Shale gas content physical simulation device and method

Abstract

The invention relates to the technical field of experimental instruments, in particular to a shale gas content physical simulation device and method. The shale gas content physical simulation device comprises a reference tank, a sample tank, a constant temperature box, a gas increasing mechanism, a vacuum mechanism, a back pressure mechanism, a gas volume measuring mechanism and a computer. A high-precision pressure sensor is adopted, the pressure change in the system can be accurately measured, the gas inlet pressure is controlled through the arrangement of a gas increasing mechanism, the pressure drop change in the coring process can be accurately simulated through the arrangement of a pressure return mechanism, the whole simulation is closer to the real situation, and the shale sample is small in gas content, so that the coring accuracy is improved. The desorption is a long process, the gas volume measuring mechanism can be used for collecting the volume change condition of tiny gas, the experimental data is more reliable, and in conclusion, when the method is used for measuring the gas content of the shale, the experimental data is more accurate.

Description

Technical Field

[0001] The invention relates to the technical field of experimental instruments, and in particular to a shale gas content physical simulation device and method. Background Art

[0002] Gas content is an important parameter in shale gas evaluation. It is an important indicator for evaluating whether a shale gas reservoir has reached the shale gas production layer. It is also an important parameter and basis for resource evaluation, favorable area selection, and exploration and development deployment. At present, the most commonly used method for calculating shale gas content is the direct method, that is, measuring the gas content of actual rock samples on site. The gas content results are composed of desorbed gas, lost gas, and residual gas. Among them, since the lost gas volume cannot be obtained directly, it needs to be calculated based on relevant models. Therefore, the lost gas volume is the key to determining the shale gas content.

[0003] In the prior art, when shale is mined underground, there will be a gas loss process, which will affect the measurement of the gas content of shale. The current solution to this problem is to calculate according to the United States Bureau of Mines (USBM) method specified in the national standard GB / T19559-2008 Coalbed Methane Content Determination Method. However, this method is proposed for coalbed methane, and the burial depth of shale is much greater than that of coal seams. The two also have large differences in occurrence mechanism and fluid migration. In addition, the USBM method not only assumes that the gas concentration on the outer surface of the core is zero during the coring process, and the pressure is stable at atmospheric pressure, but also that the gas loss time it uses is less than the actual gas loss time; it also assumes that the diffusion rate is constant throughout the desorption experiment, which is inconsistent with the actual situation. Using this method will seriously misjudge the amount of lost gas, resulting in a large difference between the calculated shale gas content and the actual situation.

[0004] In summary, in the prior art, when measuring the gas content of shale, the lost gas volume is seriously misjudged, resulting in a large difference between the calculated shale gas content and the actual situation, leading to inaccurate experimental results. Summary of the invention

[0005] The purpose of the present invention is to provide a shale gas content physical simulation device and method to solve the problem that in the prior art, when measuring the gas content of shale, the lost gas volume is seriously misestimated, resulting in a large difference between the calculated shale gas content and the actual situation, resulting in inaccurate experimental results.

[0006] To achieve the above-mentioned purpose, the present invention provides a physical simulation device for shale gas content, which includes a reference tank, a sample tank, a constant temperature box, a gas adding mechanism, a vacuum mechanism, a back pressure mechanism, a gas volume measuring mechanism and a computer. The reference tank and the sample tank are both arranged inside the constant temperature box, the output end of the gas adding mechanism is connected to the reference tank, the bottom of the reference tank is connected to the sample tank through a pipeline, a shale sample is placed inside the sample tank, the vacuum mechanism is connected to the reference tank through a pipeline, the gas volume measuring mechanism is connected to the sample tank through a pipeline, the back pressure mechanism is arranged between the connecting pipeline between the sample tank and the gas volume measuring mechanism, the input end of the reference tank is provided with a main valve and a first pressure sensor, the input end of the sample tank is provided with a second pressure sensor, the connecting pipeline between the bottom of the reference tank and the input end of the sample tank is provided with a first valve, and the gas adding mechanism, the first pressure sensor, the second pressure sensor and the gas volume measuring mechanism are all communicatively connected to the computer.

[0007] Among them, the gas increasing mechanism includes a gas cylinder, a booster pump and a pressure gauge, the input end of the booster pump is connected to the gas cylinder pipeline, the output end of the booster pump is connected to the input end pipeline of the reference tank, and the pressure gauge is arranged between the connecting pipeline of the booster pump and the reference tank.

[0008] Wherein, the vacuum mechanism includes a vacuum pump and a vacuum valve, the input end of the vacuum pump is connected to the reference tank pipeline, and the vacuum valve is arranged between the connecting pipeline of the vacuum pump and the reference tank.

[0009] Wherein, the gas volume measuring mechanism includes a gas cylinder, a volume flow meter, a rubber hose, a measuring cylinder, a sling and a lifter, the input end of the gas cylinder is connected to the sample tank pipeline, the measuring cylinder is located on one side of the gas cylinder, the measuring cylinder is parallel to the gas cylinder, the bottom of the gas cylinder is connected to the bottom of the measuring cylinder through the rubber hose, the volume flow meter is arranged on the rubber hose, distilled water is arranged inside the measuring cylinder, and the top of the measuring cylinder is connected to the lifter through the sling.

