CN110082280B - Device and method for simulating and testing coalbed methane productivity change caused by discontinuous drainage - Google Patents
Device and method for simulating and testing coalbed methane productivity change caused by discontinuous drainage Download PDFInfo
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- CN110082280B CN110082280B CN201910522748.0A CN201910522748A CN110082280B CN 110082280 B CN110082280 B CN 110082280B CN 201910522748 A CN201910522748 A CN 201910522748A CN 110082280 B CN110082280 B CN 110082280B
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- 238000012360 testing method Methods 0.000 title claims abstract description 88
- 230000008859 change Effects 0.000 title claims abstract description 52
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 36
- 238000000034 method Methods 0.000 title claims abstract description 21
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 170
- 238000004088 simulation Methods 0.000 claims abstract description 105
- 230000035699 permeability Effects 0.000 claims abstract description 92
- 238000002474 experimental method Methods 0.000 claims abstract description 60
- 238000003795 desorption Methods 0.000 claims abstract description 44
- 238000012545 processing Methods 0.000 claims abstract description 39
- 238000001514 detection method Methods 0.000 claims abstract description 34
- 238000004519 manufacturing process Methods 0.000 claims abstract description 28
- 230000007246 mechanism Effects 0.000 claims abstract description 24
- 230000005540 biological transmission Effects 0.000 claims abstract description 17
- 238000005192 partition Methods 0.000 claims abstract description 11
- 238000010998 test method Methods 0.000 claims abstract description 6
- 238000007405 data analysis Methods 0.000 claims abstract description 4
- 239000007789 gas Substances 0.000 claims description 186
- 238000003860 storage Methods 0.000 claims description 94
- 239000007788 liquid Substances 0.000 claims description 45
- 239000011435 rock Substances 0.000 claims description 16
- 230000005514 two-phase flow Effects 0.000 claims description 15
- 230000001105 regulatory effect Effects 0.000 claims description 12
- 230000001502 supplementing effect Effects 0.000 claims description 10
- 238000007599 discharging Methods 0.000 claims description 9
- 230000008569 process Effects 0.000 claims description 9
- 230000009467 reduction Effects 0.000 claims description 9
- 238000000926 separation method Methods 0.000 claims description 9
- 238000005065 mining Methods 0.000 claims description 4
- 238000009826 distribution Methods 0.000 claims description 3
- 230000006698 induction Effects 0.000 claims description 3
- 239000011261 inert gas Substances 0.000 claims description 3
- 230000006855 networking Effects 0.000 claims description 3
- 238000004458 analytical method Methods 0.000 claims description 2
- 238000004891 communication Methods 0.000 claims description 2
- 238000004364 calculation method Methods 0.000 claims 1
- 230000006837 decompression Effects 0.000 claims 1
- 238000005070 sampling Methods 0.000 claims 1
- 239000003245 coal Substances 0.000 abstract description 39
- 238000006073 displacement reaction Methods 0.000 abstract description 5
- 238000012544 monitoring process Methods 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 7
- 239000012530 fluid Substances 0.000 description 6
- 238000011160 research Methods 0.000 description 5
- 230000003139 buffering effect Effects 0.000 description 3
- 238000007689 inspection Methods 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000010354 integration Effects 0.000 description 2
- 230000001788 irregular Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000003068 static effect Effects 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 230000008676 import Effects 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 230000008439 repair process Effects 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/0806—Details, e.g. sample holders, mounting samples for testing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/082—Investigating permeability by forcing a fluid through a sample
- G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N7/00—Analysing materials by measuring the pressure or volume of a gas or vapour
- G01N7/14—Analysing materials by measuring the pressure or volume of a gas or vapour by allowing the material to emit a gas or vapour, e.g. water vapour, and measuring a pressure or volume difference
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Abstract
The invention relates to a simulated testing device for coalbed methane productivity change caused by discontinuous drainage, which comprises a wellhead device simulation device, a permeability testing device, a hydraulic pressure transmission simulation device, a gas desorption simulation device, an experiment cabinet and a data acquisition and processing device, wherein the experiment cabinet is divided into an experiment detection cavity, three experiment driving cavities and a control cavity by a partition board, the permeability testing device is positioned in the experiment detection cavity, and the wellhead device simulation device, the hydraulic pressure transmission simulation device and the gas desorption simulation device are respectively positioned in each experiment driving cavity and are respectively communicated with the permeability testing device. The method comprises the experimental steps of equipment assembly, setting initial experimental parameters, displacement operation, experimental detection, data analysis and test ending. The invention can effectively improve the working efficiency and the detection precision of the detection operation on one hand, has low test risk on the other hand, has convenient and accurate test method, has high similarity with the mechanism of the coal bed gas drainage and production water and can realize dynamic monitoring.
Description
Technical Field
The invention belongs to the technical field of coal mine safety, and particularly relates to a device and a method for simulating and testing coalbed methane productivity change caused by discontinuous drainage.
Background
The surface coal-bed gas well is produced by desorbing the coal-bed gas by discharging water in the coal-bed to lower the reservoir pressure. The drainage work is longest in the whole coal bed gas development process, and when the coal bed gas well is drained, the discontinuous drainage of the coal bed gas well caused by the reasons such as power failure and pump detection well repairing operation of a generator and the like can be avoided. When the drainage and production equipment stops running in the single-phase water flow stage, the working fluid level in the coal bed gas well can rise, water in the coal bed is gradually changed from a flowing state to a static state, and the effective stress value born by the coal bed can be changed, so that the permeability of the coal bed is changed. When the method is restarted, the difference of starting pressure gradients required by water flow is caused due to the change of the permeability of the coal bed, so that not only is the drainage and production influence radius of the coal bed gas well influenced, but also the gas production of the coal bed gas well is influenced; in the gas/water two-phase flow phase, the bottom hole pressure rise caused by the pump stopping can not only cause the change of the water flowing state, but also influence the distribution of the reservoir pressure and the gas flowing state, thereby changing the gas production of the coal bed gas.
Currently, there is relatively little research on changes in permeability and productivity of coal seams caused by discontinuous drainage. More research is being conducted on the relationship between effective stress changes and permeability of coal seams caused by drainage. The method is mainly characterized in that parameters such as confining pressure, injected gas pressure and the like of a coal pillar are changed in a laboratory, and the change of flow is tested, so that the permeability of the coal pillar under different effective stresses is calculated, and the change of the permeability along with the effective stress in a negative index is obtained. However, after the on-site coal-bed gas well stops discharging, a certain time is needed from slow flowing to static of water in the coal bed, and the difference of the discharging stopping time leads to the difference of water flowing distance, flowing quantity and the like in the coal bed, so that the difference of the influence of the water flowing distance, the flowing quantity and the like on the permeability and the productivity of the coal bed is caused; meanwhile, the coal-bed gas well can stop discharging in a single-phase water flow stage and also can stop discharging in a gas/water two-phase flow stage, when the gas/water two-phase flow stage stops discharging, the bottom hole pressure rise can cause that part of free gas is adsorbed again, so that the normal output of the coal-bed gas is influenced, and the productivity of the coal-bed gas well is influenced. At present, experiments performed in a laboratory cannot test the drainage of a coal-bed gas well in different drainage stages and a series of changes caused by the change of fluid flow states such as water, gas and the like after the drainage, and cannot more accurately answer the changes of the capacity of the coal-bed gas caused by the drainage time, drainage stopping times and the like of the coal-bed gas well in different drainage stages such as a single-phase water flow stage or a gas/water two-phase flow stage and the like.
