Shale reservoir artificial fracture relative permeability testing method based on resistivity

Abstract

The invention relates to a resistivity-based shale reservoir artificial fracture relative permeability testing method, which comprises the following steps of: respectively placing a plunger sample rock core, a parallel sample rock core X1, a parallel sample rock core X2 and a parallel sample rock core X3 which are subjected to resistivity testing and are filled with a propping agent into a special insulating rock core holder, and connecting the special insulating rock core holder into a rock core permeability testing device; reducing the reservoir temperature and pressure conditions of the core X3, and performing an independent measurement experiment on the core X3 by a steady-state method; drawing a relational graph of the propping agent filling crack resistance value and the water saturation: performing an experiment on the core X1 and the core X2 by a steady-state method, changing the oil-water injection ratio, and performing a re-experiment; determining the water saturation of the rock core proppant filling crack of the experimental group; calculating the relative permeability of the rock core X1 proppant filling crack; and drawing an oil-water relative permeability curve chart. The method can measure the water saturation of the proppant filling crack in real time under the shale oil reservoir temperature and pressure condition.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development, specifically to a method for testing the relative permeability of oil and water in artificially fractured fractures filled with proppant in shale reservoirs based on the resistivity method. Background Technology

[0002] Hydraulic fracturing is a crucial measure to enhance the productivity of shale reservoirs. It involves injecting proppant-laden fracturing fluid into the formation using high-pressure pumps on the surface, creating artificial fractures with a certain conductivity and providing seepage channels for oil and gas extraction. The two-phase flow characteristics of oil and water in proppant-filled fractures play a vital role in predicting and assessing reservoir productivity after fracturing. Among these, the water saturation of proppant-filled fractures is a key indicator for quantitatively evaluating the fluid flow characteristics of artificially fracturing fractures. This experiment requires real-time monitoring of the resistivity of proppant-filled fractures as a function of fluid saturation during displacement.

[0003] Existing technologies for measuring the relative permeability of oil and water mainly rely on the petroleum industry standard SYT5345-2007, which is divided into steady-state and non-steady-state methods. However, none of these methods address the measurement of oil-water relative permeability in core proppant-filled fracturing fractures based on resistivity methods. Existing technology (CN112986097A) discloses a method for measuring the relative permeability of oil and water in tight sandstone using a steady-state method incorporating resistivity measurement. However, this method involves measuring resistivity at room temperature and then inverting it to reservoir temperature and pressure conditions before calculating water saturation. This method cannot accurately reflect the resistivity values ​​under reservoir conditions, and the calculations are quite complex. Existing technology (CN113850030A) discloses a method and apparatus for determining the relative permeability of shale oil reservoirs, calculating relative permeability by establishing an oil-water two-phase flow model. However, this method involves significant computational load and complexity, and it does not consider the water absorption characteristics of shale. Existing technology (CN112881472A) uses nuclear magnetic resonance (NMR) and resistivity to measure various parameters of rock cores during displacement. However, when measuring water saturation, the resistivity value is primarily used as a correction tool. Existing technology (CN118794856A) discloses a resistivity-based visual monitoring method for fluid seepage in fractured rock masses, which characterizes seepage features within rock pores using resistivity, but does not use real fluids in experiments. The above methods are not applicable to proppant-filled fracturing fractures. Summary of the Invention

[0004] The purpose of this invention is to provide a resistivity-based method for testing the relative permeability of artificial fractures in shale reservoirs. This resistivity-based method addresses the problem that existing technologies cannot accurately reflect the relative permeability of artificial fractures filled with proppant in shale reservoirs under temperature and pressure conditions.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows: This method for testing the relative permeability of artificial fractures in shale reservoirs based on resistivity includes the following steps: Step 1: Place the plunger core samples X1, X2, and X3, which have been tested for resistivity and filled with proppant, into dedicated insulated core holders and connect them to the core permeability testing device. The surface of shale core X1 is in close contact with the test end of the strain sensor, which is connected to the strain sensor. Cores X1 and X2 in the core permeability testing device are connected to form a synchronous measurement system, while core X3 is measured separately. All dedicated insulated core holders are placed in a constant temperature system. Cores X1, X2, and X3 are connected to resistivity meters, and their respective rock portions are measured in parallel with the proppant. Step 2: After filling the fractures in core X3 with proppant and injecting fluid, restore the reservoir temperature and pressure conditions. Conduct a separate measurement experiment on core X3 using the steady-state method, and record the readings of the resistivity meter for core X3, including the initial resistance value R. 30 Record the oil flow rate, water flow rate, and resistivity meter reading R at the inlet and outlet of core X3 at time i. 3i ; Step 3: Draw a graph showing the relationship between the resistivity of the proppant-filled crack and the water saturation: Calculate the resistivity R of the proppant-filled crack. 3f , will be related to the resistance value R 3f Corresponding water saturation S w3 Importing the data points into a coordinate system with the corresponding water saturation level as the X-axis and the proppant-filled fracture resistance value as the Y-axis, a fitted linear regression equation is obtained through linear regression to obtain the proppant-filled fracture resistance value R. f With water saturation S w Relationship template; Step four: After restoring the reservoir temperature and pressure conditions of cores X1 and X2, experiments were conducted on cores X1 and X2 using the steady-state method. First, the resistivity meter readings and initial resistance values ​​R of cores X1 and X2 were recorded. 10 R 20 Using conversion factors through core X2 β The relationship between the resistivity and fluid saturation of shale core X1 in the experimental group was determined. Then, oil and water were injected into core X1 at a set ratio and flow rate. Water was then injected into core X2 at the same flow rate. Once the data stabilized, the volumetric flow rate of oil at the i-th injection ratio was recorded. Volumetric flow rate of water Resistivity meter reading R 1i R 2i The reading S from the strain sensor; Step 5, change the oil-water injection ratio: Under the condition that the total injection rate remains unchanged, inject oil and water in the following volume ratios: pure water, 1:20, 1:10, 1:5, 1:1, 5:1, 10:1, 20:1, pure oil. Repeat step 4 until the last oil-water injection ratio ends the test. When injecting at each level of oil-water flow rate ratio, each fluid should be injected at least 3 times the volume of the rock sample fracture, and the pressure difference between the two ends of the rock sample should be stable for more than 4 hours. When both of the above conditions are met, it is judged to be stable. Step 6: Determine the water saturation of the proppant-filled fractures in the core samples of the experimental group: Calculate the resistivity of the proppant-filled layer X1 in the core sample at the i-th injection ratio. Substituting this value into the template for the relationship between the resistance value of the proppant-filled crack and the water saturation, the corresponding water saturation S of the proppant-filled layer is obtained. w1 ; Step 7: Calculate the width of the proppant-filled fracture in core X1. : ; ; ; ; In the formula: p e Initial effective stress on shale proppant filling fractures; S For effective stress p e The readings of the strain sensor under the given conditions; W f For effective stress p e The proppant-filled crack width under the given conditions; L is the effective stress p e Perimeter of shale core X1 under the given conditions; ΔV c For effective stress p e Volume change of shale core X1 under the given conditions; C f V0 is the compressibility coefficient of the shale core; V0 is the initial volume of the core; h is the fracture length; d is the effective stress p. e Diameter of shale core X1 under the given conditions; Step 8, Calculation of relative permeability of core X1 proppant-filled fractures: As described in steps 4 and 5, after the strain sensor readings stabilize during pure water injection, immediately measure the permeability K of core X1 proppant-filled fractures, and use this as the absolute permeability of core X1; then calculate the relative permeability of oil and water in the proppant-filled fractures. , ; Step 9: Plot the oil-water relative permeability curve: using the water saturation S of the proppant-filled layer obtained in Step 6. w1 The corresponding oil and water relative permeability of the proppant-filled cracks was calculated in step eight. , Create a graph showing the relative permeability of oil and water.