[0010] Among them, the back pressure mechanism includes a manual pump and a third pressure sensor, a back pressure valve and an exhaust valve are arranged in sequence between the connecting pipeline between the sample tank and the air cylinder, the manual pump is connected to the back pressure valve pipeline, and the third pressure sensor is arranged between the manual pump and the connecting pipeline of the back pressure valve.

[0011] Wherein, the boost pump, the first pressure sensor, the second pressure sensor and the volume flow meter are all connected to the computer for communication via data lines.

[0012] The present invention also provides a shale gas content physical simulation method, which is applied to the shale gas content physical simulation device as described above, and comprises the following steps:

[0013] preparing shale samples, drying and weighing the shale samples;

[0014] placing the weighed dry sample in the sample jar;

[0015] Set the thermostat temperature according to the reservoir temperature or experimental requirements. After the thermostat temperature stabilizes, check the air tightness of the entire simulation device.

[0016] The shale sample in the sample tank is measured using a simulation device.

[0017] Among them, in the step of "using a simulation device to measure the shale sample in the sample tank", the measurement contents include free space volume measurement, isothermal adsorption measurement, pressure reduction desorption measurement, desorption measurement in exposure to air, natural desorption measurement and residual gas measurement.

[0018] The specific formula for determining the free space volume is as follows:

[0019]

[0020] Where: V f is the volume of free space, in cubic centimeters; p1 is the initial pressure of the reference tank, in MPa; p2 is the initial pressure of the sample tank, in MPa; p3 is the pressure of the reference tank after equilibrium, in MPa; p4 is the pressure of the sample tank after equilibrium, in MPa; T1 is the initial temperature of the reference tank, in Kelvin; T2 is the initial temperature of the sample tank, in Kelvin; T3 is the temperature of the reference tank after equilibrium, in Kelvin; T4 is the temperature of the sample tank after equilibrium, in Kelvin; Z1 is the compressibility factor of the initial gas in the reference tank, dimensionless; Z2 is the compressibility factor of the initial gas in the sample tank, dimensionless; Z3 is the compressibility factor of the gas after equilibrium in the reference tank, dimensionless; Z4 is the compressibility factor of the gas after equilibrium in the sample tank, dimensionless; V1 is the total volume of the reference tank and part of the pipeline, in cubic centimeters;

[0021] V s =V2-V f

[0022] Where: V2 is the total volume of the sample tank and part of the pipeline, in cubic centimeters; V s is the skeleton volume of the shale sample in cubic centimeters.

[0023] The specific formula of the isothermal adsorption determination includes the calculation of the amount of adsorbed gas, the relative adsorption volume of the particles of the rock sample, the pore volume of the sample, the volume of free gas in the pores of the sample at the target pressure, and the volume of the remaining free gas in the free space at the target pressure, wherein the calculation of the amount of adsorbed gas includes the following formula:

[0024]

[0025] Where: n1 is the number of moles of adsorbed phase at the current pressure point, in moles; V f V is the free space volume of the test sample in cubic centimeters; r is the reference tank volume in cubic centimeters; P r7 is the pressure of the reference tank before equilibrium, in MPa; P5 is the pressure of the reference tank after equilibrium, in MPa; P6 is the pressure of the sample tank before equilibrium, in MPa; P8 is the pressure of the sample tank after equilibrium, in MPa; T5 is the temperature of the reference tank before equilibrium, in Kelvin; T7 is the temperature of the reference tank after equilibrium, in Kelvin; T6 is the temperature of the sample tank before equilibrium, in Kelvin; T7 is the temperature of the sample tank after equilibrium, in Kelvin; Z5 is the compression factor of the reference tank before equilibrium, dimensionless; Z6 is the compression factor of the reference tank after equilibrium, dimensionless; Z7 is the compression factor of the reference tank before equilibrium, dimensionless; Z8 is the compression factor of the sample tank after equilibrium, dimensionless;

[0026] The relative adsorption volume of particles in rock samples is calculated as follows:

[0027] V ad =n1*22.4*1000

[0028] Where: V ad is the relative adsorption volume in cubic centimeters;

[0029] After adsorption equilibrium, the adsorbed gas in the sample tank and pipeline at the target pressure includes: the sample adsorbed gas volume, the free gas volume in the sample pores and the remaining free gas in the free space;

[0030] The sample pore volume is calculated using the formula:

[0031]

[0032] Where: V φ V is the pore volume of the sample in cubic centimeters; b is the apparent volume of the sample, in cubic centimeters; φ is the porosity of the sample, dimensionless;

[0033] The sample apparent volume is calculated using the formula:

[0034]

[0035] Where: M g is the sample mass in grams; ρ c is the apparent density of the sample in grams per cubic centimeter;

[0036] The volume of free gas in the pores of the sample at the target pressure is calculated using the formula:

[0037]

[0038] Where: V g is the volume of free gas in the pores of the sample, in cubic centimeters; p is the gas pressure, in megapascals; V is the gas volume, in cubic centimeters; Z is the compressibility factor of the gas, dimensionless; R is the molar gas constant, in joules per mole; Z is the gas temperature, in degrees Kelvin;

[0039] The remaining free gas volume in the free space at the target pressure is calculated using the formula:

[0040]

[0041] Where: V gf is the remaining free gas volume in free space, in cubic centimeters; p is the gas pressure, in MPa; V is the gas volume, in cubic centimeters; Z is the gas compressibility factor, dimensionless; R is the molar gas constant, in joules per mole; T is the gas temperature, in Kelvin.

