An experimental device and method for simulating coalbed methane drainage

Abstract

The application relates to the technical field of coal bed gas exploitation, in particular to an experimental device and method for simulating coal bed gas drainage and extraction. The experimental device comprises a coal bed simulation unit, a drainage absorption unit, a gas extraction flow control unit and a gas extraction flow monitoring unit which are sequentially connected. The coal bed simulation unit comprises a first clamp, a constant pressure displacement assembly and a pressure boosting assembly. The drainage absorption unit is used for measuring the water production of the coal bed simulation unit. The gas extraction flow control unit is used for controlling the gas extraction flow by adjusting the gas extraction pressure entering the gas extraction flow control unit to simulate fixed production. The gas extraction flow monitoring unit is used for monitoring and recording the gas extraction flow data of the coal bed simulation unit. The experimental device can simulate the coal bed gas drainage and extraction process of a target reservoir to determine the optimal drainage and extraction system of the target reservoir.

Description

Technical Field

[0001] This application relates to the field of coalbed methane extraction technology, specifically to an experimental apparatus and method for simulating coalbed methane drainage. Background Technology

[0002] my country has abundant coalbed methane resources. Based on assessments, the predicted reserves of coalbed methane in China are approximately 26 × 10⁻⁶. 4 With reserves of hundreds of millions of cubic meters, efficient development of coalbed methane is one of the reliable ways to ensure the country's energy supply. However, due to the complex geological structure of coalfields and the many tectonic movements that have occurred, coalbed methane in my country is generally characterized by low pressure, low permeability, and low saturation, which poses a huge challenge to the efficiency of coalbed methane recovery.

[0003] Coalbed methane (CBM) production involves four main processes: drainage and depressurization, desorption, migration, and extraction. Drainage and depressurization is the most crucial step in the entire CBM production process. The removal of formation water inevitably alters the adsorption capacity of the coal seam, and the rapidly flowing water carrying coal dust can easily clog seepage channels. Rapid drainage of water near the wellbore can lead to the closure of seepage channels in the vicinity of the wellbore. Therefore, a suitable drainage and depressurization rate is of practical significance for improving CBM production capacity and recovery efficiency. Summary of the Invention

[0004] To simulate the coalbed methane drainage process of a target reservoir and evaluate the fluid production characteristics during drainage, thereby optimizing the drainage regime for the target reservoir and determining the optimal drainage regime, this application discloses an experimental apparatus and method for simulating coalbed methane drainage.

[0005] In a first aspect, this application provides an experimental device for simulating coalbed methane drainage, the experimental device comprising a coal seam simulation unit, a drainage absorption unit, a gas production flow control unit, and a gas production flow monitoring unit connected in sequence.

[0006] The coal seam simulation unit includes a first clamp, a constant pressure displacement component, and a pressurization component;

[0007] The pressurization component is located at the inlet end of the first clamp, and the constant pressure displacement component is located at the outlet end of the first clamp.

[0008] The first clamp is used to fill the target storage sample;

[0009] The pressurization component is used to simulate the original state of the target reservoir;

[0010] The constant pressure displacement component is used to control the drainage rate by adjusting the pressure difference between the inlet and outlet ends of the first clamp.

[0011] The drainage absorption unit is used to determine the water production of the coal seam simulation unit.

[0012] The gas extraction flow control unit is used to control the gas extraction flow by adjusting the gas extraction pressure entering the gas extraction flow control unit, so as to simulate fixed production.

[0013] The gas production flow monitoring unit is used to monitor and record the gas production flow data of the coal seam simulation unit.

[0014] Optionally, the constant pressure displacement assembly includes a back pressure valve and a first pressure tracking pump;

[0015] The back pressure valve is located at the outlet end of the first clamp, and the first pressure tracking pump is connected to the back pressure valve. It is used to adjust the pressure value of the back pressure valve according to the set pressure difference between the inlet end and the outlet end of the first clamp, so as to control the drainage speed.

[0016] Optionally, the gas sampling flow control unit includes a pressure regulating valve, a third clamp, and a third pressure tracking pump;

[0017] The pressure regulating valve is located between the third clamp and the drainage absorption unit, and is used to regulate the gas sampling pressure entering the gas sampling flow control unit;

[0018] The third clamp is filled with a fake core, which is used to control the gas production flow rate by permeating the gas production under constant pressure, so as to simulate fixed production.

[0019] The third pressure tracking pump is connected to the inside of the third clamp and is used to adjust the internal pressure value of the third clamp according to the set pressure difference and the pressure value at the inlet end of the third clamp, so that the fake core is tightly attached to the inner wall of the third clamp.

[0020] Optionally, the drainage absorption unit includes a second clamp, a desiccant assembly, a rock electrical detector, and a second pressure tracking pump;

[0021] The first clamp outlet end, the back pressure valve, and the second clamp are connected in sequence;

[0022] The desiccant assembly is filled inside the second holder to absorb formation water discharged from the target reservoir sample;

[0023] The rock electrical detector is used to determine the water production of the target reservoir sample by detecting the resistivity at both ends of the desiccant assembly.

[0024] The second pressure tracking pump is connected to the inside of the second clamp and is used to adjust the internal pressure value of the second clamp according to the set pressure difference and the pressure value at the inlet end of the second clamp, so that the desiccant assembly is in close contact with the inner wall of the second clamp.

[0025] Optionally, the coal seam simulation unit further includes a constant pressure and constant speed pump;

[0026] The constant pressure and constant speed pump is connected to the inside of the first clamp and is used to set and maintain the internal pressure of the first clamp.

[0027] Optionally, the coal seam simulation unit further includes a constant temperature chamber;

[0028] The first clamp is located inside the constant temperature chamber, which is used to simulate the formation temperature of the target reservoir sample.

[0029] Optionally, a pressure detection unit may also be included;

[0030] The pressure detection unit is used to detect the pressure at the inlet and outlet of the coal seam simulation unit, drainage absorption unit, and gas production flow control unit.

[0031] Optionally, the experimental apparatus may further include a control and analysis unit;

[0032] The control and analysis unit is connected to the gas flow monitoring unit and the pressure detection unit, respectively, and is used to monitor and record the pressure value detected by the pressure detection unit and the gas flow value detected by the gas flow monitoring unit.

[0033] Secondly, this application discloses an experimental method for simulating the selection of drainage regimes in coalbed methane wells, using the experimental apparatus described in the first aspect, comprising:

[0034] S100: Perform an airtightness test on the experimental setup;

[0035] S200: The drainage absorption unit is calibrated to obtain the relationship between the resistivity and water absorption rate of the drainage absorption unit;

[0036] S300: Calibrate the volume of the first gripper space to obtain the remaining volume of the first gripper. p ;

[0037] S400: Target reservoir original state restoration: The target storage sample is filled into the first holder, pressurized by the pressurization component, and simulated formation water is injected into the first holder to restore the pressure and water saturation in the first holder to the original state of the target reservoir.

