Preparation method of ultra-deep multi-scale fractured rock sample

Abstract

The invention belongs to the technical field of physical simulation of oil and gas reservoirs, and discloses a preparation method of an ultra-deep multi-scale fracture rock sample, which comprises the following steps: a geometric physical model of an actual reservoir fracture is reduced in equal proportion, and the geometric physical model of the actual reservoir fracture has a multi-scale fracture model; cutting the rock according to the established geometric physical model of the actual reservoir fracture; the cut rock blocks are spliced into one piece again according to a geometric physical model of the actual reservoir fracture, the cut rock fracture is filled with filler, and the actual reservoir fracture is reduced in an equal proportion; and putting the manufactured rock model into a rock core holder, and pressurizing and compacting. According to the method, the defects that a sand filling model is not resistant to high pressure and small-size rock samples are poor in representativeness are overcome, model preparation of complex fracture net combination can be achieved, and multi-scale characteristics of ultra-deep low-porosity sandstone fractures can be well depicted.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas reservoir physical simulation technology, specifically relating to a method for preparing ultra-deep multi-scale fractured rock samples. Background Technology

[0002] Onshore oil exploration and development is shifting its focus from deep to ultra-deep formations. Ultra-deep low-porosity sandstone fractured gas reservoirs are buried at greater depths and are essentially ultra-deep gas reservoirs. They are located in an abnormally high-pressure environment with strong heterogeneity in fracture development and complex geological conditions. The reservoir space types are diverse and varied, containing both small-scale micro-fractures and large-scale fractures. Unlike other gas reservoirs, the fluid migration in these reservoirs exhibits a multi-medium flow of "pore-fracture-fault," with complex and diverse distribution and connection patterns of media at different scales. Researchers need to prepare core samples according to the actual stratigraphic reservoir characteristics to provide the necessary rock sample models for physical simulation experiments of ultra-deep fractured gas reservoirs. Currently, the methods for creating multi-scale fracture physical models for experiments fall into three categories: First, core sampling is used to extract core samples. However, due to limitations, core sampling is often incomplete or insufficient in fractured sections, and sampling costs are high, with significant difficulties in field sampling, making experimental analysis impossible. Second, artificial cores are used, based on fracture-creating techniques including uniform splitting, stress loading, and directional etching. These are mostly standard samples with limited core size, failing to meet the geometric similarity requirements of real oil and gas reservoirs. Third, visual flat plate models are used, but these are not suitable for high-temperature and high-pressure physical experiments. Therefore, developing a method for preparing ultra-deep multi-scale fractured rock samples that can better meet the characteristics of ultra-deep gas reservoirs, is suitable for experimental analysis, and satisfies practical field needs is of great significance for the development of ultra-deep low-porosity sandstone fractured gas reservoirs.

[0003] Chinese patent publication number CN117147321A, entitled "A Method and Experimental Apparatus for Characterizing Fracture Morphology in Experimental Rock Samples," describes a method that includes real-time monitoring of fracture propagation within experimental rock samples during hydraulic fracturing simulation tests to obtain fracture distribution morphology parameters. The method involves injecting a casting liquid into the fracturing rock sample to create a main fracture characterization body, scanning this body to obtain a numerical model of the main fractures, mapping the fracture morphology to obtain fracture morphology parameters, and combining the fracture distribution morphology parameters, the main fracture numerical model, and the fracture morphology parameters to simulate the fracturing fracture model of the experimental rock sample using 3D software. While this patent application also simulates rock sample fractures using numerical models and physical models, it fails to address the simulation problem of multi-scale characteristics in actual reservoirs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing multi-scale fractured rock samples in ultra-deep reservoirs. Existing fractured rock sample preparation methods have limitations in model pressure resistance and characterizing the multi-scale features of actual reservoirs, leading to discrepancies between experimental conclusions and actual field development conditions, making it difficult to provide effective reference data for real-world development. This invention, targeting the different scale characteristics of fractures in ultra-deep gas reservoirs, prepares a large-scale physical model rock sample with three-dimensional model parameter features, realizing different scale fracture network combinations, and can realistically reflect reservoir characteristics, possessing practical representativeness. It is applicable to actual field conditions and can predict gas field development dynamics.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing ultra-deep multi-scale fractured rock samples includes the following steps: The geometric and physical model of the actual reservoir fracture is reproduced on a proportional scale, and the geometric and physical model of the actual reservoir fracture has a multi-scale fracture model. The rock is cut according to the established geometric and physical model of the actual reservoir fractures; Based on the geometric and physical model of the actual reservoir fractures, the cut rock blocks were reassembled into a single piece, and the filler was inserted into the cut rock fractures to restore the actual reservoir fractures to a proportional scale. After the prepared rock model is placed into the core holder, it is pressed and compacted.