[0042] A shale gas content physical simulation device and method of the present invention comprises a reference tank, a sample tank, a thermostat, a gas increasing mechanism, a vacuum mechanism, a back pressure mechanism, a gas volume measuring mechanism and a computer. The thermostat can be used to accurately control the temperature change during the entire simulation experiment. The high-precision pressure sensor can be used to accurately measure the pressure change in the system. The control of the intake pressure is completed by setting the gas increasing mechanism. The back pressure mechanism can accurately simulate the pressure drop change during the coring process, making the entire simulation closer to the actual situation. Since the shale sample has a small gas content and desorption is a long process, the gas volume measuring mechanism can be used to collect tiny gas volume changes, and the experimental data is more reliable. In summary, by using the above method, when the gas content of shale is measured, the experimental data is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0044] Figure 1 It is a structural schematic diagram of a shale gas content physical simulation device provided by the present invention.

[0045] Figure 2 It is a flow chart of the steps of the physical simulation method of shale gas content provided by the present invention.

[0046] 1-gas cylinder, 2-boosting pump, 3-pressure gauge, 4-vacuum valve, 5-vacuum pump, 6-main valve, 7-first pressure sensor, 8-reference tank, 9-first valve, 10-second pressure sensor, 11-sample tank, 12-shale sample, 13-third pressure sensor, 14-back pressure valve, 15-exhaust valve, 16-manual pump, 17-constant temperature box, 18-gas storage cylinder, 19-volume flow meter, 20-rubber hose, 21-distilled water, 22-measuring cylinder, 23-hanging rope, 24-lifter, 25-data cable, 26-computer. DETAILED DESCRIPTION

[0047] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0048] See also Figure 1 The present invention provides a physical simulation device for shale gas content, the physical simulation device for shale gas content comprises a reference tank 8, a sample tank 11, a thermostat 17, a gas adding mechanism, a vacuum mechanism, a back pressure mechanism, a gas volume measuring mechanism and a computer 26, the reference tank 8 and the sample tank 11 are both arranged inside the thermostat 17, the output end of the gas adding mechanism is connected to the reference tank 8, the bottom of the reference tank 8 is connected to the sample tank 11 through a pipeline, a shale sample 12 is placed inside the sample tank 11, the vacuum mechanism is connected to the reference tank 8 through a pipeline, the gas volume measuring mechanism is connected to the reference tank 8 through a pipeline, and the back pressure mechanism is connected to the reference tank 8 through a pipeline. The gas volume measuring mechanism is connected to the sample tank 11 through a pipeline, the back pressure mechanism is arranged between the connecting pipeline of the sample tank 11 and the gas volume measuring mechanism, the input end of the reference tank 8 is provided with a main valve 6 and a first pressure sensor 7, the input end of the sample tank 11 is provided with a second pressure sensor 10, and the connecting pipeline between the bottom of the reference tank 8 and the input end of the sample tank 11 is provided with a first valve 9, the gas adding mechanism, the first pressure sensor 7, the second pressure sensor 10 and the gas volume measuring mechanism are all communicatively connected to the computer 26.

[0049] In this embodiment, the constant temperature box 17 is used to accurately control the temperature change during the entire simulation experiment. The high-precision pressure sensor is used to accurately measure the pressure change in the system. The control of the intake pressure is completed by the setting of the gas increasing mechanism. The setting of the back pressure mechanism can accurately simulate the pressure drop change during the coring process, making the entire simulation closer to the actual situation. Since the shale sample 12 has a small gas content and desorption is a long process, the gas volume measurement mechanism can be used to collect tiny gas volume changes, and the experimental data is more reliable. In summary, when the gas content of shale is measured by the above method, the experimental data is more accurate.

[0050] Furthermore, the gas increasing mechanism includes a gas cylinder 1, a booster pump 2 and a pressure gauge 3, the input end of the booster pump 2 is connected to the pipeline of the gas cylinder 1, the output end of the booster pump 2 is connected to the input end pipeline of the reference tank 8, and the pressure gauge 3 is arranged between the connecting pipeline of the booster pump 2 and the reference tank 8.

[0051] In this embodiment, the gas in the gas cylinder 1 can be delivered to the reference tank 8 by the booster pump 2 , and the booster pump 2 can control the intake pressure through the computer 26 .

[0052] Furthermore, the vacuum mechanism includes a vacuum pump 5 and a vacuum valve 4 , the input end of the vacuum pump 5 is connected to the pipeline of the reference tank 8 , and the vacuum valve 4 is provided between the connecting pipeline of the vacuum pump 5 and the reference tank 8 .

[0053] In this embodiment, the residual gas in the reference tank 8, the sample tank 11 and the entire pipeline can be extracted by setting the vacuum pump 5 and the vacuum valve 4.