In order to find out the capacity change of the coal-bed gas well caused by different drainage time and drainage times in different drainage stages such as a single-phase water flow stage and a gas/water two-phase flow stage, a simulation test device for the capacity change of the coal-bed gas caused by discontinuous drainage is specially developed, so that guidance is provided for a drainage work system, pump inspection and well repair time and the like of the on-site coal-bed gas well.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a device and a method for simulating and testing the productivity change of coal bed gas caused by discontinuous drainage.
In order to achieve the above object, the present invention is realized by the following technical scheme:
the utility model provides a coalbed methane productivity change simulation testing arrangement that discontinuous drainage arouses, includes wellhead assembly analogue means, permeability testing arrangement, hydraulic propagation analogue means, gaseous desorption analogue means, experiment cabinet and data acquisition processing apparatus, and the experiment cabinet is the airtight cavity structure that axis and horizontal plane vertically distributed, equipartition a plurality of baffles in the experiment cabinet to divide into an experiment detection chamber, three experiment drive chamber and a control chamber with the experiment cabinet through the baffle, wherein permeability testing arrangement at least one, be located the experiment detection chamber, wellhead assembly analogue means, hydraulic propagation analogue means, gaseous desorption analogue means are located each experiment drive chamber respectively and communicate with permeability testing arrangement respectively, wherein permeability testing arrangement one end communicates with wellhead assembly analogue means through honeycomb duct, gaseous desorption analogue means respectively, and hydraulic propagation analogue means, gaseous desorption analogue means are parallelly connected each other, data acquisition processing apparatus is located the control chamber, and is connected with wellhead assembly analogue means, permeability testing arrangement, hydraulic propagation analogue means, gaseous desorption analogue means electric connection respectively.
Further, an operation door is arranged on the front end face and the rear end face of the experiment cabinet, which correspond to the experiment detection cavity, the experiment driving cavity and the control cavity, wherein the experiment detection cavity is located at the center of the experiment cabinet, the experiment driving cavity and the control cavity are uniformly distributed around the experiment detection cavity, the control cavity is located under the experiment detection cavity, and at least two guide sliding rails are arranged on the upper end face of the partition plate at the bottom of the control cavity and are electrically connected with the data acquisition and processing device through the guide sliding rails.
Further, the wellhead device simulation device comprises a buffer bottle I, a hydraulic pressure differential pressure one-way control valve, a gas flowmeter, a gas-liquid separation tank and a gas collecting and processing mechanism, wherein two ends of the gas flowmeter are respectively communicated with the gas collecting and processing mechanism and the gas-liquid separation tank, the gas-liquid separation tank is communicated with the buffer bottle I through the hydraulic pressure differential pressure control valve, the buffer bottle I is further communicated with a permeability test device, and the hydraulic pressure differential pressure one-way control valve, the gas flowmeter and the gas collecting and processing mechanism are electrically connected with a data collecting and processing device.
Further, the permeability testing device comprises an inlet pressure gauge, an outlet pressure gauge, a liquid flowmeter, a core holder and a buffer bottle II, wherein the core holder comprises a bearing shell, an axial pressure piston, an elastic bearing sleeve, a flow guide pipe, a hydraulic driving mechanism and a stress induction gasket, wherein the bearing shell is a closed cavity mechanism with axes distributed horizontally in parallel, the outer surfaces of the bearing shell are connected with a partition plate through a positioning mechanism, the axial pressure pistons are two in total and embedded in the bearing shell and are coaxially distributed with the bearing shell, the two axial pressure pistons are symmetrically distributed at the middle points of the bearing shell and are slidably connected with the inner surface of the bearing shell, the elastic bearing sleeve is of a closed cavity structure and is coaxially distributed with the bearing shell, the two ends of the elastic bearing sleeve are respectively connected with the axial pressure pistons, the interval between the outer side surface of the elastic bearing sleeve and the inner side surface of the bearing shell is not less than 5 mm, the two guide pipes are uniformly distributed around the axis of the elastic bearing sleeve and embedded in the elastic bearing sleeve, the two guide pipes are respectively positioned at two ends of the bearing shell and are coaxially distributed with the bearing shell, the front end face of each guide pipe is embedded in the bearing shell and is mutually communicated with the side end face of the elastic bearing sleeve, through holes are respectively arranged on the bearing shell corresponding to the guide pipes and the axial pressure piston and are coaxially distributed with the guide pipe, at least one pressure regulating port is arranged on the side end face of the bearing shell corresponding to the axial pressure piston, at least one pressure regulating port is arranged on the side surface of the bearing shell corresponding to the elastic bearing sleeve, all the pressure regulating ports are mutually connected in parallel and are respectively mutually communicated with the hydraulic driving mechanism, in the guide pipe, the end of the inlet of the bearing shell is communicated with the buffer bottle II through the guide pipe inlet pressure gauge, the honeycomb duct that is located the shell export one end of bearing carries out the intercommunication of export manometer and wellhead device analogue means's buffering bottle I, and export manometer and I construction liquid flowmeter intercommunication each other of buffering bottle, buffering bottle II communicates each other with water pressure propagation analogue means, gaseous desorption analogue means respectively through the three-way valve, wherein import manometer, export manometer, liquid flowmeter and the hydraulic drive mechanism of rock core holder, stress-sensing gasket all are connected with data acquisition processing apparatus electricity.
Further, the water pressure propagation simulation device comprises a constant-pressure water storage tank, a constant-volume water storage tank, a hydraulic pressure differential unidirectional control valve, a liquid pressure gauge and a liquid supplementing device, wherein one end of the constant-pressure water storage tank is communicated with the liquid supplementing device, the other end of the constant-pressure water storage tank is communicated with the constant-volume water storage tank, the constant-volume water storage tank is communicated with a buffer bottle II of the permeability testing device, at least two constant-volume water storage tanks are communicated with the constant-pressure water storage tank and the buffer bottle II and two adjacent constant-volume water storage tanks through the hydraulic pressure differential unidirectional control valves, a liquid pressure gauge is arranged between the hydraulic pressure differential unidirectional control valve which is communicated with the buffer bottle II and the constant-volume water storage tank which is communicated with the constant-volume water storage tank, and the hydraulic pressure differential unidirectional control valve, the liquid pressure gauge and the liquid supplementing device are electrically connected with the data acquisition and processing device.
