Device and method for testing gas content in coal rock fracturing process

Abstract

According to the device and method for testing the gas-bearing property in the coal rock fracturing process, the axial pressure control assembly and the confining pressure control assembly are arranged to apply different axial pressures and confining pressures to the rock core sample so as to simulate the reservoir environment of the coal rock, and the acting force on the rock core sample can be changed by adjusting the axial pressure and the confining pressure; a fracturing process can be simulated, the axial expansion and contraction amount and the radial expansion and contraction amount of the rock core sample under different axial pressures and confining pressures can be acquired through the strain acquisition assembly, and the total volume variation of the rock core sample can be obtained based on the axial expansion and contraction amount and the radial expansion and contraction amount. The free gas content and the adsorbed gas content of the rock core sample are obtained based on the total volume variable quantity, so that the gas content change condition of the deep coal rock in the fracturing process is represented; the problem that the gas content change condition of deep coal rock in the fracturing process cannot be represented in existing coal rock gas content evaluation can be solved.

Description

Technical Field

[0001] This invention relates to the field of geochemical exploration technology, and in particular to a device and method for testing the gas content of coal and rock fracturing processes. Background Technology

[0002] The types of gas contained in deep coal and rock mainly include adsorbed gas and free gas. A comprehensive and accurate evaluation of the adsorbed gas content and free gas content in deep coal and rock can provide a more complete understanding of the gas storage and production characteristics of coal and rock, and provide a scientific basis for the exploration and development of coalbed methane.

[0003] Existing methods for evaluating the gas content of coal and rock can be mainly divided into two categories: one is the gas content evaluation method with variable boundary pressure; the other is the gas content evaluation method with constant boundary pressure. These two types of methods can be used to evaluate the gas content characteristics of coal and rock under different temperature, pressure and water content conditions, but they cannot characterize the changes in gas content of deep coal and rock during the fracturing process. Summary of the Invention

[0004] This invention provides a device and method for testing the gas content of coal and rock during fracturing, which can solve the problem in existing coal and rock gas content evaluation methods that cannot characterize the changes in gas content of deep coal and rock during fracturing.

[0005] In a first aspect, embodiments of this application provide a gas-bearing testing device for the coal fracturing process, comprising:

[0006] Clamping assembly, in which a core sample is placed;

[0007] An inflation control assembly, connected to the clamping assembly, is used to inflate the core sample with test gas;

[0008] An axial pressure control assembly, connected to the clamping assembly, is used to apply axial pressure to the core sample;

[0009] A confining pressure control assembly, connected to the clamping assembly, is used to apply confining pressure to the core sample;

[0010] The strain acquisition component is connected to the core sample and is used to acquire the axial and radial expansion and contraction of the core sample under different axial and confining pressures. Based on the axial and radial expansion and contraction, the total volume change of the core sample is obtained, and based on the total volume change, the free gas content and adsorbed gas content of the core sample are obtained.

[0011] In some embodiments, the clamping assembly includes:

[0012] The triaxial core holder has two opposite ends. One end is provided with a fluid inlet / outlet channel and an axial pressure channel, and the other end is provided with a confining pressure exhaust channel. A confining pressure air inlet channel is provided on its side. The fluid inlet / outlet channel is connected to the inflation control component, the axial pressure channel is connected to the axial pressure control component, and the confining pressure air inlet channel is connected to the confining pressure control component.

[0013] The triaxial core holder is provided with a sample chamber. One end of the sample chamber is connected to the axial pressure channel, and the other end of the sample chamber is connected to the fluid inlet and outlet channel. The side of the sample chamber is connected to the confining pressure air inlet channel and the confining pressure exhaust channel.

[0014] The core sample is placed inside the sample chamber.

[0015] In some embodiments, the clamping assembly further includes an axial pressure gauge disposed within the axial pressure channel for detecting the axial pressure exerted by the axial pressure control assembly on the core sample.

[0016] In some embodiments, the inflation control component includes:

[0017] gas tank;

[0018] Booster pump;

[0019] An inflation pipe connects the air storage tank and the booster pump, and is equipped with an inflation pressure gauge and an inflation regulating valve.

[0020] In some embodiments, the strain acquisition component includes:

[0021] Strain gauges are installed on the end face and side face of the core sample;

[0022] A strain acquisition device is connected to the strain gauge.

[0023] In some embodiments, the gas content testing device for coal and rock fracturing process further includes a heat insulation component and a vacuum component;

[0024] The clamping assembly is placed inside the insulation assembly, and the vacuum assembly is connected to the clamping assembly for evacuating the clamping assembly.

[0025] In some embodiments, the gas content testing device for coal and rock fracturing process further includes a nuclear magnetic resonance (NMR) component, which is used to scan the core sample to obtain a test gas T2 spectrum, and to obtain the free gas content and adsorbed gas content in the core sample based on the test gas T2 spectrum.

[0026] Secondly, embodiments of this application provide a method for testing the gas content during coal fracturing, including:

[0027] A preset axial pressure is applied to the core sample by the axial pressure control component;

[0028] A preset confining pressure is applied to the core sample by the confining pressure control component;

[0029] The core sample is filled with test gas to a preset test gas pressure using the gas filling control component;

[0030] The strain acquisition component acquires the axial and radial expansion and contraction of the core sample under the preset axial pressure, the preset confining pressure, and the preset test gas pressure, and obtains the total volume change of the core sample based on the axial and radial expansion and contraction.

[0031] The free gas content and adsorbed gas content of the core sample are obtained based on the total volume change.

