Method for measuring the amount of gas adsorbed by humid shale under high pressure and variable temperature conditions

Abstract

The application discloses an experimental method for measuring the adsorption capacity of humid shale under high-pressure and variable-temperature conditions, and comprises the following steps: step 100: after the shale sample is crushed, drying is performed, the mass of the dried shale sample is recorded, and a humid shale sample is prepared by using a water balance method; step 200: the void volume of a sample chamber of a high-pressure gas adsorption instrument is calibrated; step 300: the excess adsorption capacity of the humid shale sample is measured under high-pressure and variable-temperature conditions in a closed system, and a gas adsorption isotherm is drawn; and step 400: the adsorption thermodynamic parameters of the humid shale sample are calculated. According to the application, a plurality of gas adsorption isotherms at different temperatures can be obtained through one high-pressure gas adsorption experiment, the whole experiment is completed in a closed system, and the moisture content in the system is always unchanged at different temperatures. Compared with a traditional continuous test method, the test time is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of unconventional natural gas exploration and development, specifically to an experimental method for measuring the amount of gas adsorbed in moist shale under high pressure and variable temperature conditions. Background Technology

[0002] Shale is a low-porosity, low-permeability sedimentary rock rich in organic matter, containing abundant natural gas resources. As an unconventional reservoir, the adsorbed gas ratio in shale-retained natural gas can reach as high as 60%. Therefore, the amount of adsorbed gas in shale is an important indicator for evaluating its reservoir properties, development potential, and natural gas geological reserves. Subsurface shale reservoirs typically contain a certain amount of water in their pores. These water molecules compete with hydrocarbon gases such as methane for adsorption, preferentially occupying some polar adsorption sites (such as hydroxyl groups), thus significantly affecting the amount of hydrocarbon gases adsorbed. Accurately predicting the amount of adsorbed gas in moist shale is of great significance for assessing its in-situ natural gas geological reserves.

[0003] Currently, the temperature sensitivity of gas adsorption in moist shale remains highly controversial, primarily due to limitations in traditional gas adsorption experimental methods. Traditional methods involve placing shale samples that have reached moisture adsorption equilibrium under specific humidity conditions in a high-pressure adsorption (HPA) apparatus and conducting multiple HPA gas adsorption experiments at different temperatures to obtain gas adsorption isotherms at those temperatures. Alternatively, the moist shale samples are divided into multiple subsamples, and HPA gas adsorption experiments are performed on each subsample at different temperatures to obtain gas adsorption isotherms at those temperatures. However, it is well known that even small changes in the moisture content of shale samples can significantly affect the amount of gas adsorbed. Since the pre-experiment degassing process is unavoidable, neither of these methods can guarantee the consistency of moisture content in the shale samples at different temperatures, thus making it impossible to study the effect of temperature as a single factor on the amount of gas adsorbed in moist shale. Furthermore, traditional continuous testing methods require multiple degassing processes, which consumes a significant amount of experimental time. Summary of the Invention

[0004] The purpose of this invention is to provide an experimental method for measuring the amount of adsorbed gas in moist shale under high pressure and variable temperature conditions, so as to solve the technical problems in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution:

[0006] An experimental method for measuring the amount of adsorbed gas in moist shale under high pressure and variable temperature conditions includes the following steps:

[0007] Step 100: After crushing and drying the shale sample, record the mass of the dried shale sample and prepare a moist shale sample using the moisture balance method.

[0008] Step 200: Calibrate the void volume of the sample chamber of the high-pressure gas adsorption instrument;

[0009] Step 300: Measure the excess adsorption of the wet shale sample under high pressure and variable temperature conditions in a closed system and plot the gas adsorption isotherm.

[0010] Step 400: Calculate the adsorption thermodynamic parameters of the moist shale sample.

[0011] Furthermore, the specific method for preparing moist shale samples using the moisture balance method is as follows:

[0012] At room temperature, dry powdered shale samples are placed in a pre-weighed aluminum pan and placed in a desiccator containing saturated K2SO4 solution, and left to stand.