Further, the gas desorption simulation device comprises a gas supplementing device, a constant-pressure gas storage tank, a constant-volume gas storage tank, a pressure differential unidirectional control valve, a switch and a gas flowmeter, wherein a plurality of constant-volume gas storage tanks are connected in series, two pressure differential unidirectional control valves are respectively arranged at the connecting end of one constant-volume gas storage tank to form a working group, the working groups are connected in parallel, one end of each working group is communicated with the constant-pressure gas storage tank through a flow guide pipe after being connected in parallel, the other end of each working group is communicated with a buffer bottle II of the permeability testing device through the switch, two adjacent working groups are connected in parallel through the switch, a gas flowmeter is arranged at the switch connected with the buffer bottle II in the switch, the gas supplementing device is communicated with the constant-pressure gas storage tank, and the gas supplementing device, the pressure differential unidirectional control valve, the switch and the gas flowmeter are all electrically connected with the data acquisition processing device.
Further, the data acquisition and processing device comprises at least one driving circuit based on an industrial computer and at least one data control platform based on a PC computer.
A testing method of a coalbed methane productivity change simulation testing device caused by discontinuous drainage comprises the following steps:
s1, equipment is assembled, firstly, a wellhead device simulation device, a permeability testing device, a water pressure propagation simulation device, a gas desorption simulation device, an experiment cabinet and a data acquisition processing device which form the novel equipment are connected, and a control device is respectively connected with an external driving circuit and a data transmission network device to complete the novel equipment networking for standby, wherein after the equipment is assembled, the wellhead device simulation device, the permeability testing device, the water pressure propagation simulation device and the gas desorption simulation device are mutually communicated, then inert gas with the pressure of 2MPa is injected into an assembled system, the pressure is maintained for 12-24 hours, and the residual pressure in the system after the pressure is maintained is not more than 1.9MPa, so that the air tightness of the system meets the use requirement, then the pressure is released, a plurality of rock samples are prepared according to the use requirement after the pressure release, the rock samples for detection are respectively embedded into one permeability testing device, and then the system is restored for standby;
S2, setting initial experimental parameters, firstly opening all differential pressure control valves in the water pressure propagation simulation device, regulating the differential pressure value to be the lowest, closing a switch at the water path communication position of the gas path, only enabling the wellhead device simulation device, the permeability test device and the water pressure propagation simulation device to be mutually communicated, filling water into each constant-pressure water storage tank, the constant-volume water storage tank and the buffer bottle I and the buffer bottle II, enabling the pressure value of the liquid pressure gauge to be 2MPa, and enabling the pressure in the permeability test device, the wellhead device simulation device and the water pressure propagation simulation device to be 2MPa. And then regulating the pressure difference between the constant-pressure gas storage tank and the constant-volume gas storage tank to control the valve pressure value to be 0.9MPa, continuously injecting gas into the constant-pressure gas storage tank, and keeping the gas pressure in the constant-pressure gas storage tank to be 2MPa and the gas pressure in the constant-volume gas storage tank to be 1.1MPa.
S3, the permeability test operation is carried out, firstly, a data acquisition and processing device drives a core holder to operate according to experimental requirements, confining pressure and axial pressure are loaded on a rock sample in the core holder, when a pressure difference control valve pressure value in a wellhead device simulation device begins to be reduced, namely, after drainage begins to be carried out, liquid pressure in a buffer bottle 2 is continuously reduced, water is continuously fed into the buffer bottle 2 through the rock sample by the buffer bottle 1, at the moment, water inlet pressure gauge and water outlet pressure gauge readings are recorded as P1 and P2 respectively, liquid flowmeter readings at the outlet end of the core holder in unit time are q, and the initial permeability Kc of the core is calculated according to the viscosity mu of water and the length L of a phase rock sample and a classical formula is calculated by combining the permeability. Along with the continuous reduction of the pressure value of the pressure difference control valve in the wellhead device simulation device, the drainage and the production are continued, and the dynamic change of the instantaneous permeability Kt of the rock sample in the single-phase water stage can be monitored in real time.
S4, experimental detection, wherein in the permeability test process of the step S3, along with the change of the instantaneous permeability Kt along with time, the pressure difference control valve between each water storage tank of the water pressure propagation simulation device and the pressure difference control valve pressure value Pt between each constant-volume air storage tank and the buffer bottle 1 in the gas desorption simulation device are changed along with the change of the permeability, and the relation is Pt=0.3 MPa, K/Kt. Along with the reduction of the pressure value of the differential pressure control valve in the wellhead device simulation device, in the continuous process of drainage, recording the pressure gauge indication P2 in the wellhead device simulation device at any time as the change of the bottom hole flow pressure along with the time, recording the dynamic change of the instantaneous permeability Kt along with the time, recording the indication S1 in the unit time of the liquid flowmeter in the wellhead device simulation device before gas is not produced as the change of the water yield along with the time in the single-phase water flow stage, and recording the indication S2 in the unit time of the gas flowmeter in the wellhead device simulation device after gas is produced and the total indication Q as the change of the gas yield and the total gas yield along with the time in the unit time of the gas-water two-phase flow stage;
s5, data analysis, namely after the step S4 is completed, performing comparison analysis on all data recorded in the experimental process, and determining the influence of the stop times, stop time and the like on productivity in discontinuous drainage;
And S6, after the test is finished, releasing pressure, discharging all water in the device, closing all switches in the device, and treating the gas collected in the experimental process.
Compared with the prior art, the invention has the following beneficial effects: the device has simple structure, high degree of automation and integration of operation and control, and can effectively improve the working efficiency and the detection precision of detection operation; on the other hand, the test risk is low, the test method is convenient and accurate, the test can be carried out in a laboratory to dynamically monitor the discharge of the coal-bed gas well in different discharge and production stages and a series of changes caused by the change of fluid flow states such as water, gas and the like after the discharge, and the change of the capacity of the coal-bed gas caused by the discharge time, the discharge stopping times and the like in different discharge and production stages such as single-phase water flow stage or gas/water two-phase flow stage and the like of the coal-bed gas well can be accurately answered, so that guidance is provided for on-site coal-bed gas well discharge and production system, pump inspection and well repairing time and the like.
Drawings
The invention is described in detail below with reference to the drawings and the detailed description.
FIG. 1 is a schematic diagram of the structure of the present invention;
FIG. 2 is a schematic diagram of the closed state structure of the experimental cabinet;
FIG. 3 is a schematic diagram of a wellhead simulator;
FIG. 4 is a schematic diagram of a permeability test apparatus;
FIG. 5 is a schematic view of a hydraulic propagation simulator;
FIG. 6 is a schematic diagram of a gas desorption simulation apparatus;
FIG. 7 is a schematic diagram of the system operation principle structure of the present invention;
FIG. 8 is a schematic diagram of experimental data distribution in accordance with the present invention;
FIG. 9 is a flow chart of the experimental method of the present invention.