[0032] In some embodiments, the total volume change includes the skeleton volume change and the pore volume change;

[0033] The process of obtaining the free gas content and adsorbed gas content of the core sample based on the total volume change includes:

[0034] The pore volume change is obtained based on the total volume change, the skeleton volume compressibility coefficient, and the pore volume compressibility coefficient.

[0035] The free gas content is obtained based on the pore volume change and the ideal gas law.

[0036] The adsorbed gas content is obtained based on the total amount of the test gas and the free gas content.

[0037] In some embodiments, the method for testing the gas content of coal and rock fracturing processes further includes:

[0038] Establish a free gas content intensity map corresponding to the free gas content and the free gas signal intensity;

[0039] Establish an adsorbed gas content intensity diagram corresponding to the adsorbed gas content and the adsorbed gas signal intensity;

[0040] The core sample was scanned using a nuclear magnetic resonance (NMR) array to obtain the T2 spectrum of the test gas.

[0041] The free gas content and the adsorbed gas content are obtained based on the T2 spectrum of the test gas, the intensity diagram of the free gas content, and the intensity diagram of the adsorbed gas content.

[0042] In some embodiments, obtaining the free gas content and the adsorbed gas content based on the test gas T2 spectrum, the free gas content intensity map, and the adsorbed gas content intensity map includes:

[0043] Based on the different relaxation times of adsorbed gas and free gas in the core sample, the current adsorbed gas signal intensity and the current free gas signal intensity are obtained from the T2 spectrum of the test gas.

[0044] The free gas content is obtained based on the current free gas signal intensity and the free gas content intensity map;

[0045] The adsorbed gas content is obtained based on the current adsorbed gas signal intensity and the adsorbed gas content intensity map.

[0046] In some embodiments, before applying a preset axial pressure to the core sample via the axial pressure control assembly, the method further includes:

[0047] The triaxial core holder is evacuated to a preset vacuum pressure using a vacuum assembly.

[0048] Shut down the vacuum assembly;

[0049] The triaxial core holder is placed in the insulation component, and the insulation temperature of the insulation component is set to a preset temperature.

[0050] In some embodiments, the step of filling the core sample with test gas to a preset test gas pressure via the gas filling control component further includes:

[0051] After the core sample has maintained a preset pressure for a preset time under the preset test gas pressure, the gas filling control component is turned off.

[0052] Compared with the prior art, the advantages of the embodiments of this application are that, by setting the axial pressure control component and the confining pressure control component, different axial pressures and confining pressures can be applied to the core sample to simulate the reservoir environment of coal and rock. By adjusting the axial pressure and confining pressure, the force applied to the core sample can be changed, which can simulate the fracturing process. The strain acquisition component can collect the axial expansion and contraction of the core sample under different axial pressures and confining pressures. Based on the axial expansion and contraction and the radial expansion, the total volume change of the core sample can be obtained, and based on the total volume change, the free gas content and adsorbed gas content of the core sample can be obtained, thereby characterizing the gas content change of deep coal and rock during the fracturing process. Attached Figure Description

[0053] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0054] Figure 1This is a schematic diagram of a gas-bearing testing device for the coal fracturing process provided in an embodiment of this application;

[0055] Figure 2 This is a schematic diagram of a triaxial core holder structure provided in one embodiment of this application;

[0056] Figure 3 This is a schematic diagram of core sample deformation provided in an embodiment of this application;

[0057] Figure 4 This is a test gas pressure intensity diagram provided in one embodiment of this application;

[0058] Figure 5 This is a free gas content intensity diagram provided in one embodiment of this application;

[0059] Figure 6 This is an adsorption gas content intensity diagram provided in one embodiment of this application;

[0060] Figure 7 This is a stress-strain curve of a core sample provided in an embodiment of this application;

[0061] Figure 8 This is a schematic diagram of a gas-containing testing device with variable boundary pressure provided by existing technology;

[0062] Figure 9 This is a schematic diagram of a fixed boundary pressure gas-containing test device provided by existing technology;

[0063] Figure 10 This is a flowchart of a method for testing the gas content of coal and rock fracturing process according to an embodiment of this application.

[0064] Figure label:

[0065] 10. Clamping assembly; 110. Axial pressure channel; 120. Fluid inlet / outlet channel; 130. Confining pressure air inlet channel; 140. Confining pressure exhaust channel; 150. Core sample;

[0066] 20. Inflation control assembly; 210. Air tank; 220. Booster pump; 230. Inflation pressure gauge; 240. Inflation piping; 250. Inflation regulating valve;

[0067] 30. Axial pressure control assembly;

[0068] 40. Strain acquisition assembly; 410. Strain gauge;

[0069] 50. Confining pressure control components;

[0070] 60. Thermal insulation components;

[0071] 70. Vacuum assembly; 710. Vacuum regulating valve; 720. Vacuum pump;

[0072] 80. Nuclear magnetic resonance assembly. Detailed Implementation

[0073] The invention will now be further described with reference to the accompanying drawings.

[0074] Coalbed methane reservoirs are formed by the enrichment of methane adsorbed gas in coal seams. The main types of gas in deep coal and rock formations include adsorbed gas, free gas, and dissolved gas. Adsorbed gas refers to gas molecules adsorbed onto the surfaces of pores and fractures in coal and rock, and is usually closely related to the organic matter content and pore structure of the coal and rock. Free gas exists in the pores and fractures of coal and rock in a free state. Dissolved gas is gas dissolved in formation water, and its content is usually negligible.