[0038] S500: Simulate target reservoir production: Set the pressure difference between the inlet and outlet of the first holder through the constant pressure displacement component, and adjust the gas production pressure entering the gas production flow control unit to a constant value, so that the target reservoir sample enters the drainage and depressurization stage, the stable production stage and the depletion development stage in sequence, and obtain the corresponding recovery rate.

[0039] S600: The total amount of produced gas and the total amount of unproduced gas are obtained through the gas production flow monitoring unit, and the recovery rate is calculated.

[0040] S700: Replace the target reservoir sample filled into the first holder, change the pressure difference between the inlet and outlet of the first holder set by the constant pressure displacement component, re-execute the above steps of restoring the original state of the target reservoir and simulating the production of the target reservoir, and calculate the corresponding recovery rate.

[0041] Optionally, the experimental method further includes: comparing the recovery rates obtained from multiple experiments to obtain the optimal drainage system.

[0042] Optionally, S500 includes:

[0043] S501: Connect the coal seam simulation unit, drainage absorption unit, gas production flow control unit and gas production flow monitoring unit in sequence, and adjust the gas production pressure entering the gas production flow control unit to a constant value;

[0044] S502: The pressure difference between the inlet and outlet of the first holder is set by the constant pressure displacement component, and the target reservoir sample enters the drainage and depressurization stage.

[0045] S503: If the resistivity at both ends of the desiccant assembly does not change significantly and the target reservoir sample enters the stable production stage, then the constant pressure displacement assembly is turned off.

[0046] S504: If the flow rate detected by the gas production flow monitoring unit cannot maintain a constant rate of increase, and the target reservoir sample enters the depletion development stage, the gas production pressure entering the gas production flow control unit will be adjusted to the maximum pressure until gas production ends.

[0047] Optionally, S300 includes:

[0048] S301: Fill a standard tank with a volume of V0 with gas, and record the initial pressure value of the standard tank after the pressure of the standard tank stabilizes.

[0049] S302: Connect the standard tank from step S301 to the first clamp, and record the stable pressure value 1 of the standard tank after the pressure in the first clamp stabilizes.

[0050] S303: After the gas in the first clamp is discharged, a pad with a known volume is placed into the standard tank. Repeat steps S301-S302 to obtain the initial pressure value and stable pressure value of the standard tank again.

[0051] S304: Replace the gasket in the standard tank several times, repeat step S303, and obtain multiple sets of initial pressure values ​​and stable pressure values ​​of the standard tank.

[0052] S305: Fit multiple sets of data according to the following relationship to obtain the remaining volume of the first gripper;

[0053]

[0054] Where V is the volume of the pad block, V0 is the volume of the standard tank, and V p P represents the remaining volume of the first clamp, P1 represents the initial pressure value of the standard tank, and P... 11 This is the stable pressure value of the standard tank.

[0055] Optionally, the drainage absorption unit includes a desiccant assembly; the calibration of the drainage absorption unit to obtain the relationship between the resistivity and water absorption rate of the drainage absorption unit includes:

[0056] The desiccant assembly was calibrated to obtain the relationship between the resistivity and water absorption rate of the desiccant assembly.

[0057] Optionally, the S600 further includes:

[0058] Calculate the adsorbed gas content and non-adsorbed gas content in the target reservoir sample.

[0059] Optionally, calculating the adsorbed gas content and non-adsorbed gas content in the target reservoir sample includes:

[0060] The adsorbed gas content and non-adsorbed gas content in the target reservoir sample are calculated using the following formula:

[0061]

[0062] Q nadst =Q1+Q2-Q adst -Q t

[0063] Among them, V p To simulate formation water injection, V ωt Let Q be the volume of water produced at time t. t Q1 is the total gas produced at time t, Q2 is the total gas produced at the end of the experiment, and Q3 is the total gas not produced at the end of the experiment. adst Let Q be the adsorbed gas content at time t. nadst Let t be the content of non-adsorbed gas at time t.

[0064] Based on the above technical solution, the beneficial effects of this application compared with the prior art are as follows:

[0065] 1. The experimental apparatus in this application embodiment changes the production pressure to alter the drainage regime of the target reservoir sample. Combined with the final recovery rate of the target reservoir to reflect the recovery efficiency of the corresponding sample, the drainage regime is selected to determine the optimal drainage regime for the target reservoir.

[0066] 2. The experimental apparatus in this application embodiment can reflect the fluid production characteristics during the coalbed methane drainage process, including water production, drainage rate, gas production, and gas production rate. It can also calculate the adsorbed and non-adsorbed gas content of the target reservoir, and can be used to quantitatively analyze the coalbed methane desorption rate under different drainage regimes. This provides fundamental data and technical support for studying the properties of coalbed methane in target reservoir samples and for establishing production regimes such as production pressure, drainage rate, and drainage combination methods in the coalbed methane field. Attached Figure Description

[0067] Figure 1 This is a flowchart illustrating the various modules of the experimental apparatus in the embodiments of this application;

[0068] Figure 2 This is a schematic diagram of the overall structure of the experimental apparatus in the embodiments of this application;

[0069] Figure 3 This is a schematic diagram of the second clamp and desiccant assembly in an embodiment of this application; Figure 4 This is a flowchart illustrating the experimental method in an embodiment of this application;

[0070] Explanation of reference numerals in the attached figures:

[0071] 1. Coal seam simulation unit; 11. First clamp; 12. Pressurization component; 121. Gas cylinder; 122. Pressurization pump; 13. Constant pressure displacement component; 131. Back pressure valve; 132. First pressure tracking pump; 14. Constant pressure and constant speed pump; 15. Constant temperature chamber; 2. Drainage absorption unit; 21. Second clamp; 22. Desiccant component; 23. Rock electrical detector; 24. Second pressure tracking pump; 3. Gas production flow control unit; 31. Pressure regulating valve; 32. Third clamp; 33. Third pressure tracking pump; 4. Gas production flow monitoring unit; 5. Pressure detection unit; 6. Control and analysis unit; 7. Sub-pipelines; a. Valve 1; b. Valve 2; c. Valve 3; d. Valve 4; e. Valve 5; f. Valve 6; g. Valve 7; h. Valve 8; i. Valve 9. Detailed Implementation

[0072] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0073] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0074] In the description of this disclosure, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0075] In the description of this disclosure, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linkage" 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 connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this disclosure based on the specific circumstances.

[0076] The inventors discovered that during coalbed methane (CBM) extraction, the drainage and depressurization rate must be neither too fast nor too slow. The appropriate drainage and depressurization rate depends on the established drainage regime for CBM wells. Currently, the establishment of CBM well drainage regimes is based on production data from experimental areas or drainage intensity models during the drainage phase. Both methods have limitations: the former is limited by the completeness of data from production wells, and the latter by the completeness of existing fundamental theories. Therefore, establishing an experimental method to simulate the fluid production characteristics during CBM drainage under different drainage regimes is of great significance. This method can provide fundamental data and technical support for establishing production regimes such as production pressure, drainage rate, and drainage combination methods in CBM field operations.

