CN109946215B - In-situ coal gas adsorption capacity test simulation device - Google Patents
In-situ coal gas adsorption capacity test simulation device Download PDFInfo
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Abstract
The invention relates to an in-situ coal gas adsorption quantity measurement simulation device which comprises an in-situ coal simulation system, a coal water injection system, an adsorption balance system, an adsorption monitoring system and a data acquisition and analysis system, wherein the in-situ coal gas adsorption quantity measurement simulation device comprises a coal gas adsorption quantity measurement system, an adsorption balance system and an adsorption monitoring system; in the in-situ coal simulation system, a columnar coal test is adopted, the stress borne by the in-situ coal is simulated through a confining pressure loader and a shaft pressure loader, the water content of the in-situ coal is simulated through a coal water injection system, the dynamic change characteristic of the coal strain in the gas adsorption process is used for reflecting the gas adsorption dynamic process of the coal, the time node before and after the coal reaches adsorption equilibrium is used as a key point, the pressure change of a gas reference cylinder caused by the adsorption effect of the coal is determined, the adsorption capacity of the coal on the gas under different conditions is obtained by changing the simulated stress and the water content borne by the coal, the defect of a conventional capacity method is overcome, and a method is provided for accurately evaluating the adsorption capacity of the coal on the gas under the in-situ condition.
Description
Technical Field
The invention belongs to the field of unconventional natural gas development, and particularly relates to an in-situ coal gas adsorption capacity test simulation device.
Background
At present, the test of the gas adsorption capacity of the coal reservoir is to carry out a static isothermal adsorption experiment on pulverized coal under the condition of no load, and the adsorption capacity of the pulverized coal to the gas in the experimental process is used for evaluating basic parameters such as the adsorption capacity of the coal reservoir to the gas and the gas saturation of the coal reservoir under the in-situ condition, so as to guide the implementation of coal bed gas development engineering. However, the pulverized coal is completely inconsistent with the actual coal reservoir in terms of granularity and stress state, which results in that the gas adsorption test result obtained by the static isothermal adsorption test of the pulverized coal under the unloaded condition is seriously inconsistent with the actual coal reservoir, and the situation is more obvious for the coal reservoir under the conditions of high temperature and high ground stress in the deep part. In addition, in the conventional static isothermal adsorption experiment based on the capacity method, the adsorption expansion of the pulverized coal can cause the change of the free space volume of the sample cylinder, and errors are further formed on the test result of the pulverized coal gas adsorption amount obtained based on the free space volume of the sample cylinder in the capacity method. However, due to the influence of the test difficulty, no correction method for the influence of the adsorption expansion of the pulverized coal on the free space volume of the sample cylinder exists at present.
Disclosure of Invention
In order to solve the defects of the prior art, the invention provides an in-situ coal gas adsorption capacity test simulation device, which is characterized in that dynamic change characteristics of coal strain in the process of gas adsorption by coal are used for reflecting the adsorption dynamics process of the coal on gas, a time node before and after the coal reaches adsorption balance is used as a key point, the pressure change of a gas reference cylinder caused by the adsorption of the coal is determined, and then the adsorption capacity of the coal on the gas under simulated in-situ conditions is obtained by combining a real gas state equation.
The aim and the technical problems of the invention are realized by adopting the following technical proposal. The invention provides an in-situ coal gas adsorption quantity measurement simulation device, which comprises an in-situ coal simulation system, a coal water injection system, an adsorption balance system, an adsorption monitoring system and a data acquisition and analysis system;
the in-situ coal body simulation system comprises a clamp holder, an electric heater, a columnar coal body and a hydraulic servo system; the hydraulic servo system comprises a hydraulic pump, a confining pressure loader and a shaft pressure loader; the electric heater is arranged on the outer surface of the clamp holder through the base and heats the clamp holder to enable the temperature inside the clamp holder to reach a preset temperature; the columnar coal body is arranged in the clamp holder, the hydraulic pump is connected with the confining pressure loader and the axial pressure loader through the hydraulic pipeline and the overflow valve, the confining pressure loader is arranged on the outer surface of the clamp holder, and the axial pressure loader is arranged at the left end of the clamp holder;
The coal body water injection system comprises a water storage tank, a high-pressure water pump, a water flow valve, a water pressure gauge and a water flow gauge, wherein the high-pressure water pump, the water flow valve, the water pressure gauge and the water flow gauge are arranged on a water injection pipeline, the water storage tank is connected with a clamp through the water injection pipeline, and the high-pressure water pump, the water flow valve, the water pressure gauge and the water flow gauge are sequentially arranged on the water injection pipeline along the direction from the water storage tank to the clamp;
The adsorption balance system comprises a holder outlet valve, a CH 4 gas cylinder, a CO 2 gas cylinder, a gas booster pump, a CH 4 reference cylinder, a CO 2 reference cylinder, a first valve arranged on a CH 4 gas cylinder output pipeline, a second valve arranged on a CO 2 gas cylinder output pipeline, a third valve arranged on a vacuum pump vacuum pipeline, a fourth valve arranged on a gas booster pump outlet, a fifth valve, a sixth valve, a vacuum pump, a CH 4 reference cylinder inlet valve, a CH 4 reference cylinder outlet valve, a CO 2 reference cylinder inlet valve, a CO 2 reference cylinder outlet valve, a seventh valve and an eighth valve; the CH 4 gas cylinder and the CO 2 gas cylinder are connected with the gas booster pump, the vacuum pump is arranged behind the CH 4 gas cylinder and the CO 2 gas cylinder and in front of the gas booster pump, and the CH 4 reference cylinder and the CO 2 reference cylinder are sequentially arranged behind the gas booster pump; the vacuum pump is connected with the gas conveying pipeline through a vacuumizing pipeline;
The adsorption monitoring system comprises a first gas pressure gauge arranged at the inlet end of the CH 4 reference cylinder, a second gas pressure gauge arranged at the inlet end of the CO 2 reference cylinder, a third gas pressure gauge, a gas pressure automatic tracker arranged behind the CH 4 reference cylinder and the CO 2 reference cylinder, a first gas flow meter, a first strain gauge, a second strain gauge and a second gas flow meter; the seventh valve and the eighth valve are respectively arranged at two ends of the automatic gas pressure tracker; the left end of the seventh valve and the right end of the eighth valve are also connected with an auxiliary pipeline provided with a fifth valve, the auxiliary pipeline is connected with a gas output pipeline where the automatic gas pressure tracker is positioned in parallel, and a third gas pressure gauge, a first gas flowmeter and a sixth valve are sequentially arranged on the gas output pipeline behind the eighth valve; the first strain gauge is axially arranged on the surface of the columnar coal body, and the second strain gauge is radially arranged on the surface of the columnar coal body; the second gas flowmeter is arranged behind the holder outlet valve;
The data acquisition and analysis system comprises a data acquisition box and a computer, wherein the data acquisition box is connected with the hydraulic pump, the first gas pressure gauge, the second gas pressure gauge, the third gas pressure gauge, the gas pressure automatic tracker, the first gas flow meter, the second gas flow meter, the first strain gauge, the second strain gauge and the computer through data lines.
