechanical energy or electricity.

[0027] The fracturing treatment may comprise additives such as particulates and / or fibers to control fluid loss into the formation. In a specific embodiment of the present invention particulated thermally conductive materials or additives may be used for creation of heterogeneous heattransfer system. In one specific embodiment of the present invention, said particulated thermally conductive materials or additives may be placed in the created hydraulic fracture system, including the main and side fractures, or said particulated thermally conductive materials or additives may leak off into complex fractures, natural fractures, and / or bedding planes in the subterranean formation forming fins and / or pillars. Additionally, proppants themselves may be constructed of a coating, partial or complete, which is thermally conductive. Thermally conductive additives, thermally coated proppants, or both may be used in the fracturing treatment, wherein said materials may be alloys, amalgams, and / or combinations of materials, which may themselves be fully or partially thermally conductive, taking on any number of shapes and forms (e.g., irregular, spherical, nearly spherical, substantially rounded, fibrous, powder, macro particles, nano (micro) particles, metal shot / beads, flakes, plates and the like). Expressly, any number of hybrid additives and / or proppants may exist within a single or across multiple areas in a formation.

[0028] BREIF DESCRIPTION OF THE DRAWINGS

[0029] Advantages and other aspects of the invention will be readily appreciated by those having skill in the art and may be better understood with further reference to the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawings and wherein:

[0030] FIGS, la-le depict a representational view of various types of heterogeneous heat-transfer structures.

[0031] FIG. 2 shows relationship between dimensionless water outlet temperature versus dimensionless time for different fracture spacing distances.

[0032] FIG. 3 illustrates a map view of a heterogeneous heat transfer structure.

[0033] FIG. 4 shows Side view of a hydraulic fracture with fins composed of heat transfer materials.

[0034] FIG. 5 depicts a side view of a hydraulic fracture with pillars.

[0035] It should, however, be understood that the above figures and summary are not intended to limit the invention to the particular embodiment in each figure, on the contrary, the invention disclosure is intended to cover all modifications, alternatives and equivalents falling within the spirit and scope of the invention as defined within the claim’s broadest reasonable interpretation consistent with the specification.

[0036] Detailed Description

[0037] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] A detailed description of the preferred embodiments of the invention are provided herewith and described in further detail below. Yet, each and every possible dimension and arrangement, within the limits of the specification, are not disclosed as various permutations are postulated to be in the purview and contemplation of those having skill in the art wherein the present invetion pertains directly to various different configurations based on natural and man-made fractures in subsurface formations. It is therefore possible for those that have skill in the art to practice the disclosed invention while observing that certain features and spatial arrangements are relative and capable of being amended and adapted, arranged and rearranged at various points about the present invention that nonetheless accomplishes the remediation of one or more of the infirmities as outlined and discussed above in the field of procuring of alternative forms of naturally occurring energy sources. As well, the concepts are described singularly, but may occur in multiple arrangements and configurations, which are infinite, so long as details of this disclosure are maintained allowing for the proper functioning of the present invention - which is subject to alternative methods which may fall within the doctrine of equivalents .

[0039] Equally, it should be observed that the present invention can be understood, in terms of both structure and function, from the accompanying disclosure as well as claims taken in context with the associated drawings. And whereas the present invention, system and method of use are capable of several different embodiments and permutations, which can be modified into several different configurations, each exhibiting accompanying interchangeable functionalities without departing from the scope and spirit of the present application as shown and described.

[0040] Succinctly, in cases where there exist man-made (hydraulicly or mechanically-created) and / or natural fractures in the subterranean formation of a closed-loop geothermal system (e.g., co-axial design, multiple string design, or U-shape design), heat transfer fins and / or heat transfer pillars may be utilized in these fractures to enhance the performance of the geothermal system. In such applications, small heat transfer materials (e.g., 100 mesh - smaller than 149 micron; or smaller particles) may be injected into the well at a low pump rate to leak off into fractures. A blend of different particle sizes may be used to promote plugging of the fractures, which would reduce leak off and improve the integrity of the closed-loop system during geothermal operations. Various examples of thermally conductive materials exist with heat conductivity of equal to or greater than 5 W / m / K and lower than 10,000 W / m / K (i.e., ranging from approximately 5 W / m / K to 10,000 W / m / K), or equal to or greater than 10 W / m / K and lower than 5,000 W / m / K, or, equal to or greater than 50 W / m / K and lower than 2,000 W / m / K, between 50 -100 W / m / K or between 100 W / m / K and 10,000 W / m / K include but not limited to metals such as silver (-429 W / m K), copper (-401 W / m K), gold ( -318 W / m K), aluminum (-237 W / m K), tungsten ( -173 W / m K), molybdenum ( -138 W / m K), zinc ( -116 W / m K), nickel ( -91 W / m K), iron (-80 W / m K), platinum (-72 W / m K), palladium ( -72 W / m K), tin ( -67 W / m K), cobalt (-69 W / m K), rhodium (-150 W / m K), iridium (-147 W / m K); alloys such as aluminum bronze ( -60- 70 W / m K), beryllium copper ( -100-200 W / m K), brass (-120 W / m K), bronze (-50-70 W / m K), nickel-silver (Cu-Ni-Zn, -50-60 W / m K), magnesium alloys (Mg-Al-Zn, -50-100 W / m K), titanium alloys (Ti-Al-V, -50-60 W / m K); carbon-based materials such as diamond (-1000-2200 W / m K), graphene (-2000-5000 W / m K), in-plane graphite ( -1500-2000 W / m K), carbon nanotubes (-3000-6000 W / m K), pyrolytic graphite (-1500-2000 W / m K); ceramics and refractory materials such as beryllium oxide (-285 W / m K), aluminum nitride ( -200-250 W / m K), silicon carbide ( -120-200 W / m K), boron nitride (-250-600 W / m K), magnesium oxide (-50-60 W / m K); semiconductor materials such as silicon (-150 W / m K), gallium nitride (-130 W / m K), gallium arsenide (-55 W / m K), indium phosphide (-70 W / m K), boron arsenide (-1300 W / m K), superconductors such as niobium (-54 W / m K), niobium-tin (Nb3Sn, -50-60 W / m K), yttrium barium copper oxide (-50-100 W / m K); composite materials such as copper-diamond composites (-500-1000 W / m K), aluminum-silicon carbide composites (-150-200 W / m K), graphite-epoxy composites (-50-100 W / m K), carbon fiber reinforced polymers (-50-100

