Core fracturing process resistivity measuring device under high temperature and high pressure and fracture measuring and calculating method

Abstract

The application belongs to the field of core fracturing test, and particularly relates to a device for measuring resistivity in a core fracturing process under high temperature and high pressure and a method for measuring and calculating fractures. The method for measuring and calculating fractures measures and corrects the rock resistance in the fracturing process, establishes an evolution model of the resistance in the fracturing process, and calculates the equivalent hydraulic opening of the rock fractures after fracturing under different temperature and confining pressure conditions. The method for measuring and calculating fractures collects the injection pressure and the evolution of the resistivity in the fracturing process under different temperature and confining pressure conditions, establishes the relationship between the resistivity and the rock cracking, and explores the precursor of the hydraulic fracturing of the rock. The method for measuring and calculating fractures can also establish the relationship between the fracture pressure and the opening and development area of the hydraulic fractures formed by the hydraulic fracturing of the high temperature and high pressure rock.

Description

Technical Field

[0001] This application relates to the field of core fracturing test technology, and in particular to a resistivity measuring device and a method for calculating fractures during the core fracturing process under high temperature and high pressure. Background Technology

[0002] Since the beginning of the 21st century, the global energy crisis and environmental pollution have intensified, making the development and application of clean and sustainable energy a focus of global attention. Geothermal resources are widely distributed, rich in energy, and possess enormous development potential. Studies show that utilizing geothermal energy can save the equivalent of 596 million barrels (81 million tons) of oil annually, preventing the emission of 78.1 million tons of carbon and 252.6 million tons of carbon dioxide into the atmosphere. Enhanced Geothermal Systems (EGS) are an important means of developing and utilizing geothermal resources. EGS refers to injecting a heat transfer medium into an artificially modified high-permeability fracture system to extract the thermal energy contained in high-temperature underground rocks. The heat transfer medium can be injected downwards along the injection well, heated through contact with the rock, and then pumped to the surface through production wells.

[0003] Electromagnetic methods are effective in reflecting the electrical evolution of rocks during hydraulic fracturing. However, in geothermal reservoirs, the electrical evolution of rocks and the development of fractures during reservoir stimulation are both influenced by the high-temperature and high-pressure environment in which the rocks are located. Moreover, the fracture aperture of the rocks after reservoir stimulation is a key factor in evaluating the reservoir stimulation status. Therefore, it is necessary to conduct research on the resistivity evolution of rocks during fracturing under high-temperature and high-pressure conditions, obtain the rock resistivity evolution throughout the fracturing process, and propose a method for measuring the fracture development of rocks after fracturing. Summary of the Invention

[0004] This application provides a resistivity measuring device and a fracture calculation method for the core fracturing process under high temperature and high pressure. It is intended to explore the resistivity change characteristics of rocks and their influencing factors during the core fracturing process, as well as the fracture development after core fracturing under different conditions.

[0005] To achieve the above objectives, this application provides a resistivity measuring device for core fracturing under high temperature and high pressure, comprising a core holder, a temperature control system, a pressure application system, a fracturing fluid injection system, a high-resolution X-ray three-dimensional monitoring system, and a resistivity measuring system. The core holder includes a core chamber, with a right insulating plug and a left insulating plug respectively installed at both ends of the core chamber. A right electrode and a left electrode are respectively embedded on opposite sides of the right and left insulating plugs. An inlet guide pipe is provided on the right insulating plug. A right conical ring and a left conical ring are respectively fitted onto the right and left insulating plugs. A rubber sleeve is provided between the right and left conical rings. The interior of the rubber sleeve is used to hold the rock sample. A metal cylinder is provided outside the rubber sleeve. The right and left insulating plugs respectively seal both ends of the metal cylinder. The metal cylinder and the rubber sleeve... A confining pressure cavity is formed between the metal cylinder and the left insulating plug. A right locking cap and a left locking cap are respectively provided on the outer sides of the right insulating plug and the left insulating plug. A nut is provided on the right locking cap, and the nut passes through the right locking cap to press against the rock sample. An axial pressure cavity is provided on the left locking cap, and an annular slider is provided in the axial pressure cavity to press against the rock sample and apply axial pressure. A heat insulation layer is provided on the outer sides of the metal cylinder, the right locking cap, and the left locking cap. The temperature control system is electrically connected to a heating resistor, which is located between the metal cylinder and the heat insulation layer. The pressure application system is connected to the confining pressure cavity and the axial pressure cavity to provide confining pressure and axial pressure to the rock sample. The fracturing fluid injection system injects fracturing fluid into the rock sample through the inlet guide pipe. The resistivity measurement system is used to electrically connect the right electrode and the left electrode to obtain the resistance value of the rock sample.