Further, the CH 4 reference cylinder and the CO 2 reference cylinder are fixed-volume rigid cylinders with precise fixed values.
Further, the diameter of the columnar coal body is 50cm, and the length is 100cm.
Further, the first gas pressure gauge, the second gas pressure gauge and the third gas pressure gauge have an accuracy of 0.01MPa.
Further, the first strain gauge and the second strain gauge have an accuracy of 10 -8.
The method for testing the in-situ coal gas adsorption capacity by the in-situ coal gas adsorption capacity testing simulation device comprises the following steps of:
(1) Sample preparation: drilling columnar coal bodies along the vertical bedding direction, and polishing rough surfaces on the positions of the columnar coal bodies, which are respectively pre-adhered with the strain gauges along the axial direction and the radial direction, by using sand paper; respectively sticking a first strain gauge on the surface of the columnar coal body along the axial direction and a second strain gauge along the radial direction;
(2) Sample mounting: opening the clamp holder, putting the columnar coal body stuck with the strain gauge into the clamp holder, and connecting the first strain gauge and the second strain gauge to the data acquisition box by using a data wire; the electric heater is started to heat the clamp holder to the experimental temperature, so that the columnar coal body is ensured to be in the set temperature environment;
(3) And (3) alternately loading confining pressure and axial pressure: the hydraulic servo system is connected, and the hydraulic servo system is operated according to the principle of firstly adding confining pressure and then adding shaft pressure, and comprises the following operation steps of: a. firstly, starting a hydraulic pump, and suspending loading after applying confining pressure of 2MPa to a columnar coal body by using a confining pressure loader; b. opening the axial pressure loader to apply an axial pressure of 2MPa to the columnar coal body, then suspending loading, repeating the steps a and b until the axial pressure and the confining pressure are both in a stress state set in an experiment, and closing the hydraulic pump;
(4) And (3) air tightness test: after the confining pressure and the shaft pressure are alternately loaded, firstly closing all valves, then opening a third valve, a fourth valve, a CH 4 reference cylinder inlet valve, a CH 4 reference cylinder outlet valve, a CO 2 reference cylinder inlet valve, a CO 2 reference cylinder outlet valve, a fifth valve and a sixth valve, starting a vacuum pump to vacuumize the whole device system until the pressure values of a first gas pressure gauge, a second gas pressure gauge and a third gas pressure gauge are all-0.1 MPa, then closing the third valve, and observing whether the pressure values are stable; if the pressure value is kept stable, then carrying out the step (5); if the pressure value is unstable, repeating the steps (2) and (3);
(5) And (3) water injection: after the air tightness test, starting a high-pressure water pump, opening a water flow valve, keeping the value of a water pressure meter to be a pressure value of 2MPa, injecting water into the columnar coal body, and closing the water flow valve to finish water injection when the value displayed by the water flow meter is a preset water injection volume;
(6) Steady-state adsorption gas source preparation: closing all valves except the second valve, the fourth valve and the CO 2 reference cylinder inlet valve, starting a gas booster pump to boost CO 2 gas to the CO 2 reference cylinder, and closing the CO 2 reference cylinder inlet valve to stop boosting when the pressure value displayed by the second gas pressure gauge is higher than the highest experimental pressure value by 3 MPa;
(7) Gas injection adsorption: after the steady-state adsorption gas source preparation is completed, all valves are closed, an automatic gas pressure tracker is set as an experimental pressure value, the gas pressure injected into the columnar coal body is controlled to be the set experimental pressure value all the time, steady-state adsorption of the columnar coal body in the clamp holder is ensured under constant pressure, then a CO 2 reference cylinder outlet valve, a seventh valve, an eighth valve and a sixth valve are sequentially opened to inject CO 2 gas into the columnar coal body, an adsorption experiment is carried out, and a first gas flowmeter collects the gas quantity injected into the clamp holder; in the experimental process, the computer records axial strain data, radial strain data and CO 2 reference cylinder gas pressure change data, and forms a curve on a graph, and when the axial strain data, the radial strain data and the CO 2 reference cylinder gas pressure data are all stable and unchanged, the gas injection adsorption experiment is ended; then all valves are closed, the outlet valve of the clamp holder is opened to release CO 2 gas in the clamp holder, and the second gas flowmeter collects the amount of the gas released by the clamp holder; and then, closing all valves except the third valve, the fourth valve, the fifth valve and the sixth valve, starting a vacuum pump to vacuumize the columnar coal body, removing residual CO 2 gas in the coal body, and ending the experiment.
(8) Judging key points under the adsorption action: selecting a turning point of the axial strain curve as a starting time of adsorption of the coal body based on the axial strain curve of the coal body recorded by the first strain sheet, and selecting a stable and unchanged position of the axial strain curve as an end time of adsorption saturation of the coal body, wherein the starting time and the end time respectively correspond to pressure data P 2 and P 3 on a CO 2 reference cylinder gas pressure change curve; during the adsorption of the coal, the pressure of CO 2 in the reference cylinder is reduced from P 2 to P 3, and the reduction of the CO 2 in the reference cylinder is the adsorption of the CO 2 by the coal in a simulated state;
(9) Calculation of gas adsorption amount: calculating gas adsorption quantity by taking the gas molar quantity as a unit, calculating a gas molar quantity n 2、n3 corresponding to P 2、P3 according to a real gas state equation n i＝PiV/(Zi RT), and then calculating the adsorption quantity delta n of the coal body on CO 2 gas in a simulated in-situ state according to a formula delta n=n 2-n3; true gas state equation n i＝PiV/(Zi RT), P i is gas pressure, unit: 10 -3 MPa, V is the volume of the gas reference cylinder, unit: cm 3,Zi is the compression factor of the gas corresponding to the gas pressure P i, R is the gas constant, T is the temperature, unit: k, n i are the molar amounts of the gases, unit: mol.
