Breakage control type fracture-cavity rock core preparation method considering reserve ratio

Abstract

The invention belongs to the field of oil and gas field development, and relates to a break-control fracture-cavity rock core preparation method considering the reserve ratio, an outcrop rock core is adopted for manufacturing, so that the roughness and wettability of a fracture-cavity wall surface are kept consistent with those of a real reservoir, the shapes and connectivity relations of rock core cracks and holes are controllable, and the reserve ratios of different parts in a rock core can be considered; meanwhile, the rock core can bear high temperature and high pressure and is suitable for being put into a rock core holder for high-temperature and high-pressure experiments. According to the method for preparing the artificial breaking control type fracture-cavity rock core, the reliability of an oil and gas reservoir indoor physical simulation experiment result is improved, so that physical property parameters such as porosity, permeability and saturation and a seepage mechanism of a full oil field reservoir are simulated more accurately, and a relatively strong technical support is provided for obtaining the physical property parameters such as porosity, permeability and saturation required by oil and gas development of an oil field.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas field development, and in particular relates to a method for preparing fault-controlled fracture-cavity cores taking reserve ratio into consideration. Background Art

[0002] Indoor simulation experiments using representative reservoir cores are usually necessary to obtain key reservoir parameters, understand reservoir development laws, and formulate scientific development plans. Fractures and holes are the main storage space and seepage channels for fault-controlled fracture-cavity reservoirs. Since the size, shape, and connectivity of fractures and holes in such reservoirs are very complex, and the reservoir physical properties are highly heterogeneous, it is difficult to obtain representative reservoir cores, whether it is downhole coring or field outcrop coring.

[0003] At present, there are three main ways to prepare simulated cores: one is to use a plug core with poorly developed fractures in the actual reservoir to establish a one-dimensional core model by artificially creating fractures and holes; the other is to use an etched transparent glass plate to establish a two-dimensional large-size flat core model, and to use 3D sand filling technology to prepare a three-dimensional core model. Peng Song et al. (Peng Song, Guo Ping. Physical simulation of water injection development of fracture-cavity carbonate condensate gas reservoirs [J]. Experimental Petroleum Geology, 2014 (5): 5.) used plug cores to artificially create holes and used stress fracturing to establish connected fractures to simulate fracture-cavity cores, but this method is too rough in depicting fractures and holes, and is quite different from the fracture-cavity connection mode in the real reservoir. Wang Lu et al. (Wang Lu, Yang Shenglai, Peng Xian, et al. Visualization experiment of water storage characteristics in multiple reservoir types of fracture-cavity carbonate gas reservoirs [J]. Acta Petrolei Sinica, 2018 (6): 11.) used the fracture-cavity carbonate reservoir of the Sinian system in the Sichuan Basin as a template, and used laser to perform fine engraving on organic glass to construct a visualized fracture-cavity structure model composed of different reservoir spaces such as fractures, cracks, etc. However, the flat core model cannot withstand high temperature and high pressure, and also ignores the influence of the porous medium of the reservoir on the fluid and the interaction between the rock and the fluid. Zheng Jun et al. proposed a "parameter-controllable fracture-cavity reservoir artificial core preparation method" (CN109357921A), which poured cement mortar into a core mold made of paraffin, and then melted the paraffin into liquid and flowed out of the core through the cracks, thereby obtaining an artificial core of a fracture-cavity reservoir. However, the fracture-cavity characterization of the three-dimensional core cannot accurately characterize parameters such as cave size or fracture aperture. At present, the geometric dimensions of fractures and holes in physical simulation are relatively regular and the degree of characterization is relatively rough, which makes it difficult to characterize the actual fracture and hole morphology; at the same time, the existing physical simulation models cannot simulate the actual wettability, roughness and adsorption performance, resulting in large differences from the actual capillary force.

[0004] In view of the problem that the core preparation in the current indoor experiments on fault-controlled fracture-cavity oil and gas reservoirs is not representative enough, it is necessary to conduct in-depth research. Summary of the invention

[0005] The object of the present invention is to provide a preparation method of a fault-controlled fracture-vug core considering reserve ratio, which solves the problem of insufficient representativeness in the preparation of cores for indoor physical simulation experiments of fault-controlled fracture-vug oil and gas reservoirs.