[0054] Furthermore, the gas volume measuring mechanism includes a gas cylinder 18, a volume flow meter 19, a rubber hose 20, a measuring cylinder 22, a sling 23 and a lifter 24. The input end of the gas cylinder 18 is connected to the pipeline of the sample tank 11, the measuring cylinder 22 is located on one side of the gas cylinder 18, the measuring cylinder 22 is parallel to the gas cylinder 18, the bottom of the gas cylinder 18 is connected to the bottom of the measuring cylinder 22 through the rubber hose 20, the volume flow meter 19 is arranged on the rubber hose 20, the interior of the measuring cylinder 22 is arranged with distilled water, and the top of the measuring cylinder 22 is connected to the lifter 24 through the sling 23.

[0055] In this embodiment, the volume of gas discharged from the sample tank 11 is measured by the arrangement of the gas storage cylinder 18 , the volume flow meter 19 and the measuring cylinder 22 .

[0056] Furthermore, the back pressure mechanism includes a manual pump 16 and a third pressure sensor 13, a back pressure valve 14 and an exhaust valve 15 are arranged in sequence between the connecting pipeline of the sample tank 11 and the air storage cylinder 18, the manual pump 16 is connected to the back pressure valve 14 through a pipeline, and the third pressure sensor 13 is arranged between the connecting pipeline of the manual pump 16 and the back pressure valve 14.

[0057] In this embodiment, the pressure change of the sample tank 11 is controlled by the provision of the back pressure valve 14 and the manual pump 16 .

[0058] Furthermore, the boost pump 2 , the first pressure sensor 7 , the second pressure sensor 10 and the volume flow meter 19 are all connected to the computer 26 for communication via a data line 25 .

[0059] In this embodiment, the boost pump 2 , the first pressure sensor 7 , the second pressure sensor 10 , the volume flow meter 19 and the computer 26 are connected in communication by setting the data line 25 .

[0060] Furthermore, the shale gas content physical simulation device also includes a vacuum drying box, an electronic balance and a residual gas measuring instrument.

[0061] In this embodiment, the temperature control accuracy of the vacuum drying oven is ±0.5°C, the vacuum degree is not less than 10Pa, and the accuracy of the electronic balance is not less than 0.0001g.

[0062] See also Figure 2 The present invention also provides a shale gas content physical simulation method, which is applied to the shale gas content physical simulation device as described above, and comprises the following steps:

[0063] S1: preparing a shale sample 12, and drying and weighing the shale sample 12;

[0064] S2: placing the weighed dry sample in the sample tank 11;

[0065] S3: setting the temperature of the thermostat 17 according to the reservoir temperature or the experimental requirements, and after the temperature of the thermostat 17 is stabilized, performing an air tightness check on the entire simulation device;

[0066] S4: Using a simulation device to measure the shale sample 12 in the sample tank 11.

[0067] Among them, in step S1, the prepared shale sample 12 is a rock sample with a particle size of about 0.25mm~0.18mm (60 mesh-80 mesh) or a cylindrical rock sample with a diameter of 25mm×length not less than 30mm; the specific steps of drying and weighing the shale sample 12 are: putting the container containing the shale sample 12 into a drying oven, setting the vacuum drying oven to 105°C, and after the drying time is not less than 8h, the shale sample 12 is placed in a glass container filled with a desiccant for cooling, and then placed on an electronic balance to weigh the mass of the shale sample 12.

[0068] Further, in step S2, the mass of the loaded sample is recorded as M g .

[0069] Furthermore, in step S3, the specific steps of checking the air tightness of the entire simulation device are: setting the temperature of the thermostat 17 according to the reservoir temperature or experimental requirements; after the temperature of the thermostat 17 is stabilized, opening the main valve 6 and the first valve 9, and filling the reference tank 8 and the sample tank 11 with helium through the booster pump 2 to the highest test pressure of the experiment; the first pressure sensor 7 and the second pressure sensor 10 collect the pressure data of the reference tank 8 and the sample tank 11, and if the pressure remains unchanged within 1 hour, the system is deemed to be airtight.

[0070] Among them, in the step of "using a simulation device to measure the shale sample 12 in the sample tank 11", the measurement contents include free space volume measurement, isothermal adsorption measurement, decompression desorption measurement, desorption measurement in exposure to air, natural desorption measurement and residual gas measurement.

[0071] Furthermore, the specific internal process of the free space volume measurement includes the following steps: opening the vacuum valve 4, the main valve 6 and the first valve 9, closing the exhaust valve 15, turning on the switch of the vacuum pump 5, evacuating the reference tank 8, the sample tank 11 and the pipeline for no less than 30 minutes, collecting experimental data through the first pressure sensor 7 and the second pressure sensor 10, and recording data including the initial pressure (p1) of the reference tank 8, the initial temperature (T1) of the reference tank 8, the initial pressure (p2) of the sample tank 11, and the initial temperature (T2) of the sample tank 11. Then close the vacuum valve 4, the main valve 6, the first valve 9 and the vacuum pump 5, turn on the switch of the gas cylinder 1, the booster pump 2, and the main valve 6, fill with helium until the pressure value of the reference tank 8 reaches the target pressure, close the main valve 6, open the first valve 9, and collect experimental data through the first pressure sensor 7 and the second pressure sensor 10 after the pressure is balanced. The recorded data includes the balanced pressure (p3) of the reference tank 8, the balanced temperature (T3) of the reference tank 8, and the balanced pressure (p4) and the balanced temperature (T4) of the sample tank 11. Open the exhaust valve 15 to exhaust the gas, and repeat the above operation 3 to 5 times. Repeat the measurement of the free space volume 3-5 times, and calculate the free space volume (V f ), where the distance between any two values ​​is not less than 0.1cm 3 .