[0075] A comprehensive and accurate evaluation of the adsorbed gas and free gas content in deep coal and rock formations can provide a more complete understanding of the gas storage and production characteristics of coal and rock formations, and provide a scientific basis for the exploration and development of coalbed methane. Among them, the content of adsorbed gas reflects the adsorption capacity and gas storage potential of coal and rock formations, and is an important indicator for assessing coalbed methane resources. High adsorbed gas content indicates that coal and rock formations have good gas storage capacity and are suitable for coalbed methane extraction. On the other hand, the content of free gas determines the permeability and gas production capacity of coal and rock formations. High free gas content means that there is more mobile gas in the coal and rock formations, which is conducive to improving the gas production rate.

[0076] Existing experimental methods for evaluating the gas content of coal and rock are mainly divided into two categories. The first category is the gas content evaluation method based on variable boundary pressure, such as... Figure 8 As shown: Sealed container 1 and sealed container 2 are connected by a pipe with a valve in the middle. Sealed container 1 is used as a reference container, and its volume is measured as V0. Sealed container 2 contains a coal and rock sample, and its pore volume is measured as Vp using helium gas. After evacuating the entire apparatus, methane is introduced into sealed container 1 until the gas pressure in sealed container 1 reaches P1. The valve is then opened, and the gas diffuses from sealed container 1 to sealed container 2, where it adsorbs onto the pore surface of the coal and rock sample. When the pressure reaches equilibrium, the equilibrium pressure P2 is recorded. Based on V0, P1, P2, and V... P The adsorbed gas and free gas content in sealed container 2 can be calculated using four parameters and the ideal gas law. By repeatedly using the above pressurization-adsorption-equilibrium method, the adsorbed gas and free gas content in coal and rock samples under different equilibrium pressures can be obtained.

[0077] The second category is the gas-bearing evaluation method under constant boundary pressure, such as... Figure 9As shown, the main difference from the first type of gas content evaluation method is that a precision volumetric pump is connected to the sealed container 1. The volumetric pump has a built-in movable piston. The movement of the movable piston changes the volumetric pump's volume V, which in turn indirectly changes the connected volume of the sealed container 1. When the gas in the sealed container 2 diffuses into the sealed container 1, the pressure in the sealed container 1 can be kept constant by adjusting the volumetric pump's volume V, thus ensuring that the boundary pressure remains constant during the gas diffusion process. Based on the boundary pressure, sample pore volume, sealed container volume, and pump volume change, the adsorbed gas and desorbed free gas content of the coal and rock sample can be calculated using the ideal gas law.

[0078] Currently, the two methods mentioned above can be used to evaluate the gas-bearing characteristics of coal and rock under different temperature, pressure, and water-bearing conditions, but they cannot characterize the changes in gas content in deep coal and rock during fracturing. Large-scale fracturing and horizontal well technology are key technologies for developing deep coalbed methane. Therefore, developing experimental devices and methods that can simulate the changes in gas content during deep coal and rock fracturing in a deep environment is of great significance for a deeper understanding of the gas occurrence characteristics during deep coal and rock fracturing and for optimizing coalbed methane extraction technology.

[0079] Firstly, such as Figure 1 As shown, to address the aforementioned technical problems, this application provides a gas-bearing testing device for the coal fracturing process, comprising:

[0080] Clamping assembly 10, in which core sample 150 is placed;

[0081] The gas filling control component 20 is connected to the clamping component 10 and is used to fill the core sample 150 with test gas.

[0082] Axial pressure control assembly 30, connected to the clamping assembly 10, is used to apply axial pressure to the core sample 150;

[0083] The confining pressure control component 50 is connected to the clamping component 10 and is used to apply confining pressure to the core sample 150.

[0084] The strain acquisition component 40 is connected to the core sample 150 and is used to acquire the axial expansion and radial expansion of the core sample 150 under different axial pressures and confining pressures. Based on the axial expansion and radial expansion, the total volume change of the core sample 150 is obtained, and based on the total volume change, the free gas content and adsorbed gas content of the core sample 150 are obtained.

[0085] It should be noted that the inflation control component 20, the axial pressure control component 30, and the confining pressure control component 50 are respectively connected to the clamping component 10 through pipes, and the strain acquisition component 40 is electrically connected to the clamping component 10.

[0086] In some embodiments, the clamping assembly 10 includes:

[0087] The triaxial core holder has two opposing ends. One end is provided with a fluid inlet / outlet channel 120 and an axial pressure channel 110, and the other end is provided with a confining pressure exhaust channel 140. A confining pressure air inlet channel 130 is provided on its side. The fluid inlet / outlet channel 120 is connected to the inflation control component 20, the axial pressure channel 110 is connected to the axial pressure control component 30, and the confining pressure air inlet channel 130 is connected to the confining pressure control component 50.

[0088] The triaxial core holder is provided with a sample chamber. One end of the sample chamber is connected to the axial pressure channel 110, and the other end of the sample chamber is connected to the fluid inlet and outlet channel 120. The side of the sample chamber is connected to the confining pressure air inlet channel 130 and the confining pressure exhaust channel 140.

[0089] Core sample 150 is placed inside the sample cavity.

[0090] It should be noted that, as Figure 2 As shown, the core sample 150 has a free end on the left and a fixed end on the right. The axial pressure channel 110 is provided at the center of the left end of the triaxial core holder. The fluid inlet / outlet channel 120 is provided on the outside of the axial pressure channel 110. The right end of the fluid inlet / outlet channel 120 is connected to the right end of the core sample 150 for filling the core sample 150 with the test gas (methane). The top of the triaxial core holder is provided with the confining pressure inlet channel 130, and the right end of the triaxial core holder is provided with the confining pressure exhaust channel 140. A movable piston may be provided in the axial pressure channel 110. The axial pressure control component 30 applies axial pressure to the core sample 150 through the movable piston. The confining pressure control component 50 applies confining pressure to the core sample 150 through the confining pressure inlet channel 130 and can release confining pressure through the confining pressure exhaust channel 140.