[0013] Set a time interval, and at the same time interval, take out the aluminum pan containing the shale sample, weigh it once with a balance, and record the mass of the sample;

[0014] Weigh the shale sample multiple times until the difference between two consecutive weighings is less than the predetermined range of mass change. Record the mass of the shale sample at this point when it is in moisture balance, and denote it as the moist shale sample.

[0015] Calculate the moisture content of the moist shale sample:

[0016]

[0017] Where mc is the sample moisture content, %; m e The mass of the moisture balance sample is expressed in kg; m dry The mass of the dried sample is expressed in kg.

[0018] Furthermore, calibrating the void volume of the sample chamber of the high-pressure gas adsorption instrument specifically includes the following steps:

[0019] Test the airtightness of the high pressure gas adsorption instrument. After the airtightness of the high pressure gas adsorption instrument is qualified, evacuate the reference chamber and sample chamber of the high pressure gas adsorption instrument.

[0020] After vacuuming, the void volume of the sample chamber was calibrated using the helium expansion method.

[0021] Furthermore, the steps for calibrating the void volume of the sample chamber using the helium expansion method are as follows:

[0022] Helium gas at a set pressure is rapidly introduced into the reference chamber, the vent valve is closed, and the gas is considered to have reached thermal equilibrium when the pressure change in the reference chamber is less than the set value.

[0023] Open the valve between the reference chamber and the sample chamber to allow helium gas to expand from the reference chamber to the sample chamber. When the gases in the reference chamber and the sample chamber reach thermal equilibrium, record the gas pressure at this point.

[0024] Based on the law of conservation of mass, the mass of helium gas transferred from the reference chamber is converted into the void volume of the sample chamber.

[0025] Furthermore, measuring the excess adsorption capacity of the moist shale sample and plotting the gas adsorption isotherm under high pressure and variable temperature conditions includes the following steps:

[0026] After loading the moist shale sample into the sample chamber of the high pressure gas adsorption instrument, the air tightness of the high pressure gas adsorption instrument is tested. After the air tightness of the high pressure gas adsorption instrument is qualified, the reference chamber and sample chamber of the high pressure gas adsorption instrument are evacuated.

[0027] The excess adsorption of wet shale samples was measured under high pressure and variable temperature conditions.

[0028] Plot gas adsorption isotherms at different temperatures.

[0029] Furthermore, the specific method for measuring the excess adsorption of moist shale samples under high pressure and variable temperature conditions is as follows:

[0030] At an initial temperature T0, a low-pressure adsorbent gas is first introduced into the reference chamber, the vent valve is closed, and the gas pressure in the reference chamber is recorded after the gas in the reference chamber reaches thermal equilibrium.

[0031] Open the valve between the reference chamber and the sample chamber to allow gas to expand from the reference chamber to the sample chamber. At this time, the moist shale sample begins to adsorb gas. After the gas in the reference chamber and the sample chamber reaches thermal equilibrium and adsorption equilibrium, record the gas pressure at this time.

[0032] Raise the device temperature to temperature T. j Due to the enhanced thermal motion of gas molecules within the confined space and the temperature sensitivity of the shale-adsorbed gas, the gas pressure in the reference chamber and sample chamber changes continuously over time. Once the gas reaches equilibrium again, the gas pressure is recorded. This process of heating and gas equilibrium is repeated, and the temperature T is recorded each time the temperature is increased. j The pressure of the gas after it reaches equilibrium;

[0033] Once the temperature is raised to the maximum preset temperature and the gas reaches equilibrium, the temperature is lowered back to the initial temperature T0, and the gas is allowed to reach equilibrium again. The gas pressure is then recorded.

[0034] Close the valve between the reference chamber and the sample chamber, then fill the reference chamber with gas at a higher pressure for the second time, close the vent valve, and record the gas pressure in the reference chamber after the gas in the reference chamber reaches thermal equilibrium.

[0035] Open the valve between the reference chamber and the sample chamber to allow gas to expand from the reference chamber to the sample chamber. Once the gas in the reference chamber and the sample chamber reaches thermal and adsorption equilibrium, record the gas pressure at this point. Repeat the above heating and gas equilibrium process, recording the gas pressure after reaching equilibrium at different temperatures. Finally, cool down to the initial temperature T0.