Detailed Description
The invention is further described in connection with the following detailed description, in order to make the technical means, the creation characteristics, the achievement of the purpose and the effect of the invention easy to understand.
The simulated test device for the coalbed methane productivity change caused by discontinuous drainage as shown in fig. 1-7 comprises a wellhead device simulation device 1, a permeability test device 2, a hydraulic pressure transmission simulation device 3, a gas desorption simulation device 4, an experiment cabinet 5 and a data acquisition and processing device 6, wherein the experiment cabinet 5 is of a closed cavity structure with an axis and a horizontal plane distributed vertically, a plurality of partition plates 7 are uniformly distributed in the experiment cabinet, the experiment cabinet 5 is divided into an experiment detection cavity 101, three experiment driving cavities 102 and a control cavity 103 through the partition plates 7, at least one permeability test device 2 is positioned in the experiment detection cavity 101, the wellhead device simulation device 1, the hydraulic pressure transmission simulation device 3 and the gas desorption simulation device 4 are respectively positioned in the experiment driving cavities 102 and are respectively communicated with the permeability test device 2, one end of the permeability test device 2 is respectively communicated with the wellhead device simulation device 1 through a flow guide pipe, the other end of the permeability test device 2 is respectively communicated with the hydraulic pressure transmission simulation device 3 and the gas desorption simulation device 4, the transmission simulation device 3 and the gas desorption simulation device 4 are mutually connected in parallel, and the data acquisition and processing device 6 is positioned in the control cavity 103 and is respectively connected with the wellhead device simulation device 1, the hydraulic pressure transmission simulation device 3 and the hydraulic pressure test device 4.
The experimental detection cavity 101, the experimental driving cavity 102 and the control cavity 103 are corresponding to the experimental cabinet 5, the front end face and the rear end face of the experimental cabinet 5 are respectively provided with an operation door 8, the experimental detection cavity 101 is located at the center of the experimental cabinet 5, the experimental driving cavity 102 and the control cavity 103 are evenly distributed around the experimental detection cavity 101, the control cavity 103 is located under the experimental detection cavity 101, and the upper end face of the partition board 7 at the bottom of the control cavity 103 is provided with at least two guide slide rails 9 and is electrically connected with the data acquisition and processing device 6 through the guide slide rails 9.
In this embodiment, the wellhead simulator 1 includes a buffer bottle i 11, a hydraulic pressure differential unidirectional control valve 12, a gas flowmeter 13, a gas-liquid separation tank 14, and a gas collecting and processing mechanism 15, where two ends of the gas flowmeter 13 are respectively communicated with the gas collecting and processing mechanism 15 and the gas-liquid separation tank 14, the gas-liquid separation tank 14 is mutually communicated with the buffer bottle i 11 through the hydraulic pressure differential control valve 12, the buffer bottle i 11 is further communicated with the permeability testing device 2, and the hydraulic pressure differential unidirectional control valve 12, the gas flowmeter 13, and the gas collecting and processing mechanism 15 are all electrically connected with the data collecting and processing device 6.
In this embodiment, the permeability testing device 2 includes an inlet pressure gauge 21, an outlet pressure gauge 22, a liquid flow meter 23, a core holder 25, and a buffer bottle ii 24, where the core holder 25 includes a bearing shell 251, an axial pressure piston 252, an elastic bearing sleeve 253, a flow guiding tube 254, a hydraulic driving mechanism 255, and a stress sensing gasket 256, where the bearing shell 251 is a closed cavity mechanism with an axis parallel to the horizontal, the outer surface of the bearing shell is connected with the partition 7 through a positioning mechanism 257, the axial pressure pistons 252 are totally two, embedded in the bearing shell 251 and coaxially distributed with the bearing shell 251, the two axial pressure pistons 252 are symmetrically distributed at the midpoint of the bearing shell 251 and slidably connected with the inner surface of the bearing shell 251, the elastic bearing sleeve 253 is a closed cavity structure, embedded in the bearing shell 251 and coaxially distributed with the bearing shell 251, two ends of the elastic bearing sleeve 253 are respectively connected with the axial pressure pistons 252, the space between the outer side surface of the elastic bearing sleeve 253 and the inner side surface of the bearing shell 251 is not less than 5 mm, at least two stress-sensing gaskets 256 are uniformly distributed around the axis of the elastic bearing sleeve 253 and embedded in the elastic bearing sleeve 253, the two guide pipes 254 are respectively positioned at two ends of the bearing shell 251 and coaxially distributed with the bearing shell 251, wherein the front end surface of the guide pipe 254 is embedded in the bearing shell 251 and mutually communicated with the side end surface of the elastic bearing sleeve 253, through holes 258 are respectively arranged on the bearing shell 251 and the axial pressure piston 252 corresponding to the guide pipe 254, the through holes 258 are coaxially distributed with the guide pipe 254, at least one pressure regulating opening 259 is arranged on the side end surface of the bearing shell 251 corresponding to the axial pressure piston 252, at least one pressure regulating opening 259 is arranged on the side surface of the bearing shell 251 corresponding to the elastic bearing sleeve 253, the pressure regulating openings 259 are mutually parallel and mutually communicated with the hydraulic driving mechanism 255 respectively, in the guide pipe 254, the flow guide tube 254 at the inlet end of the bearing shell 251 is communicated with the buffer bottle II 24 through the inlet pressure gauge 21, the flow guide tube 254 at the outlet end of the bearing shell 21 is communicated with the buffer bottle I11 of the wellhead device simulation device 1 through the outlet pressure gauge 22, the outlet pressure gauge 22 and the buffer bottle I11 are mutually communicated with each other to construct a liquid flow meter 23, the buffer bottle II 24 is respectively mutually communicated with the water pressure propagation simulation device 3 and the gas desorption simulation device 4 through three-way valves, and the inlet pressure gauge 21, the outlet pressure gauge 22, the liquid flow meter 23, the hydraulic driving mechanism 255 of the core holder 25 and the stress induction gasket 256 are electrically connected with the data acquisition and processing device 6.
In this embodiment, the hydraulic propagation simulation device 3 includes a constant-pressure water storage tank 31, a constant-volume water storage tank 32, a hydraulic pressure differential unidirectional control valve 33, a liquid pressure gauge 34, and a liquid replenishing device 35, where one end of the constant-pressure water storage tank 31 is mutually communicated with the liquid replenishing device 35, the other end is mutually communicated with the constant-volume water storage tank 32, and is mutually communicated with the buffer bottle ii 24 of the permeability test device 2 through the constant-volume water storage tank 32, at least two constant-volume water storage tanks 32, and the constant-pressure water storage tank 32, the buffer bottle ii 31, the buffer bottle ii 24, and two adjacent constant-volume water storage tanks 32 are mutually communicated through the hydraulic pressure differential unidirectional control valve 33, and in the hydraulic pressure differential unidirectional control valve 33, a liquid pressure gauge 34 is disposed between the hydraulic pressure differential unidirectional control valve 33 mutually communicated with the buffer bottle ii and the constant-volume water storage tank 32, and the hydraulic pressure differential unidirectional control valve 34, and the liquid replenishing device 35 are electrically connected with the data acquisition processing device 6.