[0077] To simulate the coalbed methane drainage process of a target reservoir and evaluate the fluid production characteristics during drainage, thereby optimizing the drainage regime for the target reservoir and determining the optimal drainage regime, the inventors further developed and created this invention.

[0078] Firstly, referring to Figure 1 and Figure 2This application discloses an experimental apparatus for simulating coalbed methane drainage and production. The apparatus includes a coal seam simulation unit 1, a drainage absorption unit 2, a gas production flow control unit 3, and a gas production flow monitoring unit 4 connected in sequence. The coal seam simulation unit 1 includes a first clamp 11, a constant pressure displacement component 13, and a pressurization component 12. The pressurization component 12 is located at the inlet end of the first clamp 11, and the constant pressure displacement component 13 is located at the outlet end of the first clamp 11. The first clamp 11 is used to fill the target storage sample. The pressurization component 12 is used to simulate the original state of the target reservoir. The constant pressure displacement component 13 is used to achieve constant pressure displacement gas production by setting the pressure difference between the inlet and outlet ends of the first clamp 11. The drainage absorption unit 2 is used to measure the water production of the coal seam simulation unit 1. The gas production flow control unit 3 is used to adjust the gas production pressure entering the gas production flow control unit 3 and to simulate fixed production by controlling the gas production flow of the target reservoir sample. The gas production flow monitoring unit 4 is used to monitor and record the gas production flow data of the coal seam simulation unit 1.

[0079] The experimental apparatus in this embodiment simulates the original state of the target reservoir using a coal seam simulation unit 1 to implement the coalbed methane well drainage process; it absorbs simulated formation water discharged from the target reservoir using a drainage absorption unit 2 to detect water production; it controls the flow rate of the target reservoir sample using a gas production flow control unit 3 to simulate fixed-production; and it detects the gas production flow rate after passing through the gas production flow control unit 3. This allows for changing the drainage regime of the target reservoir sample by altering the production pressure, and by combining the final recovery rate of the target reservoir with the recovery efficiency of the corresponding sample, thus determining the optimal drainage regime.

[0080] In an optional embodiment, refer to Figure 2 The constant pressure displacement assembly 13 includes a back pressure valve 131 and a first pressure tracking pump 132. The back pressure valve 131 is located at the outlet end of the first clamp 11, and the first pressure tracking pump 132 is connected to the back pressure valve 131. In specific implementation, the back pressure valve 131 can adjust its opening degree according to the set pressure value of the first pressure tracking pump 132, so that the outlet of the first clamp 11 always maintains a certain pressure. The first pressure tracking pump 132 can adjust the pressure value of the back pressure valve by tracking the pressure value at the inlet end of the first clamp 11 under a set pressure difference, thereby controlling the drainage rate of the target reservoir sample. In simulated coalbed methane drainage, the constant pressure displacement assembly 13, as a pressure regulating assembly, can adjust the pressure difference between the two ends of the target reservoir sample to change the drainage rate.

[0081] In an optional embodiment, refer to Figure 2 The experimental setup of this application is equipped with control valves between every two units to facilitate control over the connectivity of each unit. See also Figure 1Specifically, it includes valve 1a, valve 2b, valve 3c, valve 4d, valve 5e, valve 6f, valve 7g, valve 8h, and valve 9i.

[0082] In an optional embodiment, refer to Figure 2 The pressurization assembly 12 includes a gas cylinder 121 and a booster pump 122 connected in sequence. The outlet of the booster pump 122 is connected to the inlet of the first clamp 11. The gas cylinder 121 can be filled with simulated coalbed methane or other gases to saturate the first clamp 11 with gas, thereby restoring the original state of the coal seam.

[0083] In an optional embodiment, refer to Figure 2 The coal seam simulation unit 1 also includes a constant pressure and constant speed pump 14, which is internally connected to the first clamp 11. Specifically, when the target reservoir sample produces gas, the constant pressure and constant speed pump 14 can absorb the gas in the first clamp 11 and then output the gas at a constant pressure and speed, so that the pressure inside the first clamp 11 is maintained at a constant level, thereby simulating the coal seam pressure.

[0084] Furthermore, in an optional embodiment, refer to Figure 2 The inlet end of the first holder 11 is also equipped with a branch line 7, which is used to connect to a vacuum pump, a displacement pump, or a standard tank. When the branch line 7 is connected to the vacuum pump, all valves except valve three c and valve four d can be closed, and the vacuum pump will evacuate the first holder 11. When the branch line 7 is connected to the displacement pump, the displacement pump can saturate the first holder 11 with simulated formation water to simulate the original state of the coal seam. When the branch line 7 is connected to a standard tank with a known volume, the standard tank can be used to calibrate the remaining volume of the first holder after filling the target reservoir sample.

[0085] In an optional embodiment, refer to Figure 2 The coal seam simulation unit 1 also includes a constant temperature chamber 15, and a first clamp 11 is located inside the constant temperature chamber 15. By setting the temperature of the constant temperature chamber 15, the temperature of the first clamp 11 can be kept constant, thereby simulating the formation temperature where the target reservoir sample is located.

[0086] According to the content of the coal seam simulation unit 1, when restoring the original state of the target reservoir, a vacuum is first applied to the first clamp 11. Then, the inlet and outlet ends of the first clamp 11 are sealed, and the pressure difference between the inlet and outlet ends of the first clamp 11 is set. Simulated coalbed methane is then introduced into the first clamp 11 through the pressurization component 12 until the pressure in the first clamp 11 reaches the target reservoir pressure. Next, simulated formation water is introduced into the first clamp 11. It should be noted that the amount of simulated formation water is calculated from the water saturation of the actual selected target reservoir. After saturating the simulated formation water, the simulated coalbed methane is repeated until the pressure in the first clamp 11 finally stabilizes at the target reservoir pressure value.

[0087] In an optional embodiment, refer to Figure 2 , Figure 3 The drainage absorption unit 2 includes a second holder 21, a desiccant assembly 22, a rock electrical detector 23, and a second pressure tracking pump 24. The desiccant assembly 22 is filled inside the first holder 11 and is used to absorb formation water discharged from the target reservoir sample. The rock electrical detector 23 is connected to both ends of the second holder 21 and is used to determine the water production of the target reservoir sample by detecting the resistivity at both ends of the desiccant assembly 22. The second pressure tracking pump 24 is internally connected to the second holder 21 and can adjust the internal pressure of the second holder 21 according to a set pressure difference and the inlet pressure of the second holder 21. This provides radial pressure to the desiccant assembly, making it adhere tightly to the inner wall of the second holder, thus ensuring that all formation water entering the second holder 21 passes through the desiccant and reducing experimental errors caused by some formation water entering the gap between the two. The pressure difference ranges from 1.5 to 2 MPa.

[0088] In an optional embodiment, the resistivity of the desiccant is measured using a rock electrical analyzer, while the desiccant water absorption rate is obtained by measuring its mass change throughout the entire drainage process. During preliminary experiments, the inventors discovered a linear relationship between the desiccant resistivity increase coefficient and the desiccant water absorption rate. Having obtained this relationship, in subsequent drainage experiments, the desiccant water absorption rate can be directly obtained by measuring the resistivity, thereby determining the water production of the target reservoir sample.