[0036] Repeat the above operation by filling the reference chamber with gas i times, gradually increasing the pressure of the gas each time, until the gas pressure in the sample chamber reaches the preset pressure.

[0037] Calculate the excess adsorption amount of the moist shale sample at different temperatures after the i-th gas injection;

[0038] Gas adsorption isotherms of moist shale samples at different temperatures were plotted based on the excess adsorption data obtained from i gas injections.

[0039] Furthermore, the temperature T after the i-th gas injection is calculated. j Excess adsorbed mass and amount of substance in the wetted shale sample:

[0040]

[0041]

[0042] Where, m excess,i (T j ) and n excess,i (T j ) represent the temperatures at temperature T after the i-th gas injection. j The excess adsorbed mass of the sample, kg, and the amount of excess adsorbed substance, mmol / g;

[0043] V rc Let m be the volume of the reference chamber. 3 V void m is the void volume in the sample chamber. 3 N represents the total number of times gas is injected into the reference chamber;

[0044] ρ rc,i (T0) is the gas density in the reference chamber when the gas reaches equilibrium at the initial temperature T0 after the i-th injection, in kg / m³. 3 ;

[0045] ρ eq,i (T j ) represents the temperature T after the i-th gas injection. j The gas density in the reference chamber and sample chamber when the gas reaches equilibrium again, kg / m³ 3 ;

[0046] m drydenoted as mass of the dried sample, kg; M is the molar mass of the adsorbed gas, g / mol.

[0047] Furthermore, the calculation of the adsorption thermodynamic parameters of the moist shale sample specifically includes the following steps:

[0048] The adsorption model was fitted at temperature T. j Based on the measured excess adsorption data under different pore pressures, the Langmuir volume and Langmuir pressure were obtained by nonlinear regression.

[0049] The adsorption enthalpy and adsorption entropy of the sample were calculated using the temperature sensitivity of the Langevin pressure.

[0050] Furthermore, the expression for the adsorption model is:

[0051]

[0052] in, For at temperature T j The amount of excess adsorbed substance fitted below, mmol / g; n L The fitted Langevin volume, mmol / g; p L (T j ) for at temperature T j The fitted Langmuir pressure, MPa; p is the pore pressure of the shale sample, MPa; ρ g (p,T j ) for at temperature T j And the density of free gas under pressure p, kg / m³ 3 ;ρ ads The density of the adsorbed phase is kg / m³. 3 ;

[0053] In the adsorption model, a nonlinear regression method is used to fit the adsorption at temperature T. j The amount of excess adsorbed material under different pore pressures is used to solve for the optimal solutions for the Langmuir volume and Langmuir pressure.

[0054] Furthermore, the temperature sensitivity formula for the Langmuir pressure is:

[0055]

[0056] Where ΔH is the adsorption enthalpy, J / mol; ΔS is the adsorption entropy, J / (mol·K); p 0 Standard atmospheric pressure, 0.1 MPa; P L R is the Langevin volume, MPa; R is the ideal gas constant, 8.314 J / mol; T is the temperature, K.

[0057] Compared with the prior art, the present invention has the following advantages:

[0058] This invention measures the adsorption isotherms of moist shale samples at different temperatures through an experiment conducted in a closed system. The entire experiment is completed in a closed system, ensuring that the moisture content within the system remains constant at different temperatures. This enables accurate measurement of the amount of gas adsorbed by shale samples under high pressure and variable temperature conditions, unaffected by minute changes in other factors. Furthermore, based on the measurement of the adsorption isotherms, thermodynamic parameters during gas adsorption can be calculated, and a mathematical model can be constructed to predict the in-situ adsorption amount of shale under different pore pressures and temperatures. Attached Figure Description

[0059] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0060] Figure 1 This is a diagram of the high-pressure adsorption experimental apparatus described in an embodiment of the present invention;

[0061] Figure 2 This is a schematic flowchart of the experimental method in an embodiment of the present invention;

[0062] Figure 3 This is a temperature control process during a gas injection process according to an embodiment of the present invention;