[0072] Calculation of free space volume and shale sample 12 volume:

[0073]

[0074] Where: V f is the volume of free space in cubic centimeters (cm 3 ); p1 is the initial pressure of the reference tank 8, in megapascals (MPa); p2 is the initial pressure of the sample tank 11, in megapascals (MPa); p3 is the pressure of the reference tank 8 after equilibrium, in megapascals (MPa); p4 is the pressure of the sample tank 11 after equilibrium, in megapascals (MPa); T1 is the initial temperature of the reference tank 8, in Kelvin (K); T2 is the initial temperature of the sample tank 11, in Kelvin (K); T3 is the temperature of the reference tank 8 after equilibrium, in Kelvin (K); T4 is the temperature of the sample tank 11 after equilibrium, in Kelvin (K); Z1 is the compressibility factor of the initial gas in the reference tank 8, dimensionless; Z2 is the compressibility factor of the initial gas in the sample tank 11, dimensionless; Z3 is the compressibility factor of the gas in the reference tank 8 after equilibrium, dimensionless; Z4 is the compressibility factor of the gas in the sample tank 11 after equilibrium, dimensionless; V1 is the total volume of the reference tank 8 and part of the pipeline, in cubic centimeters (cm 3 ).

[0075] V s =V2-V f

[0076] Where: V2 is the total volume of the sample tank 11 and part of the pipeline, in cubic centimeters (cm 3 );V s is the skeleton volume of shale sample 12, in cubic centimeters (cm 3 ).

[0077] Further, the specific internal of the isothermal adsorption determination includes the following steps: open the vacuum valve 4, the main valve 6, and the first valve 9, close the exhaust valve 15, turn on the vacuum pump 5 switch, vacuum the reference tank 8, the sample tank 11 and the pipeline for no less than 30 minutes, collect experimental data through the first pressure sensor 7 and the second pressure sensor 10, and record data including the initial pressure (p5) of the reference tank 8, the initial temperature (T5) of the reference tank 8, the initial pressure (p6) of the sample tank 11, and the initial temperature (T6) of the sample tank 11. Then close the vacuum valve 4, the main valve 6, the first valve 9 and the vacuum pump 5, turn on the gas cylinder 1 switch, the booster pump 2, and the main valve 6, fill with adsorbed gas (methane, nitrogen and carbon dioxide) until the pressure value of the reference tank 8 reaches the target pressure, and close the main valve 6. Open the first valve 9, and the adsorption equilibrium time should be no less than 12 hours. After the pressure is balanced, the experimental data is collected through the first pressure sensor 7 and the second pressure sensor 10. The recorded data includes the pressure (p7) and temperature (T7) of the reference tank 8 after balance and the pressure (p8) and temperature (T8) of the sample tank 11 after balance, and the adsorbed gas amount of the shale sample 12 is calculated.

[0078] Calculation of adsorbed gas volume:

[0079] According to the principle of Boyle's law PV = nZRT, the relationship before and after pressure balance can be obtained:

[0080]

[0081] Where: n1 is the number of moles of adsorbed phase at the current pressure point, in mol; V f is the free space volume of the test sample, in cubic centimeters (cm 3 );V r is the volume of reference tank 8, in cubic centimeters (cm 3 );P r7is the pressure of reference tank 8 before equilibrium, in megapascals (MPa); P5 is the pressure of reference tank 8 after equilibrium, in megapascals (MPa); P6 is the pressure of sample tank 11 before equilibrium, in megapascals (MPa); P8 is the pressure of sample tank 11 after equilibrium, in megapascals (MPa); T5 is the temperature of reference tank 8 before equilibrium, in Kelvin (K); T7 is the temperature of reference tank 8 after equilibrium, in Kelvin (K); T6 is the temperature of sample tank 11 before equilibrium, in Kelvin (K); T7 is the temperature of sample tank 11 after equilibrium, in Kelvin (K); Z5 is the compression factor of reference tank 8 before equilibrium, dimensionless; Z6 is the compression factor of reference tank 8 after equilibrium, dimensionless; Z7 is the compression factor of reference tank 8 before equilibrium, dimensionless; Z8 is the compression factor of sample tank 11 after equilibrium, dimensionless;

[0082] Calculate the relative adsorption volume (V ad ):

[0083] V ad =n1*22.4*1000

[0084] Where: V ad is the relative adsorption volume in cubic centimeters (cm 3 ).

[0085] After adsorption equilibrium, the adsorbed gas in the sample tank 11 and the pipeline under the target pressure (p) includes: sample adsorbed gas volume, free gas volume in sample pores, and remaining free gas in free space (free gas volume in free space minus free gas volume in sample pores).

