Coal rock reservoir stress sensitivity quantitative evaluation device and method

Abstract

The invention discloses a coal rock reservoir stress sensitivity quantitative evaluation device and method, and relates to the technical field of reservoir evaluation. The method comprises the following steps: preparing and assembling a rock core sample, performing a stress sensitivity test by using a calibrated coal rock reservoir stress sensitivity quantitative evaluation device, and applying confining pressure to the rock core sample by adopting a preset stress loading strategy until the rock core sample reaches a stable state; the method comprises the following steps: measuring confining pressure values of a rock core sample in real time by using a confining pressure sensor, determining latch points of the rock core sample under each confining pressure value, obtaining effective stress and permeability of the rock core sample at each latch point, constructing an effective stress and permeability relation curve, and quantitatively calculating stress sensitivity evaluation parameters of the rock core sample. And evaluating the stress sensitivity of the coal rock reservoir. By acquiring the structural response and permeability change of the coal rock under the multi-rate loading and unloading conditions, accurate evaluation of the stress sensitivity of the coal rock reservoir is realized, and a basis is provided for guiding exploration and development of the coal rock reservoir.

Description

Technical Field

[0001] This invention relates to the field of reservoir evaluation technology, specifically to a device and method for quantitatively evaluating the stress sensitivity of coal and rock reservoirs. Background Technology

[0002] Coal reservoirs are typical low-permeability, high-stress-sensitive media, and their permeability is significantly affected by changes in effective stress. In recent years, with the advancement of coalbed methane extraction technology, the study of coal stress sensitivity has become an important part of reservoir evaluation and production dynamic analysis. Traditional studies on coal stress sensitivity often employ experimental methods such as steady-state methods, transient methods, or backpressure methods, measuring permeability changes under different confining pressures and fitting empirical relationships to characterize the degree of stress sensitivity.

[0003] The above methods have been widely used in early-stage research on oil and gas field development, but their theoretical and experimental systems still have significant limitations, mainly the following problems: (1) Existing methods for evaluating the stress sensitivity of coal and rock use power-law parameters or irreversible permeability loss rate as the main sensitivity indicators. Although these sensitivity indicators can reflect the trend of permeability decline, they cannot reveal the energy dissipation and fracture closure dynamics of the internal structure of coal and rock during loading-unloading cycles, and cannot characterize the differences in hysteresis, closure point and residual permeability of coal and rock reservoirs through single parameters.

[0004] (2) Lack of a mechanism to distinguish the unloading path response process. The stress sensitivity curve used in traditional coal and rock stress sensitivity evaluation methods only focuses on the attenuation process during the loading stage and lacks a mechanism to distinguish the unloading path response process, thus failing to accurately identify the stress unloading stage of the coal and rock reservoir.

[0005] (3) The impact of stress loading rate on the stress sensitivity response of coal and rock is not quantifiable, and dynamic response indicators are lacking. Traditional coal and rock stress sensitivity evaluation experiments mostly use a fixed rate of stress loading, without considering the impact of stress loading rate on the evolution path of coal and rock reservoir permeability. However, the fracture deformation rate and gas flow hysteresis response of coal and rock reservoirs differ significantly under different stress loading rates, and traditional methods cannot reflect this dynamic effect. Furthermore, the study of the dynamic adaptability of coal and rock reservoirs is still at the stage of qualitative description.

[0006] (4) Data processing for coal reservoir stress sensitivity assessment experiments relies on manual experience, lacks automation and repeatability, and has low data processing efficiency. Currently, traditional coal reservoir stress sensitivity assessment experiments generally use manual stability assessment, manual recording, and offline calculation to process experimental data. The results of experimental data processing are highly dependent on the operational experience of the staff, and the impact of data fluctuations and sampling cycles on coal reservoir stress sensitivity assessment is not considered, resulting in strong subjectivity and poor repeatability in steady-state identification of coal reservoirs.

[0007] Therefore, there is an urgent need to propose a quantitative evaluation device and method for the stress sensitivity of coal and rock reservoirs, which can comprehensively characterize the structural response and permeability changes of coal and rock under multi-rate stress loading and unloading conditions, and provide a basis for optimizing the production parameters of coal and rock reservoirs. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a device and method for quantitatively evaluating the stress sensitivity of coal and rock reservoirs. By acquiring the structural response and permeability changes of coal and rock under multi-rate loading and unloading conditions, the device quantitatively determines the hysteresis energy, irreversible closure initiation stress, and loading rate sensitivity index of the coal and rock reservoir, thereby achieving an accurate evaluation of the stress sensitivity of the coal and rock reservoir and providing a basis for guiding the exploration and development of coal and rock reservoirs.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A quantitative evaluation device for stress sensitivity of coal and rock reservoirs includes a gas storage cylinder, a core holder, a constant temperature chamber, a pore pressure servo device, a confining pressure servo device, and a central processing unit. The core holder is placed in a constant temperature chamber, and a core sample is placed inside the core holder. The side wall of the core sample is in close contact with the inner wall of the core holder. The inlet end of the core holder is connected to a gas storage cylinder through an input pipe, the outlet end of the core holder is connected to an output pipe, and the side wall of the core holder is connected to a confining pressure servo device through a confining pressure pipe. An inlet pressure sensor is installed on the input pipe, and the inlet pressure sensor is located on the side near the inlet end of the core holder; a back pressure valve and a mass flow meter are installed on the output pipe, wherein the inflow end of the back pressure valve is connected to the pore pressure servo device through a pore pressure pipe, and an outlet pressure sensor is installed on the pore pressure pipe; a confining pressure sensor is installed on the confining pressure pipe. The inlet pressure sensor, outlet pressure sensor, confining pressure sensor, mass flow meter, constant temperature chamber, pore pressure servo device, and confining pressure servo device are all connected to the central processing unit.