[0006] This application also provides a fracture calculation method based on the resistivity measuring device for the core fracture process under high temperature and high pressure described above. The fracture calculation method includes the following steps: S1. Measure the resistance of the inlet guide tube and record it as... ; S2. Select a rock sample in the resource target area and drill a fracturing hole on the end face of one end of the rock sample. The depth of the fracturing hole is the same as the length of the inlet guide pipe extending out of the right insulating plug. S3. Place the rock sample in the core chamber, put the left locking cap and the right locking cap on both ends of the metal cylinder respectively, insert the inlet guide tube into the fracturing hole on the rock sample, tighten the left locking cap, the right locking cap and the nut, and seal and fix the rock sample in the core chamber; S4. Apply a preset axial pressure and a preset temperature to the rock sample, and then apply a preset confining pressure to the rock sample after holding it at the preset temperature for more than 2 hours. S5. Cyclicly discharge the left and right electrodes, and measure the resistance R of the entire rock sample using the resistivity measurement system; S6. The apparent resistivity of a rock sample with a central hole before fracturing is calculated using the following formula: (1) (2) (3) in, R The resistance of the entire rock sample. and For the resistivity of rock samples from different regions, The apparent resistivity of the rock sample before fracturing. This refers to the cross-sectional area of ​​the rock sample excluding the fracture holes. This represents the cross-sectional area of ​​the fracturing hole; S7. The fracturing fluid injection system injects fracturing fluid into the fracturing hole of the rock sample through the inlet guide pipe, and records the resistivity of the rock sample throughout the fracturing process. R Injection pressure in the inlet guide tube P and fluid flow rate Q Inject pressure P The first peak value is the crack initiation pressure value. P 0; S8. After hydraulic fracturing, stop the injection of fracturing fluid and measure the resistivity of the entire rock sample after hydraulic fracturing. The hydraulic fracture resistance formed by hydraulic fracturing is calculated using the following formula: (4) in, This represents the electrical resistance of the entire rock sample after fracturing. and The hydraulic fracture resistance is distributed on both sides of the fracturing hole. The electrical resistance of the rock matrix after fracturing; S9. X-ray scan the rock samples from the fracturing process and convert them into CT projection images of hydraulic fractures to obtain the distribution area of ​​hydraulic fractures after fracturing, as well as the length and width of the fractures; S10. Disconnect the power supply to the heating resistor, unload the confining pressure and axial pressure, and remove the rock sample after the device has cooled naturally; S11. After drying the fractured rock sample, place it in the clamp and set the same temperature, confining pressure, and axial pressure as in step S4. Measure the resistance of the entire rock sample in step S5 and substitute it into formula (1). Then, in formula (1)... Replace with Since hydraulic fractures are mainly distributed on the side of the fracturing hole, assuming The electrical resistance of the fractured rock matrix remains unchanged. Perform calculations; S12. The hydraulic fracture resistance is defined as: (5) in, The length of the crack is in meters (m). The width of the crack is expressed in meters (m). The equivalent hydraulic aperture of the fracture is expressed in meters (m). The resistivity of water; S13. Calculate according to formula (5) respectively. and Then and Substituting into formula (4), the equivalent hydraulic aperture of the fracture formed after hydraulic fracturing is calculated. ; S14. Repeat steps S1-S13 under different conditions of temperature, confining pressure, axial pressure, and fracturing fluid to obtain the injection pressure, apparent resistivity, fracture development area, and equivalent hydraulic aperture of the rock samples under different conditions.

[0007] The resistivity measuring device and fracture calculation method for core fracturing under high temperature and high pressure provided in this application have the following advantages compared with the prior art: 1. The resistivity measuring device for core fracturing under high temperature and high pressure can be tested under the simultaneous action of high temperature and high pressure to simulate the fracturing of rocks in deep geothermal reservoirs. At the same time, the resistivity measuring system can monitor the changes in rock resistivity in real time during the fracturing process. 2. Fracture Calculation Method: By measuring and correcting the rock resistance during the fracturing process, a resistance evolution model of the fracturing process is established, and the equivalent hydraulic aperture of the rock fracture after fracturing under different temperature and confining pressure conditions is calculated. 3. Fracture Calculation Method: By collecting data on the evolution of injection pressure and resistivity during the fracturing process under different temperature and confining pressure conditions, the relationship between resistivity and rock fracturing initiation is established, and the precursors of hydraulic fracturing in rocks are explored. It can also establish the relationship between fracturing initiation pressure and the aperture and development area of ​​hydraulic fractures formed by high-temperature and high-pressure rock hydraulic fracturing.