In this embodiment, the gas desorption simulation device 4 includes a gas replenishing device 41, a constant pressure gas storage tank 42, a constant volume gas storage tank 43, a pressure differential unidirectional control valve 44, a switch 45 and a gas flowmeter 46, where a plurality of constant volume gas storage tanks 43, two pressure differential unidirectional control valves 44 are respectively disposed at the connection ends of one constant volume gas storage tank 43 and are connected in series to form a working group, the working groups are connected in parallel, one end of each working group is communicated with the constant pressure gas storage tank 41 through a flow guide pipe, the other end of each working group is communicated with a buffer bottle II 24 of the permeability testing device 2 through the switch 45, and two adjacent working groups are connected in parallel through the switch 45, in the switch 45 connected with the buffer bottle II 24, a gas flowmeter 46 is disposed, the gas replenishing device 41 is communicated with the constant pressure gas storage tank 42, and the gas replenishing device 41, the pressure differential unidirectional control valve 44, the switch 45 and the gas flowmeter 46 are all electrically connected with the data collecting and processing device 6.
In this embodiment, the data acquisition and processing device includes at least one driving circuit based on an industrial computer and at least one data manipulation platform based on a PC computer.
As shown in fig. 8-9, the test method of the simulated test device for the coalbed methane productivity change caused by discontinuous drainage comprises the following steps:
s1, assembling equipment, namely connecting a wellhead device simulation device, a permeability testing device, a water pressure propagation simulation device, a gas desorption simulation device, an experiment cabinet and a data acquisition processing device which form the novel equipment, respectively connecting a control device with an external driving circuit and a data transmission network device to finish the novel equipment networking for standby, wherein after the equipment is assembled, the wellhead device simulation device, the permeability testing device, the water pressure propagation simulation device and the gas desorption simulation device are mutually communicated, then injecting inert gas with the pressure of 2MPa into an assembled system, then maintaining the pressure for 12-24 hours, and after the pressure is maintained, the residual pressure in the system is not more than 1.9MPa, proving that the air tightness of the system meets the use requirement, then releasing the pressure of the system, preparing coal samples with the diameter of 50mm and the length of 100mm according to the use requirement, embedding the rock samples into the permeability testing device, and then restoring the system for standby;
S2, setting initial experimental parameters, setting reservoir pressure Pa, coalbed methane critical desorption pressure Pb, hydraulic pressure propagation simulation device and differential pressure control valves Y4, Y3, Y2, Y1, Q1-2, Q2-2 and Q3-2 in the gas desorption simulation device aiming at the field specific conditions of a research area, setting Pc { specific values are determined according to the number n of water storage tanks, wherein Pc=x1X Pa/n, X1E (0, 1) is the experimental parameters such as the ratio of the minimum permeability to the original permeability of the single-phase water flow phase of the experimental well in the research area, and the like, setting the unit time deceleration of the working fluid level (bottom hole flow pressure) of a shaft according to a designed drainage working system, and controlling the change of the differential pressure value of a differential pressure electromagnetic valve H along with the time through a computer terminal program;
s3, preparing an experiment, namely driving the core holder to operate by a data acquisition and processing device according to experiment requirements, and loading confining pressure and axial pressure on a coal sample in the core holder. Then, each control valve of the hydraulic propagation simulation device is opened, the pressure value is regulated to be the lowest, the switch K1 is opened, the switches K5, K4, K3 and K2 are closed, the pressure value of the differential pressure control valve H is regulated to be the largest, the wellhead device simulation device, the permeability testing device and the hydraulic propagation simulation device are mutually communicated, the pressure in the wellhead device simulation device, the permeability testing device and the hydraulic propagation simulation device reaches the reservoir pressure Pa by continuously injecting water into the constant-pressure water storage tank L1, and the pressure difference value of each control valve of the hydraulic propagation simulation device is recovered to be an initial value Pc after the pressure indication is stable for 5 minutes and basically unchanged.
And the other end, the differential pressure control valves Q1-1, Q2-1, Q3-1 and Q4-1 are set to have fixed values Pa-Pb, the initial differential pressure values of Q1-2, Q2-2 and Q3-2 are set to be Pc, and the constant-volume gas storage tank G1 is continuously injected with gas to enable the pressure value of the constant-volume gas storage tank to reach the critical desorption pressure Pb, and the pressure is unchanged after the constant-volume gas storage tank is stabilized for 5 minutes, so that the experiment is ready.
It should be added that, in the experimental test process, the core original permeability is determined as K, the core permeability measured in the t time period is Kt, and the differential pressure values of the differential pressure control valves Y4, Y3, Y2, Y1, Q1-2, Q2-2, Q3-2 are changed along with the change of the core permeability, specifically, pt=pc×k/Kt.
S4, experimental detection:
(1) in the initial stage of the experiment, the pressure values at all nodes of the whole discontinuous drainage simulation test device are equal and are in a stable state.
(2) After the pressure difference value of the electromagnetic valve H begins to decrease according to the design speed reduction, fluid in the buffer bottle 2 flows out through the electromagnetic valve H, the internal pressure and the indication of the pressure gauge P4 are reduced, water in the buffer bottle 1 flows into the buffer bottle 2 through the core in the core holder under the action of the pressure difference, once the water passes through a coal pillar, a classical formula is calculated by combining the water phase permeability, the indication (displacement pressure) of the pressure gauge P3, the indication (outlet pressure) of the pressure gauge P4 and the indication (the flow of the water passing through the coal pillar in unit time) of the liquid flow meter in unit time, the original permeability Kc of the core can be calculated (wherein L is the length of the coal pillar, m; q is the flow of the water passing through the coal pillar in unit time, m3/s; mu is the viscosity of the water, mpa.s; r is the radius of the coal pillar, m; P1 is the pressure in the displacement, MPa; P2 is the outlet pressure and MPa).
(3) The drainage and collection are continued, and then the water in the constant-volume water storage tank L5 is transferred and supplied to the buffer bottle 1. Along with the continuous reduction of the pressure difference of the electromagnetic valve H, the water in the water storage tanks L4, L3, L2 and L1 is gradually transported and produced, the distance representing the propagation of the water pressure is continuously extended to the far distance, the dynamic change value Kt of the permeability along with time during the continuous outward extension of the water pressure can be calculated through the test mode in the step (2), and the dynamic change of the coal pillar permeability during the single-phase water flow drainage and mining stage can be monitored at any time.