[0006] The present invention is realized through the following technical solutions:

[0007] The present invention discloses a preparation method of a fault-controlled fracture-vug core considering reserve ratio, comprising the following steps:

[0008] 1) Select outcrop rock samples of the target block, cut the outcrop rock samples in half, select the part of the outcrop rock samples without cracks and holes, and drill full-diameter cores;

[0009] 2) Clean and dry the drilled full-diameter cores, test the porosity of the full-diameter cores, and then cut the full-diameter cores in half along the axis;

[0010] 3) Extract the fracture-vug network and connectivity according to the typical profile of the target fault-controlled fracture-vug oil and gas reservoir to obtain the extracted profile; the extracted profile includes main fractures, branch fractures, main holes and branch holes;

[0011] 4) Numerically process the extracted profile to obtain the sizes of the main fractures, branch fractures, main holes and branch holes;

[0012] 5) Calculate the main fracture reserves based on the size of the main fractures, calculate the branch fracture reserves based on the size of the branch fractures, calculate the main hole reserves based on the size of the main holes, and calculate the branch hole reserves based on the size of the branch holes;

[0013] According to the main fracture reserves V1, branch fracture reserves V2, main hole reserves V3, branch hole reserves V4, the size of the full-diameter core obtained in step 1) and the porosity obtained in step 2), calculate the core matrix pore reserves V5;

[0014] 6) Adjust the depth sizes of the main fractures, branch fractures, main holes and branch holes so that V1∶V2∶V3∶V4∶V5 meets the design requirements, then the adjusted target fault-controlled fracture-vug oil and gas reservoir is obtained;

[0015] 7) Import the adjusted target fault-controlled fracture-vug oil and gas reservoir into the processing equipment, place the core cut in half in step 2) on the processing equipment, and perform carving;

[0016] 8) Evenly apply epoxy resin glue to the surface of the core without carved fractures and vugs, then align the cores cut in half, fix them, and cure them to obtain the prepared fault-controlled fracture-vug core.

[0017] Further, in step 2), petroleum ether is used for cleaning.

[0018] Further, in step 2), the core is dried at 70 - 100 °C.

[0019] Further, in step 2), the porosity of the full - diameter core is tested according to the core analysis method.

[0020] Further, in step 4), the extracted profile is numerically processed using Auto CAD software.

[0021] Further, in step 4), the sizes of the main cracks, branch cracks, main holes and branch holes are specifically as follows:

[0022] The width of the main crack is X1, the length is L1, and the depth is h1;

[0023] The width of the branch crack is X2, the length is L2, and the depth is h2;

[0024] The surface area of the main hole is S1, and the depth is h3;

[0025] The surface area of the branch hole is S2, and the depth is h4.

[0026] Further, in step 5), the calculation formula for the main crack reserve is V1 = X1×L1×h1, the calculation formula for the branch crack reserve is V2 = X2×L2×h2, the calculation formula for the main hole reserve is V3 = S1×h3, and the calculation formula for the branch hole reserve is V4 = S2×h4.

[0027] Further, the calculation formula for the core matrix pore reserve is

[0028] wherein, the radius of the full - diameter core is r and the length is L.

[0029] Further, in step 7), a corundum jade carving knife is used for carving.

[0030] Further, in step 8), after fixation, the curing is specifically as follows: after fixing with a round hoop, it is placed in a high - temperature oven and kept at a constant temperature of 400 - 500 K for 2 - 3 hours.