[0008] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] in: Figure 1 This is a schematic diagram of the resistivity measuring device for core fracturing under high temperature and high pressure conditions, as shown in one embodiment of this application. Figure 2 yes Figure 1 A schematic diagram of the core holder structure; Figure 3 This is a simplified electrical resistance model of a rock sample before fracturing. Figure 4 This is a simplified electrical resistance model of a rock sample after fracturing.

[0011] Explanation of key component symbols: 101-Inlet guide pipe; 102-Outlet guide pipe; 103-Core chamber; 104-Rubber sleeve; 105-First water-stop rubber ring; 106-Containing pressure cavity; 107-Right insulating plug; 108-Left insulating plug; 109-Right conical ring; 110-Left conical ring; 111-Right electrode; 112-Left electrode; 113-Metal cylinder; 114-Nut; 115-Insulation layer; 116-Annular slider; 117-Right locking cap; 118-Left locking cap; 119-Right bolt; 120-Left bolt; 121-Second water-stop rubber ring; 122-Third water-stop rubber ring; 123-Fourth water-stop rubber ring; 124-Fifth water-stop rubber ring; 201-Resistivity measuring instrument; 202-Wire; 203-Computer acquisition system; 301-Fracturing fluid container; 302-Constant speed and constant pressure pump; 303-Air pump; 304-Tail fluid collection container; V1-First valve; V2-Second valve; 401-Pressure pump; 402-Confining pressure inlet; 403-Axial pressure inlet; V3-Third valve; V4-Fourth valve; P1-Axial pressure gauge; P2-Confining pressure gauge; 501-Temperature control component; 502-Heating component; 503-Heating resistor; 504-Temperature probe; 601-High-resolution X-ray three-dimensional monitoring system; T-Temperature meter. Detailed Implementation To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many other different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0012] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0013] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0014] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this application, "a plurality of" means two or more, unless otherwise expressly and specifically defined.

[0015] 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 application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0016] Embodiments of this application provide a resistivity measuring device for the core fracturing process under high temperature and high pressure, such as... Figure 1 and Figure 2As shown, the system includes a core holder, a temperature control system, a pressure application system, a fracturing fluid injection system, a high-resolution X-ray three-dimensional monitoring system 601, and a resistivity measurement system. The core holder has a core chamber 103, with a right insulating plug 107 and a left insulating plug 108 at its two ends. A right electrode 111 and a left electrode 112, made of brass, are respectively embedded in the right insulating plug 107 and the left insulating plug 108. The right electrode 111 and the left electrode 112 are in close contact with the two end faces of the rock sample during measurement. The right insulating plug 107 and the left insulating plug 108 are respectively... An inlet guide pipe 101 and an outlet guide pipe 102 are provided. The portion of the inlet guide pipe 101 extending beyond the right insulating plug 107 is used to enter the fracturing hole at one end of the rock sample. A first water-stopping rubber ring 105 is provided between the fracturing hole and the inlet guide pipe 101. A right conical ring 109 and a left conical ring 110 are respectively fitted outside the right insulating plug 107 and the left insulating plug 108. The opposite side of the right conical ring 109 and the left conical ring 110 is conical and fitted with a rubber sleeve 104. The inside of the rubber sleeve 104 is used to place the rock sample. The rubber sleeve 104 holds the core chamber 103, the right insulating plug 107, and the left insulating plug 108. The outer side of the insulating plug 108 is tightly fitted and wrapped. A metal cylinder 113 is fitted over the rubber sleeve 104. A second water-stop rubber ring 121 and a third water-stop rubber ring 122 are respectively provided between the metal cylinder 113 and the right conical ring 109 and the left conical ring 110. A confining pressure cavity 106 is formed between the metal cylinder 113 and the rubber sleeve 104. The confining pressure cavity 106 is connected to the pressure application system through the confining pressure inlet 402. The outer sides of the right insulating plug 107 and the left insulating plug 108 are the right locking cap 117 and the left locking cap 118, respectively. The right locking cap 117 and the left locking cap 118 are respectively secured by the right bolt 1. 19 and left bolt 120 are connected to both ends of metal cylinder 113. A nut 114 is provided on right locking cap 117. The rock sample is fixed and sealed by tightening nut 114. A pressure cavity is provided inside left locking cap 118. The pressure cavity is connected to pressure application system through pressure inlet 403. Annular slider 116 applies axial pressure to rock sample in core chamber 103 under axial pressure. A fourth water-stop rubber ring 123 and a fifth water-stop rubber ring 124 are provided between annular slider 116 and left locking cap 118. Heat insulation layer 115 is provided on the outside of metal cylinder 113, right locking cap 117 and left locking cap 118.

[0017] The resistivity measurement system includes a resistivity measuring instrument 201, a wire 202, and a computer acquisition system 203. The resistivity measuring instrument 201 is electrically connected to the left electrode 112 and the right electrode 111 via the wire 202. By cyclically discharging the electrodes, the resistivity value at different locations on the rock sample during the fracturing process is measured. It can measure the resistance value at different locations at both ends of the rock sample in real time, and the computer acquisition system 203 collects and calculates the resistance value data.