[0089] Specifically, the second clamp 21 is a dedicated clamp for rock electric power testing. The desiccant assembly 22 includes an installation tube and metal gaskets. The installation tube can be a thick-walled PVC pipe (with a pressure resistance of 10 MPa), and the metal gaskets are threaded to both ends of the installation tube. The desiccant assembly 22 can be made of activated alumina, and the activated alumina is specifically made into a columnar shape adapted to the shape of the installation tube. Of course, granular desiccant can also be selected in other embodiments, but in order to reduce the error caused by the filling method of the desiccant assembly 22 to the resistivity test, the filling process should be consistent each time when filling granular desiccant.

[0090] Specifically, for granular desiccants, the filling process can be determined as follows: Granular desiccants of different sizes are filled into the installation tube according to a certain process, and the weight m of the desiccant in the installation tube is recorded. A certain amount of simulated formation water is added to the installation tube, and the resistivity at both ends of the installation tube is measured. After completion, the desiccant is placed in a constant temperature chamber 15 to repeat this operation. If the resistivity at both ends of the desiccant assembly 22 is inconsistent after two fillings, the desiccant filling process is adjusted so that the resistivity measured twice for desiccant assembly 22 saturated with the same amount of water is consistent. This filling process is the standard desiccant filling process.

[0091] Furthermore, in an optional embodiment, refer to Figure 2 The inlet end of the second clamp 21 is also provided with a branch line 7, which can be connected to a displacement pump to saturate the formation water in the second clamp 21 to obtain the relationship between the water absorption rate and resistivity of the desiccant assembly.

[0092] In an optional embodiment, the relationship between the water absorption rate and resistivity of the desiccant assembly can be obtained according to the following process: First, the desiccant assembly 22 is filled into the second holder 21, and the pressure value of the second pressure tracking pump 24 connected to the second holder 21 is set to 1.5-2 MPa. The displacement pump is connected to valve six f, all valves except valve six f are closed, and the displacement pump is started to inject simulated formation water into the second holder 21. The amount of simulated formation water injected is the maximum amount of water that the desiccant in the installation tube can absorb. After the system has been standing for 1-2 hours, the resistivity R1 at both ends of the second holder 21 is tested. Then, the displacement pump and the second pressure tracking pump 24 are turned off, the desiccant is taken out and placed in the constant temperature chamber 15 for baking, and the weight m1 is measured in real time. When the water absorption rate of the desiccant drops to another value, the desiccant is put into the installation tube again according to the filling process, and the desiccant assembly 22 is put back into the second holder 21. The resistivity is measured again to obtain multiple resistivity values ​​R. i The resistivity of the desiccant at different water absorption rates is divided by its resistivity at the maximum water absorption rate; the ratio is the resistivity increase index I. i Finally, the logarithm of the desiccant water absorption rate ω and the resistivity increase index I were calculated. i By fitting the logarithmic values, the relationship between the water absorption rate and the resistivity increase exponential of the desiccant is obtained, which is the relationship between the resistivity and water absorption rate of the desiccant component 22.

[0093] In an optional embodiment, refer to Figure 2The gas production flow control unit 3 includes a pressure regulating valve 31, a third clamp 32, and a third pressure tracking pump 33. The pressure regulating valve 31 is located between the third clamp 32 and the drainage absorption unit 2, and is used to regulate the gas production pressure entering the gas production flow control unit 3. Furthermore, the third clamp 32 is filled with a fake core, which is used to control the gas production flow by permeating the gas under constant pressure, thus simulating fixed-production. The third pressure tracking pump 33 is internally connected to the third clamp 32 and is used to adjust the internal pressure of the third clamp 32 according to a set pressure difference and the inlet pressure value of the third clamp 32, so as to provide radial pressure to the fake core to make it adhere tightly to the inner wall of the third clamp 32. This ensures that all the produced gas passes through the fake core, reducing experimental errors caused by some gas passing through gaps.

[0094] Specifically, by setting the pressure value of the pressure regulating valve 31, the produced gas from the target reservoir sample enters the third clamp 32 at a constant pressure, and the gas production flow rate is controlled by the permeability of the fake core within the third clamp 32. When the pressure is constant, the amount of gas produced through the fake core per unit time is constant, thus simulating fixed-production. When the pressure value of the pressure regulating valve 31 is changed, the gas production flow rate at the outlet of the third clamp 32 also changes accordingly. Therefore, this application utilizes the property that the permeability of the fake core to the gas production is constant under a certain pressure to achieve control of the flow rate of the produced gas from the target reservoir sample connected to the gas production flow control unit 3.

[0095] Furthermore, in an optional embodiment, refer to Figure 2 The third clamp 32 inlet end is also provided with a branch line 7, which is used for temporary connection with other auxiliary systems, including vacuum pumps, displacement pumps, standard tanks, etc.

[0096] In an optional embodiment, the gas flow monitoring unit 4 may specifically be a gas flow meter, which is connected to the outlet of the third clamp 32 and is able to acquire the gas flow rate after passing through the third clamp 32.

[0097] In an optional embodiment, refer to Figure 2 The experimental apparatus of this application also includes a pressure detection unit 5, which is used to detect the pressure at the gas inlet and outlet of the coal seam simulation unit 1, the drainage absorption unit 2, and the gas production flow control unit 3. Specifically, the pressure detection unit 5 includes several pressure sensors, which are respectively installed at the first clamp 11, the second clamp 21, the third clamp 32, and the gas flow meter inlet to detect the pressure at each node of the entire experimental apparatus to ensure the airtightness of the entire experimental apparatus.

[0098] Furthermore, refer to Figure 2The experimental apparatus of this application also includes a control and analysis unit 6, which is connected to the gas flow monitoring unit 4 and the pressure detection unit 5 respectively, and is used to monitor and record the pressure value detected by the pressure detection unit 5 and the gas flow value detected by the gas flow control unit 3.

[0099] Based on the above, when testing the airtightness of the entire experimental setup, inert gas was first introduced into cylinder 121, and dummy cores were placed in the first holder 11, the second holder 21, and the third holder 32. Then, the pressure values ​​of the constant pressure and constant speed pump 14, the second pressure tracking pump 24, and the third pressure tracking pump 33 were adjusted so that the pressure in each holder was 1.5-2 MPa higher than the corresponding holder inlet. This ensures proper fit between the end cap at the holder inlet and the main body, preventing leakage. The pressure of the first pressure tracking pump 132, connected to the back pressure valve 131, was set to 0. Further, valves a, b, d, e, and h were opened, pressure regulating valve 31 was adjusted to its maximum, and valves c, f, g, and i were closed. Then, booster pump 122 was used to fill the system with inert gas, making the system pressure 1.5-2 MPa higher than the formation pressure of the sample being tested. After the pressure stabilized, all valves were closed. After standing for 24 hours, observe the values ​​of each pressure sensor. If the pressure value does not change, it indicates that the system is airtight and the experiment can begin. If the pressure changes, use soapy water to detect leaking parts in the pressure change range, seal them, and then perform the airtightness test again until the entire system is airtight.