[0041] W / m K); and combinations and mixtures thereof. The relationship between dimensionless water outlet temperature versus dimensionless time for different fracture spacings was published by Gringarten et al, 1975 (see FIG.2). This plot is often referred to as the thermal decline type curve. The dimensionless fracture spacing XED is dependent on the ratio of the fracture spacing XE and the effective thermal conductivity of the formation KR. This invention provides a means to increase and the effective thermal conductivity of the formation KR (which will depend on thermal conductivities for both the rock and the heat transfer fins and / or pillars created by means of this invention), which allows for an increase in fracture spacing to deliver the same XED type curve. For example, doubling KR allows for doubling the fracture spacing, thereby reducing the required number of hydraulic fractures along a given horizontal wellbore length in a given EGS project.

[0042] Fig. 3. Dimensionless water outlet temperature versus dimensionless time showing effect of fracture spacing.

[0043] FIG.2

[0044] FIG.2 evidences the relationship between dimensionless water outlet temperature versus dimensionless time for different fracture spacing distances Gringarten et al, 1975 ). For comparison, the thermal conductivity for formation-forming rock materials, such as sandstone, shale, and limestone, is between 2 and 4 W / m / K (See Table 1), about 0.8 W / m / K for concrete, and approximately 0.6 W / m / K for water at 20C. Hence, this invention utilizes heat transfer materials with thermal conductivities of equal to or greater than 5 W / m / K and lower than 10,000 W / m / K (i.e., ranging from approximately 5 W / m / K to 10,000 W / m / K), or equal to or greater than 10 W / m / K and lower than 5,000 W / m / K, or, equal to or greater than 50 W / m / K and lower than 2,000 W / m / K, between 50 -100 W / m / K or between 100 W / m / K and 10,000 W / m / K to provide heat transfer contrast relative to materials naturally encountered in the subsurface.

[0045] Table 1 lists mean thermal conductivity of various exemplary sedimentary rocks in the

[0046] Sichuan basin, Southwest China (Tang et al, 2018).

[0047] Table 1

[0048] Specific to the present invention, heat transfer fins are created by adding small particles (e.g., 100 mesh (smaller than 149 micron)or ) or smaller particles of heat transfer material (such as metals, for example aluminum particles or aluminum powder) in the fracturing fluid in a manner similar to the use of fluid loss additives. The heat transfer material is transported with leak off into natural fractures, complex fracture side branches, and / or dilated rock fabric or bedding planes where heat transfer materials are deposited. When the fractures close, after treatment, the heat transfer materials are crushed and creep (travel) to form heat transfer material -filled or partially filed side fractures that extend fully or partially from the main fracture into the formation. These side fractures act like “fins” on a heat exchanger thereby increasing the surface area available for heat exchange and thereby the rate of heat exchange itself.

[0049] FIG. 3

[0050] FIG. 3 is “Map View” of a heterogeneous heat transfer structure comprising hydraulic fracture system connecting the treatment well to the EGS production well. 20 - Horizontal treatment well and EGS injection well; 21 - main fracture, 22 - heat transfer fins, 23 - horizontal EGS production well.

[0051] Fig. 3 illustrates a map view of a heterogeneous heat transfer structure formed during hydraulic fracturing of well 20 and comprising a hydraulic fracture system with the main hydraulic fracture 21 with “fins” 22 containing heat transfer materials (i.e., perpendicular gray “spikes”) created in natural fractures and / or complex fractures intersected by the hydraulic fracture, with the main hydraulic fracture 21 connected to the horizontal EGS production well 23. The white space within the main hydraulic fracture 21 may be void space or occupied by proppant material and may serve as the flow path for injected fluids during EGS operations. As depicted, the fins serve to increase heat transfer from the formation to the injected fluids that flow along the hydraulic fracture from the injection well to the production well.