In the stress loading process of the step (3), in order to prevent the columnar coal body from cracking, a stress control mode is adopted for loading, and the loading speed is less than or equal to 0.05MPa/s.
Further, the experimental temperature in the step (2) can be 25-60 ℃, the stress set in the step (3) can be 8-50 MPa, and the water injection volume preset in the step (5) can be 5-30 mL.
Further, after the in-situ coal adsorption quantity is calculated, starting a vacuum pump to vacuumize the clamp holder; the steps (3), (4), (5), (6), (7), (8) and (9) can be repeated, the test experiment of the gas adsorption capacity of the in-situ coal under different conditions can be further developed by changing the stress state of the coal, the water content of the coal and the gas injection pressure, finally, the influence rule of stress, water content and gas pressure on the gas adsorption capacity of the in-situ coal can be summarized, and the basis is provided for researching the evaluation of the gas adsorption capacity of the coal under different geological background conditions.
Further, the testing device and the testing method can be used for simulating the test of the in-situ coal body on the adsorption quantity of CH 4 and/or CO 2 gas.
By adopting the technical scheme, the invention has the following advantages:
According to the invention, the coal body is adopted to replace pulverized coal, the hydraulic servo system is adopted to carry out stress loading on the coal body, and the original state of the coal bed can be simulated by using the in-situ coal body simulation system and the coal body water injection system, so that the stress environment, the stratum temperature, the water content information and the like of the coal body are truly reflected; the automatic gas pressure tracker installed in front of the clamp holder can realize tracking control of gas pressure and ensure stable adsorption of columnar coal bodies. According to the invention, an experimental sample adopted for gas content test is a columnar coal body instead of pulverized coal, gas adsorption quantity test is carried out under the condition of simulating an original stratum, dynamic change characteristics of strain of the coal body in the adsorption process of the coal body on the gas are used for reflecting the adsorption dynamic process of the coal body on the gas, a time node before and after the coal body reaches adsorption equilibrium is used as a key point, further pressure change of a gas reference cylinder caused by the adsorption effect of the coal body is determined, further the adsorption quantity of the coal body on the gas under the simulated in-situ condition is obtained by combining a real gas state equation, the microscopic behavior of the adsorption effect of the coal body on the gas is measured through the strain in the adsorption expansion process of the coal body, and experimental data reliability is high; the method can test the adsorption capacity of the in-situ coal body to the gas under the conditions of different stress, different temperatures and different water contents, provides a technical scheme for reasonably evaluating the resource quantity of the coalbed methane in the block, not only solves the defects of the conventional capacity method, but also provides a method for accurately evaluating the adsorption capacity of the coal body to the gas under the in-situ condition.
Drawings
Fig. 1 is a schematic structural view of the present invention.
Fig. 2 is a perspective view of the columnar coal body of fig. 1 according to the present invention.
FIG. 3 is a graph of data recorded for axial strain, radial strain, and CO 2 reference cylinder gas pressure for a cylindrical coal body in the method of the present invention.
[ Main element symbols description ]
1: Gas transfer line 2: gas output line 3: vacuumizing pipeline 4: auxiliary pipeline
5: Water injection line 11: gripper 12: an electric heater 13: columnar coal body 14: hydraulic pump
15: Confining pressure loader 16: axle pressure loader 17: hydraulic lines 18: overflow valve
21: Water storage tank 22: high-pressure water pump 23: water flow valve 24: water pressure gauge 25: water flowmeter
31: Gripper outlet valve 32: CH 4 cylinder 33: CO 2 gas cylinder 34: gas booster pump
35: CH 4 reference cylinder 36: CO 2 reference cylinder 37: first valve 38: second valve 39: third valve
40: Fourth valve 41: fifth valve 42: sixth valve 43: vacuum pump
44: CH 4 reference cylinder inlet valve 45: CH 4 reference cylinder outlet valve 46: CO 2 reference cylinder inlet valve
47: CO 2 reference cylinder outlet valve 48: seventh valve 49: eighth valve 51: first gas pressure gauge
52: Second gas pressure gauge 53: third gas pressure gauge 54: automatic gas pressure tracker
55: First gas flow meter 56: first strain gage 57: second strain gage
58: A second gas flow meter 61: data acquisition box 62: computer with a memory for storing data
Detailed Description
In order to further describe the technical means and effects adopted by the invention to achieve the preset aim, the following is a specific implementation, structure, characteristics and effects of an in-situ coal gas adsorption test simulation device according to the invention, which are described in detail below with reference to the accompanying drawings and examples.
As shown in fig. 1 to 3, the present invention provides the following technical solutions: the simulation device for the in-situ coal gas adsorption capacity test comprises an in-situ coal simulation system, a coal water injection system, an adsorption balance system, an adsorption monitoring system and a data acquisition and analysis system;
the in-situ coal body simulation system comprises a clamp 11, an electric heater 12, a columnar coal body 13 and a hydraulic servo system; the electric heater is arranged on the outer surface of the clamp holder through the metal base, the diameter of the columnar coal body is 50cm, the length of the columnar coal body is 100cm, and the columnar coal body in the clamp holder is in a preset temperature environment by heating the clamp holder. The hydraulic servo system comprises a hydraulic pump 14, a confining pressure loader 15 and a shaft pressure loader 16; the hydraulic pump is connected with a confining pressure loader and a shaft pressure loader through a hydraulic pipeline 17 and a relief valve 18, the confining pressure loader is arranged on the outer surface of the clamp holder, and the shaft pressure loader is arranged at the left end head of the clamp holder.