[0006] Optionally, a geometric-physical model of the actual reservoir fractures can be established using drawing software.

[0007] Optionally, the number of fractures in the actual reservoir fracture geophysical model is less than or equal to two.

[0008] Optionally, the geophysical model of the actual reservoir fractures has more than two fracture networks.

[0009] Optionally, the scale of fracture aperture in the geophysical model of actual reservoir fractures includes the micrometer and centimeter levels.

[0010] Optionally, the rocks used are natural outcrops from the actual reservoir site or rocks with the same lithology as those at the site.

[0011] Alternatively, the rock can be cut using a saw blade or wire cutting.

[0012] Alternatively, ceramsite can be used as the filler for rock fissures.

[0013] Optionally, pressure is applied to the rock sample using a clamp for 1 to 1.5 hours, followed by slow decompression to remove the rock sample from the core clamp.

[0014] Optionally, the compacted rock sample can be sealed from the outside.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing ultra-deep multi-scale fractured rock samples. Compared with traditional rock sample preparation techniques, the large-scale three-dimensional physical model used in this invention can achieve the design of fractures with different apertures, while overcoming the shortcomings of sand-filled models such as poor pressure resistance and poor representativeness of small-sized rock samples. It can also realize the preparation of models with complex fracture network combinations, and can well characterize the multi-scale features of fractures in ultra-deep low-porosity sandstone.

[0016] Furthermore, this invention employs large-scale physical model rock samples, possessing three-dimensional model parameter characteristics. It can achieve fracture network combinations at different scales based on stratigraphic features, realistically reflecting reservoir characteristics and possessing representativeness of actual reservoir features. The method of this invention can provide the necessary reservoir physical models for conducting in-situ environmental conditions for ultra-deep fractured gas reservoir gas two-phase flow physical experiments and water intrusion experiments in fractured bottom-water gas reservoirs. It provides a reference basis for actual field development, is of great significance for improving the recovery rate of fractured low-porosity sandstone gas reservoirs, and has strategic guiding significance for the exploitation of ultra-deep gas reservoirs. Attached Figure Description

[0017] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely schematic to aid in understanding the invention and do not specifically limit the shapes and proportions of the components. In the drawings: Figure 1 This is an example of designing a rock sample model using the software of this invention; Figure 2 This is a fractured rock sample after splicing and filling according to the present invention; Figure 3 This invention relates to a core holder; Figure 4 This is a schematic diagram of the process of the present invention; Figure 5 This is a rock sample diagram showing the design and final fabrication of a simple seam mesh model according to Embodiment 2 of the present invention; where a is the seam mesh assembly design diagram and b is the seam mesh model diagram; Figure 6 The rock sample diagrams are for the design and final fabrication of the complex seam mesh model in Embodiment 3 of the present invention; where a is the seam mesh assembly design diagram and b is the seam mesh model diagram.

[0018] Among them: 1. Core holder inlet; 2. Core; 3. Pressurization port; 4. Vent port; 5. Core holder outlet; 6. Core holder cylinder. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0020] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0021] The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0022] It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] The present invention will now be described in detail with reference to the accompanying drawings.

[0025] like Figure 1 As shown, a method for preparing ultra-deep multi-scale fractured rock samples according to the present invention includes the following steps: The geometric and physical model of the actual reservoir fracture is reproduced on a proportional scale, and the geometric and physical model of the actual reservoir fracture has a multi-scale fracture model. The rock is cut according to the established geometric and physical model of the actual reservoir fractures; Based on the geometric and physical model of the actual reservoir fractures, the cut rock blocks were reassembled into a single piece, and the filler was inserted into the cut rock fractures to restore the actual reservoir fractures to a proportional scale. After the prepared rock model is placed into the core holder, it is pressed and compacted.