[0100] The experimental apparatus described in this application can quantitatively test the coalbed methane production rate and recovery efficiency under different drainage regimes by simulating the complete coalbed methane production process, while simultaneously detecting various characteristics of the produced fluid. This allows for the optimization of the drainage regime for the target reservoir, determining the optimal drainage regime. Furthermore, this application can calculate the adsorbed and non-adsorbed gas content of the target reservoir, which can be used to quantitatively analyze the coalbed methane desorption rate under different drainage regimes.

[0101] Secondly, this application discloses an experimental method for simulating coalbed methane drainage, using the experimental apparatus as described in the first aspect, with reference to... Figure 3 Specifically, this includes S100-S700:

[0102] S100: Perform an airtightness test on the experimental setup;

[0103] S200: Calibrate the drainage absorption unit 2 to obtain the relationship between the resistivity and water absorption rate of the drainage absorption unit 2.

[0104] S300: The spatial volume of the first clamp 11 is calibrated to obtain the remaining volume p of the first clamp.

[0105] Specifically, step S300 includes S301-S305:

[0106] S301: Fill the standard tank with gas, and record the initial pressure value of the standard tank after the pressure of the standard tank stabilizes.

[0107] S302: Connect the standard tank from step S301 to the first clamp 11, and record the stable pressure value 1 of the standard tank after the pressure inside the first clamp 11 stabilizes.

[0108] S303: After the gas in the first clamp 11 is discharged, a pad with a known volume is placed into the standard tank. Repeat steps S301-S302 to obtain the initial pressure value and stable pressure value of the standard tank again.

[0109] S304: Replace the gasket in the standard tank several times, repeat step S303, and obtain multiple sets of initial pressure values ​​and stable pressure values ​​of the standard tank.

[0110] S305: Fit multiple sets of data according to the following relationship to obtain the remaining volume of the first gripper;

[0111]

[0112] Where V is the volume of the pad block, V0 is the volume of the standard tank, and V p P represents the remaining volume of the first clamp, P1 represents the initial pressure value of the standard tank, and P... 11 This is the stable pressure value of the standard tank.

[0113] S400: Target reservoir original state restoration: The target storage sample is filled into the first holder 11, pressurized by the pressurization component 12, and simulated formation water is injected into the first holder 11 to restore the pressure and water saturation in the first holder 11 to the original state of the target reservoir.

[0114] In an optional embodiment, during the experiment, to simulate the production process of a real coal seam, the target reservoir sample is selected from those with micro-cracks along the axial direction. If the sample does not have natural micro-cracks along the axial direction, artificial cracking is required along the axial direction. Furthermore, to maintain the columnar shape of the coal sample, the sample is first wrapped with raw rubber tape and then placed in the first holder 11.

[0115] S500: Simulate target reservoir production: Set the pressure difference between the inlet and outlet of the first clamp 11 through the constant pressure displacement component 13, and adjust the gas production pressure entering the gas production flow control unit 3 to a constant value, so that the target reservoir sample enters the drainage and depressurization stage, the stable production stage and the depletion development stage in sequence, and obtain the corresponding recovery rate.

[0116] Specifically, step S500 includes S501-S504:

[0117] S501: Connect the coal seam simulation unit 1, drainage absorption unit 2, gas production flow control unit 3 and gas production flow monitoring unit 4 in sequence, and adjust the gas production pressure entering the gas production flow control unit 3 to a constant value.

[0118] S502: The pressure difference between the inlet and outlet of the first clamp 11 is set by the constant pressure displacement component 13, and the target reservoir sample enters the drainage and depressurization stage.

[0119] S503: If the resistivity at both ends of the desiccant assembly 22 does not change significantly and the target reservoir sample enters the stable production stage, then the constant pressure displacement assembly 13 is turned off.

[0120] S504: If the flow rate detected by the gas production flow monitoring unit 4 cannot maintain a constant rate of increase, and the target reservoir sample enters the depletion development stage, the gas production pressure entering the gas production flow control unit 3 will be adjusted to the maximum pressure until gas production ends.

[0121] S600: The total produced gas and the total unproduced gas are obtained through the gas production flow monitoring unit 4, and the recovery rate is calculated. Specifically, the total produced gas is measured by the flow meter at the outlet of the third clamp 32. When the gas flow rate through the flow meter is less than the flow meter's measurement accuracy, the flow meter is connected to valve 3c, valve 5e is closed, valve 3c is opened, and the pressure value of the constant speed and constant pressure pump connected to the first clamp 11 is slowly reduced to measure the remaining flow rate in the first clamp 11. This remaining flow rate is the total unproduced gas.

[0122] Furthermore, step S600 also includes: calculating the adsorbed gas content and non-adsorbed gas content in the target reservoir sample.

[0123] Specifically, the adsorbed gas content Qadst and the non-adsorbed gas content Qnadst in the target reservoir sample at time t are calculated using the following formulas:

[0124]

[0125] Q nadst =Q1+Q2-Q adst -Q t (3)

[0126] Where P is the pressure value at time t in the first clamp 11, Z is the compressibility coefficient, M is the relative gas molecular weight, R is the universal gas constant, ρ is the adsorbed phase density, and V p To simulate formation water injection, V ωt Let Q be the volume of water produced at time t. tQ1 is the total gas produced at time t, Q2 is the total gas produced at the end of the experiment, and Q3 is the total gas not produced at the end of the experiment. adst Let Q be the adsorbed gas content at time t. nadst Let t be the content of non-adsorbed gas at time t.

[0127] Furthermore, based on the adsorbed gas content Q in the target reservoir sample... adst Non-adsorbed gas content Q nadst Calculate the adsorbed gas production rate V in coalbed methane ads Non-adsorbed gas production rate V nads :

[0128]

[0129]

[0130] Among them, Q ads(t+Δt) Let Q be the adsorbed gas content at time t+Δt. nads(t+Δt) Let be the adsorbed gas content at time t+Δt.

[0131] S700: Replace the target reservoir sample filled into the first holder 11, change the pressure difference between the inlet and outlet ends of the first holder 11 set by the constant pressure displacement component 13, repeat the above steps of restoring the original state of the target reservoir and simulating the production of the target reservoir, and calculate the corresponding recovery rate.

[0132] Furthermore, by comparing the recovery rates obtained from multiple experiments, the optimal drainage system was determined.

[0133] To more clearly illustrate the experimental apparatus and method for simulating coalbed methane drainage provided by the present invention, the following detailed description of the experimental apparatus and method is provided with reference to specific embodiments.