[0018] Among them, the brass electrodes on the right insulating plug 107 and the left insulating plug 108 are connected to the resistivity measuring instrument 201 through the wire 202. The resistivity measuring instrument 201, the wire 202, the right electrode 111, the rock sample, and the left electrode 112 form a closed circuit.

[0019] The electrode points on the right insulating plug 107 and the left insulating plug 108 correspond to each other. The metal cylinder 113, the right insulating plug 107 and the left insulating plug 108 have scale markings. During installation, the insulating plugs are fixed at both ends of the core chamber 103 according to the scale markings.

[0020] The fracturing fluid injection system includes a fracturing fluid container 301, a constant speed and pressure pump 302, an air pump 303, and a tail fluid collection container 304. The fracturing fluid container 301 is connected to the inlet guide pipe 101 through the constant speed and pressure pump 302. A second valve V2 is provided between the inlet guide pipe 101 and the constant speed and pressure pump 302. The constant speed and pressure pump 302 is also connected to the air pump 303, which provides high-pressure air to the constant speed and pressure pump 302. A first valve V1 is provided between the air pump 303 and the constant speed and pressure pump 302. The fracturing fluid injection system is used to control the flow rate and injection pressure of the injected fracturing fluid. The constant speed and pressure pump 302 can inject the prepared fracturing fluid at a set pressure or flow rate, and can also collect the injection pressure and flow rate of the fracturing fluid. The fracturing fluid container 301 is used to store the prepared fracturing fluid. The constant speed and constant pressure pump 302 controls the injection pressure and flow rate of the fracturing fluid. The fracturing fluid enters the core holder through the second valve V2. After the rock is fracturing, it flows out from the outlet guide pipe 102 and is collected by the tail fluid collection container 304.

[0021] The pressure application system includes a pressure pump 401, a confining pressure inlet 402 connected to the confining pressure cavity 106, an axial pressure inlet 403 connected to the axial pressure cavity, and axial pressure gauges P1 and P2. The confining pressure inlet 402 is located on the metal cylinder 113, and the axial pressure inlet 403 is located on the left locking cap 118. The pressure pump 401 is connected to both the confining pressure inlet 402 and the axial pressure inlet 403. The confining pressure gauge P2 is located on the communication path between the pressure pump 401 and the confining pressure inlet 402. Gauge P2 reads the confining pressure value through confining pressure inlet 402. Axial pressure gauge P1 is located on the communication path between pressure pump 401 and axial pressure inlet 403. Axial pressure gauge P1 reads the axial pressure value through axial pressure inlet 403. A third valve V3 is located upstream of confining pressure gauge P2, and a fourth valve V4 is located upstream of axial pressure gauge P1. The third valve V3 is a confining pressure valve, and the fourth valve V4 is an axial pressure valve. Pressure pump 401 controls the injection of hydraulic oil through the third valve V3 and the fourth valve V4. The pressure application system is used to provide and control the confining pressure and axial pressure for the rock sample.

[0022] The temperature control system includes a temperature control component 501, a heating component 502, a heating resistor 503, a temperature probe 504, a heat insulation layer 115, and a temperature meter T. The heating component 502 is connected to the heating resistor 503 and controls the power of the heating resistor 503. The temperature probe 504 is mounted on the metal cylinder 113. The temperature control system is used to provide a high-temperature environment for the core chamber 103. The heating resistor 503 can heat the core chamber 103 to 250℃, meeting the temperature requirements for geothermal development. The heating resistor 503 is installed on the outer circumference of the metal cylinder 113 to provide heat to the core chamber 103. The heat insulation layer 115 wraps around the metal cylinder 113, the right locking cap 117, and the left locking cap 118. The temperature probe 504 is mounted on the metal cylinder 113. The heating component 502 is connected to the heating resistor 503, and the temperature control component 501 is connected to the temperature probe 504. The heating component 502 controls the on / off state of the heating resistor 503 to heat the core chamber 103. The temperature control component 501 monitors the temperature in real time via the temperature probe 504. The temperature measured by the temperature probe 504 is displayed by the temperature meter T and fed back to the temperature control component 501, thereby maintaining an accurate and constant temperature. The insulation layer 115 maintains the temperature inside the core chamber 103 at a high temperature.