[0052] Heat transfer fins can also be created near the top and / or bottom of the hydraulic fracture using low density and high-density heat transfer materials, respectively. During fracturing treatment, the materials with the density that is lower than the density of the fracturing fluid will preferentially be transported towards the top of the fracture, whereas the materials with the density that is higher than the density of the fracturing fluid will preferentially be transported to the bottom of the fracture system, (similar to the J-frac technique used by SLB to control fracture height growth). Hematite is an example of a high-density heat transfer material that may be transported to the bottom of a fracture as it has a desirable thermal conductivity of 1250 W / m / K and a high density of 5.2 g / cm3. Other examples of materials with high heat conductivity and a density higher than the density of a fracturing fluid (typically about lg / cm3) include but are not limited to aluminum (237 W / m K, 2.7 g / cm3), copper (401 W / m K, 8.96 g / cm3), silver (429 W / m K, 10.49 g / cm3), brass (120 W / m K, 8.4-8.7 g / cm3), bronze (50-70 W / m K, 8.8 g / cm3), diamond (1000- 2200 W / m K, 3.5 g / cm3), graphite (150-200 W / m K, 2.09-2.23 g / cm3), carbon nanotubes (3000- 6000 W / m K, 1.3-2.1 g / cm3), silicon carbide (120-200 W / m K, 3.21 g / cm3), beryllium oxide (285 W / m K, 3.01 g / cm3).

[0053] Examples of materials with high heat conductivity and a density lower than the density of a fracturing fluid (typically about lg / cm3) include but are not limited to aluminum spheres such as hollow aluminum spheres or aluminum spheres filled with low-density liquids and materials such as paraffin, diesel and other low-density materials, aerogel (10-20 W / m K, 0.001-0.1 g / cm3), expanded graphite (10-150 W / m K, 0.02-0.2 g / cm3), carbon foam (10-60 W / m-K, 0.2-0.6 g / cm3), graphene foam (10-500 W / m K, 0.1-0.5 g / cm3), boron nitride foam (10-50 W / m K, 0.1-0.3 g / cm3), aluminum foam (10-50 W / m K, 0.2-0.6 g / cm3), silica aerogel (10-20 W / m K, 0.001-0.1 g / cm3), polymer composites with high filler content (10-50 W / m K, 0.5-0.9 g / cm3), metal -coated polymer foams (10-30 W / m K, 0.3-0.8 g / cm3), lightweight carbon composites (10-100 W / m K, 0.5-0.9 g / cm3).

[0054] After fracture closure, heat transfer materials act as heat transfer “fins” vertically from the fracture and contact a large surface area of the fracture. In cases without heat transfer fins, the surface area near the top and bottom of the fracture are likely to be ineffective for heat transfer as the injected fluid flow would be low in these locations and have limited contribution to heat transfer in the fracture system.

[0055] FIG. 4 FIG. 4 is a side view of a hydraulic fracture with fins composed of heat transfer materials (expanded grey) created near the top and bottom of the hydraulic fracture. 30- horizontal treatment well and EGS injection well, 31 - heat transfer fin created from a low-density heat transfer material, 32 - heat transfer fin created from a high-density heat transfer material, 33 - horizontal EGS production well, 34 - hydraulic fracture.

[0056] FIG. 4. illustrates a side view of a hydraulic fracture 34 with fins 31 and 32 composed of heat transfer materials (expanded grey) created near the top and bottom of the hydraulic fracture connecting the horizontal treatment well and EGS injection well 30 and horizontal EGS production well 33. The white space between the fins may be void space or occupied by proppant material and serves as the flow path for injected fluids during EGS operations. As depicted, heat-transfer “fins” serve to increase heat transfer from the formation to the injected fluids which may then be delivered to the surface for energy generation.

[0057] In a specific embodiment of the present invention materials with high heat conductivity and density that is higher or lower than the density of the fracturing fluid may be pumped into the hydraulic fracture system as a part of multi-modal mixture of particulate materials.

[0058] In another preferred embodiment of the present invention the amount and size of particles of each mode in such mixture may be designed for reducing permeability of a pack of particles formed from such mixture. For example, the amount and size of particles of a second largest size may be designed to fill the gaps between the particles of a first largest size in the pack of such particles, then the amount and size of particles of a third largest size may be designed to fill the gaps between the particles of the first and second largest sizes et cetera where varying sizes of particles may be combined in a fluid as to accommodate various sized fissures and fractures within a formation. In yet another specific embodiment of the present invention all particles in such mixtures may have densities that are higher than the density of the fracturing fluid, particles may have the density lower than the density of the fracturing fluid, or a combination thereof. Pumping such mixtures in the hydraulic fracture systems will result in specific placement of these mixtures at the top of the hydraulic fracture system or at the bottom of the hydraulic fracture system respectively, based on density relative to the fracturing fluid, thus forming heat conductive fins with low flow conductivity. Such fins will further act as a heat-transfer areas and the permeability barriers for the heat-collecting fluid, thus increasing heat transfer to this fluid from the formation and minimizing the leak-off losses of the heat-collecting fluid into said formation at the same time.

[0059] In yet another embodiment of the present invention pumping multi-modal mixtures of particulate materials comprising at least one type of particulate having heat conductivity of equal to or greater than 5 W / m / K and lower than 10,000 W / m / K (i.e., ranging from approximately 5 W / m / K to 10,000 W / m / K), or equal to or greater than 10 W / m / K and lower than 5,000 W / m / K, or, equal to or greater than 50 W / m / K and lower than 2,000 W / m / K, between 50 -100 W / m / K or between 100 W / m / K and 10,000 W / m / K may be used for plugging side fractures and natural fractures, thus resulting in creating heat-transfer fins with low flow conductivity at the entry into these side fractures or natural fractures. That will have a positive impact on heat transfer to the heat-collecting fluid and minimizing its losses to the formation during the geothermal energy harvesting.