The coal body water injection system comprises a water storage tank 21, a high-pressure water pump 22, a water flow valve 23, a water pressure meter 24 and a water flow meter 25. The water storage tank 26 is connected with the clamp 11 through the water injection pipeline 5, and the high-pressure water pump, the water flow valve, the water pressure gauge and the water flow gauge are sequentially arranged on the water injection pipeline along the direction from the water storage tank to the clamp.
The adsorption balance system comprises a holder outlet valve 31, a CH 4 gas cylinder 32, a CO 2 gas cylinder 33, a gas booster pump 34, a CH 4 reference cylinder 35, a CO 2 reference cylinder 36, a first valve 37, a second valve 38, a third valve 39, a fourth valve 40, a fifth valve 41, a sixth valve 42, a vacuum pump 43, a CH 4 reference cylinder inlet valve 44, a CH 4 reference cylinder outlet valve 45, a CO 2 reference cylinder inlet valve 46, CO 2 refers to cylinder outlet valve 47, seventh valve 48, eighth valve 49. The CH 4 gas cylinder 32 and the CO 2 gas cylinder 33 are connected with the gas booster pump 34, the vacuum pump 43 is arranged behind the CH 4 gas cylinder and the CO 2 gas cylinder and in front of the gas booster pump 34, and the CH 4 reference cylinder 35 and the CO 2 reference cylinder 36 are sequentially arranged behind the gas booster pump 34; wherein, CH 4 reference cylinder and CO 2 reference cylinder are fixed volume rigid cylinder bodies with precise fixed values. The output pipelines of the CH 4 gas cylinder and the CO 2 gas cylinder are respectively provided with a first valve 37 and a second valve 38, and CH 4 or CO 2 enter a gas booster pump through a gas conveying pipeline 1 and enter a CH 4 reference cylinder, a CO 2 reference cylinder and then enter a clamp holder through a gas output pipeline 2 respectively for gas injection experiments. The vacuum pump 43 is connected to the gas delivery line 1 through the evacuation line 3 fitted with the third valve 39; a fourth valve 40 is provided at the outlet of the gas booster pump 34.
The adsorption monitoring system comprises a first gas pressure gauge 51, a second gas pressure gauge 52, a third gas pressure gauge 53, a gas pressure automatic tracker 54, a first gas flow meter 55, a first strain gauge 56, a second strain gauge 57 and a second gas flow meter 58; the first gas pressure gauge is arranged at the inlet end of the CH 4 reference cylinder, and the second gas pressure gauge is arranged at the inlet end of the CO 2 reference cylinder; the automatic gas pressure tracker is arranged behind the CH 4 reference cylinder and the CO 2 reference cylinder, the two ends of the automatic gas pressure tracker are respectively provided with a seventh valve and an eighth valve, the left end of the seventh valve and the right end of the eighth valve are also connected with an auxiliary pipeline 4 provided with a fifth valve, and the auxiliary pipeline 4 is connected with a gas output pipeline where the automatic gas pressure tracker 54 is arranged in parallel; a third gas pressure gauge 53, a first gas flow meter 55 and a sixth valve 42 are sequentially arranged on the gas output pipeline behind the eighth valve 49; the first strain gauge 56 is axially arranged on the surface of the columnar coal body, and the second strain gauge 57 is radially arranged on the surface of the columnar coal body; the first gas pressure gauge 51, the second gas pressure gauge 52 and the third gas pressure gauge 53 have an accuracy of 0.01MPa, and the first strain gauge and the second strain gauge have a strain epsilon accuracy of 10 -8.
The data acquisition and analysis system comprises a data acquisition box 61 and a computer 62, wherein the data acquisition box is an integrated data acquisition box, and can be respectively connected with a hydraulic pump, a first gas pressure gauge, a second gas pressure gauge, a third gas pressure gauge, a gas pressure automatic tracker, a first gas flow meter, a second gas flow meter, a first strain gauge, a second strain gauge and the computer through data lines, wherein the computer can realize analysis and mapping of data acquired by the data acquisition box.
The first strain gauge and the second strain gauge solve the problem that the conventional static isothermal adsorption experiment cannot react to the gas adsorption process by detecting strain change in the process of adsorbing gas by columnar coal bodies and adopting the mode that the gas adsorbed by the coal bodies is dynamically changed by Cheng Zhongmei body strain, and meanwhile, the gas pressure values of CH 4 reference cylinders or CO 2 reference cylinders before and after the adsorption and expansion balance of the coal bodies are read by taking the time node before and after the adsorption and expansion balance of the coal bodies as a key point, so that the adsorption quantity of the in-situ coal bodies to CH 4 or CO 2 gas is calculated by combining the state equation of the reference cylinders and the real gas.
In order to verify the effectiveness of the simulation device for in-situ coal gas adsorption capacity test, the inventor collects long flame coal in Monshan mining areas, takes CO 2 gas as an example, and adopts the simulation device for in-situ coal gas adsorption capacity test.