[0134] Example 1

[0135] Reference Figure 2The experimental apparatus in this embodiment includes a coal seam simulation unit 1, a drainage absorption unit 2, a gas production flow control unit 3, and a gas production flow monitoring unit 4 connected in sequence. The coal seam simulation unit 1 includes a first clamp 11, a back pressure valve 131, a first pressure tracking pump 132, a constant pressure and constant speed pump 14, a gas cylinder 121, and a booster pump 122. The drainage absorption unit 2 includes a second clamp 21, a desiccant assembly 22, a rock electrical detector 23, and a second pressure tracking pump 24. The gas production flow control unit 3 includes a pressure regulating valve 31, a third clamp 32, and a third pressure tracking pump 33. The first clamp 11, the second clamp 21, and the third clamp 32 in this application are connected in sequence. The first clamp 11 is used to fill the target reservoir sample to simulate the original state of the target reservoir and implement the coalbed methane drainage process. The second clamp 21 is used to fill the desiccant to determine the water production of the target reservoir sample by measuring the change in the resistivity of the desiccant. The third clamp 32 is used to fill the fake core to control the gas production flow rate by measuring the permeability of the fake core to gas production under constant pressure, so as to simulate fixed production.

[0136] In addition, this application also monitors the gas flow rate of the target reservoir sample through the gas flow monitoring unit 4, and monitors and records the volumetric flow rate, pressure, temperature, and other data of the sample during the gas extraction process through the control and analysis unit 6. The high temperature and high pressure resistance of each component meets the experimental requirements, ensuring stable experimental test signals. The applicable temperature range of this experimental device is 0-180℃, the pressure range is 0-70MPa, the measurement range of each pressure sensor is 0-70MPa, and the measurement range of the gas flow meter is 0-10000ml.

[0137] The specific process of the simulation experiment is described in detail below:

[0138] System airtightness test: Connect all components, fill the gas cylinder with helium, and then perform an airtightness test on the entire experimental setup according to the relevant procedures for airtightness testing described above. These procedures will not be repeated here.

[0139] Calibration of the drainage absorption unit:

[0140] In this embodiment, the desiccant is columnar activated alumina. First, the columnar activated alumina is filled into the installation tube. After assembling the desiccant assembly, it is placed into the second holder. The pressure of the second pressure tracking pump connected to the second holder is set to 2 MPa. The displacement pump is connected to valve six, and simulated formation water is injected into the second holder. Based on the maximum water volume that activated alumina can absorb, the injected simulated formation water volume is half the weight of the activated alumina. After the system has stood for 2 hours, the resistivity R1 at both ends of the installation tube is measured using a rock electrical detector. The displacement pump and the second pressure tracking pump are then turned off. The activated alumina in the desiccant assembly is removed and placed in a 200°C constant temperature oven for baking, with the weight m measured in real time.i It should be noted that the desiccant water absorption rate is calculated according to w i =(m i The calculation is based on (-m) / m. When the desiccant's water absorption rate is 45%, 40%, 35%, 30%, 20%, 15%, 10%, and 5%, it is placed back into the PVC pipe according to the filling process. The desiccant assembly is then placed back into the second holder, and the corresponding resistivity R is measured under the same pressure conditions. i Then, a desiccant component with a water absorption rate of 10% was placed in the second holder for subsequent experiments.

[0141] The resistivity R of activated alumina at different water absorption rates was compared. i Dividing the resistivity R1 of activated alumina at its maximum water absorption rate yields the resistivity increase factor I of activated alumina at different water absorption rates. i Specifically, activated alumina at different water absorption rates (w) i resistivity R i The resistivity increase index is shown in Table 1:

[0142] Table 1. Resistivity and resistivity increase index at both ends of the desiccant component under different water absorption rates.

[0143]

[0144]

[0145] Based on the data in Table 1, the water absorption rate w i The logarithm and resistivity increase index I i By fitting the logarithmic values, the water absorption rate w is obtained. i and resistivity increase index I i The relation is:

[0146] log I i =3.036-1.806log w i ;

[0147] Furthermore, the water absorption rate w i and resistivity R i The relation is:

[0148] First clamp remaining volume calibration: Place the sample into clamp 1. The pressure value of the constant speed and constant pressure pump connected to the first clamp is 1.5 MPa higher than the target reservoir pressure. Connect valve 3 to a standard tank with a known volume. Then calibrate the remaining volume of the first clamp according to the steps in step S3. The volume of the pad V, the initial pressure value P1 of the standard tank, and the stable pressure value P of the standard tank are recorded each time. 11 As shown in Table 2:

[0149] Table 2. Remaining Volume Calibration Data of the First Clamp

[0150]

[0151] Furthermore, the above data is fitted using the following formula:

[0152]

[0153] Where V is the volume of the pad block, V0 is the volume of the standard tank, P1 is the initial pressure value of the standard tank, and P 11 V is the stable pressure value of the standard tank. p This represents the remaining volume of the first gripper.

[0154] The calibration relation is further obtained as follows: Therefore, in this embodiment, the remaining volume V of the first clamp is... p It is 42.747cm 3 .

[0155] Target reservoir original state restoration:

[0156] Specifically, the fake core is placed in the third holder, the pressure of the third pressure tracking pump is set to 2 MPa, and the temperature of the constant temperature chamber is set to the actual formation temperature of the target reservoir. Then, a vacuum is drawn into the first holder 11. The pressure of the first pressure tracking pump is set to 2 MPa, and the gas in the gas cylinder is replaced with simulated coalbed methane, preferably methane. After opening valves one, two, and four, the gas cylinder and booster pump are opened, and simulated coalbed methane is slowly injected into the first holder. When the pressure in the first holder reaches the formation pressure, the gas injection is stopped. In this embodiment, the pressure of the target reservoir sample is 22 MPa. Next, valve three is opened, and the displacement pump injects simulated formation water into the first holder at a constant speed. The amount of simulated formation water is calculated from the water saturation of the actual reservoir. In this embodiment, the water saturation of the target reservoir is 70%. Since water saturation is the ratio of the volume of pores occupied by water to the volume of pores in the rock in the target reservoir sample, the amount of saturated water in the first holder is calculated to be 30 mL based on the remaining volume of the first holder. After saturation, valve three is closed, and the entire system pressure is allowed to stabilize. Generally, the system pressure is still lower than the actual pressure of the target reservoir at this time. The above gas injection steps are repeated until the pressure of the first holder finally stabilizes at the actual formation pressure of the target reservoir, thus completing the restoration of the original state of the coal seam.

[0157] Simulating target reservoir production: First, close all valves, then sequentially open valves five, eight, and nine, adjusting the pressure regulating valve to a constant value. Simultaneously, set the pressure value of the first pressure tracking pump connected to the back pressure valve, ensuring the pressure difference between the inlet and outlet of the first clamp is 0.2 MPa, thus initiating the coal seam drainage and pressure reduction stage. Turn on the rock electrical analyzer and the flow and pressure data recording software to record various data in real time. When the rock electrical analyzer detects no significant change in resistivity across the desiccant assembly, gas production from the target reservoir enters a fixed-production stage. At this point, shut down the first pressure tracking pump connected to the back pressure valve, eliminating back pressure at the outlet of the first clamp. When the flow rate detected by the gas flow meter cannot maintain a constant rate of increase, gas production from the target reservoir enters a depletion development stage. At this point, adjust the pressure regulating valve to its maximum pressure. The experiment stops when the flow rate through the flow meter is less than its measurement accuracy. Connect the flow meter to valve three, close valve five and open valve three, slowly reduce the pressure value of the constant speed and constant pressure pump connected to the first clamp, and measure the remaining flow in the first clamp, which is the total amount of gas not produced in the target reservoir.