[0023] The core holder forms a closed space through a rubber sleeve 104, a right insulating plug 107, a left insulating plug 108, a right conical ring 109, a left conical ring 110, a metal cylinder 113, a nut 114, a right locking cap 117, a left locking cap 118, a right bolt 119, and a left bolt 120. The rock sample used in the test is placed in the closed space. The rubber sleeve 104 and each water-stopping rubber ring are made of high-temperature, high-pressure, and corrosion-resistant materials, which are not easily damaged under high temperature, high pressure, and fracturing fluid and can be used multiple times in the test. The right electrode 111 and the left electrode 112 are respectively embedded inside the right insulating plug 107 and the left insulating plug 108. Through the squeezing of the annular slider 116 and the nut 114, the right electrode 111 and the left electrode 112 are in close contact with the two end faces of the rock sample, thereby reducing the resistivity measurement error. Both the right insulating plug 107 and the left insulating plug 108 are made of high-temperature and high-pressure resistant insulating materials, forming a sealed space with the rubber sleeve 104, so that the current flows only between the electrode and the rock sample; the inlet guide pipe 101 extends into the fracture hole of the rock sample, which can deliver the fracturing fluid to the designated fracturing position. A first water-stop rubber ring 105 is provided between the inlet guide pipe 101 and the fracture hole to prevent leakage of fracturing fluid during the test; the left locking cap 118 is provided with an axial pressure cavity, and a fourth water-stop rubber ring 123 and a fifth water-stop rubber ring 124 are provided between the annular slider 116 and the left locking cap 118. When the axial pressure cavity is injected with axial pressure oil through the axial pressure inlet 403, the annular slider 116 will apply axial pressure to the rock sample; The rubber sleeve 104, the right conical ring 109, the left conical ring 110 and the metal cylinder 113 constitute the confining pressure cavity 106. When confining pressure oil is injected into the confining pressure cavity 106 through the confining pressure inlet 402, the rock sample inside the rubber sleeve 104 will be subjected to confining pressure. The resistivity measurement system can measure the resistance value of rock samples at different locations in real time during the hydraulic fracturing process of rock under high temperature and high pressure; the fracturing fluid injection system provides fracturing fluid with stable pressure and flow rate to the core holder; the pressure application system provides pressure to the confining pressure chamber 106 and the axial pressure chamber of the core holder and controls it; the temperature regulation system can provide a high temperature environment for the core holder and control it.

[0024] This invention also provides a method for measuring fractures during the hydraulic fracturing process of rock under high temperature and high pressure conditions. The method utilizes the aforementioned resistivity measuring device for the hydraulic fracturing process of rock under high temperature and high pressure. The specific operation process is as follows: S1. Measure the resistance of the inlet guide tube 101 and record it as... ; S2. Select rock samples in the resource target area and drill a fracturing hole on the end face of one end of the rock sample. The depth of the fracturing hole is the same as the length of the inlet guide pipe 101 extending out of the right insulating plug 107. The rock sample preparation is as follows: a complete rock sample is selected from the resource target area, and the rock sample is processed into a cylindrical sample with a diameter of Φ50mm×100mm in the laboratory. A circular hole with a diameter of Φ10mm is drilled at the center of one end of the sample using a drilling machine. The drilling depth is matched with the length of the inlet guide pipe 101 extending out of the right insulating plug 107. Before the test, the height a and radius b of the cylindrical sample need to be measured again to avoid processing errors. The fracturing fluid is prepared according to the groundwater of the thermal reservoir in the resource target area or the fracturing fluid developed. S3. Place the rock sample in the core chamber 103, put the left locking cap 118 and the right locking cap 117 on both ends of the metal cylinder 113 respectively, insert the inlet guide tube 101 into the fracturing hole on the rock sample, tighten the left locking cap 118, the right locking cap 117 and the nut 114 to seal and fix the rock sample in the core chamber 103; The rock sample loading and sealing process is as follows: Place the processed cylindrical sample into the core chamber 103, place the right insulating plug 107 and the left insulating plug 108 into both ends of the rock, put the right locking cap 117 and the left locking cap 118 onto both ends of the metal cylinder 113, tighten the nut 114, and seal and fix the rock sample. S4. Apply a preset axial pressure and a preset temperature to the rock sample, and then apply a preset confining pressure to the rock sample after holding it at the preset temperature for more than 2 hours. The axial pressure loading test is as follows: Open the fourth valve V4 and control the pressure pump 401 to inject high-temperature hydraulic oil into the axial pressure cavity through the axial pressure inlet 403. After the value on the axial pressure gauge P1 stabilizes at the set value, close the fourth valve V4. By pushing the annular slider 116 and the nut 114 together, the insulating plug is pressed, so that the sixth water-stop rubber ring 125 is pressed, preventing the brass electrode from contacting water and making the brass electrode close to the end face of the rock sample. The first water-stop rubber ring 105 between the fracturing hole on the rock sample and the inlet guide pipe 101 is pressed to prevent the fracturing fluid from leaking during the test. The test temperature loading is as follows: The metal cylinder 113 is heated by heating component 502 and heating resistor 503. After the temperature display of temperature meter T reaches the set value, the temperature is maintained and controlled at the set value for more than 2 hours. The specific confining pressure loading test is as follows: Open the third valve V3, control the pressure pump 401 to inject high-temperature resistant hydraulic oil into the confining pressure chamber 106 through the confining pressure inlet 402, and close the third valve V3 after the confining pressure value on the confining pressure gauge P2 stabilizes at the set value to maintain the confining pressure. S5. Cyclicly discharge the left electrode 112 and the right electrode 111, and measure the resistance of the entire rock sample using a resistivity measurement system. R ; Specifically, the resistance measurement adopts electrical data acquisition, as follows: turn on the resistivity measuring instrument 201, perform cyclic discharge on the right electrode 111 and the left electrode 112, and at the same time, collect the current and voltage of the electrodes through the computer acquisition system 203.