[0006] The preparation methods of core X1, core X2 and core X3 in the above scheme are as follows: Parallel core samples with a diameter of 2.5 cm and a length of 5 cm are drilled from a full-size core sample of the shale oil reservoir and named core X1, core X2 and core X3 respectively; the precise lengths of the three core samples are measured as L1, L2 and L3, and the diameters of the three core samples are measured as D1, D2 and D3 respectively; a rough artificial crack is created on the three parallel core samples by wire cutting, passing through the center of the cross-section.

[0007] In the above scheme, the oil used in the steady-state method for individual measurement experiments on core X3 and the steady-state method for experiments on cores X1 and X2 is simulated shale oil. Simulated shale oil is prepared by blending dehydrated crude oil from the shale reservoir surface with kerosene, ensuring that the simulated shale oil has the same viscosity as the corresponding shale oil under reservoir temperature conditions. The water used in the experiment was formation water, and its viscosity under reservoir temperature conditions was [specifically determined]. .

[0008] The resistivity testing method described above is as follows: Cores X1, X2, and X3 are dried, and core X1 is then saturated with water. After complete saturation, it is placed in a dedicated insulated core holder. A core positioning auxiliary plug is used to fix the core in the middle position of the core holder. The temperature is increased to the reservoir temperature, and the confining pressure is increased. The resistivity value of the saturated water is then measured. Once the resistivity meter reading stabilizes, the initial resistivity value R of core X1 at 100% water saturation is obtained. w Then, core X1 was removed and dried. Next, cores X1, X2, and X3 were saturated with simulated oil. After full saturation, they were placed in a special insulated core holder. The cores were fixed in the middle position of the core holder using a core positioning auxiliary plug. The temperature was increased to the reservoir temperature, and the confining pressure was increased. The resistance values ​​of the three cores saturated with oil were tested. After the resistivity meter readings stabilized, the initial resistance value R of cores X1, X2, and X3 at 100% oil saturation was obtained. o1 R o2 and R o3 .

[0009] The proppant filling method in the above scheme is as follows: proppant is filled into cores X1, X2, and X3 respectively. Cores X1 and X3 are filled with mixed particle size proppant in the same way, while core X2 is filled with 20-mesh ceramsite. During filling, proppant pads are first placed in the artificial fractures, and the cores are wrapped with thermoplastic film. Then, the thermoplastic film is heated to press the cores tightly. Propant is filled into the artificial fractures while the proppant pads are slowly pulled out.

[0010] The specific method for step two in the above scheme is as follows: Core X3 proppant filling fracture filling fluid: Turn on the confining pressure pump, set its pressure to 3MPa, apply confining pressure to the core, ensure the core holder is well sealed, evacuate for 5 minutes, and then inject water into the core at the set injection pressure of 1MPa through the constant speed and constant pressure pump. When its injection flow rate is 0, the fracture is filled with water. Reduced reservoir temperature and pressure conditions: Minimum horizontal principal stress P in shale reservoirs h With bottom hole flowing pressure P w The difference is the initial effective stress P on the shale fracture. e Gradually increase the confining pressure to the minimum principal stress at the horizontal level, and simultaneously increase the fracture injection pressure to the bottom-hole flowing pressure, restoring the shale core and fractures to the initial reservoir temperature and pressure conditions, always maintaining the difference between the confining pressure and the fracture injection pressure as the initial effective stress value P. e ; The steady-state method was used to conduct experiments on core X3, and the readings of the resistivity meter on core X3 and the initial resistance value R were recorded. 30 Then, pure oil was injected into core X3 at a set flow rate, and the oil and water flow rates and resistivity meter readings R at the inlet and outlet of core X3 were recorded at time i. 3i .

[0011] The resistivity R of the proppant filling the crack in step three of the above scheme. 3f Calculation method: .

[0012] Step six in the above scheme is specifically as follows: Determine the water saturation of the proppant-filled fractures in the core samples of the experimental group: resistivity of the proppant-filled layer X1 in the core sample at the i-th injection ratio. calculate: Core X2 proppant filling resistivity calculate: ; In the formula: The initial resistance value was simultaneously measured by the X2 resistivity meter on the core. The initial resistivity of core X2 is given when the oil saturation is 100%. The resistivity value of the proppant filling layer in core X2; The resistivity R of the rock portion of core X2 at the i-th injection ratio o2i calculate: ; In the formula: The resistance value was simultaneously measured by the X2 resistivity meter of the core at the i-th injection ratio. Here, X2 represents the rock resistivity of the core at the i-th injection ratio; and X1 represents the proppant-filled layer resistivity of the core at the i-th injection ratio. calculate: ; ; In the formula: The resistivity value of the core measured by the resistivity meter at the i-th injection ratio; The resistivity value of the proppant-filled layer in core X1 at the i-th injection ratio; β These are conversion factors; The calculated resistivity value of the proppant-filled layer in core X1 Substituting the template for the relationship between proppant-filled crack resistance and water saturation obtained in step three, the corresponding water saturation S of the proppant-filled layer can be obtained. w1 .