[0026] This invention places strict requirements on material selection and precise cutting dimensions. The prepared rock samples better reflect the multi-scale realities of ultra-deep, low-porosity sandstone fractured gas reservoirs.

[0027] To ensure that the prepared rock samples accurately reflect the actual conditions at the site, the rock samples used in this invention are outcrops from the field. A fracture model is then created using drawing software, including the model's size, shape, fracture size, and location. The rock samples are cut according to the designed model, and filler material is prepared according to the model's requirements. The cut rock blocks are then assembled according to the model, and the filler material is inserted into the fractures to ensure the multi-scale nature of the fractures. The samples are then placed in a core holder and compacted. Finally, the compacted rock samples are sealed for subsequent physical simulation experiments.

[0028] The rock samples prepared by the method for preparing ultra-deep multi-scale fractured rock samples provided by this invention can represent the reservoir characteristics of actual fractured gas reservoirs to a certain extent. They are suitable for indoor physical simulation experiments to simulate the flow law of fluids in fractured gas reservoirs and predict the development dynamics of gas fields.

[0029] Example 1 Actual reservoir fractures exhibit multi-scale characteristics, which means that the scale of the fractures ranges from micro-fractures at the micrometer level to main fractures at the tens or hundreds of meters level, demonstrating significant multi-scale characteristics.

[0030] This embodiment of a method for preparing ultra-deep multi-scale fractured rock samples includes the following steps: The first step is to prepare for rock cutting.

[0031] The prepared rocks are outcrop rocks, obtained from natural outcrop rocks at the site. These outcrop rocks are used to ensure that the rock samples prepared subsequently conform to the actual site conditions.

[0032] In one embodiment of the present invention, the prepared rock is a rock with the same lithology as the rock on site.

[0033] The rocks on site were cut into sizes that would facilitate transportation and subsequent secondary cutting.

[0034] The second step is the design of a multi-scale crack model.

[0035] Based on the actual situation of ultra-deep, low-porosity, fractured sandstone gas reservoirs, a scale model of the actual reservoir fractures is reconstructed on a proportional scale.

[0036] As one embodiment of the present invention, a schematic diagram of a multi-scale fractured rock sample model is designed using CAD or COMSOL drawing software, with the fracture aperture ranging from micrometers to centimeters, in order to characterize the multi-scale features of the actual strata.

[0037] As one embodiment of the present invention, the multi-scale crack model can employ a simple crack mesh combination.

[0038] As one embodiment of the present invention, the multi-scale crack model can employ a complex crack network combination.

[0039] like Figure 1 As shown, the physical model of the rock sample, designed using drawing software, measures 300mm × 300mm. The entire rock was cut into 16 parts. The gray part in the figure represents the rock matrix, and the thin black lines represent the cracks produced after cutting, indicating an unfilled state.

[0040] The third step is to prepare the rock samples and filling materials.

[0041] The rock sample model designed in the first step is cut according to the crack model. The cutting method is saw blade cutting or conventional wire cutting.

[0042] The filling material is used to fill the cracks in the cut rock samples. The filling material consists of ceramsite. Specifically, the ceramsite is made from bauxite, coal, and ceramic sintering, and features high temperature and pressure resistance, high strength, strong conductivity, and corrosion resistance. Different mesh sizes of the ceramsite result in different diameters, different crack filling rates, and different crack openings. Cracks with an opening of 0.1 mm are not filled. This achieves the simulation of multi-scale cracks. Table 1 below shows the particle size of ceramsite with different mesh sizes.

[0043] Table 1

[0044] The fourth step is to assemble the rock samples and fill them with filler material.

[0045] The splicing process involves arranging the cut rock blocks in sequence and filling them with a mixture of different mesh sizes of ceramic granules in a certain proportion to achieve different fracture seepage capacity and strength, thus meeting the high temperature and high pressure requirements of the gas field (temperature reaches 180℃, pressure resistance reaches 120 to 140 MPa).