[0010] Preferably, the gas storage cylinder contains nitrogen or helium.

[0011] Preferably, both the input and output pipes are equipped with control valves.

[0012] Preferably, the pore pressure servo device is configured as a pore pressure control pump, and the confining pressure servo device is configured as a confining pressure control pump.

[0013] A method for quantitatively evaluating the stress sensitivity of coal and rock reservoirs, employing the aforementioned quantitative evaluation device for the stress sensitivity of coal and rock reservoirs, includes the following steps: Step 1, Core sample preparation and assembly; Step 2: Perform metrological verification on the quantitative evaluation device for stress sensitivity of coal and rock reservoirs, and preset the stress loading strategy for core samples, including slow strategy and fast strategy; Step 3: Conduct stress sensitivity tests using a quantitative evaluation device for stress sensitivity of coal and rock reservoirs. Apply confining pressure to the core sample using a preset stress loading strategy until the core sample reaches a stable state. Use a confining pressure sensor to measure the confining pressure value of the core sample in real time, determine the latching point of the core sample under each confining pressure value, obtain the effective stress and permeability of the core sample at each latching point, and construct the relationship curve between effective stress and permeability. Step 4: Based on the effective stress-permeability relationship curve, quantitatively calculate the stress sensitivity evaluation parameters of the core sample to evaluate the stress sensitivity of the coal reservoir. Step 5: Evaluate the stress sensitivity of the coal reservoir based on the stress sensitivity evaluation parameters of the core sample and the preset stress sensitivity evaluation standard for coal reservoirs.

[0014] Preferably, in step 1, a core sample is selected. The core sample has a cylindrical structure. The cross-sectional area and length of the core sample are measured, and the sample is dried and weighed. Breathable filter sheets are attached to both ends of the core sample. After the core sample is wrapped with a heat-shrink sleeve, the wrapped core sample is placed in a core holder. A quantitative evaluation device for stress sensitivity of coal and rock reservoirs is installed, and the sealing performance of the quantitative evaluation device for stress sensitivity of coal and rock reservoirs is checked.

[0015] Preferably, in step 2, the mass flow meter is subjected to two-point range calibration or three-point range calibration, and the inlet pressure sensor, outlet pressure sensor and confining pressure sensor are subjected to zero-point calibration and linear calibration respectively. The stress loading of the core sample adopts a strategy of constant pore pressure and changing confining pressure. The pore pressure servo device is controlled to keep the pore pressure of the core sample constant, and then the confining pressure servo device is controlled to load the confining pressure on the core sample according to the preset pressure gradient. After the confining pressure on the core sample reaches the preset confining pressure value, the confining pressure on the core sample is unloaded according to the preset pressure gradient. The stress loading strategy is divided into a slow strategy and a fast strategy based on a preset pressure gradient. In the slow strategy, the pressure gradient used for confining pressure loading and unloading is set to 0.2 MPa / min. In the fast strategy, the pressure gradient used for confining pressure loading and unloading is set to 1.0 MPa / min.

[0016] Preferably, in step 3, the stress sensitivity test of the core sample is carried out using a coal reservoir stress sensitivity quantitative evaluation device with both slow and fast strategies. During the stress sensitivity test, according to the preset stress loading strategy, the confining pressure servo device is controlled to first load confining pressure onto the core sample according to the preset pressure gradient and then unload the confining pressure, so that the core sample reaches a stable state under each confining pressure value. The time point corresponding to the core sample reaching a stable state is defined as the latch point. The latch point corresponding to each confining pressure value is determined, and the measured values ​​of the inlet pressure sensor, outlet pressure sensor, confining pressure sensor, mass flow meter, and temperature value of the constant temperature chamber at each latch point are obtained. The inlet and outlet pressure difference, confining pressure value, volumetric flow rate, and temperature corresponding to each latch point are determined. The effective stress σ and permeability k at each latch point are calculated, and the effective stress-permeability relationship curve of the core sample is obtained, including the σ-logk loading curve and σ-logk unloading curve obtained by the slow strategy and the σ-logk loading curve and σ-logk unloading curve obtained by the fast strategy. The effective stress σ is the difference between the confining pressure value and the pore pressure value of the rock sample. The formula for calculating the permeability is: ; In the formula, The permeability of the rock sample; This refers to the viscosity of the gas. The length of the rock sample; Volumetric flow rate; is the cross-sectional area of ​​the rock sample; The steady-state pressure difference under stress level is determined based on the inlet and outlet pressure difference corresponding to the latch point.