[0013] Step eight in the above scheme is specifically as follows: According to steps four and five, when injecting pure water, after the value of the strain sensor tends to stabilize, immediately measure the permeability K of the core X1 proppant filling the fracture, as the absolute permeability of core X1. ; ; In the formula: This refers to the volumetric flow rate of water when pure water is injected. Where L is the viscosity of water; L is the length of the proppant-filled layer; A is the cross-sectional area of ​​the proppant-filled crack. To stabilize the pressure difference; Oil phase permeability K o : ; Aqueous phase permeability K w : ; In the formula: For volumetric flow rate; The volumetric flow rate of water; The viscosity of the oil; The viscosity of water; Propionate filling of cracks, relative permeability of oil and water , calculate: ; , Beneficial effects

[0014] 1. This invention enables real-time measurement of water saturation in proppant-filled fractures under temperature and pressure conditions in shale oil reservoirs, solving the problem of the lack of current methods for determining water saturation in proppant-filled fractures in shale oil.

[0015] 2. This invention establishes a resistivity-water saturation relationship template using parallel samples, eliminates the influence of shale matrix permeation effect on the true water saturation in the proppant-filled fractures, and improves the accuracy of saturation interpretation.

[0016] 3. This invention uses strain sensors to monitor changes in the perimeter of the core in real time, and combines the core compression coefficient and effective stress to achieve real-time monitoring of the width of the proppant-filled fractures, ensuring the accuracy and precision of subsequent calculations of the relative permeability of oil and water.

[0017] 4. Due to the water absorption characteristics of shale rock, this invention establishes a control group to monitor the impact of absorption during displacement. The experiment used three groups of core samples (experimental and control groups) connected in parallel with proppant for resistivity measurement. The two control groups determined the resistivity and fluid saturation of the proppant-filled layer within the core samples. Then, the experimental group used a steady-state method to measure the relative permeability of oil and water in the proppant-filled fractures, and used this to plot the relationship curves between oil / water relative permeability and water saturation. This allows for real-time measurement of water saturation and relative permeability curves of shale proppant-filled fractures based on resistivity at the target formation temperature. Ultimately, this provides accurate data support for predicting and evaluating reservoir productivity after hydraulic fracturing, offering favorable support for the efficient development of shale reservoirs. Attached Figure Description

[0018] Figure 1 A schematic diagram of the test system provided in this application; Figure 2 Template for the relationship between the resistivity of proppant filling cracks and water saturation; Figure 3 This is a graph showing the relative permeability of oil and water.

[0019] In the diagram: 1. Constant speed and constant pressure pump; 2. Intermediate container one; 3. Intermediate container two; 4. T-joint; 5. Water valve three; 6. Oil valve three; 7. Water valve one; 8. Oil valve one; 9. Oil valve two; 10. Water valve two; 11. Special insulated core holder three; 12. Special insulated core holder one; 13. Special insulated core holder two; 14. Resistivity meter three; 15. Resistivity meter one; 16. Resistivity meter two; 17. Differential pressure sensor; 18. Strain sensor; 19. Holder plug three; 20. Holder plug one; 2 1. Clamp plug II; 22. Confining pressure valve III; 23. Confining pressure valve I; 24. Confining pressure valve II; 25. Confining pressure pump III; 26. Confining pressure pump I; 27. Confining pressure pump II; 28. Phase separator I; 29. ​​Back pressure valve I; 30. Electric back pressure pump I; 31. Aqueous phase liquid collection system; 32. Oil phase liquid collection system; 33. Data collection system; 34. Experimental pipeline; 35. Strain sensor test terminal; 36. Data transmission line; 37. NMR constant temperature system; 38. Overpressure protection device; 39. Pressure gauge; 40. Waste liquid collection system. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings: Combination Figure 1 As shown, this method for testing the relative permeability of oil and water in proppant-filled fractures in shale cores based on resistivity utilizes a core plunger sample with a pre-set fracture diameter of approximately 2.5 cm and a length of approximately 5 cm, a dedicated core holder for resistivity testing, a strain sensor, a resistivity meter, and a phase separator to accurately determine the relative permeability of oil and water in proppant-filled fractures under shale oil reservoir conditions. The specific steps are as follows: Step 1, Preparation of experimental materials: Drill parallel core samples with a diameter of about 2.5 cm and a length of about 5 cm from the full-size core of the shale oil reservoir and name them X1, X2, and X3 respectively; measure their precise lengths as L1, L2, and L3, and their diameters as D1, D2, and D3 respectively. Create an artificial crack with a rough wall surface passing through the center of the cross-section of the three parallel core samples by wire cutting.

[0021] Step two, preparation of experimental fluids: Simulated shale oil is prepared by mixing dehydrated crude oil and kerosene from the shale reservoir surface, ensuring that it has the same viscosity as the corresponding shale oil under reservoir temperature conditions. The experimental water used was formation water, whose viscosity under reservoir temperature conditions was [not specified]. .

[0022] Step 3, Proppant Preparation: Based on the specifications of the proppant used for in-situ fracturing, determine the mesh size of the top and bottom sieves in the sieve group, screen the proppant samples, and discard all samples remaining in the top and bottom sieves. Then, screen 20-mesh ceramsite as the proppant for core X2.

[0023] Step 4: Saturate cores with fluid and test resistivity: Dry shale cores X1, X2, and X3. Then, saturate core X1 with water. Once fully saturated, place it in a dedicated insulated core holder. Use a core positioning auxiliary plug to fix the core in the center of the holder. Increase the temperature to the reservoir temperature and increase the confining pressure. Test the resistivity of the saturated water. Once the resistivity meter reading stabilizes, obtain the initial resistivity R of core X1 at 100% water saturation. w Then, core X1 was removed and dried. Cores X1, X2, and X3 were saturated with simulated oil. After full saturation, they were placed in a special insulated core holder. The cores were fixed in the middle position of the core holder using a core positioning auxiliary plug. The temperature was increased to the reservoir temperature, and the confining pressure was increased. The resistivity values ​​of the three cores saturated with oil were tested. After the resistivity meter readings stabilized, the initial resistivity R of cores X1, X2, and X3 at 100% oil saturation was obtained. o1 R o2 and R o3 .

[0024] Step 5, proppant filling: proppant is filled into three shale cores respectively. Cores X1 and X3 are filled with mixed particle size proppant in the same way, and core X2 is filled with 20-mesh ceramsite. First, proppant pads are pre-placed in the artificial fractures, and the cores are wrapped with thermoplastic film. Then, the thermoplastic film is heated to press the cores tightly. During the process of slowly removing the proppant pads, proppant is filled into the artificial fractures. Step Six, Instrument Assembly: Securely attach the test end 35 of the strain sensor to the surface of core X1, place it inside the dedicated insulated core holder, and use the core positioning auxiliary plug to fix the core in the center of the core holder. Then connect the resistivity meter and strain sensor using the data transmission line. Cores X2 and X3 are directly placed inside the dedicated insulated core holder and connected to the resistivity meter; then proceed as follows... Figure 1 The experimental pipelines are connected to the other experimental equipment as shown, so that cores X1 and X2 form a synchronous measurement system, while core X3 is measured separately. The rock portion of each core is measured in parallel with the proppant.