[0060] Similar to heat-transfer “fins”, certain heat transfer “pillars” may be created inside the hydraulic fracture system from particulate materials with heat conductivity of equal to or greater than 5 W / m / K and lower than 10,000 W / m / K, or equal to or greater than 10 W / m / K and lower than 5,000 W / m / K, or, equal to or greater than 50 W / m / K and lower than 2,000 W / m / K, between

[0061] 50 -100 W / m / K or higher than 100 W / m / K and lower than 1,000 W / m / K.

[0062] In one specific embodiment of the present invention such pillars can be formed by injecting pulses of materials in the form of particulates, granules, and / or fibers as part of a hydraulic fracturing treatment or in the form of mixtures with particulates, granules, flakes, and / or fibers of other materials. For example, the heat transfer material or a mixture comprising said heat transfer material(s) may be pulsed on and off during the proppant laden stages of the treatment.

[0063] In another specific embodiment of the present invention these pulses of heat transfer material(s) may replace a portion of the propping agent, may be combined with proppant, may involve pumping downhole a proppant coated with a heat-conductive coating, or may comprise a combination thereof. Alternatively, heat transfer materials may be pulsed on and off in the absence of proppant if the treatment does not involve proppant. The method of creating heat transfer pillars could be analogous to SLB’s HiWAY channel fracturing technology or Halliburton’s downhole proppant pulsing method.

[0064] After the treatment, the hydraulic fracture may then close and place stress on heat transfer materials. The material itself may or may not support the closure stress depending on each material’s mechanical properties. Moreover, injection “pillars”, although adopting a cylindrical connotation of a “pillar”, may be nonetheless be non-cylindrical and may take the form of one of any number of shapes, even across the same or similar areas, which may be spherical, oblong, linear, non-linear, amorphous, and / or leaching thereby forming shapes within the formation, or being shaped by the formation contiguously, non-contiguously or some combination thereof. In yet another embodiment of the present invention heat transfer “pillars” may be formed by agglomerating particles of a heat conductive material or a mixture of particles comprising heat conductive particles in the hydraulic fracture system after placement of said particles or said mixture of particles inside said hydraulic fracture system in slurried form. This agglomeration method may be driven by wettability (e.g., having oil-wetted particles dispersed in a water based fracturing fluid with addition of oil for further agglomeration of said particles ); adding fibers to the (segregating / self separating) slurry to induce bridging of particles during their settling in the hydraulic fracture system, by “gluing” particles together (e.g., by using sticky coating on the particles) or by using other agglomeration mechanisms. These heat transfer “pillars” may be formed during settling of the particles which are homogeneously dispersed in the slurry containing fibers analogous to SLB’s BroadBand Composite fluid and method of use.

[0065] Formed heat transfer pillars distribute heat more uniformly in the immediate vicinity of these “pillars”, which may be layers or threads, thereby creating thermal gradients on the fracture faces. Furthermore, in cases where heat transfer pillars have lower permeability than the propping agents, the “pillars” may increase the complexity of fluid flow paths and fluid mixing within the fractures, uniformly, intermittently, and tactically based on formation constitution and / or unevenly (strategically) across a formation which can improve heat transfer taking into consideration injection rate, depths, pressures and formation composition.

[0066]

[0067] FIG. 5

[0068] FIG. 5 is a side view of a hydraulic fracture with pillars composed of heat transfer materials connecting the treatment well to the EGS well. 40- horizontal treatment well and EGS injection well, 41 - heat transfer pillars created from a heat transfer material, 43 - horizontal EGS production well, 44 - hydraulic fracture.

[0069] FIG. 5 shows a side view of a hydraulic fracture 44 with heat transfer pillars 41 composed of heat transfer materials (grey) connecting the horizontal treatment well and EGS injection well 41 and horizontal EGS production well 43. The interspersed white space between pillars may be void space or occupied by proppant material and serving as the flow path for injected fluids during EGS operations. The pillars alter both flow paths and heat transfer from the formation to fluids pumped through the fracture and within the void space.

[0070] PREFERRED EMBODIMENTS A detailed description of the preferred embodiments of the invention is disclosed and described below. Yet, each and every possible feature, within the limits of the specification, are not disclosed as various permutations are postulated to be in the purview and contemplation of those having skill in the art.

[0071] In yet another embodiment of the present invention created heat transfer pillars may be used for preventing the hydraulic fracture from closure after release or dissipation of hydraulic pressure in the fracture system after its creation. In the case of absence of proppant between said heat transfer pillars and where the distance between said pillars is small enough for preventing the channels between said heat transfer pillars from closure, the created structure will be highly flow- conductive, thus eliminating high circulation pressures during circulating the heat-collecting fluid through such hydraulic fracture system during geothermal energy harvesting which constitutes one of the biggest challenges of the EGS systems.

[0072] In yet another embodiment of the present invention a combination of heat transfer fins and / or heat transfer pillars may be applied in the same hydraulic fracture and / or in varying combinations in a well with multistage fracturing. And, depending on where particulates of heat transfer materials are transported during the treatment to form heat transfer fins, some particulates could remain in the main fracture and form heat transfer pillar structures (i.e., a combination of both fins and pillars is possible within and throughout the same hydraulic fracture system).