[0063] Figure 4 The above are gas adsorption isotherms of a moist shale sample at different temperatures in an embodiment of the present invention. Detailed Implementation

[0064] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] This invention provides an efficient and precise experimental method for measuring the amount of gas adsorbed in moist shale at different temperatures, thereby revealing the effect of temperature on the amount of gas adsorbed in moist shale. Specifically, a traditional high-pressure gas adsorption experimental apparatus is used. Through optimization and improvement of the testing method, the amount of gas adsorbed in a shale sample can be accurately determined in a single experiment under high pressure and variable temperature conditions. The thermodynamic parameters of the gas adsorption process are also obtained, laying a solid experimental foundation for revealing the mechanism of temperature influence on the amount of gas adsorbed in shale.

[0066] Compared to traditional continuous testing methods, this invention significantly reduces testing time. The experimental method proposed in this invention is based on pressure measurement and is applicable to most adsorbents (coal, shale, mudstone, etc.) and common supercritical gases (such as CH4 and CO2). It can be widely used in calculating the geological reserves of natural gas in unconventional reservoirs (shale, mudstone, coal).

[0067] The specific experimental method involves measuring the amount of gas adsorbed by moist shale under high pressure and variable temperature conditions, such as... Figure 2 As shown, it includes the following steps:

[0068] Step 100: After crushing and drying the shale sample, record the mass of the dried shale sample and prepare a moist shale sample using the moisture balance method.

[0069] Step 200: Calibrate the void volume of the sample chamber of the high-pressure gas adsorption instrument;

[0070] Step 300: Measure the excess adsorption of the wet shale sample under high pressure and variable temperature conditions in a closed system and plot the gas adsorption isotherm.

[0071] Step 400: Calculate the adsorption thermodynamic parameters of the moist shale sample.

[0072] This invention measures the adsorption isotherms of moist shale samples at different temperatures by conducting an experiment in a closed system. The entire experiment is completed in a closed system, ensuring that the moisture content in the system remains constant at different temperatures. This enables the accurate determination of the amount of gas adsorbed on shale samples under high pressure and variable temperature conditions, unaffected by minute changes in other factors.

[0073] The following will be described in conjunction with specific embodiments.

[0074] In step 100, the shale sample is crushed to a particle size of 0.5-1.0 mm using a crusher, pre-dried in a vacuum oven for 24 h and the mass of the dried sample is recorded, and a moist sample is prepared using the moisture balance method.

[0075] The specific steps for preparing a moist sample using the moisture balance method are as follows:

[0076] The first step is to place the dried powder sample into a pre-weighed aluminum pan at room temperature, and then place it in a desiccator containing saturated K2SO4 solution and let it stand.

[0077] The second step is to remove the aluminum pan containing the sample every 24 hours, weigh it once with a balance (accuracy: 0.0001g), and record the mass of the sample.

[0078] The third step is to weigh the sample multiple times until the weight difference between two consecutive weighings is less than the predetermined range of mass change, i.e., one percent of the mass of the dried sample. This indicates that the sample has reached a moisture balance state, and the moist sample has been successfully prepared. Record the mass of the moisture-balanced sample at this point.

[0079] Fourth step, calculate the moisture content of the sample according to the following formula (1):

[0080]

[0081] Where mc is the sample moisture content, %; m e The mass of the moisture balance sample is expressed in kg; m dry The mass of the dried sample is expressed in kg.

[0082] In step 200, the specific method for calibrating the void volume of the high-pressure adsorption instrument sample chamber is as follows:

[0083] Check the high-pressure gas adsorption instrument for leaks;

[0084] If the adsorption unit is leak-free, evacuate the reference chamber and sample chamber of the adsorption unit.

[0085] After purging, the void volume of the sample chamber was calibrated using the helium expansion method.

[0086] The specific steps for checking whether a high-pressure gas adsorption instrument is leaking are as follows: In the high-pressure gas adsorption instrument, helium gas at a certain pressure is introduced into the reference chamber and the sample chamber, and the gas inlet valve is closed. When the gas pressure drop rate is <500Pa / h, it indicates that the adsorption instrument measurement system is well sealed.