[0025] S6. Simplify the rock sample resistivity distribution before fracturing to Figure 3 The apparent resistivity of a rock sample with a central pore before fracturing is calculated using the following formula: (1) (2) (3) in, R The resistance of the entire rock sample. and For the resistivity of rock samples from different regions, The apparent resistivity of the rock sample before fracturing. This refers to the cross-sectional area of ​​the rock sample excluding the fracture holes. This represents the cross-sectional area of ​​the fracturing hole; S7. The fracturing fluid injection system injects fracturing fluid into the fracturing hole of the rock sample through the inlet guide pipe 101, and records the resistivity of the rock sample throughout the fracturing process. R Injection pressure into inlet guide pipe 101 P and fluid flow rate Q Inject pressureP The first peak value is the crack initiation pressure value. P 0; The fracturing fluid injection is as follows: Open the first valve V1, air pump 303, and constant speed and pressure pump 302; open the second valve V2 to inject fracturing fluid into the core holder. Simultaneously, the tail fluid collection container 304 collects the fluid after fracturing. During the test, the constant speed and pressure pump 302 continuously monitors the injection pressure of the fracturing fluid. P Fluid flow rate Q Monitoring and data collection were conducted, and the first peak value of the injection pressure was recorded as the fracturing initiation pressure. P 0; S8. After fracturing, stop the injection of fracturing fluid, measure the resistivity of the entire rock sample after hydraulic fracturing, and simplify the resistivity distribution of the rock sample after hydraulic fracturing as follows: Figure 4 The hydraulic fracture resistance formed by hydraulic fracturing is calculated using the following formula: (4) in, This represents the electrical resistance of the entire rock sample after fracturing. and The hydraulic fracture resistance is distributed on both sides of the fracturing hole. The electrical resistance of the rock matrix after fracturing; S9. High-resolution X-ray three-dimensional monitoring system 601, which uses an X-ray source to scan rock samples in a high-temperature and high-pressure holder with X-rays, receives the X-rays that pass through the rock sample with a detector and converts them into CT projection images, which are then input into a computer for processing; the computer identifies the development of fractures based on the CT projection images. The high-resolution X-ray three-dimensional monitoring system 601 is activated to scan the rock sample during the fracturing process with X-rays, and then convert it into a CT projection image of the hydraulic fracture to obtain the distribution area of ​​the hydraulic fracture after fracturing, as well as the length and width of the fracture. S10. Disconnect the power supply to the heating resistor 503, unload the confining pressure and axial pressure, and remove the rock sample after the device has cooled naturally; S11. Due to the roughness of the rock fracture surface, the resistance of the rock matrix will increase to a certain extent. Therefore, after drying the fractured rock sample, it is placed in a holder, and the same temperature, confining pressure, and axial pressure as in step S4 are set. The resistance of the entire rock sample is measured in step S5 and substituted into formula (1). Replace with Since hydraulic fractures are mainly distributed on the side of the fracturing hole, assuming The electrical resistance of the fractured rock matrix remains unchanged. Perform calculations; S12. The hydraulic fracture resistance is defined as: (5) in, The length of the crack is in meters (m). The width of the crack is expressed in meters (m). The equivalent hydraulic aperture of the fracture is expressed in meters (m). The resistivity of water; S13. Calculate according to formula (5) respectively. and Then and Substituting into formula (4), the equivalent hydraulic aperture of the fracture formed after hydraulic fracturing is calculated. ; S14. Repeat steps S1-S13 under varying temperatures, confining pressures, axial pressures, and fracturing fluids to obtain the injection pressure, apparent resistivity, fracture development area, and equivalent hydraulic aperture of the rock samples under different conditions. Repeat steps S1-S13 under different temperatures, confining pressures, and fracturing fluids to obtain resistivity and fracture data for the rock samples under different conditions. Analyze and explore the response law of resistivity before and after hydraulic fracturing under different temperatures, confining pressures, and fracturing fluids, as well as the relationship between temperature, confining pressure, and fracture development. Furthermore, analyze the relationship between fracturing initiation pressure and fracture development to establish a correlation between the two.