[0091] In some embodiments, the clamping assembly 10 further includes an axial pressure gauge disposed within the axial pressure channel 110, for detecting the axial pressure exerted by the axial pressure control assembly 30 on the core sample 150.

[0092] In some embodiments, the inflation control assembly 20 includes:

[0093] Gas storage tank 210;

[0094] Booster pump 220;

[0095] An inflation pipe 240 is connected to the air storage tank 210 and the booster pump 220, and is equipped with an inflation pressure gauge 230 and an inflation regulating valve 250.

[0096] It should be noted that the inflation pressure gauge 230 is used to measure the pressure of the inflation pipe 240 or the booster pump 220, and the inflation regulating valve 250 is used to adjust the opening, closing and opening angle of the inflation pipe 240, thereby adjusting the flow rate and velocity of the test gas injected into the core sample 150 by the inflation assembly.

[0097] In some embodiments, the strain acquisition component 40 includes:

[0098] Strain gauges 410 are disposed on the end face and side face of the core sample 150;

[0099] The strain acquisition device is connected to the strain gauge 410.

[0100] It should be noted that, as Figure 2 As shown, the strain acquisition device is a resistance strain gauge. One or more mounting slots are provided on the left and upper end faces of the core sample 150. The mounting slots are used to install the strain gauges 410. During the test, the strain gauge 410 (i.e., the axial strain gauge) located on the left end face of the core sample 150 can collect the axial expansion and contraction ΔX of the core sample 150, and the strain gauge 410 (i.e., the radial strain gauge) located on the upper end face of the core sample 150 can collect the radial expansion and contraction ΔY of the core sample 150.

[0101] It should be noted that, based on the axial expansion and contraction and the radial expansion and contraction, the volume of the core sample 150 after changes under corresponding axial pressure, confining pressure, and test gas pressure can be obtained. The original volume of the core sample 150 Where X is the original length of core sample 150 and Y is the diameter of core sample 150; thus, the total volume change of core sample 150, ΔV = V1 - V, can be obtained, considering that the volume change of core sample 150 includes the change in skeleton volume, V. f and pore volume change V p Among them, the compressibility coefficient C of the skeleton volume f =1.2×10 -4 The compressibility coefficient C of pore volume p =1.5×10 -4 Therefore, the change in pore volume is According to the ideal gas law PV=ZnRT, given that P (pressure), Z (compressibility factor), R (molar gas constant), and T (temperature) are constant, the number of free gas molecules Δn can be determined from the change in volume V. 游(i.e., the free gas content) can be obtained by subtracting the changed free gas molecular weight from the total gas molecules to get the adsorbed gas molecular weight n. 吸 (i.e., the content of the adsorbed gas).

[0102] In some embodiments, the gas content testing device for coal and rock fracturing process further includes a heat insulation component 60 and a vacuum component 70;

[0103] The clamping component 10 is placed inside the heat preservation component 60, and the vacuum component 70 is connected to the clamping component 10 for evacuating the clamping component 10.

[0104] It should be noted that the heat preservation component 60 can be a constant temperature chamber, used to keep the temperature of the clamping component 10 constant, usually a simulated formation temperature. The vacuum component 70 is used to evacuate the core sample 150. The vacuum component 70 includes a vacuum pump 720, which is connected to the triaxial core holder through a vacuum pipe. The vacuum pipe is equipped with a vacuum regulating valve 710 and a vacuum gauge.

[0105] In some embodiments, the gas content testing device for coal and rock fracturing process further includes a nuclear magnetic resonance component 80, which is used to scan the core sample 150 to obtain the test gas T2 spectrum, and to obtain the free gas content and adsorbed gas content in the core sample 150 based on the test gas T2 spectrum.

[0106] It should be noted that the T2 spectrum is the time constant describing the recovery process of the transverse component of the nuclear magnetization intensity, and is therefore called the transverse relaxation time. During the experiment, a pressure-intensity diagram of the test gas corresponding to the signal intensity in the T2 spectrum can be established first, such as... Figure 4 As shown, (using the existing "adsorption-equilibrium-adsorption" experimental method, under known total gas volume, the isothermal adsorption curves of coal and rock under different temperatures and test gas pressures can be measured to obtain the adsorbed gas content. The free gas content of coal and rock under the corresponding conditions can be obtained by subtracting the adsorbed gas content from the total gas volume; simultaneously, the T2 spectrum of coal and rock under the corresponding conditions can be measured using nuclear magnetic resonance equipment, and a correlation model between the peak intensity of the T2 spectrum and the free gas content and adsorbed gas content of coal and rock can be established using a nonlinear regression method). Then, a free gas content intensity map corresponding to the free gas signal intensity can be established (e.g., ...). Figure 5 As shown), establish an adsorbed gas content intensity map corresponding to the adsorbed gas content and adsorbed gas signal intensity (e.g., Figure 6(As shown); During the experiment, the current adsorbed gas signal intensity and the current free gas signal intensity can be obtained from the test gas T2 spectrum based on the different relaxation times of the adsorbed gas and free gas in the core sample 150; and then the free gas content and the adsorbed gas content can be obtained.