[0025] The core permeability testing apparatus includes an NMR constant temperature system 37, a constant speed and constant pressure pump 1, intermediate container one 2, intermediate container two 3, an overpressure protection device 38, a data collection system 33, experimental pipelines 34, a data transmission line 36, and X1, X2, and X3 testing mechanisms. The inlets of intermediate containers one 2 and intermediate container two 3 are both connected to the constant speed and constant pressure pump. The X1, X2, and X3 testing mechanisms are connected in parallel to the outlet pipelines of intermediate containers one and two via a tee connector 4. Intermediate container one 2 is filled with oil, and intermediate container two 3 is filled with water. The X1 testing mechanism includes a dedicated insulated core holder 12, a differential pressure sensor 17, a strain sensor 18, a resistivity meter 15, a phase separator 28, a back pressure valve 29, an electric back pressure pump 30, an oil phase liquid collection system 32, and an aqueous phase liquid collection system 31. The dedicated insulated core holder 12 is connected to a confining pressure valve 23 and a confining pressure pump 26. The oil phase inlet of the dedicated insulated core holder 12 is equipped with an oil valve 8, and the aqueous phase inlet of the dedicated insulated core holder 12 is equipped with a water valve 7. The two ends of the core X1 are connected to the holder plugs 20. The X2 testing mechanism includes a dedicated insulated core holder 213, a resistivity meter 216, a phase separator 2, a back pressure valve 2, an electric back pressure pump 2, an oil phase liquid collection system 2, and an aqueous phase liquid collection system 2. The dedicated insulated core holder 213 is connected to the confining pressure valve 24 and the confining pressure pump 27. The oil phase inlet of the dedicated insulated core holder 213 is equipped with an oil valve 29, and the aqueous phase inlet of the dedicated insulated core holder 213 is equipped with a water valve 20. The two ends of the core X2 are connected to the holder plugs 21. The X3 testing mechanism includes a dedicated insulated core holder 311, a resistivity meter 314, a phase separator 3, a back pressure valve 3, an electric back pressure pump 3, an oil phase liquid collection system 3, and an aqueous phase liquid collection system 3. The dedicated insulated core holder 311 is connected to the confining pressure valve 322 and the confining pressure pump 325. The oil phase inlet of the dedicated insulated core holder 311 is equipped with an oil valve 36, and the aqueous phase inlet of the dedicated insulated core holder 311 is equipped with a water valve 35. The two ends of the core X2 are connected to the holder plugs 219.

[0026] Step 7, Core X3 proppant filling fracture injection fluid: Turn on confining pressure pump 325, set its pressure to 3MPa, apply confining pressure to the core, ensure the core holder is well sealed, evacuate for 5 minutes, and then inject water into the core at the set injection pressure of 1MPa through constant speed and constant pressure pump. When its injection flow rate is 0, the fracture is filled with water.

[0027] Step 8, Reduction of reservoir temperature and pressure conditions: Minimum horizontal principal stress P of shale reservoir h With bottom hole flowing pressure P w The difference is the initial effective stress P on the shale fracture. eGradually increase the confining pressure to the minimum principal stress at the horizontal level, and simultaneously increase the fracture injection pressure to the bottom-hole flowing pressure, restoring the shale core and fractures to the initial reservoir temperature and pressure conditions (always maintaining the difference between the confining pressure and the fracture injection pressure as the initial effective stress value P). e ).

[0028] Step 9: Conduct experiments on core X3 using the steady-state method: Start only the experimental setup connected to core X3, and record the initial resistance value R of the resistivity meter for core X3. 30 Then, pure oil was injected into core X3 at a set flow rate, and the oil and water flow rates and resistivity meter readings R at the inlet and outlet of core X3 were recorded at time i. 3i .

[0029] Step 10: Plot the relationship between the resistivity of the proppant-filled fracture and the water saturation: The resistivity R obtained from the X3 core experiment... 3i The resistance value R of the proppant-filled crack is calculated using formula (1). 3f

[0030] The corresponding water saturation S w3 Importing the data points into a coordinate system with the corresponding water saturation level as the X-axis and the proppant-filled fracture resistance value as the Y-axis, a fitted linear regression equation is obtained through linear regression to obtain the proppant-filled fracture resistance value R. f With water saturation S w Relationship template.

[0031] Step 11: Conduct experiments on cores X1 and X2 using the steady-state method: First, restore the reservoir temperature and pressure conditions according to the process in Step 8. Then, start the experimental setup connected to cores X1 and X2 and conduct experiments on cores X1 and X2 using the steady-state method. First, record the readings of the resistivity meters for cores X1 and X2, and the initial resistance value R. 10 R 20 Using conversion factors through core X2 The relationship between the resistivity and fluid saturation of shale core X1 in the experimental group was determined. Then, oil and water were injected into core X1 at a set ratio and flow rate. Water was then injected into core X2 at the same flow rate. Once the instrument data stabilized, the volumetric flow rates of oil and water at the i-th injection ratio were recorded. , Resistivity meter reading R 1i R 2i The reading S from the strain sensor; Step 12, change the oil-water injection ratio: Under the condition that the total injection rate remains unchanged, inject oil and water in the following volume ratios: pure water, 1:20, 1:10, 1:5, 1:1, 5:1, 10:1, 20:1, and pure oil. Repeat step 11 until the last oil-water injection ratio is reached to end the test. For each oil-water flow rate ratio, each fluid should be injected at least three times the volume of the rock sample fracture, and the pressure difference across the rock sample should be stable for more than 4 hours. Stability is determined when both of these conditions are met.

[0032] Step 13: Determine the water saturation of the proppant-filled fractures in the core samples of the experimental group: resistivity of the proppant-filled layer X1 in the core sample at the i-th injection ratio. Calculate using formulas (2), (3), (4), and (5): Core X2 proppant filling resistivity calculate: ; In the formula: —The initial resistance value, in Ω, was simultaneously measured by the X2 resistivity meter on the core. —The initial resistivity of core X2 at 100% oil saturation, in Ω; —Resistivity of the proppant-filled layer in core X2, in Ω; The resistivity R of the rock portion of core X2 at the i-th injection ratio o2i calculate: ; In the formula: —The resistance value, in Ω, was simultaneously measured by the X2 resistivity meter of the core at the i-th injection ratio; —The resistivity of the rock portion of core X2 at the i-th injection ratio, in Ω; resistivity of the proppant-filled layer in core X1 at the i-th injection ratio calculate:

[0033]

[0034] In the formula: —The resistance value measured by the resistivity meter of the core at the i-th injection ratio, in Ω; —The resistivity of the proppant-filled layer in core X1 at the i-th injection ratio, in Ω; —Conversion factor; The calculated resistivity value of the proppant-filled layer in core X1 Substituting the template for the relationship between proppant-filled crack resistance and water saturation obtained in step ten, the corresponding water saturation S of the proppant-filled layer can be obtained. w1 .