[0017] Preferably, in step 4, the stress sensitivity evaluation parameters of the core sample include hysteresis energy, irreversible closure initiation stress, and loading rate sensitivity index. Based on the S-logk loading and unloading curves obtained using the slow strategy and the S-logk unloading curves obtained using the fast strategy, the slow permeability and fast permeability of the core sample under the same confining pressure are obtained. The mean values ​​of the two under each confining pressure are calculated and smoothed to obtain the reconstructed S-logk loading and unloading curves of the core sample. The curves are then smoothed. Finally, the difference between the reconstructed S-logk loading and unloading curves is numerically integrated to obtain the hysteresis energy. The hysteresis energy is used to quantify the energy dissipation of coal and rock under cyclic stress, and the calculation formula is as follows: ; In the formula, This refers to hysteresis energy; It is a logarithmic function; To reconstruct the effective stress on the 𝜎—logk loading curve Corresponding penetration rate; To reconstruct the effective stress on the 𝜎—logk unloading curve Corresponding penetration rate; Based on the reconstructed α-logk loading curve and the reconstructed α-logk unloading curve, the permeability difference corresponding to the effective stress on the reconstructed α-logk unloading curve and the reconstructed α-logk loading curve under the same confining pressure is calculated. The relationship between the effective stress and the permeability difference is obtained, resulting in the α-Δlogk curve. The effective stress value corresponding to each inflection point in the α-Δlogk curve is obtained, and the minimum effective stress value corresponding to all inflection points is determined as the irreversible closure initiation stress. And the initial stress of irreversible closure. After normalization, we get: ; In the formula, The normalized irreversible closure initiation stress index; This represents the maximum effective stress. This represents the initial effective stress value; The normalized irreversible closure initiation stress index Used to evaluate the structural bearing capacity of coal and rock; Based on the reconstructed S-logk loading curve and reconstructed S-logk unloading curve of the core sample, the deviation between slow permeability and fast permeability under each effective stress value is calculated, and the loading rate sensitivity index corresponding to each effective stress value is obtained. The loading speed sensitivity index The formula used to evaluate the sensitivity of coal and rock to stress-time effects and creep effects is as follows: ; In the formula, To load the speed sensitivity index; Slow penetration rate; To achieve rapid penetration.

[0018] Preferably, in step 5, the preset evaluation standard for stress sensitivity of coal and rock reservoirs is: Based on the probability distribution curve of hysteresis energy in core samples from coal and rock reservoirs, the quartile method was used to determine the 25th and 75th quartiles; when the hysteresis energy of the core sample... If the hysteresis energy of the core sample does not exceed the 25th percentile, it is considered low dissipation. If the energy level is between the 25th and 75th percentiles, it is considered moderate dissipation, and the hysteresis energy of the core sample is... If the value exceeds the 75th percentile, it is considered to have high dissipation. Based on the normalized irreversible closure initiation stress index ,when When the time is right, it is determined to be early closure, at which point the coal and rock reservoir structure is sensitive; when When the closure is moderate, the coal and rock reservoir structure is relatively stable; when When the value is 0.7, it is determined to be a late-stage closure, at which point the coal and rock reservoir structure is stable; According to the loading speed index To determine the sensitivity to stress loading rate, when When the stress loading rate is not sensitive, it is determined that the stress loading rate is not sensitive; when When the stress loading rate is high, it is determined that the stress loading rate is more sensitive; when If the stress loading rate is sensitive, then it is determined to be sensitive. In summary, the hysteresis energy Normalized irreversible closure initiation stress index and loading speed index Evaluate the stress sensitivity of coal and rock reservoirs; when the hysteresis energy The stress index is determined to be high dissipation and normalized irreversible closure initiation stress. It was determined to be a late-stage closure and the loading speed index was... If the stress loading rate is determined to be sensitive, then the coal and rock reservoir is determined to be highly sensitive to stress; when the hysteresis energy Determined as having moderate dissipation and a normalized irreversible closure initiation stress index. Determined to be a medium-closed condition with a loading speed sensitivity index If the stress loading rate is determined to be relatively sensitive, then the coal and rock reservoir is determined to be moderately sensitive to stress; when the hysteresis energy Determined as a low-dissipation, normalized irreversible closure initiation stress index It was determined to be a late-stage closure and the loading speed index was... If the stress loading rate is determined to be insensitive, then the coal and rock reservoir is determined to be low-sensitivity to stress. For coal and rock reservoirs that are highly sensitive to stress, the daily pressure drop is set at 5~15 kPa / d during development; for coal and rock reservoirs that are moderately sensitive to stress, the daily pressure drop is set at 15~40 kPa / d during development; and for coal and rock reservoirs that are lowly sensitive to stress, the daily pressure drop is set at 40~80 kPa / d during development.

[0019] The beneficial technical effects of this invention are as follows: (1) This invention proposes a quantitative evaluation device and method for stress sensitivity of coal and rock reservoirs. By constructing a new index system for structural stress sensitivity of coal and rock reservoirs, hysteresis energy, irreversible closure initiation stress and loading rate sensitivity index are introduced to characterize the energy dissipation capacity, structural closure threshold and dynamic loading adaptability of coal and rock reservoirs under stress loading-unloading cycle path. This makes up for the limitation of traditional reservoir stress sensitivity evaluation relying too much on human experience to fit the index and lacking structural behavior characterization. It effectively improves the evaluation dimension of stress sensitivity of coal and rock reservoirs and realizes accurate evaluation of stress sensitivity of coal and rock reservoirs.

[0020] (2) This invention proposes a quantitative evaluation device and method for stress sensitivity of coal and rock reservoirs. By automatically identifying the initiation point of fracture closure in coal and rock reservoirs, the initiation stress of irreversible structural closure is determined, which is beneficial to provide the maximum allowable extraction pressure difference for the design of production wells in coal and rock reservoirs and effectively avoids the sharp decline in coal and rock reservoir production capacity caused by excessive stress closure.