[0107] In summary, the advantages of this embodiment are that by setting the axial pressure control component 30 and the confining pressure control component 50, different axial pressures and confining pressures can be applied to the core sample 150 to simulate the reservoir environment of coal and rock. By adjusting the axial pressure and confining pressure, the force applied to the core sample 150 can be changed, thus simulating the fracturing process. The strain acquisition component 40 can acquire the axial and radial expansion and contraction of the core sample 150 under different axial and confining pressures. Based on the axial and radial expansion and contraction, the total volume change of the core sample 150 can be obtained, and based on the total volume change, the free gas content and adsorbed gas content of the core sample 150 can be obtained, thereby characterizing the gas content change of deep coal and rock during the fracturing process.

[0108] Secondly, such as Figure 10 As shown, this application provides a method for testing the gas content of coal and rock fracturing processes, applied to the gas content testing apparatus for coal and rock fracturing processes as described in any embodiment of the first aspect, comprising:

[0109] S101: A preset axial pressure is applied to the core sample 150 by the axial pressure control component 30;

[0110] S102: Apply a preset confining pressure to the core sample 150 through the confining pressure control component 50;

[0111] It should be noted that before applying axial and confining pressure to the core sample 150, the core sample 150 should be collected, dried, and its physical properties, such as porosity, permeability, organic matter content, and yield stress, should be measured. Static characteristic parameters of the gas reservoir should also be collected. It is preferable to use a full-diameter core sample.

[0112] It should be noted that, as Figure 2 As shown, before conducting the test, strain gauges 410 need to be placed on the core sample 150. The core sample 150 has one or more mounting grooves on its left and upper end faces. One strain gauge 410 can be placed in the mounting groove on the left end face of the core sample 150, and two strain gauges 410 can be placed along the length of the side (upper end face) of the core sample 150. The strain gauges 410 are electrically connected to the strain acquisition device. Then, the core sample 150 is placed in the clamping assembly 10.

[0113] It should be noted that applying axial pressure and confining pressure to the core sample 150 can simulate the reservoir environment of the core sample 150. The preset axial pressure can be 2.5 MPa and the preset confining pressure can be 2.5 MPa. This application does not specifically limit the specific values ​​of the preset axial pressure and the preset confining pressure.

[0114] S103: The test gas is introduced into the core sample 150 to the preset test gas pressure through the gas filling control component 20;

[0115] It should be noted that the clamping assembly 10 includes: a triaxial core holder with two opposing ends, one end having a fluid inlet / outlet channel 120 and an axial pressure channel 110, and the other end having a confining pressure exhaust channel 140, with a confining pressure air inlet channel 130 on its side. The fluid inlet / outlet channel 120 is connected to the inflation control assembly 20, the axial pressure channel 110 is connected to the axial pressure control assembly 30, and the confining pressure air inlet channel 130 is connected to the confining pressure control assembly 50. The triaxial core holder contains a sample chamber, one end of which is connected to the axial pressure channel 110, and the other end of which is connected to the fluid inlet / outlet channel 120. The side of the sample chamber is connected to the confining pressure air inlet channel 130 and the confining pressure exhaust channel 140. A core sample 150 is disposed within the sample chamber.

[0116] S104: The strain acquisition component 40 acquires the axial expansion and radial expansion of the core sample 150 under the preset axial pressure, the preset confining pressure and the preset test gas pressure, and obtains the total volume change of the core sample 150 based on the axial expansion and radial expansion.

[0117] In some embodiments, the total volume change includes the skeleton volume change and the pore volume change;

[0118] The determination of the free gas content and adsorbed gas content of the core sample 150 based on the total volume change includes:

[0119] The pore volume change is obtained based on the total volume change, the skeleton volume compressibility coefficient, and the pore volume compressibility coefficient.

[0120] The free gas content is obtained based on the pore volume change and the ideal gas law.

[0121] The adsorbed gas content is obtained based on the total amount of the test gas and the free gas content.

[0122] It should be noted that, based on the axial expansion and contraction and the radial expansion and contraction, the volume of the core sample 150 after changes under corresponding axial pressure, confining pressure, and test gas pressure can be obtained. The original volume of the core sample 150 Where X is the original length of core sample 150 and Y is the diameter of core sample 150; thus, the total volume change of core sample 150, ΔV = V1 - V, can be obtained, considering that the volume change of core sample 150 includes the change in skeleton volume, V. f and pore volume change V p Among them, the compressibility coefficient C of the skeleton volume f =1.2×10 -4 The compressibility coefficient C of pore volume p =1.5×10 -4 Therefore, the change in pore volume is According to the ideal gas law PV=ZnRT, given that P (pressure), Z (compressibility factor), R (molar gas constant), and T (temperature) are constant, the number of free gas molecules Δn can be determined from the change in volume V. 游 (i.e., the free gas content) can be obtained by subtracting the changed free gas molecular weight from the total gas molecules to get the adsorbed gas molecular weight n. 吸 (i.e., the content of the adsorbed gas).

[0123] In some embodiments, the method for testing the gas content of coal and rock fracturing processes further includes:

[0124] Establish a free gas content intensity map corresponding to the free gas content and the free gas signal intensity;

[0125] Establish an adsorbed gas content intensity diagram corresponding to the adsorbed gas content and the adsorbed gas signal intensity;

[0126] The core sample 150 was scanned using the nuclear magnetic resonance assembly 80 to obtain the test gas T2 spectrum;

[0127] The free gas content and the adsorbed gas content are obtained based on the T2 spectrum of the test gas, the intensity diagram of the free gas content, and the intensity diagram of the adsorbed gas content.

[0128] In some embodiments, obtaining the free gas content and the adsorbed gas content based on the test gas T2 spectrum, the free gas content intensity map, and the adsorbed gas content intensity map includes:

[0129] Based on the different relaxation times of the adsorbed gas and the free gas in the core sample 150, the current adsorbed gas signal intensity and the current free gas signal intensity are obtained from the T2 spectrum of the test gas.