[0073] In yet another embodiment of the present invention fracture complexity may be induced along a wellbore or along fracture faces of the hydraulic fracture systems by a) applying pressure pulses (e.g., using propellent to create complex fractures) followed by pumping / injecting at least one particulated heat transfer material or a mixture or particles comprising particles of such heat transfer material to create heat transfer fins and / or heat transfer pillars in complex fractures as described above or b) pumping temperature increasing products such as sodium nanofluid or thermite as a slurry during hydraulic fracturing, whereby the temperature increase induces complex fracturing from local heat-induced fracturing. In the case of Sodium nanofluid, slurry introduction would be followed by pumping into a formation heat transfer material(s) to create heat transfer fins and / or pillars in complex fractures as described above. In the case of Thermite, the Thermite produces iron slag which can form fin-like and / or pillar-like structures within the fractures. The slag may then serve as heat transfer fins and / or heat transfer pillar, and / or may be combined with pumping heat transfer materials to create heat transfer fins in the complex fractures as described above.

[0074] For the purpose of the current invention the thermite mixture is defined as a mixture of particles of an oxide of a first metal (MelOx) with particles of a second more active metal component (Me2) capable of reacting with the oxide of the first metal (MelOx) resulting in formation of an oxide of said second metal (Me2y0x) and the free first metal (Mel) with simultaneous release of energy (Q).

[0075] Me 10x+yMe2=Me 1 +Me2y0x+Q

[0076] Thermite reaction is further defined as the reaction between the components of the thermite mixture resulting in formation of the first free metal as shown above. Numerous examples of said thermite mixtures comprise iron oxide III with aluminum, copper oxide with zinc, iron oxide with magnesium, manganese oxide with aluminum, mixtures thereof and other mixtures known to those skilled in the art.

[0077] In a specific embodiment of the present invention thermite mixture may comprise a plurality of metal oxides of various metals with plurality of second metal components comprising various metals of the second type which are more active than the metals of the first type. Said thermite mixtures may further comprise additives that reduce the amount of energy required for initiating the thermite reaction such as barium nitrate, potassium nitrate, potassium permanganate and other additives known to those skilled in the art.

[0078] In yet another embodiment of the present invention thermite can be used to generate a heat conductive material, such as iron or any other metal inside a hydraulic fracture system or a part of the hydraulic fracture system. For example, thermite mixture may be placed in the slurried form into side hydraulic fractures, or may be bridged in such side hydraulic fractures and then plug these side fractures, followed by ignition of the thermite before, during, or after closure of these side fractures. Or, for example, thermite mixture may be placed into the main hydraulic fracture and then be ignited before, during, or after the hydraulic fracture closure.

[0079] In yet another embodiment of the present invention thermite mixture may be ignited in fractures during closure of these fractures by self-ignition of additives susceptible to mechanical load and mechanical shocks. Examples of such additives include but not limited to iodine nitride (I2N4), nitrogen triiodide (NL), silver acetylide (Ag2C2), lead azide (Pb(Na)2), sodium azide (NaNs), hydrogen azide (HN3) and other chemicals known to those skilled in the art.

[0080] In yet another embodiment of the present invention a thermite mixture may be injected into the hydraulic fracture system in a slurried form wherein the liquid phase of said slurry may be oil, diesel, gelled hydrocarbon fluid, crosslinked hydrocarbon fluid, gelled diesel, water, gelled water, crosslinked guar solution, alcohol, gelled alcohol, and other liquids known to those skilled in the art. In another embodiment of the present invention the described systems and methods may be applied to a closed-loop geothermal or enhanced geothermal systems (EGS).

[0081] In still yet another embodiment of the present invention the heat conductive material or heat conductive materials may be of any size, shape or form and may be injected in a parti culated form or in the form of a mixture with other particulated materials of any size, shape or form. Various shapes of said heat conductive material(s) and other materials injected together with said heat conductive material(s) include but are not limited to grains, beads, flakes, fiber, spheres including hollow and solid spheres, crashed particles, rods, particles or any 2D and 3D polygonal shapes including tetrahedron, cube, octahedron, dodecahedron, icosahedron and other shapes known to those skilled in the art.

[0082] In yet another specific embodiment of the present invention the mean size of particles of heat conductive material(s) and the mean size of particles of other materials that may be injected together with said heat conductive material(s) may be from 0.1 micron to 5mm, or from 1 micron to 2mm, or from 10 micron to 1mm.

[0083] In yet another embodiment of the present invention the heat conductive material(s) may be pumped in pulses or continuously as part of the proppant-laden stages of a hydraulic fracturing treatment.

[0084] In yet another embodiment of the present invention the heat transfer material may have a short aspect length or diameter less than the diameter of perforations where such material is pumped, more preferably with a short aspect length or diameter less than the entrance width of the fractures.

[0085] Yet another preferred embodiment comprising pumping / inj ecting a material or materials with thermal conductivity of equal to or greater than 5 W / m / K and lower than 10,000 W / m / K (i.e., ranging from approximately 5 W / m / K to 10,000 W / m / K), or equal to or greater than 10 W / m / K and lower than 5,000 W / m / K, or, equal to or greater than 50 W / m / K and lower than 2,000 W / m / K, between 50 -100 W / m / K or between 100 W / m / K and 10,000 W / m / K. into a subterranean formation to enhance heat transfer of the enhanced geothermal system (EGS), wherein the materials are pumped as part of a hydraulic fracturing treatment.