[0086] The sample pore volume is calculated using the formula:

[0087]

[0088] Where: V φ V is the pore volume of the sample in cubic centimeters; b is the apparent volume of the sample, in cubic centimeters; φ is the porosity of the sample, dimensionless;

[0089] The sample apparent volume is calculated using the formula:

[0090]

[0091] Where: M g is the sample mass in grams; ρ c is the apparent density of the sample in grams per cubic centimeter;

[0092] The volume of free gas in the pores of the sample at the target pressure (p) is calculated using the formula:

[0093]

[0094] Where: V g is the volume of free gas in the pores of the sample, in cubic centimeters (cm 3 ); p is the gas pressure in megapascals (MPa); V is the gas volume in cubic centimeters (cm 3 ); Z is the compressibility factor of the gas, dimensionless; R is the molar gas constant, in joules per mole (J·mol -1 ·K -1 ) ; Z is the gas temperature, the unit is Kelvin (K).

[0095] During the depressurization process, the change in the free gas content in the sample pores is ΔV2, using the formula:

[0096]

[0097] Where: ΔV2 is the change in free gas in the sample pores during the depressurization stage, in cubic centimeters per gram; V g1 V is the volume of free gas in the sample pores under standard conditions at the previous pressure stage, in cubic centimeters; g2 M is the volume of free gas in the sample pores under standard conditions at the next pressure stage, in cubic centimeters (cm3); g is the sample mass in grams.

[0098] The remaining free gas volume in the free space at the target pressure (p) is calculated using the formula:

[0099]

[0100] Where: V gf is the volume of free gas remaining in free space, in cubic centimeters (cm 3 ); p is the gas pressure in megapascals (MPa); V is the gas volume in cubic centimeters (cm 3 ); Z is the compressibility factor of the gas, dimensionless; R is the molar gas constant, in joules per mole (J·mol -1 ·K -1 );T is the gas temperature, the unit is Kelvin (K).

[0101] During the depressurization process, the change in the amount of free gas outside the sample pores is ΔV3, using the formula:

[0102]

[0103] Where: ΔV3 is the change in free gas outside the sample pores during the depressurization stage, in cubic centimeters per gram; V gf1 V is the volume of free gas outside the sample pores under standard conditions at the previous pressure stage, in cubic centimeters; gf2M is the volume of free gas outside the sample pores under standard conditions at the next pressure stage, in cubic centimeters; g is the sample mass in grams.

[0104] Furthermore, the specific internal structure of the decompression desorption measurement includes the following steps: controlling the pressure of the pressure reducing valve to be greater than the pressure in the sample tank 11 through the manual pump 16, and setting the temperature of the thermostat 17 according to the temperature of the drilling fluid during the coring process; after the temperature of the thermostat 17 stabilizes, opening the exhaust valve 15, adjusting the manual pump 16 to control the pressure drop of the pressure reducing valve, controlling the pressure reduction to the first pressure point through the pressure reducing valve, recording the pressure p and temperature T in the sample tank 11, and performing the decompression desorption experiment at each pressure point from high to low until the last pressure point reaches atmospheric pressure.

[0105] The gas discharged from the sample tank 11 enters the gas cylinder 18 through the pipeline and the exhaust valve 15, and the distilled water in the gas cylinder 18 enters the measuring cylinder 22 through the rubber hose 20 and the volume flow meter 19. The volume flow meter 19 is used to measure the volume of the distilled water flowing through; the lifter 24 is connected to the measuring cylinder 22 through the suspension rope 23, and the liquid level in the gas cylinder 18 and the measuring cylinder 22 is adjusted to be the same through the lifter 24. The volume of gas discharged from the sample tank 11 is transmitted to the computer 26 through the data line 25. The volume of gas discharged after each decompression desorption V is recorded. m , the atmospheric pressure at that time is P m and atmospheric temperature T m data.

[0106] Control of pressure reduction points: when the maximum experimental equilibrium pressure is greater than 10MPa, the pressure reduction is 1MPa each time, and the number of experimental pressure points is not less than 11; when the maximum experimental equilibrium pressure is less than or equal to 10MPa, the pressure reduction is 0.5MPa each time, and the number of experimental pressure points is not less than 10.

[0107] Decompression desorption time: Determined according to the actual situation of on-site coring.

[0108] The correction of the desorbed gas volume in each decompression desorption stage is performed using the formula:

[0109]

[0110] Where: V cl is the volume of gas under standard conditions, in cubic centimeters (cm 3 );P m is atmospheric pressure, in kilopascals (kPa); T m is the atmospheric temperature in degrees Celsius (℃); V m is the volume of gas in cubic centimeters (cm3 ).

[0111] During the pressure reduction process, the change in gas volume collected by the high-precision flow meter is ΔV4, using the formula:

[0112]

[0113] Where: ΔV4 is the change in the gas produced in the sample during the depressurization stage, in cubic centimeters per gram; V cl1 The high-precision flow meter records the cumulative gas volume in the last pressure stage, in cubic centimeters; V cl2 The high-precision flow meter records the accumulated gas volume for the next pressure stage in cubic centimeters; M g is the sample mass in grams.

[0114] During the depressurization process, the change in the gas content adsorbed by the sample skeleton is ΔV1, using the formula:

[0115] ΔV1+ΔV2+ΔV3+ΔV4=0

[0116] Wherein: ΔV1 is the change of the adsorbed gas in the sample skeleton at each depressurization stage, in cubic centimeters per gram; ΔV2 is the change of the free gas in the pores of the sample at each depressurization stage, in cubic centimeters per gram; ΔV3 is the change of the free gas outside the pores of the sample at each depressurization stage, in cubic centimeters per gram; ΔV4 is the change of the produced gas in the sample at each depressurization stage, in cubic centimeters per gram.