[0158] Based on the resistivity R at time t t The resistivity R0 of the desiccant at its maximum water absorption rate is calculated using the following formula to determine the weight m of saturated water in the sample. w And the output water volume Δm:

[0159]

[0160] Δm=m t+Δt -m t

[0161] Where, m t+Δt m is the weight of saturated water in the sample at time t+Δt; t Let t be the weight of saturated water in the sample at time t.

[0162] The raw data of the target reservoir production simulated by the experimental setup in this embodiment are shown in Table 3:

[0163] Table 3. Raw data of simulated target reservoir production in Example 1.

[0164]

[0165] Table 3 (Continued from Example 1) - Simulated Target Reservoir Production Data

[0166]

[0167]

[0168] Table 3 (Continued from Example 1) - Simulated Target Reservoir Production Data

[0169]

[0170]

[0171] Table 3 (Continued from Example 1) - Simulated Target Reservoir Production Data

[0172]

[0173]

[0174] Table 3 (Continued from Example 1) - Simulated Target Reservoir Production Data

[0175]

[0176]

[0177] As shown in Table 3, the target reservoir sample entered the production stage after 11 minutes, with the produced water volume stabilizing at 22.45 ml, and entered the depletion development stage after 942 minutes.

[0178] Due to the remaining volume V of the first clamp in this embodiment p It is 42.747cm 3 Simulated formation water volume V ω The volume was 30 mL, and the total gas produced at the end of the experiment, Q1, was 7247.2 cm³. 3 The total amount of unproduced gas, Q2, is 8519.70 cm³. 3 The recovery rate was 45.96%. Furthermore, according to Table 3, the produced water volume V at time t... ωt The total gas production Q at time t t The adsorbed gas content Q in the target reservoir sample at time t is calculated using the following formula. adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads :

[0179]

[0180] Q nadst =Q1+Q2-Q adst -Q t

[0181]

[0182]

[0183] The adsorbed gas content Q at time t adst Non-adsorbed gas content Q nads Adsorbed gas production rate V adsNon-adsorbed gas production rate V nads The calculation results are shown in Table 4:

[0184] Table 4. Adsorbed gas content Q in Example 1 adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads Calculation results

[0185]

[0186]

[0187] Table 4 shows the adsorbed gas content Q in Example 1. adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads Calculation results

[0188]

[0189]

[0190] Table 4 shows the adsorbed gas content Q in Example 1. adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads Calculation results

[0191]

[0192] Table 4 shows the adsorbed gas content Q in Example 1. adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads Calculation results

[0193]

[0194] Table 4 shows the adsorbed gas content Q in Example 1. adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads Calculation results

[0195]

[0196] Table 4 shows the adsorbed gas content Q in Example 1. adst Non-adsorbed gas content Q nadsAdsorbed gas production rate V ads Non-adsorbed gas production rate V nads Calculation results

[0197]

[0198]

[0199] Example 2

[0200] The experimental apparatus in this embodiment is the same as that in Embodiment 1. The difference between the specific process of the simulation experiment in this embodiment and that in Embodiment 1 is that, in simulating the production of the target reservoir, the first pressure tracking pump connected to the back pressure valve is turned off, so that there is no back pressure at the outlet of the first clamp.

[0201] The original production data of the target reservoir simulated in this embodiment are shown in Table 5:

[0202] Table 5. Raw data of simulated target reservoir production in Example 2.

[0203]

[0204] Table 5 continues with the original data of simulated target reservoir production from Example 2.

[0205]

[0206]

[0207] Table 5 continues with the original data of simulated target reservoir production from Example 2.

[0208]

[0209]

[0210] Table 5 continues with the original data of simulated target reservoir production from Example 2.

[0211]

[0212]

[0213] Table 5 continues with the original data of simulated target reservoir production from Example 2.

[0214]

[0215]

[0216] As shown in Table 5, the target reservoir sample entered the production stage after 24 minutes, with the produced water volume stabilizing at around 20 ml, and entered the depletion development stage after 1324 minutes.

[0217] Due to the remaining volume V of the first clamp in this embodiment p It is 42.747cm 3 Simulated formation water volume V ω The volume was 30 mL, and the total gas produced at the end of the experiment, Q1, was 7562.1 cm³. 3 The total amount of unproduced gas, Q2, is 10203.33 cm³. 3 The harvest rate was 42.57%.

[0218] According to calculations, the adsorbed gas content Q at time t in this embodiment is... adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads The calculation results are shown in Table 6:

[0219] Table 6. Adsorbed gas content Q in Example 2 adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads Calculation results

[0220]

[0221]

[0222] Table 6 shows the adsorbed gas content Q in Example 2. adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads Calculation results

[0223]

[0224]

[0225] Table 6 shows the adsorbed gas content Q in Example 2. adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads Calculation results

[0226]

[0227]

[0228] Table 6 shows the adsorbed gas content Q in Example 2. adst Non-adsorbed gas content Q nads Adsorbed gas production rate V adsNon-adsorbed gas production rate V nads Calculation results

[0229]

[0230]

[0231] Table 6 shows the adsorbed gas content Q in Example 2. adst Non-adsorbed gas content Q nads Adsorbed gas production rate V ads Non-adsorbed gas production rate V nads Calculation results

[0232]

[0233] In summary, comparing the coalbed methane recovery rates of the target reservoir samples in Examples 1 and 2, the recovery rate in Example 1 is higher than that in Example 2, indicating that the drainage mode in Example 1 has higher coalbed methane development efficiency. Therefore, Example 1 is selected as the optimal drainage system in both examples.

[0234] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments, but those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," just as "comprising" is interpreted as a conjunction in the claims. Additionally, the use of the term "or" in any of the claims and specification is intended to mean "non-exclusive or."