[0035] Step Fourteen, Calculation of Propionate Filling Crack Width: Calculate the proppant filling crack width of core X1 using the strain sensor readings obtained in Step Eleven according to formulas (6), (7), (8), and (9). : ; ; ; ; In the formula: —Initial effective stress on shale proppant filling fractures, MPa; —Effective stress p e The strain sensor reading under the given conditions, in cm; —Effective stress p e The width of the proppant-filled crack under the specified conditions, in cm; L—Effective stress p e Perimeter of shale core X1 under the given conditions, in cm; —Effective stress p e Volume change of shale core X1 under the given conditions, in m 3 ; —Compression coefficient of shale core, MPa -1 ; —Initial core volume, m 3 ; — Crack length, cm; —Effective stress p e Diameter of shale core X1 under the given conditions, in cm.

[0036] Step 15, Calculation of relative permeability of core X1 proppant filling fractures: According to steps 11 and 12, after the value of the strain sensor tends to stabilize when injecting pure water, immediately measure the permeability K of core X1 proppant filling fractures, which is taken as the absolute permeability of core X1. ; ; In the formula: —Volume flow rate of water when pure water is injected, (cm³ / s); — Viscosity of water, (mPa·s); L—Length of proppant-filled layer, cm; A—Cross-sectional area of ​​the proppant filling the crack, cm²; —Stable pressure difference, MPa Oil phase permeability K o : ; Aqueous phase permeability K w : ; In the formula: , — Viscosity of oil and water (mPa·s) Propionate filling of cracks, relative permeability of oil and water , Calculated using formulas (14) and (15): ; ; Step 16, plot the oil-water relative permeability curve: Calculate the water saturation S of the proppant-filled layer obtained in Step 13. w1 The corresponding oil and water relative permeability of the proppant-filled cracks was calculated in step fifteen. , Plot the relative permeability curves of oil and water.

[0037] Example: Step 1: Material Preparation: Parallel core samples, approximately 2.5 cm in diameter and 5 cm in length, were drilled from a full-size core sample of the shale oil reservoir and named X1, X2, and X3 respectively. Their precise lengths L were measured to be 5.016 cm, 4.992 cm, and 5.008 cm, and their diameters D were 2.514 cm, 2.498 cm, and 2.498 cm. An artificial crack with a roughened surface was created on each of the three parallel core samples by wire cutting, passing through the center of the cross-section. Specific core parameters are shown in Table 1.

[0038] Table 1. Experimental Core Parameters Core Name Length L (cm) Diameter D (cm) <![CDATA[Volume V0 (cm³)]]> <![CDATA[X1]]> 5.016 2.514 24.90 <![CDATA[X2]]> 4.992 2.498 24.47 <![CDATA[X3]]> 5.008 2.498 24.54 Step two, preparation of experimental fluid: Simulated shale oil is prepared by mixing dehydrated crude oil and kerosene from the shale reservoir surface in a specific ratio. This simulated shale oil has the same viscosity as the corresponding shale oil at a reservoir temperature of 90℃. The pressure was 1.08 mPa•s; the experimental water was formation water, which was of the NaHCO3 type and had a salinity of 7.5 × 10⁻⁶. 3 mg / L, its viscosity at a reservoir temperature of 90℃ The value is 0.45 mPa·s.

[0039] Step 3, Proppant Preparation: Based on the specifications of the proppant used for in-situ fracturing, select a mixed particle size proppant with a ratio of 30 / 50 mesh: 40 / 70 mesh: 70 / 140 mesh = 1:3:6. Determine the mesh sizes of the top and bottom sieves in the sieve set to 30 mesh and 140 mesh, respectively. Screen the proppant sample, discarding all samples remaining in the top and bottom sieves. Then, screen 20-mesh ceramsite as the proppant for core X2.

[0040] Step 4: Saturate cores with fluid and test resistivity: Dry shale cores X1, X2, and X3 for 72 hours. Then, saturate core X1 with formation water. Once fully saturated, place it in a dedicated insulated core holder - 12. Use the core positioning auxiliary plug (holder plug - 20) to fix the core in the middle of the core holder. Raise the temperature to the reservoir temperature of 90℃, open the confining pressure pump - 26, and increase the confining pressure to 3MPa using the confining pressure valve 23. Test the resistance value of the saturated water. Once the reading on the resistivity meter - 15 stabilizes, obtain the initial resistance value R of core X1 when the water saturation is 100%. w The resistance was 311.62Ω. Then, core X1 was removed and dried for 72 hours. Simulated oil was saturated in cores X1, X2, and X3. After full saturation, the cores were placed in dedicated insulated core holders 3-11, 12-12, and 2-13. The cores were fixed in the middle position of the holders using plugs 3-19, 1-20, and 2-21. The temperature was raised to the reservoir temperature of 90℃. Confining pressure valves 3-22, 1-23, and 2-24 were opened. Confining pressure pumps 3-25, 1-26, and 2-27 were used to increase the confining pressure to 3MPa. The resistance values ​​of the three cores saturated with oil were tested. Once the readings of resistivity meters 3-14, 1-15, and 2-16 stabilized, the initial resistance value R of cores X1, X2, and X3 at 100% oil saturation was obtained. o1 1073.35Ω, R o2 For 1081.77Ω and R o3 It is 1086.34Ω.

[0041] Step 5, proppant filling: proppant is filled into three shale cores respectively. Cores X1 and X3 are filled with mixed particle size proppant in the same way, while core X2 is filled with 20-mesh ceramsite. The sand concentration is 5 kg / m² for all cores. First, proppant pads are pre-placed in the artificial fractures. The cores are then wrapped with thermoplastic film. The film is then heated to press the cores tightly. Propant is filled into the artificial fractures while the proppant pads are slowly removed.