[0031] Compared with the prior art, the present invention has the following beneficial technical effects:

[0032] The present invention provides a method for preparing a fracture-controlled vuggy core considering the reserve ratio. By using outcrop cores, the roughness and wettability of the vuggy wall surfaces are made consistent with those of the actual reservoir. Moreover, the shapes and connectivity relationships of the fractures and pores in the core are controllable, and the reserve ratio of different parts of the core can be considered, making it more in line with the geological characteristics of fracture-controlled vuggy oil and gas reservoirs. At the same time, the core can withstand high temperature and high pressure and is suitable for being placed in a core holder for high temperature and high pressure experiments. The method of preparing the artificial fracture-controlled vuggy core of the present invention improves the reliability of the indoor physical simulation experiment results of such oil and gas reservoirs, enables more accurate simulation of the physical properties such as porosity, permeability, and saturation and the seepage mechanism of the reservoirs in the Fuman Oilfield, and provides strong technical support for obtaining the physical property parameters such as porosity, permeability, and saturation required for oil and gas development in the oilfield. Description of the Drawings

[0033] Figure 1 is the full-diameter core section drilled;

[0034] Figure 2 is the schematic diagram of a typical section of the target fracture-controlled vuggy oil and gas reservoir;

[0035] Figure 3 is the image after numericalization of the core of the typical section;

[0036] Figure 4 is the physical diagram of the completed fracture-controlled vuggy core;

[0037] Wherein: 1, main fracture; 2, main pore; 3, branch fracture; 4, branch pore. Detailed Embodiment

[0038] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further detailed description is given in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0039] The components described and shown in the drawings and embodiments of the present invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present invention provided in the following drawings is not intended to limit the scope of the present invention claimed, but only represents a selected embodiment of the present invention. Based on the drawings and embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention.

[0040] It should be noted that: The term "comprising", "including" or any other variant is intended to cover non-exclusive inclusion, such that a process, element, method, article or device that comprises a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article or device.

[0041] The present invention discloses a method for preparing a fracture-controlled and cavernous core considering reserve ratio, comprising the following steps:

[0042] 1) Select outcrop rock samples from the target block, cut the outcrop rock samples in half, select the part of the outcrop rock samples without cracks and holes, and drill full-diameter cores;

[0043] 2) Clean the drilled full-diameter cores, dry them at 70-100 °C, test the porosity of the full-diameter cores, and then cut the full-diameter cores in half along the axis;

[0044] 3) Extract the fracture-cavity network and connectivity according to the typical profile of the target fracture-controlled and cavernous oil and gas reservoir to obtain the extracted profile; the extracted profile includes main fracture 1, branch fracture 3, main cavity 2 and branch cavity 4;

[0045] 4) Numerically process the extracted profile to obtain the sizes of main fracture 1, branch fracture 3, main cavity 2 and branch cavity 4;

[0046] 5) Calculate the reserve of main fracture 1 based on the size of main fracture 1, calculate the reserve of branch fracture 3 based on the size of branch fracture 3, calculate the reserve of main cavity 2 based on the size of main cavity 2, and calculate the reserve of branch cavity 4 based on the size of branch cavity 4;

[0047] According to the reserve V1 of main fracture 1, the reserve V2 of branch fracture 3, the reserve V3 of main cavity 2, the reserve V4 of branch cavity 4, the size of the full-diameter core obtained in step 1) and the porosity obtained in step 2), calculate the pore reserve V5 of the core matrix;

[0048] 6) Adjust the depth sizes of main fracture 1, branch fracture 3, main cavity 2 and branch cavity 4 so that V1∶V2∶V3∶V4∶V5 meets the design requirements, then the adjusted target fracture-controlled and cavernous oil and gas reservoir is obtained;

[0049] 7) Import the adjusted target fracture-controlled and cavernous oil and gas reservoir into the processing equipment, place the core cut in half in step 2) on the processing equipment, and perform carving;

[0050] 8) Evenly apply epoxy resin glue to the surface of the core without carved fractures and cavities, then fit the cut-in-half cores together, fix them, and cure them to obtain the prepared fracture-controlled and cavernous core.

[0051] After fixation, the curing is specifically as follows: After fixing with a round hoop, it is placed in a high-temperature oven and kept at a constant temperature of 400 - 500 K for 2 - 3 hours.

[0052] The features and performance of the present invention will be further described in detail below in conjunction with embodiments.