[0021] (3) This invention proposes a quantitative evaluation device and method for stress sensitivity of coal and rock reservoirs, which realizes the explicit quantification of stress loading rate on the structural response of coal and rock reservoirs. It uses the loading rate sensitivity index to evaluate the difference in permeability loss of coal and rock reservoirs during rapid stress relief and slow stress relief processes, providing a quantitative basis for regulating the drainage rate of coal and rock reservoirs, which is conducive to optimizing the dynamic development system of coal and rock reservoirs.

[0022] (4) This invention proposes a quantitative evaluation device and method for stress sensitivity of coal and rock reservoirs. Compared with the traditional reservoir stress sensitivity evaluation process of manual judgment of steady state and post-test data processing, the quantitative evaluation device for stress sensitivity of coal and rock reservoirs proposed in this invention integrates automatic steady state judgment, real-time output of coal and rock reservoir stress sensitivity evaluation index, and output of coal and rock reservoir stress sensitivity evaluation results, laying the foundation for the commercial promotion of the quantitative evaluation method for stress sensitivity of coal and rock reservoirs of this invention. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the quantitative evaluation device for stress sensitivity of coal and rock reservoirs according to the present invention.

[0024] Figure 2 This is a flowchart of the quantitative evaluation method for stress sensitivity of coal and rock reservoirs according to the present invention.

[0025] Figure 3 This is a flow rate change curve during the stress loading and unloading process of the present invention.

[0026] Figure 4 This is a schematic diagram of the relationship between effective stress and permeability of the core sample of this invention.

[0027] Figure 5This is a schematic diagram of the hysteresis energy of the present invention.

[0028] Figure 6 This is a schematic diagram of the α-Δlogk curve in this invention.

[0029] In the diagram, 1 is a gas storage cylinder, 2 is a core holder, 3 is a constant temperature chamber, 4 is a pore pressure servo device, 5 is a confining pressure servo device, 6 is an inlet pressure sensor, 7 is a back pressure valve, 8 is a mass flow meter, 9 is an outlet pressure sensor, 10 is a confining pressure sensor, and 11 is a constant temperature chamber. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0031] Example 1 This embodiment discloses a device for quantitatively evaluating the stress sensitivity of coal and rock reservoirs, such as... Figure 1 As shown, it includes a gas storage cylinder 1, a core holder 2, a constant temperature chamber 3, a pore pressure servo device 4, a confining pressure servo device 5, and a central processing unit.

[0032] The core holder is placed in a constant temperature chamber, and a core sample is placed inside the core holder. The side wall of the core sample is in close contact with the inner wall of the core holder. The inlet end of the core holder is connected to a gas storage cylinder through an input pipe, the outlet end of the core holder is connected to an output pipe, and the side wall of the core holder is connected to a confining pressure servo device through a confining pressure pipe.

[0033] The input pipe is equipped with an inlet pressure sensor 6 and a control valve. The inlet pressure sensor is located near the inlet end of the core holder and is used to measure the inlet pressure of the core holder. The output pipe is equipped with a back pressure valve 7, a mass flow meter 8, and a control valve. The inflow end of the back pressure valve is connected to the pore pressure servo device through a pore pressure pipe. The pore pressure pipe is equipped with an outlet pressure sensor 9 and is used to measure the outlet pressure of the core holder. The confining pressure pipe is equipped with a confining pressure sensor 10 and is used to measure the confining pressure on the core sample.

[0034] The inlet pressure sensor, outlet pressure sensor, confining pressure sensor, mass flow meter, constant temperature chamber, pore pressure servo device, and confining pressure servo device are all connected to the central processing unit.

[0035] Specifically, the gas storage cylinder described in this embodiment stores nitrogen gas, which can provide a pressure of 0~30MPa.

[0036] The pore pressure servo device is configured as a pore pressure control pump to provide pore pressure for the core sample; the confining pressure servo device is configured as a confining pressure control pump to provide confining pressure for the core sample.

[0037] Example 2 This embodiment discloses a method for quantitatively evaluating the stress sensitivity of coal and rock reservoirs, such as... Figure 2 As shown, the quantitative evaluation device for stress sensitivity of coal and rock reservoirs disclosed in Example 1 includes the following steps: Step 1, Core sample preparation and assembly; Specifically, a core sample is selected, which is a cylinder with a diameter of 25 mm and a length of 50 mm. The sample is dried at 60~80℃ and weighed. 10~40 μm air-permeable filter sheets are attached to both ends of the core sample to ensure that the flatness of the core sample end face does not exceed 0.02 mm. After wrapping the core sample with a heat-shrink sleeve, the wrapped core sample is placed in a core holder. An axial preload of 0.2~0.5 kN is applied to the core sample. The quantitative evaluation device for stress sensitivity of coal and rock reservoirs is installed, and the sealing performance of the quantitative evaluation device for stress sensitivity of coal and rock reservoirs is checked.

[0038] Step 2: Perform metrological verification on the quantitative evaluation device for stress sensitivity of coal and rock reservoirs, and preset the stress loading strategy for core samples, including slow strategy and fast strategy.