[0130] The free gas content is obtained based on the current free gas signal intensity and the free gas content intensity map;

[0131] The adsorbed gas content is obtained based on the current adsorbed gas signal intensity and the adsorbed gas content intensity map.

[0132] It should be noted that the T2 spectrum is the time constant describing the recovery process of the transverse component of the nuclear magnetization intensity, and is therefore called the transverse relaxation time. During the experiment, a pressure-intensity diagram of the test gas corresponding to the signal intensity in the T2 spectrum can be established first, such as... Figure 4 As shown, (using the existing "adsorption-equilibrium-adsorption" experimental method, under known total gas volume, the isothermal adsorption curves of coal and rock under different temperatures and test gas pressures can be measured to obtain the adsorbed gas content. The free gas content of coal and rock under the corresponding conditions can be obtained by subtracting the adsorbed gas content from the total gas volume; simultaneously, the T2 spectrum of coal and rock under the corresponding conditions can be measured using nuclear magnetic resonance equipment, and a correlation model between the peak intensity of the T2 spectrum and the free gas content and adsorbed gas content of coal and rock can be established using a nonlinear regression method). Then, a free gas content intensity map corresponding to the free gas signal intensity can be established (e.g., ...). Figure 5 As shown), establish an adsorbed gas content intensity map corresponding to the adsorbed gas content and adsorbed gas signal intensity (e.g., Figure 6 (As shown); During the experiment, the current adsorbed gas signal intensity and the current free gas signal intensity can be obtained from the test gas T2 spectrum based on the different relaxation times of the adsorbed gas and free gas in the core sample 150; and then the free gas content and the adsorbed gas content can be obtained.

[0133] It should be noted that by adjusting the preset axial pressure and the preset confining pressure, the effective stress on the core sample 150 can be changed to simulate the crack formation process. Then, the gas-bearing characteristics of coal and rock at different locations (i.e., different confining pressures and axial pressures) can be monitored in real time using the nuclear magnetic resonance assembly 80. The specific operation is as follows:

[0134] First, the T2 signal of the test gas (e.g., methane) in the core sample 150 under initial conditions (i.e., preset confining pressure, preset axial pressure, and preset test gas pressure) is measured using the nuclear magnetic resonance (NMR) assembly 80. The changes in the ratio of adsorbed to free states of the test gas under the initial conditions are observed. By adjusting the confining pressure control assembly 50, the confining pressure is gradually increased, causing deformation of the core sample 150 and a corresponding change in the position of the strain gauge 410. The stress-strain curve of the core sample 150 (e.g., methane) is recorded. Figure 7As shown, before the confining pressure reaches the pre-measured yield stress, i.e., the curve OA and AB segments, the confining pressure is stopped from increasing. Then, the confining pressure is slowly reduced to the initial confining pressure size. The position of strain gauge 410 is observed at this time to ensure that strain gauge 410 returns to its original position. This confining pressure segment is the elastic deformation pressure segment. The confining pressure is increased again, and the stress-strain curve is observed to reach segment CD, i.e., after the confining pressure increases to the pre-measured yield stress. The confining pressure is then reduced to the initial confining pressure size. The position of strain gauge 410 is observed at this time. If it does not return to its original position, it is considered that the core sample 150 has started to fracture and artificial cracks have begun to be generated, and the plastic deformation stage has begun. If it returns to its original position, the core sample 150 has not been fractured, and the confining pressure needs to be increased until the plastic deformation stage begins. The confining pressure size at this time is recorded.

[0135] Then, after confirming the start of plastic deformation in the core sample 150, the confining pressure was slowly increased until it reached 2 MPa above the yield stress. The pressure increase was then stopped, and nuclear magnetic resonance (NMR) was performed on the core sample 150 to obtain the T2 signal intensity map of methane inside the sample (i.e., the test gas T2 spectrum). The pressure was then increased, and the methane T2 signal intensity maps (i.e., the test gas T2 spectrum) were measured at 4 MPa, 6 MPa, 8 MPa, and 10 MPa above the yield stress, with each 2 MPa increase as a node. Combined with the initial methane T2 signal intensity map, and based on the established free gas content intensity map and adsorbed gas content intensity map, the adsorbed gas content, free gas content, their proportions, and their dynamic changes within the core sample 150 during fracturing were determined. Simultaneously, the stress-strain curve of the core sample 150 during fracturing was recorded and observed. The confining pressure was then slowly decreased back to the initial confining pressure (i.e., the preset confining pressure), and the positional changes of strain gauge 410 were observed. Figure 3 As shown, if the position of the strain gauge 410 returns to the left of the initial position, the pore volume of the core sample 150 increases. Since the axial pressure applied to the left side of the core sample 150 is constant, the pore pressure of the core sample 150 is constant. The increase in pore volume proves that the free gas content has increased. Similarly, if the position of the strain gauge 410 returns to the right of the initial position, it means that the free gas content has decreased.

[0136] In some embodiments, before applying a preset axial pressure to the core sample 150 via the axial pressure control assembly 30, the method further includes:

[0137] The triaxial core holder is evacuated to a preset vacuum pressure using the vacuum assembly 70.

[0138] The vacuum assembly 70 is shut off;

[0139] The triaxial core holder is placed in the insulation component 60, and the insulation temperature of the insulation component 60 is set to a preset temperature.

[0140] It should be noted that when using the vacuum assembly 70 to evacuate the triaxial core holder, the vacuum regulating valve 710 should be opened slowly to evacuate the triaxial core holder to a vacuum pressure of 0.0001 Pa. Then, the vacuum regulating valve 710 and the vacuum pump 720 should be closed to ensure the vacuum state of the triaxial core holder. The preset temperature is generally the formation temperature simulating a gas reservoir.