When the invention is used for in-situ coal gas adsorption test, the invention is operated according to the following steps:
(a) Sample preparation: long flame coal collected from a Mongolian mining area is drilled into columnar coal bodies along the vertical bedding direction, wherein the diameter of the columnar coal bodies is 50cm, and the length of the columnar coal bodies is 100cm; grinding the cylindrical coal surface with sand paper to obtain rough surface at the position of pre-sticking strain gauge along axial and radial directions; further, referring to fig. 2, a first strain gauge is stuck to the surface of the columnar coal body along the axial direction, and a second strain gauge is stuck to the surface of the columnar coal body along the radial direction;
(b) Sample mounting: opening the clamp holder, putting the columnar coal body stuck with the strain gauge into the clamp holder, and connecting the first strain gauge and the second strain gauge to a data acquisition box through a data line after the columnar coal body is placed; then, an electric heater is started to heat the clamp holder to an experimental temperature which can be 30 ℃ to ensure that the columnar coal body is in a set temperature environment;
(c) And (3) alternately loading confining pressure and axial pressure: the hydraulic servo system is connected, the operation is carried out according to the principle of firstly adding confining pressure and then adding shaft pressure, and the operation steps are as follows: a. firstly, starting a hydraulic pump, and suspending loading after applying confining pressure of 2MPa to a columnar coal body by using a confining pressure loader; b. b, opening the axial pressure loader to apply an axial pressure of 2MPa to the columnar coal body, then suspending loading, repeating the steps a and b until the axial pressure is loaded to a stress state of 10MPa and the confining pressure is 10MPa, and closing the hydraulic pump; in the stress loading process, in order to prevent the columnar coal body from cracking, loading is performed in a stress control mode, and the loading speed is less than or equal to 0.05MPa/s;
(d) And (3) air tightness test: after the confining pressure and the shaft pressure are alternately loaded, firstly closing all valves, then opening a third valve, a fourth valve, a CH 4 reference cylinder inlet valve, a CH 4 reference cylinder outlet valve, a CO 2 reference cylinder inlet valve, a CO 2 reference cylinder outlet valve, a fifth valve and a sixth valve, starting a vacuum pump to vacuumize the whole device system, vacuumizing until the pressure values of a first gas pressure gauge, a second gas pressure gauge and a third gas pressure gauge are all-0.1 MPa, then closing the third valve, and observing whether the pressure values are stable; if the pressure value remains stable, then proceeding to step (e); repeating steps (b) and (c) if the pressure value is unstable;
(e) And (3) water injection: after the air tightness test, all valves are closed, a high-pressure water pump is started, a water flow valve is opened, the numerical value of a water pressure meter is kept to be 2MPa, water is injected into the columnar coal body, when the numerical value displayed by the water flow meter is 10mL (which is equivalent to the water content of the coal body at the moment to be about 10 percent), the water flow valve is closed, and water injection is ended;
(f) Steady-state adsorption gas source preparation: in order to ensure that sufficient air sources exist when the coal body is subjected to steady-state adsorption under constant gas adsorption pressure, steady-state adsorption air source preparation is carried out before an experiment starts, firstly, all valves except a second valve, a fourth valve and a CO 2 reference cylinder inlet valve are closed, a gas booster pump is started to carry out CO 2 gas pressurization on a CO 2 reference cylinder, and when the pressure value displayed by a second gas pressure gauge is higher than the highest experimental pressure value by 3MPa, the CO 2 reference cylinder inlet valve is closed, and the pressurization is stopped;
(g) Gas injection adsorption: after the steady-state adsorption gas source preparation is completed, all valves are closed, taking the adsorption of the coal under the gas pressure of 6MPa (experimental pressure value) as an example, setting the gas pressure automatic tracker to be 6MPa, controlling the gas pressure injected into the columnar coal to be 6MPa all the time, guaranteeing the columnar coal in the clamp to be subjected to steady-state adsorption under constant pressure, and then sequentially opening a CO 2 reference cylinder outlet valve, a seventh valve, an eighth valve and a sixth valve to inject CO 2 gas into the columnar coal to carry out adsorption experiments; the first gas flowmeter collects the gas quantity injected into the clamp holder; in the experimental process, the computer records axial strain data, radial strain data and CO 2 reference cylinder gas pressure change data, and forms a curve on the same graph, and when the axial strain data, the radial strain data and the CO 2 reference cylinder gas pressure data are all stable and unchanged, the gas injection adsorption experiment is ended; then, all valves are closed, a holder outlet valve is opened to discharge CO 2 gas in the holder, and a second gas flowmeter collects the amount of the gas discharged by the holder; and then, closing all valves except the third valve, the fourth valve, the fifth valve and the sixth valve, starting a vacuum pump to vacuumize the columnar coal body, removing residual CO 2 gas in the coal body, and ending the experiment.
(H) And selecting a strain curve during gas adsorption quantity calculation: as can be seen from fig. 3, in the data monitoring time, the data quality is good, so as to facilitate comparison between the change condition of the CO 2 reference cylinder gas pressure and the change condition of the strain in the CO 2 adsorption process of the columnar coal body in the CO 2 gas adsorption process, and the axial strain, the radial strain and the CO 2 reference cylinder gas pressure are plotted on the graph of the same time coordinate. Fig. 3 shows that the radial strain of the columnar coal body always shows a trend of increasing in the process of injecting the CO 2 gas into the holder for gas injection adsorption, so that the deformation caused by the gas adsorption cannot be judged from the radial strain. Since CO 2 gas is injected from the port of the holder, the pressure of CO 2 gas in the reference cylinder is rapidly reduced (from point P 1 to point P 2 in FIG. 3) at the beginning of CO 2 gas injection, the columnar coal in the holder does not adsorb CO 2 gas, the axial strain of the coal recorded by the first strain gauge under the compression action of CO 2 gas shows a decreasing trend (from point A 11 to point A 22 in FIG. 3), and at this stage is influenced by axial compression deformation, the radial strain of the coal body recorded by the second strain gauge is correspondingly increased; along with the duration of gas injection time, when reaching a point A 22, the axial strain of the coal body recorded by the first strain sheet shows a trend of increasing, obviously due to the fact that the coal body is expanded caused by the adsorption of CO 2, along with the adsorption of the coal body, the adsorption expansion deformation of the columnar coal body is changed from the compression deformation of the sections A 11 to A 22 to the adsorption expansion deformation from the point A 22, and the axial strain and the radial strain of the coal body are continuously increased, so that a turning point A 22 on an axial strain curve is the starting moment of the adsorption of the columnar coal body on CO 2 gas; until the point A 33 the columnar coal body reaches an adsorption saturation state, no adsorption action is generated on the gas, the corresponding adsorption expansion phenomenon is not generated, the axial strain and the radial strain of the coal body are continuously stabilized for a period of time, and the time corresponding to the point A 33 is the final moment when the columnar coal body reaches adsorption saturation. Therefore, compared with the radial strain curve, selecting the axial strain curve of the columnar coal body in fig. 3 facilitates the judgment of the starting and ending moments of the adsorption of the coal body to the gas.