[0039] Specifically, before conducting the coal reservoir stress sensitivity test using the quantitative evaluation device for coal reservoir stress sensitivity, the mass flow meter undergoes two-point or three-point range calibration. Zero-point and linearity calibrations are performed on the inlet pressure sensor, outlet pressure sensor, and confining pressure sensor, respectively. If the zero-point drift exceeds 0.5%FS, recalibration is required, and the corresponding correction coefficient is recorded to ensure the accuracy of the measurements from the mass flow meter, inlet pressure sensor, outlet pressure sensor, and confining pressure sensor. Simultaneously, nitrogen is injected into the gas storage cylinder, and the temperature variation range of the constant temperature chamber is controlled within ±1℃. The viscosity and density parameters of the nitrogen remain consistent throughout the entire test.

[0040] The stress loading of the core sample adopts a strategy of constant pore pressure and changing confining pressure. The pore pressure servo device is controlled to keep the pore pressure of the core sample constant at 2MPa. Then, the confining pressure servo device is controlled to load the confining pressure on the core sample according to the preset pressure gradient. The confining pressure value of the core sample is loaded to 2MPa, 6MPa, 10MPa and 14MPa in sequence. Then, the confining pressure on the core sample is unloaded according to the preset pressure gradient, that is, the confining pressure value of the core sample is unloaded to 14MPa, 10MPa, 6MPa and 2MPa in sequence, thus completing the stress loading and unloading process of the core sample.

[0041] The stress loading strategy is divided into a slow strategy and a fast strategy based on a preset pressure gradient. In the slow strategy, the pressure gradient used for confining pressure loading and unloading is set to 0.2 MPa / min, that is, the core sample is subjected to stress loading and stress unloading at a stress rate of 0.2 MPa / min during the test. In the fast strategy, the pressure gradient used for confining pressure loading and unloading is set to 1.0 MPa / min, that is, the core sample is subjected to stress loading and stress unloading at a stress rate of 1.0 MPa / min during the test.

[0042] Step 3: Conduct stress sensitivity tests using a quantitative evaluation device for stress sensitivity of coal and rock reservoirs. Apply confining pressure to the core sample using a preset stress loading strategy until the core sample reaches a stable state. Use a confining pressure sensor to measure the confining pressure value of the core sample in real time, determine the latching point of the core sample under each confining pressure value, obtain the effective stress and permeability of the core sample at each latching point, and construct the relationship curve between effective stress and permeability.

[0043] Specifically, stress sensitivity tests were conducted on core samples using a quantitative evaluation device for stress sensitivity of coal and rock reservoirs, employing both slow and fast strategies.

[0044] During the stress sensitivity test, according to a preset stress loading strategy, the confining pressure servo device is controlled to first load confining pressure onto the core sample according to a preset pressure gradient, and then unload the confining pressure, so that the core sample reaches a stable state under each confining pressure value. The time point corresponding to the core sample reaching a stable state is defined as the latch point, at which point the flow rate measured by the mass flow meter no longer changes significantly. Figure 3 As shown, during the stress loading process, the latching points at confining pressures of 2MPa, 6MPa, 10MPa, and 14MPa are obtained when using slow and fast strategies for stress loading and unloading.

[0045] The latching points corresponding to each confining pressure value are determined, that is, the latching points corresponding to confining pressure values ​​of 2MPa, 6MPa, 10MPa, and 14MPa during stress loading and the latching points corresponding to confining pressure values ​​of 14MPa, 10MPa, 6MPa, and 2MPa during stress unloading are obtained. The measured values ​​of the inlet pressure sensor, outlet pressure sensor, confining pressure sensor, mass flow meter, and temperature of the constant temperature chamber at each latching point are obtained. The inlet and outlet pressure difference, confining pressure value, volumetric flow rate, and temperature corresponding to each latching point are determined.

[0046] Calculate the effective stress σ and permeability k at each latching point, where the effective stress σ is the difference between the confining pressure and the pore pressure of the rock sample; the permeability is calculated using the following formula: ; In the formula, The permeability of the rock sample; This refers to the viscosity of the gas. The length of the rock sample; Volumetric flow rate; is the cross-sectional area of ​​the rock sample; The steady-state pressure difference under stress level is determined based on the inlet and outlet pressure difference corresponding to the latch point.

[0047] Based on the effective stress *r* and permeability *k* at each latching point, the effective stress-permeability relationship curves of the core sample are obtained, including *r*-logk loading curves and *r*-logk unloading curves obtained using a slow strategy, and *r*-logk loading curves and *r*-logk unloading curves obtained using a fast strategy, such as... Figure 4 As shown.

[0048] Step 4: Based on the effective stress-permeability relationship curve, quantitatively calculate the stress sensitivity evaluation parameters of the core sample, including hysteresis energy, irreversible closure initiation stress, and loading rate sensitivity index, and evaluate the stress sensitivity of the coal and rock reservoir.

[0049] Specifically, based on the S-logk loading and unloading curves obtained using a slow strategy and the S-logk unloading curves obtained using a fast strategy, the slow permeability and fast permeability of the core sample under the same confining pressure are obtained. The mean values ​​of the two values ​​under each confining pressure are calculated and smoothed to obtain the reconstructed S-logk loading and unloading curves of the core sample, and curve smoothing is performed. Then, the difference between the reconstructed S-logk loading and unloading curves is numerically integrated, such as... Figure 5 As shown, the hysteresis energy is obtained. hysteresis energy The area enclosed between the reconstructed 𝜎—logk loading curve and the reconstructed 𝜎—logk unloading curve.