[0086] In one other embodiment, both heat transfer fins and heat transfer pillars are formed in the same treatment and / or in the same well, for example, as a result of a thermite reaction.

[0087] In yet another embodiment, chemical tracers may be included in the fluids injected and / or embedded within the heat transfer material during EGS operations to assess the impact of the heat transfer fins and / or heat transfer pillars on the flow profile and heat transfer in the fracture networks. For example, chemical tracers may be added in a form of particulate materials and pumped together with the particulated heat-transfer materials with following detection of the chemical tracers in the production fluid during the geothermal energy harvesting period to reveal information about the geometry of the created fracture and the location of the heat-transfer materials.

[0088] In one specific embodiment of the present invention the chemical tracers may be added in a form of particles covered with non-dissolvable coating which can be crashed upon fracture closure resulting in the release of the chemical tracers.

[0089] In yet another embodiment of the present invention, chemical tracers may be pumped in a form of particulated materials together with particulated plastic heat transfer materials (e.g. such as aluminum or zinc or any other plastic heat transfer material) during a fracturing treatment designed for creating non-permeable pillars comprising such plastic heat transfer materials upon their deformation during the fracture closure. In this case the majority of the chemical tracers particles will be embedded into the impermeable pillars and thus, low concertation of said chemical tracers in the heat-collecting fluid during the energy-harvesting period can be used as an indication of creation of such impermeable pillars.

[0090] In another embodiment, fiber optic cable may be utilized to assess impact of heat transfer fins and / or heat transfer pillars on heat transfer from individual fractures.

[0091] In another embodiment, the invention can be combined with methods of creating induced complex fractures such as the application of agents such as propellants or Thermite.

[0092] In another embodiment, the heat transfer materials are pumped in a J-frac application by which the materials are placed near the top and / or bottom of the fractures based on density differences wherein lower density materials may move to upper areas (i.e., closer to the surface) and higher density materials may move to lower areas (i.e., further away from the surface).

[0093] In another embodiment, the heat transfer materials may also be electrically conductive to provide for identification, monitoring and location of the particles, or a combination thereof. In a specific embodiment of the present invention creating a continuous barrier at the top and the bottom of the hydraulic fracture comprising an electrically conductive heat transfer material (e.g. such as a metal) may be confirmed by low electrical resistivity measured between the injection EGS well and the production EGS well. In yest another embodiment of the present invention formation of separated pillars comprising an electrically conductive material instead of a continuous pack of particles comprising said electrically conductive material may be confirmed by relatively high resistivity measured between the injection EGS well and the production EGS well. In one embodiment, different heat-conductive materials may be pumped at different times during fracturing wherein these materials may differ by heat conductivity and density, or both, or by any other defining properties including shapes, sizes, chemical nature, composition, electrical conductivity and other properties known to influence fluids, and the like.

[0094] Example A: Heat Transfer Fins in EGS

[0095] An EGS project such as Utah FORGE utilizes multiple horizontal wells in a hot formation (e.g., above 175C°) where injection and / or production wells are hydraulically fractured using a slickwater fluid and / or crosslinked polymer fluid. Hydraulic fractures connect the injection well to the production well, thereby providing surface area for heat transfer when fluids are injected through the network during EGS operations. To enhance heat transfer, heat transfer fins may be created using 100 mesh or smaller aluminum particles that are pumped in the pad stage of the fracturing treatment. The aluminum particles are injected into natural fractures, and, upon fracture closure after the treatment, particles are compressed into metal fins along the natural fractures. Fracture closure may then cause the aluminum material to become pressed together and / or cause creep along the fracture, thereby forming side fractures filled or partially filled with the aluminum heat transfer material. This process results in the formation of heat transfer fins to increase heat transfer from the formation to the fluids flowing through the main hydraulic fracture during EGS operations. Furthermore, some heat transfer materials with crush and / or creep, may result in low to zero hydraulic conductivity. As a result, fins placed in side-natural (or man-made) fractures and / or tops and / or bottoms of the main hydraulic fracture also serve to reduce leakoff from the circulation paths between wells. Reducing said leakoff is advantageous as it reduces loss of fluid during the life of the EGS project.

[0096] Example B: Heat Transfer Pillars in EGS An EGS project such as Utah FORGE utilizes multiple horizontal wells in a hot formation (e.g., above 175C0) where injection and / or production wells are hydraulically fractured using a slickwater fluid and / or crosslinked polymer fluid. The hydraulic fractures connect the injection well to the production well, thereby providing surface area for heat transfer when fluids are inj ected through the network during EGS operations. To enhance heat transfer, heat transfer pillars may be created using 40 / 70 mesh heat-conductive particles such as aluminum particles or stainless steel particles or any other metal or metal alloy particles plus aluminum fibers or polymer fibers that are pumped in the proppant-laden stage of the fracturing treatment. This particulate material is then pulsed on and off (e.g., approximately every 5 minutes) as part of the treatment resulting in heterogeneous distribution of slugs comprising heat-conductive particles in the hydraulic fracture system. Fracture closure causes the heat-conductive material to become pressed together and / or creep along the fracture, thereby forming pillars of heat-conductive material distributed around the fracture. These pillars act like heat transfer plates to modify heat transfer from the formation to the fluids flowing through the main hydraulic fracture during EGS operations. Furthermore, these formed pillars may not be permeable upon compaction, hence they alter the flow of injected fluids to create a more complex flow path with longer residence time to also increase heat transfer.