(4) After the drainage period, the pressure in the buffer bottle 1 is reduced below the critical desorption pressure Pb, the gas in the constant-volume gas storage tank G5 starts to move towards the buffer bottle, the drainage enters a gas-water two-phase flow stage from a single-phase water flow stage, and the differential pressure values of the differential pressure control valves Y4, Y3, Y2, Y1, Q1-2, Q2-2 and Q3-2 are locked and do not change any more. Along with the continuous decrease of the pressure difference of the electromagnetic valve H, the water pressure continuously extends to the water storage tanks L4, L3 and L2, the corresponding switches K4, K3 and K2 are opened along with the continuous decrease of the pressure difference, the desorption output range of the coalbed methane is enlarged, and the gas in the constant-volume gas storage tanks G4, G3 and G2 is sequentially transported to the buffer bottle 1 for output.
The gas in the constant-pressure gas storage tank can be continuously supplied into the constant-volume gas storage tank with reduced pressure (the gas in the coal storage tank is continuously produced from the adsorption state to the free state), and the drainage and mining are changed from the single-phase water flow stage to the gas-water two-phase flow stage.
(5) When the pressure difference of the electromagnetic valve H1 is uniformly reduced, the water production and the gas production are relatively uniform, or the stable trend is changed, and when the pressure difference and the pressure drop of the electromagnetic valve H1 which are set at the beginning are uneven, or the middle of the electromagnetic valve H1 is stopped, the irregular change of the permeability leads to larger gas production resistance and the gas production capacity is influenced. And finally, observing the instantaneous capacity and the total capacity under different drainage and production working systems according to the indication numbers of the gas flow meters.
S5, data analysis, namely after the step S4 is completed, analyzing the influence of discontinuous drainage on the productivity of the coal bed gas by comparing the influence of the drainage stopping stage, drainage stopping time and drainage stopping times in the drainage working system on the dynamic change of the permeability of the single-phase water flow stage and the gas production rule of the gas-water two-phase flow stage;
s6, after the test is finished, closing all switches, collecting and treating the gas used in the test, discharging water in all devices, wiping the instrument clean, and finishing the test.
The device and the method for simulating and testing the coalbed methane productivity change caused by discontinuous drainage are expected to realize the aim:
(1) Simulating the whole process of hydraulic pressure transmission in a single-phase water flow stage and gas desorption in a gas/water two-phase flow stage of coal bed gas drainage and extraction;
(2) Testing dynamic change of core water phase permeability in discontinuous drainage single-phase water flow stage;
(3) Monitoring the dynamic change of gas production (enough gas source) in the discontinuous drainage gas-production water two-phase flow stage;
(4) And verifying the influence of discontinuous drainage and production caused by different shutdown times on gas production (capacity).
During detection operation, the connection mode of the simulated test device for the coalbed methane productivity change caused by discontinuous drainage is mainly as follows: taking reservoir pressure pa=2 MPa and critical desorption pressure pb=1.1 MPa as an example, setting the original differential pressure values of differential pressure control valves Y4, Y3, Y2 and Y1 to pc=0.3 MPa { specific values are determined according to the number n of the water storage tanks, wherein pc=x1×pa/n, and x1∈ (0, 1) is the ratio of the minimum permeability value to the original permeability value in the single-phase water flow stage of experimental well drainage in a research area }, and the size of the experimental coal pillar is 500mm in diameter and 100mm in length.
Before the experiment starts, an experiment core is filled in a core holder, the pressure difference control valve H is arranged in a pressure difference value in each unit time by taking 2 minutes as the unit time, and the pressure difference value is shown in fig. 7. The sudden rise part of the pressure value is the stop-discharge time period.
In the constant-pressure water storage tank L1, the constant-volume water storage tanks L2, L3, L4 and L5, the buffer bottle 1 and the buffer bottle 2 are filled with water, the pressure of the water reaches 2MPa of the reservoir pressure, the constant-pressure gas storage tank G1 is filled with gas, the pressure of the water reaches 2MPa, the constant-volume gas storage tanks G2, G3, G4 and G5 are filled with gas, and the pressure of the water reaches 1.1MPa of the critical desorption pressure. The switch K1 is opened, the switches K2, K3, K4 and K5 are closed, the whole system is in a stable state, and the pressures of all the positions of the passage are basically equal, and the pressure is 2MPa.
After the experiment is started, the water pressure in the buffer bottle 2 is reduced along with the reduction of the pressure value of the differential pressure control valve H, the indication number of the pressure gauge P4 is reduced along with the reduction of the water pressure in the buffer bottle 2, but as the water flow passes through the core in the core holder and a certain power (for example, 0.1 MPa) is needed, the indication number of the pressure gauge P3 is not reduced when the pressure value of the differential pressure control valve H is just reduced to 1.95, the water flow in the buffer bottle 1 can pass through the core after the pressure value of the pressure gauge H is reduced to below 1.9, the internal pressure of the buffer bottle can also be reduced, the constant-volume water storage tank can be supplied to the buffer bottle, the water pressure starts to spread to the coal seam, the pressure in the buffer bottle 1 and the constant-volume water storage tank L5 is further reduced along with the further reduction of the pressure of the differential pressure control valve H, when the pressure difference between the L5 and the L4 exceeds 0.3MPa, the water in the constant-volume water storage tank L4 starts to be supplied to the L5, the water pressure is characterized to be further transmitted to a far distance, and the like, after the water pressure is transmitted to the constant-pressure water storage tank L1, the L1 is used for representing the water pressure transmission boundary, namely the pressure moment is the original reservoir pressure, and the pressure value of the L1 is not reduced.
On the other hand, the water storage tanks L5, L4, L3 and L2 are respectively connected with the switches K5, K4, K3 and K2 through computer control terminals, namely when water flows out of each water storage tank, the corresponding switch is changed from a closed state to an open state (along with the increase of the water pressure propagation distance, the desorption and output range of the coalbed methane gas is also increased). When the pressure value of the differential pressure control valve H is reduced below 1.9, the constant-volume water storage tank L5 just begins to supplement the buffer bottle 1, and the switch K5 is opened, but gas cannot be produced by the constant-volume air storage tank G5 to move into the buffer bottle 1, because the pressure in the buffer bottle 1 is still larger than the pressure value in the constant-volume air storage tank G5. When the pressure of the buffer bottle 1 is reduced to be lower than 1.1MPa along with the continuous reduction of the pressure of the differential pressure control valve H, the bottom hole flow pressure is represented to be reduced to be lower than the critical desorption pressure, and the gas in G5 starts to be desorbed and produced and flows into the buffer bottle; similarly, after the water pressure is sequentially transmitted to the constant-volume water storage tanks L4, L3 and L2, the gas in the constant-volume gas storage tanks G4, G3 and G2 is gradually transported into the buffer bottle 1 to be produced.