[0087] like Figure 1 In the experimental setup shown, valves V5 and V4 were opened to introduce helium gas at a certain pressure (20 MPa), while V4 was closed at the same time. The pressure drop rate was observed to be <500 Pa / h, indicating that the adsorption instrument measurement system has good sealing performance.

[0088] The specific steps for calibrating the void volume of the sample chamber using the helium expansion method are as follows:

[0089] Helium gas at a certain pressure is rapidly introduced into the reference chamber, the vent valve is closed, and the gas is considered to have reached thermal equilibrium when the pressure change in the reference chamber is very small.

[0090] Open the valve between the reference chamber and the sample chamber to allow helium gas to expand from the reference chamber to the sample chamber. When the gases in the reference chamber and the sample chamber reach thermal equilibrium, record the gas pressure at this point.

[0091] Based on the law of conservation of mass, the mass of helium gas transferred from the reference chamber is converted into the void volume in the sample chamber.

[0092] like Figure 1 In the experimental setup shown, valve V4 is opened to quickly introduce helium gas at 10 MPa, and then V4 is closed. When the pressure change in the reference chamber is very small, the gas is considered to have reached thermal equilibrium.

[0093] The second step is to open valve V5 to allow helium to expand into the sample chamber. Once the gases in the reference chamber and the sample chamber reach thermal equilibrium, record the gas pressure at this point.

[0094] The third step, based on the law of conservation of mass, is to convert the mass of the helium gas transferred from the reference chamber into the void volume V in the sample chamber. void .

[0095] The specific method for measuring the excess adsorption capacity of moist shale samples and plotting gas adsorption isotherms under high pressure and variable temperature conditions in a closed system is as follows:

[0096] After loading the moist shale sample into the sample chamber of the adsorption instrument, check whether the high-pressure gas adsorption instrument is leaking. If it is not leaking, evacuate the reference chamber and sample chamber of the entire adsorption instrument.

[0097] The excess adsorption capacity of shale samples was measured under high pressure and variable temperature conditions.

[0098] Plot gas adsorption isotherms at different temperatures.

[0099] The specific method for measuring excess adsorption is as follows:

[0100] like Figure 1 In the experimental setup shown, the temperature was raised to 45°C and kept constant. Valve V4 was opened, and methane at 1.5 MPa was quickly introduced for the first time. Then, V4 was closed. After the gas in the reference chamber reached thermal equilibrium, the gas pressure in the reference chamber was recorded.

[0101] The second step is to open valve V5 to allow methane to expand from the reference chamber to the sample chamber. At this time, the moist shale begins to adsorb methane. After the gas in the reference chamber and the sample chamber reaches thermal equilibrium and adsorption equilibrium, the gas pressure at this time is recorded.

[0102] The third step is to raise the temperature of the device to 65°C. Due to the enhanced thermal motion of gas molecules in the confined space and the temperature sensitivity of the shale-adsorbed gas, the gas pressure in the reference chamber and the sample chamber changes continuously over time. Once the gas reaches equilibrium again, the gas pressure at this time is recorded.

[0103] The fourth step is to raise the temperature of the device to 75°C and wait for the gases in the reference chamber and sample chamber to reach equilibrium. Record the gas pressure at this point.

[0104] Fifth, lower the device temperature back to 45°C. After the gas reaches equilibrium, record the gas pressure, close valve V5, open valve V4, and inject methane at 2 MPa for the second time. Repeat steps one through four, recording the pressure of the gas after reaching equilibrium at different temperatures. Finally, lower the temperature back to the initial 45°C. Repeat the above operation, injecting methane gas into the reference chamber 16 times, gradually increasing the pressure of the methane each time, until the gas pressure in the sample chamber reaches 23 MPa.

[0105] The relevant experimental procedures and temperature control processes are as follows: Figure 2 and Figure 3 As shown.