[0097] And while addressed separately above, it is well within the contemplation of inventors to employ both fins and pillars wherein a combination of example B (pillars) can be deployed in with example A (fins) in a single hydraulic fracture, across several natural and hydraulic and mechanical fractures within a system of natural and man-made factures alike.

[0098] Therefore, it is in contemplation of inventors to proffer apparatus, systems and methods of recovery of the geothermal energy from a reservoir comprising creating at least one heterogeneous heat transfer structure in a hydraulic fracture system used for the geothermal energy recovery utilizing heat-transfer “pins” or “fins” inside the hydraulic fracture system wherein creating said at least one heterogeneous heat-transfer structure comprises pumping at least one particulated heat- conductive material downhole and its heterogeneous depositing in the reservoir. The material can be particulates, granules, flakes, and / or fibers or other shapes, and mixtures and combinations thereof. Said heterogeneous depositing may comprise agglomeration, pumping by slugs, heterogeneous settling or any other methods of heterogeneous depositing creating at least one conductive heterogeneous heat-transfer structure in a hydraulic fracture system. Said at least one heterogeneous heat transfer structure comprises pumping into a formation a slurry comprising a particulated heat-conductive material in a hydraulic fracture system together with pumping a heat collecting fluid in a hydraulic fracture system that comprises this said at least one heterogeneous heat transfer structure followed by recovery or circulating said heat-colleting fluid to the surface for geothermal energy production.

[0099] The apparatus, systems and methods of recovery of the geothermal energy, comprising creating a flow-conductive hydraulic fracture system with at least one heat-conductive component, which is positioned and positionable in a “side fracture” at an angle to a main hydraulic fracture, of said hydraulic fracture system, wherein said angle is within 1-179 degrees of the main hydraulic fracture. Thereafter, a heat collecting fluid is injected or pumped into a hydraulic fracture system comprising said at least one heterogeneous heat transfer structure followed by recovery or circulating said heat-colleting fluid to the surface for geothermal energy retrieval and harvesting.

[0100] It is further posited that method of recovery of geothermal energy, comprising pumping a multi-modular mixture of particles dispersed in a pumping fluid in a hydraulic fracture system, wherein particles of at least one mode are heat-conductive and wherein the particle size distribution in said multi-modular mixture of particles is designed for forming a “pack” (accumulation or conglomeration) of particles with reduced permeability and wherein particles of at least one mode in said particles of a multi-modular mixture of particles have a density lower than the density of the liquid phase of said pumping fluid and / or at least one mode in said particles of a multi-modular mixture of particles have a density higher than the density of the liquid phase of said pumping fluid.

[0101] Ideally said multi-modular mixture of particles contains particles wherein the density of particles of at least one mode of particles is lower than 0.9kg / m3 and wherein the density of particles of at least one mode of particles is higher than 2.5kg / m3. This results in particles dispersed in a pumping fluid containing, potentially, a mixture of particles dispersed in said pumping fluid further resulting in “floating” (allowing to float) low density (in relation to pumping fluid) particles to the upper portion of the hydraulic fracture system (in a region closer to the surface) above a main hydraulic fracture, constituting the primary conduit for pumping fluid retention and movement with a hydraulic fracture system, and creating therein a barrier of conductive material, with reduced permeability, within said “side fractures” which may be largely perpendicular to the main hydraulic fracture or existing at any angle between 1 to 179 degrees relative to the main hydraulic fracture. Contrariwise, said multi-modular mixture of particles dispersed in said pumping fluid further results in setting or “sinking” (allowing to sink based on gravity) some higher density particles, relative to the pumping fluid, to the “bottom portion” of the hydraulic fracture system and creating there a barrier with reduced permeability in areas directed to the area “below” the main hydraulic fracture. Although, it is to be understood that a mixture of high density and low density particles, relative to the pumping fluid, may exist in combination in the same side fractures and / or the main hydraulic fracture simultaneously, temporally, sequentially, permanently, semi -permanently and / or transitorily based on main and side fracture size, location, length, diameter, depth, configuration, or a combination thereof, formation configuration and fracturing, the consistency, composition, density, flowrate, pressure of a pumping fluid, or a combination thereof, and the pressure, depth, orientation, and temperature of a flow-conductive hydraulic fracture system, or a combination thereof.

[0102] Moreover, plugging some portions of the hydraulic fracture system with the pack of said multi-modular mixture of particles may be utilized comprising plugging at least one side fracture or a portion of said side fracture with the pack of said multi-modular mixture of particles and / or pumping at least two chemical agents dispersed or dissolved in a pumping fluid into a hydraulic fracture system with following creating at least one heat-conductive material in said hydraulic fracture system as a product of reaction between these at least two chemical agents where said at least two chemical agents are components of thermite mixture and the reaction between these components is the thermite reaction. And while it is postulated that several components may be selected to create a thermite mixture, a thermite mixture containing iron oxide III and aluminum is proffered as an exemplary mixture.