(I) The key points are selected when the gas adsorption quantity is calculated: in fig. 3, the key points P 1 and a 11, the key points P 2 and a 22, and the key points P 3 and a 33 correspond to the same time points, respectively. Before the columnar coal body adsorbs CO 2 gas, the CO 2 reference cylinder gas pressure is rapidly reduced (corresponding to between points P 1 and P 2 in the graph of FIG. 3) under the influence of gas injection action, and meanwhile, the axial direction of the columnar coal body is compressed due to the axial injection of gas from the adder, so that the columnar coal body monitored by the first strain gauge is in a strain reduced state (corresponding to a point A 11 to a point A 22 on the axial strain curve in the graph of FIG. 3); as the columnar coal begins to adsorb CO 2 gas, the columnar coal undergoes adsorption expansion (corresponding to point a 22 in fig. 3), and when adsorbed to the time coordinate corresponding to point a 33 on the axial strain curve in fig. 3, the axial strain monitored by the first strain gauge remains substantially unchanged, while the radial strain monitored by the second strain gauge remains substantially unchanged. Meanwhile, as can be seen from fig. 3, during the adsorption period of the columnar coal body on the CO 2 gas (between the point a 22 and the point a 33 in fig. 3), the CO 2 refers to the continuous decrease of the gas pressure in the cylinder (between the point P 2 and the point P 3 in fig. 3), and the gas pressure data P 2、P3 corresponding to the key point P 2 and the point P 3 are selected and stored in the computer respectively, so as to provide parameters for the next step of calculating the gas adsorption amount of the coal body.
(J) In-situ coal gas adsorption amount calculation: the specific method for calculating the in-situ coal gas adsorption amount comprises the following steps:
The computer calculates the gas adsorption quantity n 2、n3 corresponding to the P 2、P3 in the step (i) according to the real gas state equation n i＝PiV/(Zi RT) by programming; wherein P i is gas pressure (10 -3 MPa), V is the volume of a gas reference cylinder (cm 3),Zi is a compression factor corresponding to gas under the gas pressure P i, R is a gas constant, T is temperature (K), and n i is the molar quantity (mol) of the gas after n 2、n3 is calculated, the computer is programmed according to the formula delta n=n 2-n3, and the calculated delta n is the adsorption quantity of the coal body to CO 2 gas in the simulated in-situ state;
(k) After the in-situ coal adsorption capacity is calculated, closing a seventh valve and an eighth valve, opening a third valve, a fourth valve and a fifth valve, and starting a vacuum pump to vacuumize the clamp holder; the steps (c), (d), (e), (f), (g), (h) and (i) can be repeated, the stress state of the coal body, the water content of the coal body and the gas injection pressure are changed, the test experiment of the in-situ coal body on the CO 2 gas adsorption capacity under different conditions is further developed, finally, the influence rule of stress, water content and gas pressure on the in-situ coal body on the CO 2 gas adsorption capacity is summarized, and a basis is provided for researching the evaluation of the coal body on the gas adsorption capacity under different geological background conditions.
In the method, the selection of the strain curve during the calculation of the gas adsorption quantity is based on the axial strain curve recorded by the strain gauge, and the starting time and the ending time of the adsorption of the coal body are judged. In the process of calculating the gas adsorption quantity, the turning point of the axial strain curve is taken as the starting time of adsorption of the coal body, and the stable and unchanged position of the axial strain curve is taken as the end time of adsorption saturation of the coal body. When the gas adsorption quantity is calculated, the reference cylinder volume is a known fixed volume, and the reduction quantity of the reference cylinder gas at the adsorption starting time and the adsorption ending time is obtained by using a real gas state equation by taking the gas molar mass as a unit, namely the gas adsorption quantity of the in-situ coal body in a simulation state.
The invention can change the opening and closing conditions of the valve by using the same method to research the influence rule of the in-situ coal body on the adsorption quantity of CH 4 gas. The method comprises the following steps: in the step (f), all valves except the first valve, the fourth valve and the CH 4 reference cylinder inlet valve are closed, a gas booster pump is started to boost CH 4 gas to the CH 4 reference cylinder, and when the pressure value displayed by the first gas pressure gauge is higher than the highest experimental pressure value by 3MPa, the CH 4 reference cylinder inlet valve is closed, and the pressurization is stopped;
And (c) in the step (g), ensuring that the columnar coal body in the clamp holder is adsorbed in a steady state under a constant pressure, sequentially opening a CH 4 reference cylinder outlet valve, a seventh valve, an eighth valve and a sixth valve to inject CH 4 gas into the columnar coal body, carrying out an adsorption experiment, and calculating the adsorption quantity of the in-situ coal body to CH 4 gas.
No matter the coal dust or the coal body adsorbs the gas, the adsorption expansion phenomenon only affects the free space volume of the sample cylinder, and has no influence on the free space volume of the gas reference cylinder. Under the influence of the gas adsorption effect of the coal body in the sample cylinder, the pressure of the gas in the reference cylinder is inevitably reduced, and under the condition that the free space volume of the gas reference cylinder is unchanged, when the pressure values of the gas in the gas reference cylinder before and after sample adsorption balance are acquired, the reduction of the gas in the gas reference cylinder can be obtained by further adopting a real gas state equation, and the value is the adsorption quantity of the coal body to the gas. The invention takes the free space volume of the sample cylinder as a reference, but takes the fact that the free space volumes of the gas reference cylinders before and after the adsorption balance of the coal body are not changed as an important point, and starts with the pressure change of the gas reference cylinders before and after the adsorption balance of the coal body, thereby testing the adsorption quantity of the coal body to the gas, and effectively overcoming the defect that the conventional capacity method obtains the gas adsorption quantity based on the free space volume of the sample cylinder. Because the adsorption of coal to gas is a phenomenon of molecular level and is invisible in macroscopic scale, but the expansion deformation behavior in the process of adsorbing gas by coal can be carried out by adopting a strain measurement means, after the strain curve of the expansion deformation of the gas by coal is obtained, respectively selecting time nodes of the adsorption expansion of the coal and the adsorption expansion strain balance of the coal on the strain curve as key points, and determining the gas pressure value in the gas reference cylinder corresponding to the key points by using the time nodes, so that the pressure value of the gas in the gas reference cylinder before and after the sample adsorption balance can be obtained.
The invention discloses an in-situ coal gas adsorption capacity test simulation device, which adopts coal to replace pulverized coal, adopts a hydraulic servo system to carry out stress loading on the coal, uses dynamic change characteristics of the strain of the coal in the gas adsorption process to reflect the adsorption dynamics process of the coal on the gas, uses a time node before and after the coal reaches adsorption equilibrium as a key point, further determines the pressure change of a gas reference cylinder caused by the adsorption of the coal, and further obtains the adsorption capacity of the coal on the gas under the simulated in-situ condition by combining a real gas state equation.