[0046] Control the concentration and sand-laying method of the backfill material to ensure that the backfill material meets the permeability model of the fracture under a certain aperture. For example... Figure 2 The compaction is carried out according to the set crack opening. The compaction process requires the use of, for example, [unclear text - possibly a specific type of material]. Figure 3 The core holder shown.

[0047] like Figure 3 As shown, the core holder includes a core holder cylinder 6, which has interconnected sample placement cavities and a confining pressure through-hole perpendicular to the sample placement cavities. The confining pressure through-hole penetrates the core holder cylinder 6, with one end connected to a core holder inlet pipe 1 and the other end connected to a core holder outlet pipe 5. A pressurization port pipe 3 is connected to the core holder cylinder 6, and a venting port pipe 4 is connected to the pressurization port pipe 3.

[0048] The filled rock sample is placed into the sample placement chamber of the core holder. Then, pressure is applied to the rock sample through the pressurization port pipe 3 using the holder, and pressurization is also carried out through the inlet pipe 1 and outlet pipe 5 of the core holder. The pressurization is carried out for 1 to 1.5 hours. After the rock sample is compacted, the pressure is slowly reduced through the vent pipe 4, and the rock sample can then be removed from the core holder.

[0049] Step 5: Seal the rock sample.

[0050] The encapsulation process involves sealing the rock sample from the outside to prevent it from scattering due to other reasons, thus maintaining the external state of the rock sample. This ensures that the prepared multi-scale fractured rock sample can better match the multi-scale characteristics of fractures in ultra-deep low-porosity sandstone gas reservoirs, simulate the fluid flow law of ultra-deep fractured gas reservoirs, and predict the development dynamics of the gas field.

[0051] Example 2 The following is combined Figure 5 The specific embodiments of the present invention will be further described below.

[0052] In this embodiment, the number of seams in the geometric physical model is equal to 2.

[0053] like Figure 5 As shown, in this embodiment, a 300mm×300mm×300mm low-porosity sandstone is cut into four small cubes with dimensions of 14.9cm in length, width, and height. Figure 5 As shown in Figure a, line a1 represents a crack with a crack aperture of 2 mm, which is filled with 6 to 8 mesh ceramsite. The ceramsite is bonded with epoxy resin, and the mass ratio of ceramsite to epoxy resin is 20:1. The permeability of the filled crack formed by splicing reaches 2D (Darcy, i.e., L / m²•h).

[0054] like Figure 5 As shown in Figure a, line a2 represents a crack with an aperture of 1mm, which is filled with 16-26 mesh ceramic granules. Line a3 represents a crack with an aperture of 0.1mm, which is not filled but directly spliced ​​together, then wrapped with mesh and secured with binding wire. The specific steps are as follows: The first step is to prepare an outcrop rock, cut it to create an initial rock sample model, with the sample size being 300mm×300mm×300mm.

[0055] The second step involves using CAD drawing software to reconstruct the multi-scale nature of fractures in ultra-deep, low-porosity sandstone gas reservoirs based on the actual stratigraphic reservoir characteristics, and designing a similar physical model.

[0056] The third step is to perform secondary processing on the prepared initial rock sample model, import the designed physical model (dxf format file) into the CNC wire cutting machine operating software, and then cut the rock.

[0057] The fourth step involves mixing high-temperature and high-pressure resistant ceramic particles with adhesive in a specific ratio to create a crack-filling film. This film serves as a proppant for filling cracks, and is then used to fill and splice cut rock samples, forming a crack network combination pattern of different scales. The fifth step is to secure the rock sample with gauze and binding wire, and then seal it in a packaging box to ensure the integrity and stability of the rock sample, which will facilitate subsequent physical experiments.

[0058] Example 3 The following is combined Figure 6 The specific embodiments of the present invention will be further described below.

[0059] In this embodiment, the geometrical physical model has more than two fracture networks, which, compared to the two fracture networks in Embodiment 2, more accurately reflects the multi-scale characteristics, randomness, and anisotropy of fractures in underground rocks or other media. Randomness and anisotropy refer to the fact that fracture networks often exhibit significant spatial randomness and anisotropy, with highly irregular fracture directions, lengths, and connectivity. Nonlinear flow refers to the fact that fluid flow in fractures often exhibits nonlinear behavior, especially during fluid exchange between high-permeability fractures and low-permeability matrix.