[0042] Step Six, Instrument Assembly: Tightly attach the strain sensor test end 35 to the surface of core X1, place it inside the dedicated insulated core holder 12, and use the holder plug 20 to fix the core in the middle position of the core holder. Then, connect the resistivity meter 15 and the strain sensor 18 using the data transmission line 36. Cores X2 and X3 are placed inside the dedicated insulated core holders 13 and 11 using holder plugs 21 and 319, and connected to resistivity meters 16 and 14 respectively. Then proceed as follows... Figure 1 The experimental pipeline 34 is connected to the other experimental equipment as shown, so that cores X1 and X2 become a synchronous measurement system, while core X3 is measured separately. The rock portion of each core is measured in parallel with the proppant.

[0043] Step 7, Core X3 proppant filling fracture injection fluid: Open confining pressure pump 3 25 and confining pressure valve 22, set their pressure to 3MPa, apply confining pressure to the core, ensure the core holder 3 11 is well sealed, evacuate for 5 minutes, and then inject water from intermediate container 2 3 into the core at the set injection pressure of 1MPa through constant speed and constant pressure pump 1. When its injection flow rate is 0, the fracture is filled with water.

[0044] Step 8, Reduction of reservoir temperature and pressure conditions: Minimum horizontal principal stress P of shale reservoir h With bottom hole flowing pressure P w The difference is the initial effective stress P on the shale fracture. e Open confining pressure pump 25 and confining pressure valve 22 to gradually increase the confining pressure to the minimum principal stress of 55 MPa. Open constant speed and constant pressure pump 1 to simultaneously increase the fracture injection pressure to the bottom hole flowing pressure of 21 MPa, restoring the shale core and fractures to the initial reservoir temperature and pressure conditions (always maintaining the difference between the confining pressure and the fracture injection pressure as the initial effective stress value P). e =34 MPa).

[0045] Step 9: Conduct experiments on core X3 using the steady-state method: Open water valve 3.5 and oil valve 3.6, set the pressure of the back pressure valve to 2.5 MPa using the back pressure pump, start only the experimental setup connected to core X3, and record the initial resistance value R from the resistivity meter 3.14 of core X3. 30The resistance was 1027.02 Ω. Pure oil was then injected into core X3 at a set flow rate of 1.5 mL / min. The oil and water flow rates at the outlet of core X3 and the reading R of the resistivity meter were recorded at time i. 3i .

[0046] Step 10: Plot the relationship between the resistivity of the proppant-filled fracture and the water saturation: The resistivity R obtained from the X3 core experiment... 3i The resistance value R of the proppant-filled crack is calculated using formula (1). 3f ; The corresponding water saturation S w3 Importing the data points into a coordinate system with the corresponding water saturation level as the X-axis and the proppant resistivity as the Y-axis, a fitted linear regression equation is obtained using the linear regression method, yielding the proppant-filled crack resistivity value. With water saturation S w Relationship template. Table 2 shows the resistivity and water saturation data obtained from the X3 core experiment. The template for the relationship between resistivity and water saturation in proppant-filled fractures is as follows: Figure 2 As shown.

[0047] Table 2. Data on resistivity and water saturation of proppant-filled fractures obtained from core X3 experiments. Based on the above data, the linear regression equation is as follows: =-459.29S w +63972 (R²=0.9723).

[0048] Step 11: Conduct experiments on cores X1 and X2 using the steady-state method: First, reduce the reservoir temperature to 90℃ and the reservoir pressure to the initial effective stress value P, following the process described in Step 8. e =34 MPa, then open water valve 17, oil valve 18, oil valve 29, water valve 210, and close water valve 35 and oil valve 36. Set the pressure of the back pressure valve to 2.5 MPa using the back pressure pump, and start the experimental setup connected to cores X1 and X2. Conduct experiments on cores X1 and X2 using the steady-state method. First, record the readings of resistivity meters 15 and 26 of cores X1 and X2, and the initial resistance value R. 10 1013.56Ω, R 20 It is 1014.83Ω; using the conversion factor through core X2. The relationship between the resistivity and fluid saturation of shale core X1 in the experimental group was determined. Then, oil and water were injected into core X1 at a set ratio, followed by water at the same flow rate into core X2. Once the instrument data stabilized, the volumetric flow rates of oil and water at the i-th injection ratio were recorded using phase separator 28 and the aqueous phase liquid collection system 31 and oil phase liquid collection system 32 in the metering system. , Resistivity meter readings R15 and R216 1i R 2i The reading S of strain sensor 18 is 8.246 cm; the volumetric flow rate data of oil and water under different injection ratios are shown in Table 3.

[0049] Table 3. Volumetric flow rate data of oil and water at the i-th injection ratio. Step 12, change the oil-water injection ratio: Under the condition that the total injection rate remains unchanged, inject oil and water in the following volume ratios: pure water, 1:20, 1:10, 1:5, 1:1, 5:1, 10:1, 20:1, and pure oil. Repeat step 11 until the last oil-water injection ratio is reached to end the test. For each oil-water flow rate ratio, each fluid should be injected at least three times the volume of the rock sample fracture, and the pressure difference across the rock sample should be stable for more than 4 hours. Stability is determined when both conditions are met. Resistivity meter readings under different injection ratios are shown in Table 4.

[0050] Table 4. Resistivity meter readings R15 and R26 at the i-th injection ratio. 1i R 2i Numerical table Step 13: Determine the water saturation of the proppant-filled fractures in the core samples of the experimental group: resistivity of the proppant-filled layer X1 in the core sample at the i-th injection ratio. Calculate using formulas (2), (3), (4), and (5) (taking an oil-to-water ratio of 1:20 as an example): Core X2 proppant filling resistivity calculate:

[0051] The resistivity of the proppant-filled layer in core X2 with an oil-water injection ratio of 1:20 in core X1 was obtained using formula (2). It is 16461.4Ω.

[0052] Rock resistivity value R of core X2 o2i calculate:

[0053] The rock resistivity of core X2 under an oil-water injection ratio of 1:20 was obtained using formula (3). It is 1080.7Ω.

[0054] Core X1 proppant filling resistivity calculate:

[0055]

[0056] The conversion factor is obtained using formula (5). The resistivity of the core X1 proppant-filled layer is 0.992, obtained by formula (4) with an oil-to-water ratio of 1:20. It is 20059.2Ω.

[0057] The calculated resistivity value of the proppant-filled layer in core X1 Substituting the template for the relationship between proppant-filled crack resistance and water saturation obtained in step ten, the corresponding water saturation S of the proppant-filled layer can be obtained. w1 Table 5 shows the resistivity and corresponding water saturation data of the proppant-filled layer in core X1 under different injection ratios.