[0106] Step 6: Calculate the excess adsorption mass and amount of substance of the moist shale sample at different temperatures (45, 65, 75℃) after the i-th (i = 1, ... 16) gas injection according to formulas (2) and (3). Based on the above excess adsorption data, plot the gas adsorption isotherms of the moist shale at different temperatures:

[0107]

[0108]

[0109] in, and These represent the temperatures at temperature T after the i-th gas injection. j The excess adsorbed mass (kg) and excess adsorbed amount (mmol / g) of the sample; m dry The mass of the dried sample is expressed in kg; N represents the total number of gas injections into the reference chamber.

[0110] M CH4 V is the molar mass of methane, in g / mol. rc Let m be the volume of the reference chamber. 3 V void m is the void volume in the sample chamber. 3 ;

[0111] The methane density in the reference chamber after the i-th injection, at an initial temperature of 45°C, is kg / m³. 3 ; For the i-th gas injection at temperature T j The methane density in the reference chamber and sample chamber when the lower gas reaches equilibrium again, kg / m³ 3 .

[0112] Step 7: Calculate the excess adsorption of the moist shale at different temperatures (from the initial lower temperature to the highest preset temperature) after the i-th gas injection.

[0113] Finally, based on the above excess adsorption data, gas adsorption isotherms of moist shale at different temperatures were plotted, such as... Figure 4 As shown.

[0114] The specific method for calculating the adsorption thermodynamic parameters of moist shale samples is as follows:

[0115] An adsorption model similar to Langmuir's was fitted at temperature T. j Based on the measured excess adsorption data of samples under different pore pressures, the Langmuir volume and Langmuir pressure were obtained by nonlinear regression.

[0116] The adsorption enthalpy and adsorption entropy of the sample were calculated using the temperature sensitivity of the Langevin pressure.

[0117] The specific steps for obtaining the Langevin volume and Langevin pressure using the nonlinear regression method are as follows:

[0118] The first step was to use Excel's data analysis tool, Solver, to solve for the parameters. First, the measured excess adsorption data (at temperature T) was input. j (and the amount of excess adsorbed material under different pore pressures);

[0119] The second step involves constructing an adsorption model similar to Langmuir's, as shown in equation (4), and fitting it using nonlinear regression at temperature T. j The amount of excess adsorbed material under different pore pressures is used to solve for the optimal solutions of the corresponding parameters (Randall volume and Randle pressure):

[0120]

[0121] in, For at temperature T j The amount of excess adsorbed substance fitted below, mmol / g; n L The fitted Langevin volume, mmol / g; p L (T j ) for at temperature T j The fitted Langmuir pressure, MPa; p is the pore pressure of the shale sample, MPa; ρ g (p,T j (This is at temperature T) j And the density of free gas under pressure p, kg / m³ 3 ;ρ ads The density of the adsorbed phase is kg / m³. 3 .

[0122] It is important to note that during the fitting process, in order to minimize the degrees of freedom, the parameter ρ is... ads Keeping it constant, assume it to be 423 kg / m 3 (10 5(The density of liquid methane at Pa and 111.65 K) allows the Langmuir volume and Langmuir pressure to vary with the excess adsorption. Based on nonlinear regression, the values ​​of both Langmuir volume and Langmuir pressure are simultaneously changed to make the difference between the fitted excess adsorption and the measured adsorption infinitely close, thus obtaining the optimal values ​​of Langmuir volume and Langmuir pressure.

[0123] The specific formula for the temperature sensitivity of the Langmuir pressure is shown in formula (5):

[0124]

[0125] Where ΔH is the adsorption enthalpy, J / mol; ΔS is the adsorption entropy, J / (mol·K); p 0 Standard atmospheric pressure, 0.1 MPa; P L R is the Langevin volume, MPa; R is the ideal gas constant, 8.314 J / mol; T is the temperature, K.

[0126] In ln p L In the correlation graph of -1 / T, ΔH is obtained by the slope of the linear regression line, and ΔS is obtained by the intercept of the linear regression line with the y-axis.

[0127] Based on the above, this experimental method can not only obtain gas adsorption isotherms in moist shale at different temperatures, but also calculate the thermodynamic parameters during the gas adsorption process. Based on these gas adsorption isotherms and thermodynamic parameters, a mathematical model can be constructed to predict the in-situ adsorbed gas volume in shale under different underground pore pressures and temperatures. Therefore, this experimental method provides an accurate, reliable, and effective technical means for calculating the geological reserves of natural gas in unconventional reservoirs (shale, mudstone, and coal), and has broad application prospects.