[0141] In some embodiments, the step of filling the core sample 150 with test gas to a preset test gas pressure via the gas filling control component 20 further includes:

[0142] After the core sample 150 has maintained a preset pressure for a preset time under the preset test gas pressure, the gas filling control component 20 is turned off.

[0143] It should be noted that when filling the core sample 150 with the test gas, the filling regulating valve 250 should be opened slowly to allow the test gas (such as methane) to flow slowly from the gas storage tank 210 into the triaxial core holder. The inlet pressure can be adjusted by the booster pump 220 to reach the preset test gas pressure. The change in pore pressure of the core sample 150 can be observed by the filling pressure gauge 230. After the value of the filling pressure gauge 230 reaches the preset test gas pressure and is maintained for the preset pressure holding time, the filling regulating valve 250 is closed, and the core sample 150 is allowed to saturate. At the same time, the left end of the core sample 150 needs to be sealed to prevent internal gas leakage or external gas intrusion into the triaxial core holder from affecting the experimental results. The pore pressure of the core sample 150 at this time is measured. Then, the above operation is repeated, gradually increasing the confining pressure, axial pressure and the pore pressure of the core sample 150 (i.e., the test gas pressure) until the formation conditions are met.

[0144] It should be noted that this application uses a triaxial core holder to simultaneously apply confining pressure and axial pressure to the core sample 150. A thermal insulation component 60 is used to simulate the deep formation environment. While keeping other conditions unchanged, the fracturing process of the core is simulated by changing the magnitude of the confining pressure. Strain gauges 410 are placed on the core. After fracturing the core sample 150, the initial confining pressure is restored. The change in core pore volume is obtained by analyzing the changes in the strain gauges 410, and the change in free gas content in the core sample 150 after fracturing is obtained accordingly.

[0145] It should be noted that the change in free gas content can be analyzed by observing the volume change of core sample 150. During the simulated fracturing process with increased confining pressure, fracturing connects the isolated pores inside core sample 150 with the effective pores, effectively connecting the gas in the isolated pores and increasing the free gas content. The artificial fractures cause the internal mineral structure to break, changing the mineral specific surface area, which in turn affects the adsorption capacity of the pore surface for methane and alters the number of free gas molecules in the pores. In this embodiment, an initial confining pressure (i.e., the preset confining pressure) is applied to the core sample 150 by the confining pressure control component 50. Figure 2 As shown, axial pressure is applied to the left side of core sample 150 via a movable piston, at which point the core shape is as follows. Figure 3 As shown in Figure a; adjust the confining pressure control component 50 and slowly increase the confining pressure. The position of strain gauge 410 will change accordingly. Before the confining pressure reaches the pre-measured yield stress, stop increasing the confining pressure and then slowly decrease the confining pressure back to the initial confining pressure. Observe the position of strain gauge 410 at this time. If it does not return to its original position, plastic deformation has begun, and the core sample 150 needs to be replaced and the previous steps repeated. If it returns to its original position, this confining pressure segment is the elastic deformation pressure segment. Increase the confining pressure again until it reaches the pre-measured maximum pressure, then decrease the confining pressure back to the initial confining pressure. Observe the position of strain gauge 410 at this time. If it does not return to its original position, the core sample 150 has begun to fracture, and artificial cracks have begun to form, indicating the start of the plastic deformation stage. If it returns to its original position, the core sample 150 has not been fractured, and the pressure range needs to be increased until the plastic deformation stage begins. Record the confining pressure at this time. After confirming the start of the plastic deformation stage, continue to slowly increase the confining pressure until it is 10 MPa above the yield stress. The changes in the core sample 150 at this time are as follows. Figure 3 As shown in Figure b, the confining pressure is slowly reduced again to the initial confining pressure. The stress-strain curve is recorded at this point, and the positional change of strain gauge 410 is observed. Figure 3 As shown in Figure c, if the position of strain gauge 410 returns to the left of its initial position, the pore volume of core sample 150 increases. Since the axial pressure applied to the left is constant, the pore pressure of core sample 150 remains constant. The increase in pore volume of core sample 150 indicates an increase in free gas content. Similarly, if... Figure 3 As shown in Figure d, when the position of strain gauge 410 returns to the right of its initial position, it indicates a decrease in the free gas content.

[0146] It should be noted that the nuclear magnetic resonance (NMR) assembly 80 can obtain the T2 spectrum of methane (i.e., the test gas T2 spectrum) based on the hydrogen nuclei in the methane inside the core sample 150. Furthermore, the signal intensity of adsorbed and free methane can be distinguished based on the different relaxation times of the adsorbed and free methane signals. In this embodiment, the NMR assembly 80 first measures the methane T2 signal intensity in the initial state after the core sample 150 is saturated with methane. Then, starting from the yield stress of the core sample 150, the NMR assembly 80 detects the methane T2 intensity signal every 2 MPa increase in confining pressure, until the confining pressure increases to 10 MPa above the yield stress of the core sample 150. By comparing the methane T2 intensity spectra after each pressurization stage, the dynamic changes in the proportion of adsorbed and free methane during core fracturing can be observed.