[0117] When the decompression desorption experiment is over, the correction of the desorbed gas volume in each decompression desorption stage is accumulated to obtain the cumulative gas volume V recorded by the flow meter after correction. L .

[0118] Furthermore, the specific internal process of the desorption measurement in the exposed air includes the following steps: closing the thermostat 17, collecting the experimental data of the first pressure sensor 7, the second pressure sensor 10, and the volume flow meter 19 through the computer 26, and recording the atmospheric pressure, indoor temperature, and gas volume. The desorption time in the exposed air is determined according to the actual situation of the on-site coring.

[0119] The desorbed gas content in the exposed air is calculated using the formula:

[0120] G BL =V BL / M g

[0121] Where: C BL To measure the desorbed gas content in the exposed air, the unit is cubic centimeters per gram; V BL It is a measure of the volume of desorbed gas in the exposed air, in cubic centimeters; M gis the sample mass in grams.

[0122] Furthermore, the natural desorption measurement specifically includes the following steps: setting the temperature of the thermostat 17 according to the reservoir temperature or the experimental requirements; the gas desorbed from the sample enters the gas storage cylinder 18 through the pipeline and the exhaust valve 15, the gas desorbed from the test sample is measured by the volume flow meter 19, and the measurement result is transmitted to the computer 26 for storage and display.

[0123] During natural desorption, measurement is performed at regular intervals, which may be from 1 minute to 5 minutes, depending on the pressure in the sample tank 11 .

[0124] The natural desorption gas content is calculated using the formula:

[0125] G CD =V D / M g

[0126] Where: C CD To measure the natural desorption gas content, the unit is cubic centimeters per gram; V D To measure the volume of naturally desorbed gas, the unit is cubic centimeters; M g is the sample mass in grams (g).

[0127] Furthermore, the specific internal process of residual gas determination includes the following steps: finally, pour the shale sample into a ball mill and seal it for residual gas determination, crush it for 2 to 4 hours using a residual gas meter, put it into the constant temperature box 17, measure the gas volume after the reservoir temperature is restored, and record the atmospheric pressure, indoor temperature, and gas volume.

[0128] The residual gas content is calculated using the formula:

[0129] G CR =V R / M g

[0130] Where: C CR is the residual gas content, in cubic centimeters per gram; V R is the residual gas volume in cubic centimeters; M g is the sample mass in grams.

[0131] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A physical simulation device for shale gas content, characterized in that: It includes a reference tank, a sample tank, a constant temperature box, a gas adding mechanism, a vacuum mechanism, a back pressure mechanism, a gas volume measuring mechanism and a computer. The reference tank and the sample tank are both arranged inside the constant temperature box. The output end of the gas adding mechanism is connected to the reference tank. The bottom of the reference tank is connected to the sample tank through a pipeline. A shale sample is placed inside the sample tank. The vacuum mechanism is connected to the reference tank through a pipeline. The gas volume measuring mechanism is connected to the sample tank through a pipeline. The back pressure mechanism is arranged between the connecting pipeline between the sample tank and the gas volume measuring mechanism. The input end of the reference tank is provided with a main valve and a first pressure sensor. The input end of the sample tank is provided with a second pressure sensor. The connecting pipeline between the bottom of the reference tank and the input end of the sample tank is provided with a first valve. The gas adding mechanism, the first pressure sensor, the second pressure sensor and the gas volume measuring mechanism are all communicatively connected to the computer.

2. The shale gas content physical simulation device according to claim 1, characterized in that: The gas increasing mechanism includes a gas cylinder, a booster pump and a pressure gauge. The input end of the booster pump is connected to the gas cylinder pipeline, the output end of the booster pump is connected to the input end pipeline of the reference tank, and the pressure gauge is arranged between the connecting pipeline of the booster pump and the reference tank.

3. The shale gas content physical simulation device and method according to claim 2, characterized in that: The vacuum mechanism comprises a vacuum pump and a vacuum valve. The input end of the vacuum pump is connected to the reference tank pipeline, and the vacuum valve is arranged between the connecting pipeline of the vacuum pump and the reference tank.

4. The shale gas content physical simulation device and method according to claim 3, characterized in that: The gas volume measuring mechanism includes a gas cylinder, a volume flow meter, a rubber hose, a measuring cylinder, a sling and a lifter. The input end of the gas cylinder is connected to the sample tank pipeline, the measuring cylinder is located on one side of the gas cylinder, the measuring cylinder is parallel to the gas cylinder, the bottom of the gas cylinder is connected to the bottom of the measuring cylinder through the rubber hose, the volume flow meter is arranged on the rubber hose, distilled water is arranged inside the measuring cylinder, and the top of the measuring cylinder is connected to the lifter through the sling.

5. The shale gas content physical simulation device and method according to claim 4, characterized in that: The back pressure mechanism includes a manual pump and a third pressure sensor. A back pressure valve and an exhaust valve are arranged in sequence between the connecting pipeline between the sample tank and the air cylinder. The manual pump is connected to the back pressure valve pipeline, and the third pressure sensor is arranged between the manual pump and the connecting pipeline of the back pressure valve.