[0060] like Figure 6 As shown, in this embodiment, 300mm×300mm×300mm low-porosity sandstone is cut to... Figure 6 The method involves cutting the material, with line b1 representing a crack with an aperture of 4mm. The crack is filled with 4-6 mesh ceramsite, which is then bonded with epoxy resin. The mass ratio of ceramsite to epoxy resin is 20:1. The resulting filled crack has a permeability of 2D. For example... Figure 6 As shown in line a, line b2 represents a crack with an aperture of 1mm, which is filled with 16-26 mesh ceramic granules, as indicated by line b2. Line b3 represents a crack with an aperture of 0.1mm, which is not filled but directly spliced, then wrapped with mesh and secured with binding wire. The specific steps are as follows: The first step is to prepare an outcrop rock, cut it to create an initial rock sample model, with the sample size being 300mm×300mm×300mm.

[0061] The second step involves using CAD drawing software to reconstruct the multi-scale nature of fractures in ultra-deep, low-porosity sandstone gas reservoirs based on the actual stratigraphic reservoir characteristics, and designing a similar physical model.

[0062] The third step is to perform secondary processing on the prepared initial rock sample model, import the designed physical model (dxf format file) into the CNC wire cutting machine operating software, and then cut the rock.

[0063] The fourth step involves mixing high-temperature and high-pressure resistant ceramic particles with adhesive in a specific ratio to create a crack-filling film. This film serves as a proppant for filling cracks, and is then used to fill and splice cut rock samples, forming a crack network combination pattern of different scales. The fifth step is to secure the rock sample with gauze and binding wire, and then seal it in a packaging box to ensure the integrity and stability of the rock sample, which will facilitate subsequent physical experiments.

[0064] Unless otherwise specified, the equipment components involved in the above embodiments are all conventional equipment components, and the structural settings, working methods or control methods involved are all conventional settings, working methods or control methods in the art unless otherwise specified.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing an ultra-deep multi-scale fractured rock sample, characterized in that, Includes the following steps: The geometric and physical model of the actual reservoir fracture is reproduced on a proportional scale, and the geometric and physical model of the actual reservoir fracture has a multi-scale fracture model. The rock is cut according to the established geometric and physical model of the actual reservoir fractures; Based on the geometric and physical model of the actual reservoir fractures, the cut rock blocks were reassembled into a single piece, and the filler was inserted into the cut rock fractures to restore the actual reservoir fractures to a proportional scale. After the prepared rock model is placed into the core holder, it is pressed and compacted.

2. The method according to claim 1, wherein, A geometric-physical model of the actual reservoir fractures was established using drawing software.

3. The method of claim 1, wherein the method further comprises, The number of fracture networks in the actual reservoir fracture geophysical model is less than or equal to 2.

4. The method of claim 1, wherein the method further comprises, The actual reservoir fracture geophysical model has more than two fracture networks.

5. The method of claim 1, wherein the method further comprises, The scale of fracture aperture in the geometric and physical models of actual reservoir fractures includes the micrometer and centimeter levels.

6. The method of claim 1, wherein the method further comprises, The rocks used are natural outcrops from the actual reservoir site or rocks with the same lithology as those on site.

7. The method for preparing ultra-deep multi-scale fractured rock samples according to claim 1, characterized in that, Rocks are cut using either a saw blade or wire cutting.

8. The method for preparing ultra-deep multi-scale fractured rock samples according to claim 1, characterized in that, Ceramsite was used to fill the rock fissures.

9. The method for preparing ultra-deep multi-scale fractured rock samples according to claim 1, characterized in that, Pressure is applied to the rock sample using a core holder for 1 to 1.5 hours, and then the pressure is slowly reduced to remove the rock sample from the core holder.

10. The method for preparing ultra-deep multi-scale fractured rock samples according to claim 1, characterized in that, The compacted rock sample is then sealed from the outside.

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