[0026] The influence of rock compression caused by confining pressure under different temperature conditions on the length and cross-sectional area of ​​the rock sample is considered, thereby correcting the resistivity of the rock sample. That is, between steps S4 and S5 above, the following steps are also included: Take rock samples from the same batch as the test samples and measure the elastic modulus E(T) of the rock samples under different test temperature conditions. For high temperature and high pressure conditions, the length and cross-sectional area of ​​the rock samples are corrected using the following formula: (11) (12) (13) (14) in, To correct the length of the previous rock sample, The length of the corrected rock sample; The axial compression experienced by the rock sample; To correct the diameter of the previous rock sample, To correct the diameter of the rock sample; The confining pressure exerted on the rock sample; The diameter of the fracturing hole; This represents the cross-sectional area of ​​the entire rock sample. This refers to the cross-sectional area of ​​the rock sample excluding the fracture holes. This represents the cross-sectional area of ​​the fracturing hole.

[0027] The corrected rock sample length and cross-sectional area can be substituted into the resistivity calculation formulas (4), (5) and (6) for calculation.

[0028] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0029] The above embodiments merely illustrate several implementation formulas of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for calculating cracks, characterized in that: This method utilizes a resistivity measurement device for the core fracturing process under high temperature and pressure. The device includes a core holder, a temperature control system, a pressure application system, a fracturing fluid injection system, a high-resolution X-ray three-dimensional monitoring system, and a resistivity measurement system. The core holder includes a core chamber with a right insulating plug and a left insulating plug at each end. A right electrode and a left electrode are respectively embedded on opposite sides of the right and left insulating plugs. An inlet guide tube is provided on the right insulating plug. A right conical ring and a left conical ring are respectively fitted onto the right and left insulating plugs. A rubber sleeve is placed between the right and left conical rings. The interior of the rubber sleeve is used to hold the rock sample. A metal cylinder is placed outside the rubber sleeve. The right and left insulating plugs seal both ends of the metal cylinder. The metal cylinder and the rubber sleeve are positioned to seal the interior and exterior of the metal cylinder. A confining pressure cavity is formed; a right locking cap and a left locking cap are respectively provided on the outer sides of the right insulating plug and the left insulating plug. A nut is provided on the right locking cap, and the nut passes through the right locking cap to support the rock sample. An axial pressure cavity is provided on the left locking cap. An annular slider is provided in the axial pressure cavity to support the rock sample and apply axial pressure to the rock sample. A heat insulation layer is provided on the outer sides of the metal cylinder, the right locking cap, and the left locking cap. The temperature regulation system is electrically connected to a heating resistor, which is located between the metal cylinder and the heat insulation layer. The pressure application system is connected to the confining pressure cavity and the axial pressure cavity respectively to provide confining pressure and axial pressure to the rock sample. The fracturing fluid injection system injects fracturing fluid into the rock sample through the inlet guide pipe. The resistivity measurement system is used to electrically connect the right electrode and the left electrode to obtain the resistance value of the rock sample. The crack measurement method includes the following steps: S1. Measure the resistance of the inlet guide tube and record it as... ; S2. Select a rock sample in the resource target area and drill a fracturing hole on the end face of one end of the rock sample. The depth of the fracturing hole is the same as the length of the inlet guide pipe extending out of the right insulating plug. S3. Place the rock sample in the core chamber, put the left locking cap and the right locking cap on both ends of the metal cylinder respectively, insert the inlet guide tube into the fracturing hole on the rock sample, tighten the left locking cap, the right locking cap and the nut, and seal and fix the rock sample in the core chamber; S4. Apply a preset axial pressure and a preset temperature to the rock sample, and then apply a preset confining pressure to the rock sample after holding it at the preset temperature for more than 2 hours. S5. Cyclicly discharge the left and right electrodes, and measure the resistance of the entire rock sample using the resistivity measurement system. R ; S6. The apparent resistivity of a rock sample with a central hole before fracturing is calculated using the following formula: （1） （2） （3） in, R The resistivity of the entire rock sample. and For the resistivity of rock samples from different regions, The apparent resistivity of the rock sample before fracturing. This represents the cross-sectional area of ​​the rock sample excluding the fracture holes. This represents the cross-sectional area of ​​the fracturing hole; S7. The fracturing fluid injection system injects fracturing fluid into the fracturing hole of the rock sample through the inlet guide pipe, and records the resistivity of the rock sample throughout the fracturing process. R Injection pressure in the inlet guide tube P and fluid flow rate Q Inject pressure P The first peak value is the crack initiation pressure value. P 0; S8. After hydraulic fracturing, stop the injection of fracturing fluid and measure the resistivity of the entire rock sample after hydraulic fracturing. The hydraulic fracture resistance formed by hydraulic fracturing is calculated using the following formula: （4） in, This represents the electrical resistance of the entire rock sample after fracturing. and The hydraulic fracture resistance is distributed on both sides of the fracturing hole. The electrical resistance of the rock matrix after fracturing; S9. Perform X-ray scanning on the rock samples from the fracturing process and convert them into CT projection images of hydraulic fractures to obtain the distribution area of ​​hydraulic fractures after fracturing, as well as the length and width of the fractures; S10. Disconnect the power supply to the heating resistor, unload the confining pressure and axial pressure, and remove the rock sample after the device has cooled naturally; S11. After drying the fractured rock sample, place it in the clamp and set the same temperature, confining pressure, and axial pressure as in step S4. Measure the resistance of the entire rock sample in step S5 and substitute it into formula (1). Then, in formula (1)... Replace with Since hydraulic fractures are mainly distributed on the side of the fracturing hole, assuming The electrical resistance of the fractured rock matrix remains unchanged. Perform calculations; S12. The hydraulic fracture resistance is defined as: （5） in, The length of the crack is in meters (m). The width of the crack is expressed in meters (m). The equivalent hydraulic aperture of the fracture is expressed in meters (m). The resistivity of water; S13. Calculate according to formula (5) respectively. and Then and Substituting into formula (4), the equivalent hydraulic aperture of the fracture formed after hydraulic fracturing is calculated. ; S14. Repeat steps S1-S13 under different conditions of temperature, confining pressure, axial pressure, and fracturing fluid to obtain the injection pressure, apparent resistivity, fracture development area, and equivalent hydraulic aperture of the rock samples under different conditions.