In addition, the details need to be supplemented, when water just flows from the buffer bottle 1 to the buffer bottle 2 through the core, a classical formula is calculated according to the indication of the pressure gauge P3, namely the displacement pressure, the indication of the pressure gauge P4, namely the outlet pressure, the indication of the liquid flowmeter in unit time, namely the flow through a coal pillar in unit time, and the water phase permeabilityThe original permeability Kc of the core can be calculated (wherein L is the length of the coal pillar, m; q is the flow rate of water through the coal pillar in unit time, m3/s; mu is the viscosity of water, mpa.s; r is the radius of the coal pillar, m; P1 is the pressure during displacement, MPa; P2 is the outlet pressure, MPa). Along with the continuous drainage of single-phase water flow stage, the water pressure in the core pore is reduced, the confining pressure born by the coal matrix is increased, the core permeability is reduced, the water flow state is represented, and the difficulty of water flowing from a distance to the buffer bottle 1 is increased. Therefore, the instantaneous permeability of the core in different drainage times is represented by Kt (Kt can be monitored in real time by the above formula), and then the values of the differential pressure control valves Y4, Y3, Y2 and Y1 are changed to pt=0.3 mpa×k/Kt along with the change of the permeability in the drainage unit time in the single-phase water flow stage.
In addition, the differential pressure control valves Q4-1, Q3-1, Q2-1, Q1-1 are fixed values of 0.9MPa, i.e. the difference between the reservoir pressure and the critical desorption pressure. The pressure difference control valves Q3-2, Q2-2, Q1-2 also have a pressure value of Pt=0.3 MPa.
Therefore, when the pressure difference of the electromagnetic valve H is uniformly reduced, the water production and the gas production are relatively uniform or change in a stable trend, and when the pressure difference of the electromagnetic valve H which is set at the beginning is not uniform or the middle of the electromagnetic valve H is stopped, the irregular change of the permeability leads to larger gas production resistance and the gas production capacity is influenced. Finally, the influence of stopping discharge, stopping discharge times, stopping discharge time and the like on productivity in different stages of discharge and mining can be observed through gas flowmeter indication.
The first point to be supplemented is that on the fold line of the pressure difference control valve H, which is changed along with time, the pressure is suddenly increased to 2MPa, after the water in the system has no flowing power, the flow is gradually stopped to be used for representing the drainage stop-drainage time period, but attention is paid to the fact that the bottom hole flow pressure value, namely the pressure gauge P4 indication, and the pressure value in the buffer bottle 2 are equal to the indication thereof in the stable descending stage of the pressure difference control valve H, but the pressure gauge P4 indication is increased in the drainage stop time period of the pressure value suddenly increased of the pressure difference control valve H, but the original pressure value of 2MPa is not reached, namely the pressure value of the pressure difference control valve H which is changed along with time cannot represent the bottom hole flow pressure at any moment, and the indication of the pressure gauge P4 should be taken as the reference.
The second point to be supplemented is that the coalbed methane productivity change simulation test device caused by discontinuous drainage only detects dynamic change of permeability in a single-phase water flow stage, namely, drainage reaches a certain stage, the pressure in the buffer bottle 1 is reduced below the critical desorption pressure of 1.1MPa, gas in the constant-volume gas storage tank G5 starts to move towards the buffer bottle, the drainage enters a gas-water two-phase flow stage from the single-phase water flow stage, the differential pressure values of the differential pressure control valves Y4, Y3, Y2, Y1, Q1-2, Q2-2 and Q3-2 are locked immediately, no change occurs, and the dynamic change of the core permeability is no longer monitored.
Compared with the prior art, the invention has the following beneficial effects: the device has simple structure, high degree of automation and integration of operation and control, and can effectively improve the working efficiency and the detection precision of detection operation; on the other hand, the test risk is low, the test method is convenient and accurate, the test can be carried out in a laboratory to dynamically monitor the discharge of the coal-bed gas well in different discharge and production stages and a series of changes caused by the change of fluid flow states such as water, gas and the like after the discharge, and the change of the capacity of the coal-bed gas caused by the discharge time, the discharge stopping times and the like in different discharge and production stages such as single-phase water flow stage or gas/water two-phase flow stage and the like of the coal-bed gas well can be accurately answered, so that guidance is provided for on-site coal-bed gas well discharge and production system, pump inspection and well repairing time and the like.
It will be appreciated by those skilled in the art that the invention is not limited to the embodiments described above. The foregoing embodiments and description have been presented only to illustrate the principles of the invention. The present invention is capable of various changes and modifications without departing from its spirit and scope. Such variations and modifications are intended to fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (3)
1. A test method of a coalbed methane productivity change simulation test device based on discontinuous drainage is characterized by comprising the following steps: the simulated test device for the coalbed methane productivity change caused by discontinuous drainage comprises a wellhead device simulation device, a permeability test device, a hydraulic pressure transmission simulation device, a gas desorption simulation device, an experiment cabinet and a data acquisition and processing device, wherein the experiment cabinet is of a closed cavity structure with an axis vertical to a horizontal plane, a plurality of partition plates are uniformly distributed in the experiment cabinet, the experiment cabinet is divided into an experiment detection cavity, three experiment driving cavities and a control cavity through the partition plates, at least one permeability test device is positioned in the experiment detection cavity, the wellhead device simulation device, the hydraulic pressure transmission simulation device and the gas desorption simulation device are respectively positioned in the three experiment driving cavities and are respectively communicated with the permeability test device, one end of the permeability test device is communicated with the wellhead device simulation device through a honeycomb duct, the other end of the permeability test device is respectively communicated with the hydraulic pressure transmission simulation device and the gas desorption simulation device, the hydraulic pressure transmission simulation device and the data acquisition and the gas desorption simulation device are mutually connected in parallel, and the data acquisition and processing device is positioned in the control cavity and is respectively electrically connected with the wellhead device simulation device, the permeability test device, the hydraulic pressure transmission simulation device and the gas desorption simulation device;
The wellhead device simulation device comprises a buffer bottle I, a hydraulic pressure differential unidirectional control valve, a gas flowmeter, a gas-liquid separation tank and a gas collecting and processing mechanism, wherein two ends of the gas flowmeter are respectively communicated with the gas collecting and processing mechanism and the gas-liquid separation tank, the gas-liquid separation tank is mutually communicated with one end of the buffer bottle I through the hydraulic pressure differential unidirectional control valve, the other end of the buffer bottle I is communicated with a permeability testing device, and the hydraulic pressure differential unidirectional control valve, the gas flowmeter and the gas collecting and processing mechanism are electrically connected with a data collecting and processing device;