[0053] The present invention discloses a preparation method for a fracture - controlled and vuggy core considering the reserve ratio, including the following steps:

[0054] 1) Select outcrop rock samples from the target block. Cut the outcrop rock in half, select the part of the rock without cracks and holes, and drill a full - diameter core with a radius of r = 50 mm and a length of L = 150 mm.

[0055] 2) Clean the drilled full - diameter core with petroleum ether, then dry the core at 70 °C, and then test the porosity of the full - diameter core in accordance with the national standard GB / T 29172 - 2012 "Core Analysis Method". After that, cut the full - diameter core in half along the axis (see Figure 1 );

[0056] 3) According to the typical cross - section schematic diagram of the target fracture - controlled and vuggy oil and gas reservoir ( Figure 2 ), extract the fracture - vug network and connectivity, including the trends of the main fracture 1 and branch fractures 3, and the shapes and sizes of the main vugs 2 and branch vugs 4.

[0057] 4) Use Auto CAD software to numerically process the extracted cross - section schematic diagram to obtain an image as shown in Figure 3 . In Figure 3 , the number 1 represents the main fracture, 2 represents the vug on the main fracture, i.e., the main cavity, 3 represents the branch fracture, and 4 represents the vug on the branch fracture, i.e., the branch cavity.

[0058] After measurement, the width of the main fracture 1 is X1 = 8 mm, the length is L1 = 250 mm, the depth is h1 = 20 mm, the width of the branch fracture 3 is X2 = 4 mm, the length is L2 = 200 mm, the depth is h2 = 20 mm, the surface area of the vug on the main fracture 1 is S1 = 815 mm 2 , the depth h3 = 40 mm, the surface area of the vug on the branch fracture 3 is S2 = 145 mm 2 , and the depth h3 = 20 mm;

[0059] 5) The reserve of the main fracture 1 is V1 = X1×L1×h1 = 8×250×20 = 40000 mm 3 , and the reserve of the branch fracture 3 is V2 = X2×L2×h2 = 4×200×20 = 16000 mm 3, the pore storage volume on the main crack 1 is V3 = S1×h3 = 815×40 = 32600mm 3 , the pore storage volume on the branch crack 3 is V4 (mm 3 ) = S2×h4 = 145×20 = 2900mm 3 , the pore storage volume of the core matrix is

[0060] 6) The storage volume ratio within the core is V1∶V2∶V3∶V4∶V5 = 40000∶16000∶32600∶2900∶108600 ≈ 10∶4∶8∶1∶30, meeting the requirements of the experimental design. The numerical model is imported into the numerical control machine tool;

[0061] 7) Place the core on the numerical control machine tool, use a diamond jade carving tool with a diameter of a = 1mm and an effective tool length of b = 25mm. The parameters during carving are set as follows: rotational speed c = 20000 revolutions per minute, feed d = 1000mm per minute, depth of cut per layer e = 0.005mm, and replace the carving tool every 1.5 hours;

[0062] 8) After the carved fracture - controlled fracture - cave core is completed, Figure 4 , evenly apply epoxy resin glue to the surface of the core where the fractures and caves are not carved. Then, align the split core halves, fix them with a round hoop, and place them in a high - temperature oven, keeping them at a constant temperature for two hours at 453K;

[0063] 9) After the core cools down, remove the round hoop, put on a lead cylinder, and then place it in a full - diameter core holder for standby.

[0064] The present invention uses numerical software to extract the fracture - cave network and connectivity, adjusts the main crack 1, branch crack 3, and depth using numerical software, and adopts a unique carving technique on the numerical control machine tool to make the core, which is applicable to high - temperature and high - pressure experiments and provides reliable physical property parameters for the efficient development of oil and gas fields.