6. The shale gas content physical simulation device and method according to claim 5, characterized in that: The booster pump, the first pressure sensor, the second pressure sensor and the volume flow meter are all connected to the computer for communication via data lines.

7. A method for physical simulation of shale gas content, applied to the physical simulation device for shale gas content as claimed in claim 6, characterized in that: The steps include: preparing shale samples, drying and weighing the shale samples; placing the weighed dry sample in the sample jar; Set the thermostat temperature according to the reservoir temperature or experimental requirements. After the thermostat temperature stabilizes, check the air tightness of the entire simulation device. The shale sample in the sample tank is measured using a simulation device.

8. The shale gas content physical simulation method according to claim 7, characterized in that: In the process of measuring the shale sample in the sample tank using the simulation device, the measurement contents include free space volume measurement, isothermal adsorption measurement, decompression desorption measurement, desorption measurement in exposure to air, natural desorption measurement and residual gas measurement.

9. The physical simulation method of shale gas content according to claim 8, characterized in that: The specific formula for determining the free space volume is as follows: Where: V f is the volume of free space, in cubic centimeters; p1 is the initial pressure of the reference tank, in MPa; p2 is the initial pressure of the sample tank, in MPa; p3 is the pressure of the reference tank after equilibrium, in MPa; p4 is the pressure of the sample tank after equilibrium, in MPa; T1 is the initial temperature of the reference tank, in Kelvin; T2 is the initial temperature of the sample tank, in Kelvin; T3 is the temperature of the reference tank after equilibrium, in Kelvin; T4 is the temperature of the sample tank after equilibrium, in Kelvin; Z1 is the compressibility factor of the initial gas in the reference tank, dimensionless; Z2 is the compressibility factor of the initial gas in the sample tank, dimensionless; Z3 is the compressibility factor of the gas after equilibrium in the reference tank, dimensionless; Z4 is the compressibility factor of the gas after equilibrium in the sample tank, dimensionless; V1 is the total volume of the reference tank and part of the pipeline, in cubic centimeters; V s =V2-V f Where: V2 is the total volume of the sample tank and part of the pipeline, in cubic centimeters; V s is the skeleton volume of the shale sample in cubic centimeters.

10. The shale gas content physical simulation method according to claim 8, characterized in that: The specific formula of the isothermal adsorption determination includes calculation of adsorbed gas volume, calculation of relative adsorption volume of particles of rock sample, calculation of sample pore volume, calculation of free gas volume in pores of sample at target pressure and calculation of remaining free gas volume in free space at target pressure, wherein the calculation of adsorbed gas volume includes the following formula: Where: n1 is the number of moles of adsorbed phase at the current pressure point, in moles; V f V is the free space volume of the test sample in cubic centimeters; r is the reference tank volume in cubic centimeters; P r7 is the pressure of the reference tank before equilibrium, in MPa; P5 is the pressure of the reference tank after equilibrium, in MPa; P6 is the pressure of the sample tank before equilibrium, in MPa; P8 is the pressure of the sample tank after equilibrium, in MPa; T5 is the temperature of the reference tank before equilibrium, in Kelvin; T7 is the temperature of the reference tank after equilibrium, in Kelvin; T6 is the temperature of the sample tank before equilibrium, in Kelvin; T7 is the temperature of the sample tank after equilibrium, in Kelvin; Z5 is the compression factor of the reference tank before equilibrium, dimensionless; Z6 is the compression factor of the reference tank after equilibrium, dimensionless; Z7 is the compression factor of the reference tank before equilibrium, dimensionless; Z8 is the compression factor of the sample tank after equilibrium, dimensionless; The relative adsorption volume of particles in rock samples is calculated as follows: IN ad =n1*22.4*1000 Where: V ad is the relative adsorption volume in cubic centimeters; After adsorption equilibrium, the adsorbed gas in the sample tank and pipeline at the target pressure includes: the sample adsorbed gas volume, the free gas volume in the sample pores and the remaining free gas in the free space; The sample pore volume is calculated using the formula: Where: V φ V is the pore volume of the sample in cubic centimeters; b is the apparent volume of the sample, in cubic centimeters; φ is the porosity of the sample, dimensionless; The sample apparent volume is calculated using the formula: Where: M g is the sample mass in grams; ρ c is the apparent density of the sample in grams per cubic centimeter; The volume of free gas in the pores of the sample at the target pressure is calculated using the formula: Where: V g is the volume of free gas in the pores of the sample, in cubic centimeters; p is the gas pressure, in megapascals; V is the gas volume, in cubic centimeters; Z is the compressibility factor of the gas, dimensionless; R is the molar gas constant, in joules per mole; Z is the gas temperature, in degrees Kelvin; The remaining free gas volume in the free space at the target pressure is calculated using the formula: Where: V gf is the remaining free gas volume in free space, in cubic centimeters; p is the gas pressure, in MPa; V is the gas volume, in cubic centimeters; Z is the gas compressibility factor, dimensionless; R is the molar gas constant, in joules per mole; T is the gas temperature, in Kelvin.

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