[0058] Table 5. Resistance values ​​and corresponding water saturation values ​​of the proppant-filled layer in core sample X1 at the i-th injection ratio. Step Fourteen, Calculation of Propionate Filling Crack Width: Calculate the proppant filling crack width of core X1 using the strain sensor readings obtained in Step Eleven according to formulas (6), (7), (8), and (9). ; ; ; ; ; In the formula: C f The compressibility of the shale core is 0.0002204 MPa. -1 .

[0059] The effective stress p is obtained from formula (7). e Shale core volume change X1 under certain conditions It is 0.1866 cm 3 The effective stress p is obtained through formula (8). e Shale core diameter X1 under the condition The effective stress p is 2.5046 cm, and can be obtained using formula (9). eUnder the given conditions, the perimeter L of the shale core X1 is 7.8683 cm. The effective stress p is obtained using formula (6). e Propion filling crack width under certain conditions It is 0.189 cm.

[0060] Step 15, Calculation of relative permeability of core X1 proppant filling fractures: According to steps 11 and 12, after the value of the strain sensor tends to stabilize when injecting pure water, immediately measure the permeability K of core X1 proppant filling fractures, which is taken as the absolute permeability of core X1. ; ; The cross-sectional area of ​​the proppant-filled fracture was calculated to be 0.473 cm² using formula (11). After the strain sensor reading stabilized, the absolute permeability K of the proppant-filled fracture in core X1 was calculated to be 1241.78 mD (no seepage occurred) using formula (10).

[0061] Oil phase permeability K o : ; Aqueous phase permeability K w : ; Propionate filling of cracks, relative permeability of oil and water , Calculated using formulas (14) and (15): ; .

[0062] Step 16: Plot the oil-water relative permeability curve: Repeat steps 13 to 15 to calculate the oil and water relative permeability values ​​under different injection ratios. , The calculated data are shown in Table 6. Due to the seepage and adsorption between the shale and the formation water used in the experiment, the water saturation obtained after the injection of pure water reaches stability is not 100%. The water saturation S of the proppant-filled layer obtained in step thirteen is... w1 The corresponding oil and water relative permeability of the proppant-filled cracks was calculated in step fifteen. , Plot the oil-water relative permeability curve, as follows: Figure 3 As shown.

[0063] Table 6. Relative permeability of oil and water in core X1 proppant-filled fractures under different injection ratios. This invention can accurately reflect the relative permeability of shale proppant-filled artificial fractures under reservoir temperature and pressure conditions.

Claims

1. A method for testing the relative permeability of artificial fractures in shale reservoirs based on resistivity, characterized in that... Includes the following steps: Step 1: Place the plunger core samples X1, X2, and X3, which have been tested for resistivity and filled with proppant, into dedicated insulated core holders and connect them to the core permeability testing device. The surface of shale core X1 is in close contact with the test end of the strain sensor, which is connected to the strain sensor. Cores X1 and X2 in the core permeability testing device are connected to form a synchronous measurement system, while core X3 is measured separately. All dedicated insulated core holders are placed in a constant temperature system. Cores X1, X2, and X3 are connected to resistivity meters, and their respective rock portions are measured in parallel with the proppant. Step 2: After filling the fractures in core X3 with proppant and injecting fluid, restore the reservoir temperature and pressure conditions. Conduct a separate measurement experiment on core X3 using the steady-state method, and record the readings of the resistivity meter for core X3, including the initial resistance value R. 30 Record the oil flow rate, water flow rate, and resistivity meter reading R at the inlet and outlet of core X3 at time i. 3i ; Step 3: Draw a graph showing the relationship between the resistivity of the proppant-filled crack and the water saturation: Calculate the resistivity R of the proppant-filled crack. 3f , will be related to the resistance value R 3f Corresponding water saturation S w3 Importing the data points into a coordinate system with the corresponding water saturation level as the X-axis and the proppant-filled fracture resistance value as the Y-axis, a fitted linear regression equation is obtained through linear regression, yielding the proppant-filled fracture resistance value R. f With water saturation S w Relationship template; Step four: After restoring the reservoir temperature and pressure conditions of cores X1 and X2, experiments were conducted on cores X1 and X2 using the steady-state method. First, the resistivity meter readings and initial resistance values ​​R of cores X1 and X2 were recorded. 10 R 20 Using conversion factors through core X2 β The relationship between the resistivity and fluid saturation of shale core X1 in the experimental group was determined. Then, oil and water were injected into core X1 at a set ratio and flow rate. Water was then injected into core X2 at the same flow rate. Once the data stabilized, the volumetric flow rate of oil at the i-th injection ratio was recorded. Volumetric flow rate of water Resistivity meter reading R 1i R 2i The reading S from the strain sensor; Step 5, change the oil-water injection ratio: Under the condition that the total injection rate remains unchanged, inject oil and water in the following volume ratios: pure water, 1:20, 1:10, 1:5, 1:1, 5:1, 10:1, 20:1, pure oil. Repeat step 4 until the last oil-water injection ratio ends the test. When injecting at each level of oil-water flow rate ratio, each fluid should be injected at least 3 times the volume of the rock sample fracture, and the pressure difference between the two ends of the rock sample should be stable for more than 4 hours. When both of the above conditions are met, it is judged to be stable. Step 6: Determine the water saturation of the proppant-filled fractures in the core samples of the experimental group: Calculate the resistivity of the proppant-filled layer X1 in the core sample at the i-th injection ratio. Substituting this value into the template for the relationship between the resistance value of the proppant-filled crack and the water saturation, the corresponding water saturation S of the proppant-filled layer is obtained. w1 ; Step 7: Calculate the width of the proppant-filled fracture in core X1. : ; ; ; ; In the formula: p e Initial effective stress on shale proppant filling fractures; S For effective stress p e The readings of the strain sensor under the given conditions; W f For effective stress p e The proppant-filled crack width under the given conditions; L is the effective stress p e Perimeter of shale core X1 under the given conditions; ΔV c For effective stress p e Volume change of shale core X1 under the given conditions; C f V0 is the compressibility coefficient of the shale core; V0 is the initial volume of the core; h is the fracture length; d is the effective stress p. e Diameter of shale core X1 under the given conditions; Step 8: Calculation of relative permeability of core X1 proppant-filled fractures: As described in steps 4 and 5, after the strain sensor readings stabilize during pure water injection, immediately measure the permeability K of core X1 proppant-filled fractures, and use this as the absolute permeability of core X1; then calculate the relative permeability of oil and water in the proppant-filled fractures. , ; Step 9: Plot the oil-water relative permeability curve: using the water saturation S of the proppant-filled layer obtained in Step 6. w1 The corresponding oil and water relative permeability of the proppant-filled cracks was calculated in step eight. , Create an oil-water relative permeability curve.