[0147] Although the invention has been described with reference to preferred embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. The invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A coal rock fracturing process gas content testing device, characterized in that, include: Clamping assembly, in which a core sample is placed; An inflation control assembly, connected to the clamping assembly, is used to inflate the core sample with test gas; An axial pressure control assembly, connected to the clamping assembly, is used to apply axial pressure to the core sample; A confining pressure control assembly, connected to the clamping assembly, is used to apply confining pressure to the core sample; The strain acquisition component is connected to the core sample and is used to acquire the axial and radial expansion and contraction of the core sample under different axial and confining pressures. Based on the axial and radial expansion and contraction, the total volume change of the core sample is obtained, and based on the total volume change, the free gas content and adsorbed gas content of the core sample are obtained.

2. The coal rock fracturing process gas bearing property testing device according to claim 1, characterized in that, The clamping assembly includes: The triaxial core holder has two opposite ends. One end is provided with a fluid inlet / outlet channel and an axial pressure channel, and the other end is provided with a confining pressure exhaust channel. A confining pressure air inlet channel is provided on its side. The fluid inlet / outlet channel is connected to the inflation control component, the axial pressure channel is connected to the axial pressure control component, and the confining pressure air inlet channel is connected to the confining pressure control component. The triaxial core holder is provided with a sample chamber. One end of the sample chamber is connected to the axial pressure channel, and the other end of the sample chamber is connected to the fluid inlet and outlet channel. The side of the sample chamber is connected to the confining pressure air inlet channel and the confining pressure exhaust channel. The core sample is placed inside the sample chamber.

3. The coal rock fracturing process gas bearing property testing device according to claim 2, characterized in that, The clamping assembly also includes an axial pressure gauge, which is located in the axial pressure channel and is used to detect the axial pressure exerted by the axial pressure control assembly on the core sample.

4. The gas-bearing testing device for coal and rock fracturing process according to claim 1, characterized in that, The inflation control component includes: gas tank; Booster pump; An inflation pipe connects the air storage tank and the booster pump, and is equipped with an inflation pressure gauge and an inflation regulating valve.

5. The gas-bearing testing device for coal and rock fracturing process according to claim 1, characterized in that, The strain acquisition component includes: Strain gauges are installed on the end face and side face of the core sample; A strain acquisition device is connected to the strain gauge.

6. The gas content testing device for coal and rock fracturing process according to claim 1, characterized in that, It also includes insulation components and vacuum components; The clamping assembly is placed inside the insulation assembly, and the vacuum assembly is connected to the clamping assembly for evacuating the clamping assembly.

7. The gas-bearing testing device for coal and rock fracturing process according to claim 1, characterized in that, It also includes a nuclear magnetic resonance (NMR) module, which is used to scan the core sample to obtain a test gas T2 spectrum, and to obtain the free gas content and adsorbed gas content in the core sample based on the test gas T2 spectrum.

8. A method for testing the gas content of coal and rock fracturing processes, applied to the gas content testing apparatus for coal and rock fracturing processes as described in any one of claims 1-7, characterized in that, include: A preset axial pressure is applied to the core sample by the axial pressure control component; A preset confining pressure is applied to the core sample by the confining pressure control component; The core sample is filled with test gas to a preset test gas pressure using the gas filling control component; The strain acquisition component acquires the axial and radial expansion and contraction of the core sample under the preset axial pressure, the preset confining pressure, and the preset test gas pressure, and obtains the total volume change of the core sample based on the axial and radial expansion and contraction. The free gas content and adsorbed gas content of the core sample are obtained based on the total volume change.

9. The method for testing gas content during coal and rock fracturing according to claim 8, characterized in that, The total volume change includes the change in skeleton volume and the change in pore volume; The process of obtaining the free gas content and adsorbed gas content of the core sample based on the total volume change includes: The pore volume change is obtained based on the total volume change, the skeleton volume compressibility coefficient, and the pore volume compressibility coefficient. The free gas content is obtained based on the pore volume change and the ideal gas law. The adsorbed gas content is obtained based on the total amount of the test gas and the free gas content.

10. The method for testing the gas content in the coal and rock fracturing process according to claim 8, characterized in that, Also includes: Establish a free gas content intensity map corresponding to the free gas content and the free gas signal intensity; Establish an adsorbed gas content intensity diagram corresponding to the adsorbed gas content and the adsorbed gas signal intensity; The core sample was scanned using a nuclear magnetic resonance (NMR) array to obtain the T2 spectrum of the test gas. The free gas content and the adsorbed gas content are obtained based on the T2 spectrum of the test gas, the intensity diagram of the free gas content, and the intensity diagram of the adsorbed gas content.

11. The method for testing gas content in coal and rock fracturing process according to claim 10, characterized in that, The process of obtaining the free gas content and the adsorbed gas content based on the T2 spectrum of the test gas, the free gas content intensity map, and the adsorbed gas content intensity map includes: Based on the different relaxation times of adsorbed gas and free gas in the core sample, the current adsorbed gas signal intensity and the current free gas signal intensity are obtained from the T2 spectrum of the test gas. The free gas content is obtained based on the current free gas signal intensity and the free gas content intensity map; The adsorbed gas content is obtained based on the current adsorbed gas signal intensity and the adsorbed gas content intensity map.

12. The method for testing gas content in coal and rock fracturing process according to claim 8, characterized in that, Before applying a preset axial pressure to the core sample via the axial pressure control component, the method further includes: The triaxial core holder is evacuated to a preset vacuum pressure using a vacuum assembly. Shut down the vacuum assembly; The triaxial core holder is placed in the insulation component, and the insulation temperature of the insulation component is set to a preset temperature.

13. The method for testing gas content in coal and rock fracturing process according to any one of claims 8-12, characterized in that, The step of filling the core sample with test gas to a preset test gas pressure via the gas filling control component further includes: After the core sample has maintained a preset pressure for a preset time under the preset test gas pressure, the gas filling control component is turned off.

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