The above description is only of the preferred embodiments of the present invention, and is not intended to limit the invention in any way, and any simple modification, equivalent variations and adaptations of the embodiments according to the technical principles of the present invention, which are within the scope of the technical solutions of the present invention, will be apparent to those skilled in the art without departing from the scope of the technical solutions of the present invention.
Claims (9)
1. The in-situ coal gas adsorption quantity test method is characterized by using an in-situ coal gas adsorption quantity test simulation device, wherein the in-situ coal gas adsorption quantity test simulation device comprises an in-situ coal gas simulation system, a coal water injection system, an adsorption balance system, an adsorption monitoring system and a data acquisition and analysis system;
The in-situ coal body simulation system comprises a clamp holder (11), an electric heater (12), a columnar coal body (13) and a hydraulic servo system; the hydraulic servo system comprises a hydraulic pump (14), a confining pressure loader (15) and a shaft pressure loader (16); wherein, the electric heater (12) is arranged on the outer surface of the clamp holder (11) through a base and heats the clamp holder (11) to enable the temperature inside the clamp holder to reach the preset temperature; the columnar coal body (13) is arranged in the clamp holder (11), the hydraulic pump (14) is connected with the confining pressure loader (15) and the axial pressure loader (16) through the hydraulic pipeline (17) and the overflow valve (18), the confining pressure loader (15) is arranged on the outer surface of the clamp holder (11), and the axial pressure loader (16) is arranged at the left end of the clamp holder (11);
The coal body water injection system comprises a water storage tank (21), a high-pressure water pump (22), a water flow valve (23), a water pressure meter (24) and a water flow meter (25), wherein the high-pressure water pump (22), the water flow valve (23), the water pressure meter (24) and the water flow meter (25) are arranged on a water injection pipeline (5), the water storage tank (21) is connected with a clamp holder (11) through the water injection pipeline (5), and the high-pressure water pump (22), the water flow valve (23), the water pressure meter (24) and the water flow meter (25) are sequentially arranged on the water injection pipeline (5) along the direction from the water storage tank to the clamp holder;
The adsorption balance system comprises a holder outlet valve (31), a CH 4 gas cylinder (32), a CO 2 gas cylinder (33), a gas booster pump (34), a CH 4 reference cylinder (35), a CO 2 reference cylinder (36), a first valve (37) arranged on an output pipeline of the CH 4 gas cylinder (32), a second valve (38) arranged on an output pipeline of the CO 2 gas cylinder (33), a third valve (39) arranged on a vacuumizing pipeline (3) of a vacuum pump (43), A fourth valve (40), a fifth valve (41), a sixth valve (42), a vacuum pump (43), a CH 4 reference cylinder inlet valve (44), a CH 4 reference cylinder outlet valve (45), a CO 2 reference cylinder inlet valve (46), a CO 2 reference cylinder outlet valve (47), a seventh valve (48) and an eighth valve (49) which are arranged at the outlet of the gas booster pump (34); the CH 4 gas cylinder (32) and the CO 2 gas cylinder (33) are connected with the gas booster pump (34), the vacuum pump (43) is arranged behind the CH 4 gas cylinder (32) and the CO 2 gas cylinder (33) and in front of the gas booster pump (34), and the CH 4 reference cylinder (35) and the CO 2 reference cylinder (36) are sequentially arranged behind the gas booster pump (34); the vacuum pump (43) is connected with the gas conveying pipeline (1) through the vacuumizing pipeline (3);
the adsorption monitoring system comprises a first gas pressure gauge (51) arranged at the inlet end of a CH 4 reference cylinder (35), a second gas pressure gauge (52) arranged at the inlet end of a CO 2 reference cylinder (36), a third gas pressure gauge (53), a gas pressure automatic tracker (54) arranged behind the CH 4 reference cylinder (35) and the CO 2 reference cylinder (36), a first gas flow meter (55), a first strain gauge (56), a second strain gauge (57) and a second gas flow meter (58); the seventh valve (48) and the eighth valve (49) are respectively arranged at two ends of the automatic gas pressure tracker (54); the left end of the seventh valve (48) and the right end of the eighth valve (49) are also connected with an auxiliary pipeline (4) provided with a fifth valve (41), the auxiliary pipeline (4) is connected in parallel with a gas output pipeline (2) where a gas pressure automatic tracker (54) is arranged, and a third gas pressure gauge (53), a first gas flowmeter (55) and a sixth valve (42) are sequentially arranged on the gas output pipeline behind the eighth valve (49); the first strain gauge (56) is axially arranged on the surface of the columnar coal body (13), and the second strain gauge (57) is radially arranged on the surface of the columnar coal body (13); a second gas flow meter (58) is arranged after the holder outlet valve (31);
The data acquisition and analysis system comprises a data acquisition box (61) and a computer (62), wherein the data acquisition box (61) is connected with the hydraulic pump (14), the first gas pressure gauge (51), the second gas pressure gauge (52), the third gas pressure gauge (53), the gas pressure automatic tracker (54), the first gas flow meter (55), the second gas flow meter (58), the first strain gauge (56), the second strain gauge (57) and the computer (62) through data lines;
The in-situ coal gas adsorption amount testing method comprises the following steps:
(1) Sample preparation: drilling columnar coal bodies along the vertical bedding direction, and polishing rough surfaces on the positions of the columnar coal body surfaces, which are respectively pre-adhered with strain gauges along the axial direction and the radial direction, by using sand paper; respectively sticking a first strain gauge on the surface of the columnar coal body along the axial direction and a second strain gauge along the radial direction;
(2) Sample mounting: opening the clamp holder, putting the columnar coal body stuck with the strain gauge into the clamp holder, and connecting the first strain gauge and the second strain gauge to the data acquisition box by using a data wire; the electric heater is started to heat the clamp holder to the experimental temperature, so that the columnar coal body is ensured to be in the set temperature environment;
(3) And (3) alternately loading confining pressure and axial pressure: the hydraulic servo system is connected, and the hydraulic servo system is operated according to the principle of firstly adding confining pressure and then adding shaft pressure, and comprises the following operation steps of: a. firstly, starting a hydraulic pump, and suspending loading after applying confining pressure of 2MPa to a columnar coal body by using a confining pressure loader; b. opening the axial pressure loader to apply an axial pressure of 2MPa to the columnar coal body, then suspending loading, repeating the steps a and b until the axial pressure and the confining pressure are both in a stress state set in an experiment, and closing the hydraulic pump;