[0128] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. An experimental method for measuring the amount of adsorbed gas in moist shale under high pressure and variable temperature conditions, characterized in that, Includes the following steps: Step 100: After crushing and drying the shale sample, record the mass of the dried shale sample and prepare a moist shale sample using the moisture balance method. Step 200: Calibrate the void volume of the sample chamber of the high-pressure gas adsorption instrument; Step 300: Measure the excess adsorption of the wet shale sample under high pressure and variable temperature conditions in a closed system and plot the gas adsorption isotherm. Measuring the excess adsorption capacity of a moist shale sample and plotting gas adsorption isotherms under high pressure and variable temperature conditions includes the following steps: After loading the moist shale sample into the sample chamber of the high pressure gas adsorption instrument, the air tightness of the high pressure gas adsorption instrument is tested. After the air tightness of the high pressure gas adsorption instrument is qualified, the reference chamber and sample chamber of the high pressure gas adsorption instrument are evacuated. The excess adsorption of wet shale samples was measured under high pressure and variable temperature conditions. Plot gas adsorption isotherms at different temperatures; The specific method for measuring the excess adsorption of moist shale samples under high pressure and variable temperature conditions is as follows: At the initial temperature First, a low-pressure adsorption gas is introduced into the reference chamber, the vent valve is closed, and the gas pressure in the reference chamber is recorded after the gas in the reference chamber reaches thermal equilibrium. S1: Open the valve between the reference chamber and the sample chamber to allow the gas to expand from the reference chamber to the sample chamber. At this time, the moist shale sample begins to adsorb the gas. After the gas in the reference chamber and the sample chamber reaches thermal equilibrium and adsorption equilibrium, record the gas pressure at this time. Raise the device temperature to temperature Due to the enhanced thermal motion of gas molecules in the confined space and the temperature sensitivity of the gas adsorbed by shale, the gas pressure in the reference chamber and the sample chamber changes continuously over time. Once the gas reaches equilibrium again, the gas pressure at this time is recorded. Repeat the heating and gas equilibrium process in S1, recording the temperature each time. The pressure of the gas after it reaches equilibrium; Once the temperature reaches the maximum preset temperature and the gas reaches equilibrium, the temperature will be lowered back to the initial temperature. Wait for the gas to reach equilibrium and record the gas pressure. S2: Close the valve between the reference chamber and the sample chamber, and then fill the reference chamber with gas at a higher pressure for the second time. Close the vent valve and wait for the gas in the reference chamber to reach thermal equilibrium. Record the gas pressure in the reference chamber. Open the valve between the reference chamber and the sample chamber to allow the gas to expand from the reference chamber to the sample chamber. Once the gas in the reference chamber and the sample chamber reaches thermal equilibrium and adsorption equilibrium, record the gas pressure at this point. Repeat the heating and gas equilibrium process in S2, record the pressure of the gas after reaching equilibrium at different temperatures, and finally cool down to the initial temperature. ; Repeat the above operation by filling the reference chamber with gas i times, gradually increasing the pressure of the gas each time, until the gas pressure in the sample chamber reaches the preset pressure. Calculate the excess adsorption amount of the moist shale sample at different temperatures after the i-th gas injection; Based on the excess adsorption data obtained from the i-th gas injection, gas adsorption isotherms of moist shale samples at different temperatures were plotted. Step 400: Calculate the adsorption thermodynamic parameters of the moist shale sample.

2. The experimental method for measuring the amount of adsorbed gas in moist shale under high pressure and variable temperature conditions according to claim 1, characterized in that, The specific method for preparing moist shale samples using the moisture balance method is as follows: At room temperature, dry, powdered shale samples are placed in a pre-weighed aluminum dish and then placed in a container filled with saturated... Place the solution in a desiccator and let it stand. Set a time interval, and at the same time interval, take out the aluminum pan containing the shale sample, weigh it once with a balance, and record the mass of the sample; Weigh the shale sample multiple times until the difference between two consecutive weighings is less than the predetermined range of mass change. Record the mass of the shale sample at this point when it is in moisture equilibrium, and denote it as a moist shale sample. Calculate the moisture content of the moist shale sample: ； in, The moisture content of the sample is %; The mass of the moisture-balanced sample is expressed in kg. The mass of the dried sample is expressed in kg.