[0103] Those skilled in the art will readily understand the advantages and objectives of these apparatus, this system and this method may be further facilitated, and are available for implementing the control of the features and operations described in the foregoing material, with the aid of controls, mechanisms, calculations, computers (utilizing both software and hardware) to effectuate the delivery of certain features and aspects of the present invention. Moreover, the particular choice of programming tool(s) may be governed by the specific objectives and constraints placed on the fracturing fluid composition, flow rates, particle parameters, hydraulic fracturing system configurations, area and placements in the subterranean formation, and other like considerations, and based on intended or sought results, which are selected for realizing the result of concepts and postulations set forth herein and in the appended claims.

[0104] Finally, the disclosure itself may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. For example, each of the new structures described herein, may be modified to suit particular subsurface variations or requirements while retaining the basic configurations or structural relationships with each other or while performing the same or similar functions described herein. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive. Accordingly, the scope of the inventions are established by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced herein. Further, the individual elements, combination of elements (i.e., system) and method of use provided herein are novel and the appended claims are strictly not well- understood, routine, or conventional (i.e., are non-obvious). Instead, the claims are directed to the unconventional inventive concept discussed and described in the specification.

Claims

We Claim1. A system of recovery of geothermal energy from a reservoir comprising: a fracturing fluid; said fracture fluid utilized to create a hydraulic fracture system; said fracturing fluid utilized for transport and depositing of thermally conductive materials into said hydraulic fracture system; and said thermally conductive materials utilized to create a heterogeneous heat transfer structure in the hydraulic fracture system.

2. The system of claim 1 wherein said fracturing fluid contains particulated materials in the form of propping agents to maintain fractures in an open configuration subsequent to dissipation of hydraulic pressure with fracturing fluid decrease or cessation, particulate additives to control fluid loss, or a combination thereof.

3. Tire system of claim 2 wherein said particulated materials are heat-conductive materials for the creation of at least one heterogeneous heat-transfer structure created by pumping at least one particulated heat-conductive material and its heterogeneous depositing in the reservoir.

4. The system of claim 3 wherein the material can be particulates, granules, flakes, and / or fibers or other shapes, and mixtures thereof.

5. Tire system of claim 1 wherein said depositing of thermally conductive materials is achieved through pulsing, agglomeration, pumping by slugs, pumping a self-separating slurry, heterogeneous, fluid density regulated settling or any combination thereof.

6. The system of claim 1 wherein recovering of geothemral energy comprises pumping a heat collecting fluid in a hydraulic fracture system that comprises said at least one heterogeneous heat transfer structure followed by recovery or circulating said heat-colleting fluid to the surface.

7. The system of claim 1 wherein the hydraulic fracture system comprises at least one main fracture and a least one side fracture.

8. The system of claim 7 comprising creating said at least one heat-conductive structure within a side fracture at an angle to the main hydraulic fracture of said hydraulic fracture system wherein said angle is within 1-179 degrees.

9. A method of recovery of the geothermal energy comprising the steps of: adding to a fracturing fluid heat-conductive materials as a multinodular mixture of particles; pumping said fracturing fluid into a hydraulic fracture system; said particles of at least one mode which are heat-conductive and wherein the particle size distribution in said multi-modular mixture of particles is designed for forming a pack of particles with reduced permeability: said particles in said multi-modular mixture of particles having density lower than the density of the liquid phase of said fracturing fluid; said particles of at least one mode in said particles in said multi-modular mixture of particles having density higher than the density of the liquid phase of said fracturing fluid; allowing to float lower density particles to the upper portion of the hydraulic fracture system, closer to the surface, and creating therein an upper barrier with reduced permeability; allowing to settle higher density particles in the lower portion of the hydraulic fracture system, further from the surface, and creating therein a lower barrier with reduced permeability; plugging some portions of the hydraulic fracture system with the pack of said multinodular mixture of particles; plugging at least one side fracture or a portion of said side fracture with the pack of said multinodular mixture of heat-conductive particles; creating pins, fins or pillars in at least one side fracture or main fracture; andcirculating said heat-collecting fluid through said hydraulic fracture system and recovery of said heat-colleting fluid to the surface for energy extraction.

10. The method of claim 9 comprising said multinodular mixture of particles wherein the density of heat conductive particles of at least one mode of particles is lower than 0.9kg / m3.

11. The method of claim 9 comprising said multinodular mixture of particles wherein the density of heat conductive particles of at least one mode of particles is higher than 2.5kg / m3.

12. Tire method of claim 9 wherein the density of said lower density particles are lower than the density of said fracturing fluid, said density of said of higher density particles are higher than the density of said fracturing fluid, wherein said fracturing fluid may constitute only lower density particles, only higher density particles, or a combination of both lower density and higher density particles.

13. The method of recovery of the geothermal energy of claim 9 comprising pumping at least two chemical agents dispersed or dissolved in a fracturing fluid into a hydraulic fracture system thereby creating at least one heat-conductive material in said hydraulic fracture system as a product of reaction betw een these at least tw o chemical agents.

14. A method of claim 13 wherein said at least two chemical agents are the components of thermite mixture and the reaction betw een these components is the thermite reaction.

15. A method of claim 14 wherein the thermite mixture comprises iron oxide III and aluminum.

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