2. The crack measurement method according to claim 1, characterized in that, The temperature control system further includes a temperature control component, a heating component electrically connected to the temperature control component, and a temperature probe. The heating component is connected to the heating resistor and controls the power of the heating resistor. The temperature probe is located on the metal cylinder.

3. The crack measurement method according to claim 1, characterized in that, The pressure application system includes a pressure pump, a confining pressure inlet connected to the confining pressure cavity, an axial pressure inlet connected to the axial pressure cavity, an axial pressure gauge, and a confining pressure gauge. The pressure pump is connected to both the confining pressure inlet and the axial pressure inlet. The confining pressure gauge is located on the communication path between the pressure pump and the confining pressure inlet. The axial pressure gauge is located on the communication path between the pressure pump and the axial pressure inlet. A third valve is located upstream of the confining pressure gauge, and a fourth valve is located upstream of the axial pressure gauge.

4. The crack measurement method according to claim 1, characterized in that, The fracturing fluid injection system further includes a fracturing fluid container, a constant speed and constant pressure pump, and an air pump. The fracturing fluid container is connected to the inlet guide pipe through the constant speed and constant pressure pump. A second valve is provided between the inlet guide pipe and the constant speed and constant pressure pump. The constant speed and constant pressure pump is also connected to the air pump. A first valve is provided between the air pump and the constant speed and constant pressure pump.

5. The crack calculation method according to claim 1, characterized in that, The resistivity measurement system includes a resistivity measuring instrument and a computer acquisition system connected to the resistivity measuring instrument. The resistivity measuring instrument is electrically connected to the left electrode and the right electrode respectively.

6. The crack measurement method according to claim 1, characterized in that, The high-resolution X-ray three-dimensional monitoring system includes an X-ray source, a detector, and a computer. The X-ray source is used to scan the rock sample in the high-temperature and high-pressure holder with X-rays. The detector receives the X-rays that pass through the rock sample and converts them into CT projection images, which are then input into the computer for processing. The computer identifies the development of fractures based on the CT projection images.

7. The crack calculation method according to claim 1, characterized in that, Between steps S4 and S5, the following steps are also included: Take rock samples from the same batch as the test samples and measure the elastic modulus E(T) of the rock samples under different test temperature conditions. For high temperature and high pressure conditions, the length and cross-sectional area of ​​the rock samples are corrected using the following formula: (11) (12) (13) (14) in, To correct the length of the previous rock sample, The length of the corrected rock sample; The axial compression experienced by the rock sample; To correct the diameter of the previous rock sample, To correct the diameter of the rock sample; The confining pressure exerted on the rock sample; The diameter of the fracturing hole; This represents the cross-sectional area of ​​the entire rock sample. S1 This represents the cross-sectional area of ​​the rock sample excluding the fracture holes. This represents the cross-sectional area of ​​the fracturing hole.

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