[0050] In this embodiment, the hysteresis energy Used to quantify the energy dissipation of coal and rock under cyclic stress, hysteresis energy The larger the value, the more severe the irreversible damage to the coal and rock reservoir.

[0051] The hysteresis energy The calculation formula is: ; In the formula, This refers to hysteresis energy; It is a logarithmic function; To reconstruct the effective stress on the 𝜎—logk loading curve Corresponding penetration rate; To reconstruct the effective stress on the 𝜎—logk unloading curve The corresponding penetration rate.

[0052] Based on the reconstructed α-logk loading curve and the reconstructed α-logk unloading curve, the permeability difference corresponding to the effective stress on the reconstructed α-logk unloading curve and the reconstructed α-logk loading curve under the same confining pressure is calculated. The relationship between the effective stress and the permeability difference is obtained, resulting in the α-Δlogk curve, as shown below. Figure 6 As shown, the effective stress values ​​corresponding to each inflection point in the α-Δlogk curve are obtained, and the minimum effective stress value corresponding to all inflection points is determined as the irreversible closure initiation stress. And the initial stress of irreversible closure. After normalization, we get: ; In the formula, The normalized irreversible closure initiation stress index; This represents the maximum effective stress. This represents the initial effective stress value.

[0053] Specifically, the normalized irreversible closure initiation stress index Used to evaluate the structural bearing capacity of coal and rock.

[0054] Based on the reconstructed S-logk loading curve and reconstructed S-logk unloading curve of the core sample, the deviation between slow permeability and fast permeability under each effective stress value is calculated, and the loading rate sensitivity index corresponding to each effective stress value is obtained.

[0055] In this embodiment, the loading speed sensitivity index The formula used to evaluate the sensitivity of coal and rock to stress-time effects and creep effects is as follows: ; In the formula, To load the speed sensitivity index; Slow penetration rate; To achieve rapid penetration.

[0056] Step 5: Evaluate the stress sensitivity of the coal reservoir based on the stress sensitivity evaluation parameters of the core sample and the preset stress sensitivity evaluation standard for coal reservoirs.

[0057] Specifically, the preset evaluation criteria for stress sensitivity of coal and rock reservoirs are as follows: Based on the probability distribution curve of hysteresis energy in core samples from coal and rock reservoirs, the quartile method was used to determine the 25th and 75th quartiles; when the hysteresis energy of the core sample... If the hysteresis energy of the core sample does not exceed the 25th percentile, it is considered low dissipation. If the energy level is between the 25th and 75th percentiles, it is considered moderate dissipation, and the hysteresis energy of the core sample is... If the value exceeds the 75th percentile, it is considered to have high dissipation.

[0058] Based on the normalized irreversible closure initiation stress index ,when When the time is right, it is determined to be early closure, at which point the coal and rock reservoir structure is sensitive; when When the closure is moderate, the coal and rock reservoir structure is relatively stable; when When the value is 0.7, it is determined to be a late-stage closure, at which point the coal and rock reservoir structure is stable.

[0059] According to the loading speed index To determine the sensitivity to stress loading rate, when When the stress loading rate is not sensitive, it is determined that the stress loading rate is not sensitive; when When the stress loading rate is high, it is determined that the stress loading rate is more sensitive; when If the stress loading rate is sensitive, then it is determined to be sensitive.

[0060] In summary, the above hysteresis energy Normalized irreversible closure initiation stress index and loading speed index Evaluate the stress sensitivity of coal and rock reservoirs.

[0061] When hysteresis energy The stress index is determined to be high dissipation and normalized irreversible closure initiation stress. It was determined to be a late-stage closure and the loading speed index was... If the stress loading rate is determined to be sensitive, then the coal and rock reservoir is determined to be highly sensitive to stress; when the hysteresis energy Determined as having moderate dissipation and a normalized irreversible closure initiation stress index. Determined to be a medium-closed condition with a loading speed sensitivity index If the stress loading rate is determined to be relatively sensitive, then the coal and rock reservoir is determined to be moderately sensitive to stress; when the hysteresis energy Determined as a low-dissipation, normalized irreversible closure initiation stress index It was determined to be a late-stage closure and the loading speed index was... If the stress loading rate is determined to be insensitive, then the coal and rock reservoir is determined to be low-sensitivity to stress. Furthermore, this invention also sets development strategies for coal reservoirs based on their high stress sensitivity. For coal reservoirs with high stress sensitivity, a daily pressure drop of 5-15 kPa / d is set during development; for coal reservoirs with moderate stress sensitivity, a daily pressure drop of 15-40 kPa / d is set during development; and for coal reservoirs with low stress sensitivity, a daily pressure drop of 40-80 kPa / d is set during development.

[0062] In summary, the method of this invention achieves accurate evaluation of the stress sensitivity of coal and rock reservoirs based on stress sensitivity evaluation parameters, making up for the limitations of traditional reservoir stress sensitivity evaluation methods that rely on manual experience for exponential fitting and lack accurate characterization of reservoir structure behavior, thus laying the foundation for guiding the development of coal and rock reservoirs.