2. The method for testing the relative permeability of artificial fractures in shale reservoirs based on resistivity according to claim 1, characterized in that: The preparation method of core X1, core X2 and core X3 is as follows: parallel core samples with a diameter of 2.5 cm and a length of 5 cm are drilled from the full-size core sample of the shale oil reservoir and named core X1, core X2 and core X3 respectively; the precise lengths of the three core samples are measured as L1, L2 and L3 respectively, and the diameters of the three core samples are measured as D1, D2 and D3 respectively. The three parallel core samples are then wire-cut to create a rough wall artificial crack passing through the center of the cross-section.

3. The method for testing the relative permeability of artificial fractures in shale reservoirs based on resistivity according to claim 2, characterized in that: The oil used in the steady-state method for individual measurement experiments on core X3 and the steady-state method for experiments on cores X1 and X2 was simulated shale oil. Simulated shale oil was prepared by blending dehydrated crude oil from the shale reservoir surface with kerosene, ensuring that the simulated shale oil had the same viscosity as the corresponding shale oil under reservoir temperature conditions. The water used in the experiment was formation water, and its viscosity under reservoir temperature conditions was [specifically determined]. .

4. The method for testing the relative permeability of artificial fractures in shale reservoirs based on resistivity according to claim 3, characterized in that: The method for testing resistivity is as follows: Cores X1, X2, and X3 are dried, and then core X1 is saturated with water. After complete saturation, it is placed in a special insulated core holder. The core is fixed in the middle position of the core holder using a core positioning auxiliary plug. The temperature is increased to the reservoir temperature, and the confining pressure is increased. The resistivity value of the saturated water is measured. After the resistivity meter reading stabilizes, the initial resistivity value R of core X1 under the condition of 100% water saturation is obtained. w Then, core X1 was removed and dried. Next, cores X1, X2, and X3 were saturated with simulated oil. After full saturation, they were placed in a special insulated core holder. The cores were fixed in the middle position of the core holder using a core positioning auxiliary plug. The temperature was increased to the reservoir temperature, and the confining pressure was increased. The resistance values ​​of the three cores saturated with oil were tested. After the resistivity meter readings stabilized, the initial resistance value R of cores X1, X2, and X3 at 100% oil saturation was obtained. o1 R o2 and R o3 .

5. The method for testing the relative permeability of artificial fractures in shale reservoirs based on resistivity according to claim 4, characterized in that: The proppant filling method is as follows: proppant is filled into cores X1, X2, and X3 respectively, wherein cores X1 and X3 are filled with mixed particle size proppant in the same way, and core X2 is filled with 20-mesh ceramsite; during filling, a proppant pad is first placed in the artificial crack, the core is wrapped with a thermoplastic film, and then heated to press the thermoplastic film tightly into the core. During the process of slowly removing the proppant pad, proppant is filled into the artificial crack.

6. The method for testing the relative permeability of artificial fractures in shale reservoirs based on resistivity according to claim 5, characterized in that: The specific method for step two is as follows: Core X3 proppant filling fracture filling fluid: Turn on the confining pressure pump, set its pressure to 3MPa, apply confining pressure to the core, ensure the core holder is well sealed, evacuate for 5 minutes, and then inject water into the core at the set injection pressure of 1MPa through the constant speed and constant pressure pump. When its injection flow rate is 0, the fracture is filled with water. Reduced reservoir temperature and pressure conditions: Minimum horizontal principal stress P in shale reservoirs h With bottom hole flowing pressure P w The difference is the initial effective stress P on the shale fracture. e Gradually increase the confining pressure to the minimum principal stress at the horizontal level, and simultaneously increase the fracture injection pressure to the bottom-hole flowing pressure, restoring the shale core and fractures to the initial reservoir temperature and pressure conditions, always maintaining the difference between the confining pressure and the fracture injection pressure as the initial effective stress value P. e ; The steady-state method was used to conduct experiments on core X3, and the readings of the resistivity meter on core X3 and the initial resistance value R were recorded. 30 Then, pure oil was injected into core X3 at a set flow rate, and the oil and water flow rates and resistivity meter readings R at the inlet and outlet of core X3 were recorded at time i. 3i .

7. The method for testing the relative permeability of artificial fractures in shale reservoirs based on resistivity according to claim 6, characterized in that: The resistivity R of the proppant filling the crack in step three 3f Calculation method: 。 8. The method for testing the relative permeability of artificial fractures in shale reservoirs based on resistivity according to claim 7, characterized in that: Step six specifically involves: Determine the water saturation of the proppant-filled fractures in the core samples of the experimental group: resistivity of the proppant-filled layer X1 in the core sample at the i-th injection ratio. calculate: Core X2 proppant filling resistivity calculate: ； In the formula: The initial resistance value was simultaneously measured by the X2 resistivity meter on the core. The initial resistivity of core X2 is given when the oil saturation is 100%. The resistivity value of the proppant filling layer in core X2; The resistivity R of the rock portion of core X2 at the i-th injection ratio o2i calculate: ； In the formula: The resistance value was simultaneously measured by the X2 resistivity meter of the core at the i-th injection ratio. Here, X2 represents the rock resistivity of the core at the i-th injection ratio; and X1 represents the proppant-filled layer resistivity of the core at the i-th injection ratio. calculate: ； ； In the formula: The resistivity value of the core measured by the resistivity meter at the i-th injection ratio; The resistivity value of the proppant-filled layer in core X1 at the i-th injection ratio; β These are conversion factors; The calculated resistivity value of the proppant-filled layer in core X1 Substituting the template for the relationship between proppant-filled crack resistance and water saturation obtained in step three, the corresponding water saturation S of the proppant-filled layer can be obtained. w1 .

9. The method for testing the relative permeability of artificial fractures in shale reservoirs based on resistivity according to claim 8, characterized in that: Step eight specifically involves: According to steps four and five, when injecting pure water, after the value of the strain sensor tends to stabilize, immediately measure the permeability K of the core X1 proppant filling the fracture, as the absolute permeability of core X1. ； ； In the formula: This refers to the volumetric flow rate of water when pure water is injected. Where L is the viscosity of water; L is the length of the proppant-filled layer; A is the cross-sectional area of ​​the proppant-filled crack. To stabilize the pressure difference; Oil phase permeability K o : ； Aqueous phase permeability K w : ； In the formula: For volumetric flow rate; The volumetric flow rate of water; The viscosity of the oil; The viscosity of water; Propion filling cracks, oil and water relative permeability , calculate: ； 。

Images