Claims

1. An experimental apparatus for simulating coalbed methane drainage, characterized in that, The experimental setup includes a coal seam simulation unit, a drainage absorption unit, a gas production flow control unit, and a gas production flow monitoring unit connected in sequence. The coal seam simulation unit includes a first clamp, a constant pressure displacement component, and a pressurization component; The pressurization component is located at the inlet end of the first clamp, and the constant pressure displacement component is located at the outlet end of the first clamp. The first clamp is used to fill the target storage sample; The pressurization component is used to simulate the original state of the target reservoir; The constant pressure displacement component is used to control the drainage rate by adjusting the pressure difference between the inlet and outlet ends of the first clamp. The drainage absorption unit is used to determine the water production of the coal seam simulation unit. The gas extraction flow control unit is used to control the gas extraction flow by adjusting the gas extraction pressure entering the gas extraction flow control unit, so as to simulate fixed production. The gas production flow monitoring unit is used to monitor and record the gas production flow data of the coal seam simulation unit; The constant pressure displacement assembly includes a back pressure valve and a first pressure tracking pump; The back pressure valve is located at the outlet end of the first clamp, and the first pressure tracking pump is connected to the back pressure valve. It is used to adjust the pressure value of the back pressure valve according to the set pressure difference between the inlet end and the outlet end of the first clamp, so as to control the drainage speed. The drainage absorption unit includes a second clamp, a desiccant assembly, a rock electric detector, and a second pressure tracking pump; The first clamp outlet end, the back pressure valve, and the second clamp are connected in sequence; The desiccant assembly is filled inside the second holder to absorb formation water discharged from the target reservoir sample; The rock electrical detector is used to determine the water production of the target reservoir sample by detecting the resistivity at both ends of the desiccant assembly. The second pressure tracking pump is connected to the inside of the second clamp and is used to adjust the internal pressure value of the second clamp according to the set pressure difference and the pressure value at the inlet end of the second clamp, so that the desiccant assembly is in close contact with the inner wall of the second clamp.

2. The experimental apparatus according to claim 1, characterized in that, The gas extraction flow control unit includes a pressure regulating valve and a third clamp; The pressure regulating valve is located between the third clamp and the drainage absorption unit, and is used to regulate the gas sampling pressure entering the gas sampling flow control unit; The third clamp is filled with a fake core, which is used to control the gas production flow rate by permeating the gas under constant pressure, so as to simulate fixed production.

3. The experimental apparatus according to claim 2, characterized in that, The gas extraction flow control unit also includes a third pressure tracking pump; The third pressure tracking pump is connected to the inside of the third clamp and is used to adjust the internal pressure value of the third clamp according to the set pressure difference and the pressure value at the inlet end of the third clamp, so that the fake core is tightly attached to the inner wall of the third clamp.

4. The experimental apparatus according to claim 1, characterized in that, The coal seam simulation unit also includes a constant pressure and constant speed pump; The constant pressure and constant speed pump is connected to the inside of the first clamp and is used to set and maintain the internal pressure of the first clamp.

5. The experimental apparatus according to claim 1, characterized in that, The coal seam simulation unit also includes a constant temperature chamber; The first clamp is located inside the constant temperature chamber, which is used to simulate the formation temperature of the target reservoir sample.

6. The experimental apparatus according to claim 1, characterized in that, It also includes a pressure detection unit; The pressure detection unit is used to detect the pressure at the inlet and outlet of the coal seam simulation unit, drainage absorption unit, and gas production flow control unit.

7. The experimental apparatus according to claim 6, characterized in that, The experimental setup also includes a control and analysis unit; The control and analysis unit is connected to the gas flow monitoring unit and the pressure detection unit, respectively, and is used to monitor and record the pressure value detected by the pressure detection unit and the gas flow value detected by the gas flow monitoring unit.

8. An experimental method for simulating coalbed methane drainage, using the experimental apparatus described in any one of claims 1-7, characterized in that, include: S100: Perform an airtightness test on the experimental setup; S200: The drainage absorption unit is calibrated to obtain the relationship between the resistivity and water absorption rate of the drainage absorption unit; S300: Calibrate the volume of the first gripper space to obtain the remaining volume of the first gripper. p ; S400: Target reservoir original state restoration: The target storage sample is filled into the first holder, pressurized by the pressurization component, and simulated formation water is injected into the first holder to restore the pressure and water saturation in the first holder to the original state of the target reservoir. S500: Simulate target reservoir production: Set the pressure difference between the inlet and outlet of the first holder through the constant pressure displacement component, and adjust the gas production pressure entering the gas production flow control unit to a constant value, so that the target reservoir sample enters the drainage and depressurization stage, the stable production stage and the depletion development stage in sequence, and obtain the corresponding recovery rate. S600: Obtain the total produced gas and the total unproduced gas, and calculate the recovery rate; S700: Replace the target reservoir sample filled into the first holder, change the pressure difference between the inlet and outlet of the first holder set by the constant pressure displacement component, re-execute S400-S500, and calculate the corresponding recovery rate.

9. The experimental method according to claim 8, characterized in that, The S500 includes: S501: Connect the coal seam simulation unit, drainage absorption unit, gas production flow control unit and gas production flow monitoring unit in sequence, and adjust the gas production pressure entering the gas production flow control unit to a constant value; S502: The pressure difference between the inlet and outlet of the first holder is set by the constant pressure displacement component, and the target reservoir sample enters the drainage and depressurization stage. S503: If the resistivity at both ends of the desiccant assembly does not change significantly and the target reservoir sample enters the stable production stage, then the constant pressure displacement assembly is turned off. S504: If the flow rate detected by the gas production flow monitoring unit cannot maintain a constant rate of increase, and the target reservoir sample enters the depletion development stage, the gas production pressure entering the gas production flow control unit will be adjusted to the maximum pressure until gas production ends.

10. The experimental method according to claim 8, characterized in that, The S300 includes: S301: Fill a standard tank with a volume of V0 with gas, and record the initial pressure value of the standard tank after the pressure of the standard tank stabilizes. S302: Connect the standard tank from step S301 to the first clamp, and record the stable pressure value of the standard tank after the pressure in the first clamp stabilizes. S303: After the gas in the first clamp is discharged, a pad with a known volume is placed into the standard tank. Repeat steps S301-S302 to obtain the initial pressure value and stable pressure value of the standard tank again. S304: Replace the gasket in the standard tank several times, repeat step S303, and obtain multiple sets of initial pressure values ​​and stable pressure values ​​of the standard tank. S305: Fit multiple sets of data according to the following relationship to obtain the remaining volume of the first gripper; ； Where V is the volume of the pad block, V0 is the volume of the standard tank, and V p P represents the remaining volume of the first clamp, P1 represents the initial pressure value of the standard tank, and P... 11 This is the stable pressure value of the standard tank.

11. The experimental method according to claim 8, characterized in that, The S600 also includes: Calculate the adsorbed gas content and non-adsorbed gas content in the target reservoir sample.

12. The experimental method according to claim 11, characterized in that, The calculation of the adsorbed gas content and non-adsorbed gas content in the target reservoir sample includes: The adsorbed gas content and non-adsorbed gas content in the target reservoir sample are calculated using the following formula: Q adst ； Q nadst ； Where P is the pressure value at time t in the first clamp, Z is the compressibility coefficient, M is the relative molecular weight of the gas, and R is the universal gas constant. The density of the adsorbed phase is... To simulate formation water injection volume, Let be the volume of water produced at time t. Let t be the total amount of gas produced. The total amount of gas produced at the end of the experiment, Qadst represents the total amount of gas not produced at the end of the experiment, Qnadst represents the adsorbed gas content at time t, and Qnadst represents the non-adsorbed gas content at time t.

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