(4) And (3) air tightness test: after the confining pressure and the shaft pressure are alternately loaded, firstly closing all valves, then opening a third valve, a fourth valve, a CH 4 reference cylinder inlet valve, a CH 4 reference cylinder outlet valve, a CO 2 reference cylinder inlet valve, a CO 2 reference cylinder outlet valve, a fifth valve and a sixth valve, starting a vacuum pump to vacuumize the whole device system until the pressure values of a first gas pressure gauge, a second gas pressure gauge and a third gas pressure gauge are all-0.1 MPa, then closing the third valve, and observing whether the pressure values are stable; if the pressure value is kept stable, then carrying out the step (5); if the pressure value is unstable, repeating the steps (2) and (3);
(5) And (3) water injection: after the air tightness is checked, starting a high-pressure water pump, opening a water flow valve, keeping the value of a water pressure meter to be 2 MPa, injecting water to the columnar coal body, and closing the water flow valve to finish water injection when the value displayed by the water flow meter is a preset water injection volume;
(6) Steady-state adsorption gas source preparation: closing all valves except the second valve, the fourth valve and the CO 2 reference cylinder inlet valve, starting a gas booster pump to boost CO 2 gas to the CO 2 reference cylinder, and closing the CO 2 reference cylinder inlet valve to stop boosting when the pressure value displayed by the second gas pressure gauge is higher than the highest experimental pressure value of 3 MPa;
(7) Gas injection adsorption: after the steady-state adsorption gas source preparation is completed, all valves are closed, an automatic gas pressure tracker is set as an experimental pressure value, the gas pressure injected into the columnar coal body is controlled to be the set experimental pressure value all the time, steady-state adsorption of the columnar coal body in the clamp holder is ensured under constant pressure, then a CO 2 reference cylinder outlet valve, a seventh valve, an eighth valve and a sixth valve are sequentially opened to inject CO 2 gas into the columnar coal body, an adsorption experiment is carried out, and a first gas flowmeter collects the gas quantity injected into the clamp holder; in the experimental process, a computer records axial strain data, radial strain data and CO 2 reference cylinder gas pressure change data, curves are formed on a graph, when the axial strain data, the radial strain data and the CO 2 reference cylinder gas pressure data are stable and unchanged, the gas injection adsorption experiment is ended, then all valves are closed, an outlet valve of a clamp holder is opened to discharge CO 2 gas in the clamp holder, a second gas flowmeter collects the amount of gas discharged by the clamp holder, then all valves except a third valve, a fourth valve, a fifth valve and a sixth valve are closed, a vacuum pump is started to vacuumize a columnar coal body, residual CO 2 gas in the coal body is removed, and the experiment is ended;
(8) Judging key points under the adsorption action: selecting a turning point of the axial strain curve as a starting time of adsorption of the coal body based on the axial strain curve of the coal body recorded by the first strain sheet, and selecting a stable and unchanged position of the axial strain curve as an end time of adsorption saturation of the coal body, wherein the starting time and the end time respectively correspond to pressure data P 2 and P 3 on a CO 2 reference cylinder gas pressure change curve; during the adsorption of the coal, the pressure of CO 2 in the reference cylinder is reduced from P 2 to P 3, and the reduction amount of CO 2 in the reference cylinder is the adsorption amount of the coal on CO 2 in a simulated state;
(9) Calculation of gas adsorption amount: calculating gas adsorption quantity by taking gas molar quantity as unit, and according to a real gas state equation Calculating the gas molar quantity n 2、n3 corresponding to P 2、P3, and then calculating the adsorption quantity delta n of the coal body to the CO 2 gas in the simulated in-situ state according to a formula delta n=n 2-n3; true gas State equation/>Where P i is the gas pressure, V is the volume of the gas reference cylinder, Z i is the compression factor corresponding to the gas at gas pressure P i, R is the gas constant, T is the temperature, and n i is the molar amount of the gas.
2. The method for in-situ coal gas adsorption test as recited in claim 1, wherein said CH 4 reference cylinder (35) and CO 2 reference cylinder (36) are fixed volume rigid cylinders of precise constant value.
3. An in situ coal gas adsorption test method as claimed in claim 1, wherein the columnar coal (13) has a diameter of 50 cm and a length of 100 cm.
4. An in situ coal gas adsorption test method as claimed in claim 1 wherein the first gas pressure gauge (51), the second gas pressure gauge (52) and the third gas pressure gauge (53) are 0.01 MPa in accuracy.
5. An in situ coal gas adsorption test as claimed in claim 1 wherein the first strain gauge (56) and the second strain gauge (57) are accurate to 10 -8.
6. The method for testing the gas adsorption quantity of the in-situ coal body according to claim 1, wherein in the stress loading process of the step (3), in order to prevent the columnar coal body from cracking, a stress control mode is adopted for loading, and the loading speed is less than or equal to 0.05 MPa/s.
7. The method for in-situ coal gas adsorption test according to claim 1, wherein the experimental temperature in the step (2) is 25-30 ℃, the stress experimentally set in the step (3) is 8-50 MPa, and the water injection volume preset in the step (5) is 5-30 mL.
8. The method for testing the in-situ coal gas adsorption amount according to claim 1, wherein after the calculation of the in-situ coal gas adsorption amount, a vacuum pump is started to vacuumize the clamp holder; and (3) repeating the steps (3), (4), (5), (6), (7), (8) and (9), further carrying out test experiments of the gas adsorption capacity of the in-situ coal under different conditions by changing the stress state of the coal, the water content of the coal and the gas injection pressure, and finally summarizing the influence rules of stress, water content and gas pressure on the gas adsorption capacity of the in-situ coal, thereby providing a basis for researching the evaluation of the gas adsorption capacity of the coal under different geological background conditions.
9. An in situ coal gas adsorption test method as claimed in any one of claims 1 to 8 for simulating in situ coal gas adsorption of CH 4 and/or CO 2.
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