3. The experimental method for measuring the amount of adsorbed gas in moist shale under high pressure and variable temperature conditions according to claim 1, characterized in that, The specific steps for calibrating the void volume of the sample chamber in a high-pressure gas adsorption instrument include: Test the airtightness of the high pressure gas adsorption instrument. After the airtightness of the high pressure gas adsorption instrument is qualified, evacuate the reference chamber and sample chamber of the high pressure gas adsorption instrument. After vacuuming, the void volume of the sample chamber was calibrated using the helium expansion method.

4. The experimental method for measuring the amount of adsorbed gas in moist shale under high pressure and variable temperature conditions according to claim 3, characterized in that, The steps for calibrating the void volume of the sample chamber using the helium expansion method are as follows: Helium gas at a set pressure is rapidly introduced into the reference chamber, the vent valve is closed, and the gas is considered to have reached thermal equilibrium when the pressure change in the reference chamber is less than the set value. Open the valve between the reference chamber and the sample chamber to allow helium gas to expand from the reference chamber to the sample chamber. When the gases in the reference chamber and the sample chamber reach thermal equilibrium, record the gas pressure at this point. Based on the law of conservation of mass, the mass of helium gas transferred from the reference chamber is converted into the void volume of the sample chamber.

5. The experimental method for measuring the amount of adsorbed gas in moist shale under high pressure and variable temperature conditions according to claim 1, characterized in that, Calculate the temperature after the i-th gas injection. Excess adsorbed mass and amount of substance in the wetted shale sample: ； ； in, and The temperatures after the i-th gas injection are respectively... The excess adsorbed mass of the sample, kg, and the amount of excess adsorbed substance, mmol / g; For the volume of the reference chamber, ; The void volume in the sample chamber. N represents the total number of times gas is injected into the reference chamber; For the i-th gas injection at the initial temperature The gas density in the reference chamber when the lower gas reaches equilibrium. ; For the i-th gas injection at temperature The gas densities in the reference chamber and sample chamber when the lower gas reaches equilibrium again. ; The mass of the dried sample is expressed in kg. ρ represents the molar mass of the adsorbed gas, in g / mol.

6. The experimental method for measuring the amount of adsorbed gas in moist shale under high pressure and variable temperature conditions according to claim 5, characterized in that, The calculation of the adsorption thermodynamic parameters of moist shale samples includes the following steps: The adsorption model was fitted at temperature. Based on the measured excess adsorption data under different pore pressures, the Langmuir volume and Langmuir pressure were obtained by nonlinear regression. The adsorption enthalpy and adsorption entropy of the sample were calculated using the temperature sensitivity of the Langevin pressure.

7. The experimental method for measuring the amount of adsorbed gas in moist shale under high pressure and variable temperature conditions according to claim 6, characterized in that, The expression for the adsorption model is: ； in, For temperature The amount of excess adsorbed substance under fitting, mmol / g; The fitted Langevin volume, in mmol / g; For temperature The fitted Langmuir pressure, MPa; (p,T j ) for at temperature T j And the density of free gas under pressure p, ; The density of the adsorbed phase is... ; In the adsorption model, a nonlinear regression method is used to fit the adsorption at temperature T. j The amount of excess adsorbed material under different pore pressures is used to solve for the optimal solutions for the Langmuir volume and Langmuir pressure.

8. The experimental method for measuring the amount of adsorbed gas in moist shale under high pressure and variable temperature conditions according to claim 6, characterized in that, The temperature sensitivity formula for the Langevin pressure is: ； Where ∆H is the adsorption enthalpy, J / mol; and ∆S is the adsorption entropy, J / (mol·K). Standard atmospheric pressure, 0.1 MPa; P L R is the Langevin volume, MPa; R is the ideal gas constant, 8.314 J / mol; T is the temperature, K.

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