[0063] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," "link," and "fix" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0064] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A quantitative evaluation device for stress sensitivity of coal and rock reservoirs, characterized in that, It includes gas cylinders, core holders, constant temperature chambers, pore pressure servo devices, confining pressure servo devices, and a central processing unit; The core holder is placed in a constant temperature chamber, and a core sample is placed inside the core holder. The side wall of the core sample is in close contact with the inner wall of the core holder. The inlet end of the core holder is connected to a gas storage cylinder through an input pipe, the outlet end of the core holder is connected to an output pipe, and the side wall of the core holder is connected to a confining pressure servo device through a confining pressure pipe. An inlet pressure sensor is installed on the input pipe, and the inlet pressure sensor is located on the side near the inlet end of the core holder; a back pressure valve and a mass flow meter are installed on the output pipe, wherein the inflow end of the back pressure valve is connected to the pore pressure servo device through a pore pressure pipe, and an outlet pressure sensor is installed on the pore pressure pipe; a confining pressure sensor is installed on the confining pressure pipe. The inlet pressure sensor, outlet pressure sensor, confining pressure sensor, mass flow meter, constant temperature chamber, pore pressure servo device, and confining pressure servo device are all connected to the central processing unit.

2. The quantitative evaluation device for stress sensitivity of coal and rock reservoirs according to claim 1, characterized in that, The gas cylinder contains nitrogen or helium.

3. The quantitative evaluation device for stress sensitivity of coal and rock reservoirs according to claim 2, characterized in that, Both the input and output pipes are equipped with control valves.

4. The quantitative evaluation device for stress sensitivity of coal and rock reservoirs according to claim 2, characterized in that, The pore pressure servo device is configured as a pore pressure control pump, and the confining pressure servo device is configured as a confining pressure control pump.

5. A method for quantitatively evaluating the stress sensitivity of coal and rock reservoirs, characterized in that, The quantitative evaluation device for stress sensitivity of coal and rock reservoirs as described in any one of claims 1 to 4 includes the following steps: Step 1, Core sample preparation and assembly; Step 2: Perform metrological verification on the quantitative evaluation device for stress sensitivity of coal and rock reservoirs, and preset the stress loading strategy for core samples, including slow strategy and fast strategy; Step 3: Conduct stress sensitivity tests using a quantitative evaluation device for stress sensitivity of coal and rock reservoirs. Apply confining pressure to the core sample using a preset stress loading strategy until the core sample reaches a stable state. Use a confining pressure sensor to measure the confining pressure value of the core sample in real time, determine the latching point of the core sample under each confining pressure value, obtain the effective stress and permeability of the core sample at each latching point, and construct the relationship curve between effective stress and permeability. Step 4: Based on the effective stress-permeability relationship curve, quantitatively calculate the stress sensitivity evaluation parameters of the core sample to evaluate the stress sensitivity of the coal reservoir. Step 5: Evaluate the stress sensitivity of the coal reservoir based on the stress sensitivity evaluation parameters of the core sample and the preset stress sensitivity evaluation standard for coal reservoirs.

6. The quantitative evaluation method for stress sensitivity of coal and rock reservoirs according to claim 5, characterized in that, In step 1, a core sample is selected. The core sample has a cylindrical structure. The cross-sectional area and length of the core sample are measured, and the sample is dried and weighed. Breathable filter sheets are attached to both ends of the core sample. After the core sample is wrapped with a heat-shrink sleeve, the wrapped core sample is placed in a core holder. A quantitative evaluation device for stress sensitivity of coal and rock reservoirs is installed, and the sealing performance of the quantitative evaluation device for stress sensitivity of coal and rock reservoirs is checked.

7. The quantitative evaluation method for stress sensitivity of coal and rock reservoirs according to claim 5, characterized in that, In step 2, the mass flow meter is calibrated at two points or three points, and the inlet pressure sensor, outlet pressure sensor and confining pressure sensor are calibrated at zero point and linearly respectively. The stress loading of the core sample adopts a strategy of constant pore pressure and changing confining pressure. The pore pressure servo device is controlled to keep the pore pressure of the core sample constant, and then the confining pressure servo device is controlled to load the confining pressure on the core sample according to the preset pressure gradient. After the confining pressure on the core sample reaches the preset confining pressure value, the confining pressure on the core sample is unloaded according to the preset pressure gradient. The stress loading strategy is divided into a slow strategy and a fast strategy based on a preset pressure gradient. In the slow strategy, the pressure gradient used for confining pressure loading and unloading is set to 0.2 MPa / min. In the fast strategy, the pressure gradient used for confining pressure loading and unloading is set to 1.0 MPa / min.

8. The method for quantitative evaluation of stress sensitivity in coal and rock reservoirs according to claim 5, characterized in that, In step 3, the stress sensitivity test of the core sample is carried out using the coal and rock reservoir stress sensitivity quantitative evaluation device with both slow and fast strategies. During the stress sensitivity test, according to the preset stress loading strategy, the confining pressure servo device is controlled to first load confining pressure onto the core sample according to the preset pressure gradient and then unload the confining pressure, so that the core sample reaches a stable state under each confining pressure value. The time point corresponding to the core sample reaching a stable state is defined as the latch point. The latch point corresponding to each confining pressure value is determined, and the measured values ​​of the inlet pressure sensor, outlet pressure sensor, confining pressure sensor, mass flow meter, and temperature value of the constant temperature chamber at each latch point are obtained. The inlet and outlet pressure difference, confining pressure value, volumetric flow rate, and temperature corresponding to each latch point are determined. The effective stress σ and permeability k at each latch point are calculated, and the effective stress-permeability relationship curve of the core sample is obtained, including the σ-logk loading curve and σ-logk unloading curve obtained by the slow strategy and the σ-logk loading curve and σ-logk unloading curve obtained by the fast strategy. The effective stress σ is the difference between the confining pressure value and the pore pressure value of the rock sample. The formula for calculating the permeability is: ； In the formula, The permeability of the rock sample; This refers to the viscosity of the gas. The length of the rock sample; Volumetric flow rate; is the cross-sectional area of ​​the rock sample; The steady-state pressure difference under stress level is determined based on the inlet and outlet pressure difference corresponding to the latch point.