[0065] This method is simple in making a real core, and the properties of fractures and caves, connection modes, and storage volume ratios are controllable. It is a method for making a fracture - controlled fracture - cave core applicable to high - temperature and high - pressure experiments.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific implementation manners of the present invention. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A preparation method of fracture-controlled vuggy core considering reserve ratio, characterized in that, It includes the following steps: 1) Select outcrop rock samples of the target block, cut the outcrop rock samples in half, select the part of the outcrop rock sample without cracks and holes, and drill full-diameter cores; 2) Clean and dry the drilled full-diameter cores, test the porosity of the full-diameter cores, and then cut the full-diameter cores in half along the axis; 3) Extract the fracture-vug network and connectivity according to the typical profile of the target fault-controlled fracture-vug reservoir to obtain the extracted profile; the extracted profile includes main fractures (1), branch fractures (3), main vugs (2) and branch vugs (4); 4) Numerically process the extracted profile to obtain the sizes of the main fractures (1), branch fractures (3), main vugs (2) and branch vugs (4); 5) Calculate the reserves of the main fractures (1) based on the size of the main fractures (1), calculate the reserves of the branch fractures (3) based on the size of the branch fractures (3), calculate the reserves of the main vugs (2) based on the size of the main vugs (2), and calculate the reserves of the branch vugs (4) based on the size of the branch vugs (4); According to the reserves V1 of the main fractures (1), the reserves V2 of the branch fractures (3), the reserves V3 of the main vugs (2), the reserves V4 of the branch vugs (4), the size of the full-diameter core obtained in step 1) and the porosity obtained in step 2), calculate the pore reserves V5 of the core matrix; 6) Adjust the depth sizes of the main fractures (1), branch fractures (3), main vugs (2) and branch vugs (4) so that V1∶V2∶V3∶V4∶V5 meets the design requirements, then the adjusted target fault-controlled fracture-vug reservoir is obtained; 7) Import the adjusted target fault-controlled fracture-vug reservoir into the processing equipment, place the core cut in half in step 2) on the processing equipment, and perform carving; 8) Evenly apply epoxy resin glue to the surface of the core without carved fractures and vugs, then put the core cut in half together, fix it, and cure it to obtain the prepared fault-controlled fracture-vug core.

2. The preparation method of fracture-controlled vuggy core considering reserve ratio according to claim 1, characterized in that, In step 2), petroleum ether is used for cleaning.

3. The preparation method of fracture-controlled vuggy core considering reserve ratio according to claim 1, characterized in that, In step 2), the core is dried at 70-100°C.

4. The preparation method of fracture-controlled vuggy core considering reserve ratio according to claim 1, characterized in that, In step 2), the porosity φ of the full-diameter core is tested according to the core analysis method.

5. The preparation method of fracture-controlled vuggy core considering reserve ratio according to claim 1, characterized in that, In step 4), Auto CAD software is used to numerically process the extracted profile.

6. The preparation method of fracture-controlled vuggy core considering reserve ratio according to claim 1, characterized in that, In step 4), the sizes of the main fractures (1), branch fractures (3), main vugs (2) and branch vugs (4) are specifically: The width of the main fracture (1) is X1, the length is L1, and the depth is h1; The width of the branch fracture is X2, the length is L2, and the depth is h2; The surface area of the main vug (2) is S1, and the depth is h3; The surface area of the branch vug (4) is S2, and the depth is h4.

7. The preparation method of fracture-controlled vuggy core considering reserve ratio according to claim 6, characterized in that, In step 5), the calculation formula for the reserves of the main fractures (1) is V1 = X1×L1×h1, the calculation formula for the reserves of the branch fractures (3) is V2 = X2×L2×h2, the calculation formula for the reserves of the main vugs (2) is V3 = S1×h3, and the calculation formula for the reserves of the branch vugs (4) is V4 = S2×h4.

8. The preparation method of fracture-controlled vuggy core considering reserve ratio according to claim 7, characterized in that, The calculation formula for the pore storage of the core matrix is V5 = (πr 2 ×L - V1 - V2 - V3 - V4) × φ; Among them, the radius of the full-diameter core is r and the length is L.

9. The preparation method of fracture-controlled vuggy core considering reserve ratio according to claim 1, characterized in that, In step 7), a diamond abrasive jade carving knife is used for carving.

10. The preparation method of fracture-controlled vuggy core considering reserve ratio according to claim 1, characterized in that, In step 8), after fixation, the curing is specifically as follows: After fixing with a circular hoop, it is placed in a high-temperature oven and kept at a constant temperature of 400 - 500 K for 2 - 3 hours.

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