9. The quantitative evaluation method for stress sensitivity of coal and rock reservoirs according to claim 5, characterized in that, In step 4, the stress sensitivity evaluation parameters of the core sample include hysteresis energy, irreversible closure initiation stress, and loading rate sensitivity index. Based on the S-logk loading and unloading curves obtained using the slow strategy and the S-logk unloading curves obtained using the fast strategy, the slow permeability and fast permeability of the core sample under the same confining pressure are obtained. The mean values ​​of the two under each confining pressure are calculated and smoothed to obtain the reconstructed S-logk loading and unloading curves of the core sample. The curves are then smoothed. Finally, the difference between the reconstructed S-logk loading and unloading curves is numerically integrated to obtain the hysteresis energy. The hysteresis energy is used to quantify the energy dissipation of coal and rock under cyclic stress, and the calculation formula is as follows: ； In the formula, This refers to hysteresis energy; It is a logarithmic function; To reconstruct the effective stress on the 𝜎—logk loading curve Corresponding penetration rate; To reconstruct the effective stress on the 𝜎—logk unloading curve Corresponding penetration rate; Based on the reconstructed α-logk loading curve and the reconstructed α-logk unloading curve, the permeability difference corresponding to the effective stress on the reconstructed α-logk unloading curve and the reconstructed α-logk loading curve under the same confining pressure is calculated. The relationship between the effective stress and the permeability difference is obtained, resulting in the α-Δlogk curve. The effective stress value corresponding to each inflection point in the α-Δlogk curve is obtained, and the minimum effective stress value corresponding to all inflection points is determined as the irreversible closure initiation stress. And the initial stress of irreversible closure. After normalization, we get: ； In the formula, The normalized irreversible closure initiation stress index; This represents the maximum effective stress. This represents the initial effective stress value; The normalized irreversible closure initiation stress index Used to evaluate the structural bearing capacity of coal and rock; Based on the reconstructed S-logk loading curve and reconstructed S-logk unloading curve of the core sample, the deviation of slow permeability and fast permeability under each effective stress value is calculated, and the loading rate sensitivity index corresponding to each effective stress value is obtained. The loading speed sensitivity index The formula used to evaluate the sensitivity of coal and rock to stress-time effects and creep effects is as follows: ； In the formula, To load the speed sensitivity index; Slow penetration rate; To achieve rapid penetration.

10. The method for quantitatively evaluating the stress sensitivity of coal and rock reservoirs according to claim 5, characterized in that, In step 5, the preset evaluation standard for stress sensitivity of coal and rock reservoirs is as follows: Based on the probability distribution curve of hysteresis energy in core samples from coal and rock reservoirs, the quartile method was used to determine the 25th and 75th quartiles; when the hysteresis energy of the core sample... If the hysteresis energy of the core sample does not exceed the 25th percentile, it is considered low dissipation. If the energy level is between the 25th and 75th percentiles, it is considered moderate dissipation, and the hysteresis energy of the core sample is... If the value exceeds the 75th percentile, it is considered to have high dissipation. Based on the normalized irreversible closure initiation stress index ,when When the time is right, it is determined to be early closure, at which point the coal and rock reservoir structure is sensitive; when When the closure is moderate, the coal and rock reservoir structure is relatively stable; when When the value is 0.7, it is determined to be a late-stage closure, at which point the coal and rock reservoir structure is stable; According to the loading speed index To determine the sensitivity to stress loading rate, when When the stress loading rate is not sensitive, it is determined that the stress loading rate is not sensitive; when When the stress loading rate is high, it is determined that the stress loading rate is more sensitive; when If the stress loading rate is sensitive, then it is determined to be sensitive. In summary, the hysteresis energy Normalized irreversible closure initiation stress index and loading speed index Evaluate the stress sensitivity of coal and rock reservoirs; when the hysteresis energy The stress index is determined to be high dissipation and normalized irreversible closure initiation stress. It was determined to be a late-stage closure and the loading speed index was... If the stress loading rate is determined to be sensitive, then the coal and rock reservoir is determined to be highly sensitive to stress; when the hysteresis energy Determined as having moderate dissipation and a normalized irreversible closure initiation stress index. Determined to be a medium-closed condition with a loading speed sensitivity index If the stress loading rate is determined to be relatively sensitive, then the coal and rock reservoir is determined to be moderately sensitive to stress. When hysteresis energy Determined as a low-dissipation, normalized irreversible closure initiation stress index It was determined to be a late-stage closure and the loading speed index was... If the stress loading rate is determined to be insensitive, then the coal and rock reservoir is determined to be low-sensitivity to stress. For coal and rock reservoirs that are highly sensitive to stress, the daily pressure drop is set at 5~15 kPa / d during development; for coal and rock reservoirs that are moderately sensitive to stress, the daily pressure drop is set at 15~40 kPa / d during development; and for coal and rock reservoirs that are lowly sensitive to stress, the daily pressure drop is set at 40~80 kPa / d during development.

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