the permeability testing device comprises an inlet pressure gauge, an outlet pressure gauge, a liquid flowmeter, a core holder and a buffer bottle II, wherein the core holder comprises a bearing shell, an axial pressure piston, an elastic bearing sleeve, a flow guide pipe, a hydraulic driving mechanism and a stress sensing gasket, wherein the bearing shell is a closed cavity mechanism with an axis parallel to the horizontal, the outer surfaces of the bearing shell are connected with a partition plate through a positioning mechanism, the axial pressure pistons are totally two, are embedded in the bearing shell and are coaxially distributed with the bearing shell, the two axial pressure pistons are symmetrically distributed relative to the midpoint of the bearing shell, the two axial pressure pistons are in sliding connection with the inner surface of the bearing shell, the elastic bearing sleeve is of a closed cavity structure and is embedded in coaxial distribution with the bearing shell, the two ends of the elastic bearing sleeve are respectively connected with the axial pressure pistons, the distance between the outer side surface of the elastic bearing sleeve and the inner side surface of the bearing shell is not less than 5 mm, the stress sensing gasket is at least two, the axial pistons around the elastic bearing sleeve are embedded in the elastic bearing sleeve, the two axial pistons are respectively positioned at the two axial ends of the bearing shell and coaxially distributed with the bearing shell, the flow guide pipe and coaxially distributed with the bearing shell, the two axial pistons are coaxially distributed with the flow guide pipe, the axial pressure pistons are correspondingly arranged at the front end surfaces of the bearing sleeve and correspond to at least one axial pressure adjusting side and at least two axial pressure adjusting holes are coaxially arranged, and correspond to the inlet pressure adjusting side surfaces and correspond to the inlet pressure adjusting piston, respectively, and pressure adjusting piston and pressure inlet end surfaces are respectively, and pressure adjusting piston and pressure is correspondingly connected with at least inlet end hole and pressure hole, and has a pressure-arranged in parallel to at least corresponding pressure adjusting end opening and corresponding to an axial pressure hole, the flow guide pipe at one end of the bearing shell outlet is communicated with a buffer bottle I of the wellhead device simulation device through an outlet pressure gauge, a liquid flowmeter is arranged between the outlet pressure gauge and the buffer bottle I, the buffer bottle II is respectively communicated with the water pressure propagation simulation device and the gas desorption simulation device through a three-way valve, and the inlet pressure gauge, the outlet pressure gauge, the liquid flowmeter, the hydraulic driving mechanism of the core holder and the stress induction gasket are electrically connected with the data acquisition processing device;
The hydraulic propagation simulation device comprises a constant-pressure water storage tank, a constant-volume water storage tank, a hydraulic pressure differential unidirectional control valve, a liquid pressure gauge and a liquid supplementing device, wherein one end of the constant-pressure water storage tank is communicated with the liquid supplementing device, the other end of the constant-pressure water storage tank is communicated with the constant-volume water storage tank through the constant-volume water storage tank and a buffer bottle II of the permeability testing device, at least two constant-volume water storage tanks are arranged, the constant-volume water storage tank is communicated with the constant-pressure water storage tank through the hydraulic pressure differential unidirectional control valve, the constant-volume water storage tank is communicated with the buffer bottle II and the adjacent two constant-volume water storage tanks through the hydraulic pressure differential unidirectional control valve, the liquid pressure gauge and the liquid supplementing device are all electrically connected with the data acquisition processing device;
the gas desorption simulation device comprises a plurality of gas supplementing devices, constant-pressure gas storage tanks, constant-volume gas storage tanks, a gas pressure differential unidirectional control valve, a switch and a gas flowmeter, wherein the two ends of one constant-volume gas storage tank are respectively connected with one gas pressure differential unidirectional control valve in series to form a working group;
The test method comprises the following steps:
s1, equipment is assembled, firstly, a wellhead device simulation device, a permeability testing device, a water pressure propagation simulation device, a gas desorption simulation device, an experiment cabinet and a data acquisition processing device are connected, meanwhile, a control device is respectively connected with an external driving circuit and a data transmission network device to complete assembly networking, after equipment assembly is completed, the wellhead device simulation device, the permeability testing device, the water pressure propagation simulation device and the gas desorption simulation device are mutually communicated, then inert gas with the pressure of 2MPa is injected into the assembled equipment, then the pressure is maintained for 12-24 hours, and the residual pressure in the equipment after the pressure is maintained is not less than 1.9MPa, so that the air tightness of the system meets the use requirement, then the equipment is decompressed, rock samples are prepared according to the use requirement after the decompression, the rock samples for detection are embedded into the permeability testing device, and then the equipment connection is restored for standby;
s2, setting initial parameters of an experiment, firstly opening all hydraulic pressure difference one-way control valves in a hydraulic propagation simulation device, regulating the pressure difference value to be the lowest, closing a switch at the communication position of a gas desorption simulation device and a buffer bottle II, only enabling the wellhead device simulation device, a permeability test device and the hydraulic propagation simulation device to be mutually communicated, filling water into a constant pressure water storage tank, each constant volume water storage tank, the buffer bottle I and the buffer bottle II, enabling the pressure value of a liquid pressure gauge to be 2MPa, regulating the pressure value of the hydraulic pressure difference one-way control valves between the constant pressure gas storage tank and the constant volume gas storage tank to be 0.9MPa, continuously injecting gas into the constant pressure gas storage tank, keeping the gas pressure in the constant pressure gas storage tank to be 2MPa, keeping the gas pressure in the constant volume gas storage tank to be 1.1MPa, and enabling the pressure value of the hydraulic pressure difference one-way control valve in the hydraulic propagation simulation device to be 0.3MPa;
S3, the permeability test operation is carried out, firstly, a data acquisition processing device drives a core holder to operate according to experimental requirements, confining pressure and axial pressure are loaded on a rock sample in the core holder, when the pressure value of a hydraulic pressure difference one-way control valve in a wellhead device simulation device begins to be reduced, namely, drainage begins to be carried out, then, the pressure value of liquid in a buffer bottle I is continuously reduced, water is continuously fed into the buffer bottle I through the rock sample by a buffer bottle II, at the moment, the readings of a water inlet pressure gauge and a water outlet pressure gauge of the core holder are respectively recorded as P1 and P2, the readings of a liquid flowmeter at the outlet end of the core holder in unit time are respectively q, the initial permeability Kc of the rock sample is calculated according to the P1, P2 and q, the viscosity mu of water and the length L of the rock sample as well as the radius r of the rock sample, and a permeability calculation formula is combined, the drainage and the sampling continue, and the classical instantaneous permeability Kt of the rock sample can be monitored in real time by the classical formula at the stage of single-phase water;
s4, experimental detection, wherein in the step S3, in the permeability test process, along with the change of the instantaneous permeability Kt along with time, the pressure value Pt of a hydraulic pressure difference one-way control valve between each water storage tank in the hydraulic pressure propagation simulation device and a pressure difference one-way control valve between each constant-volume air storage tank and a buffer bottle II in the gas desorption simulation device can be changed along with the change of the permeability, specifically Pt=0.3 MPa x K/Kt, wherein K is the original permeability of the core; along with the reduction of the hydraulic pressure differential unidirectional control valve pressure value in the wellhead device simulation device, drainage and production are continuously carried out, the outlet pressure gauge indication P2 of the permeability test device is recorded at any time, the outlet pressure gauge indication P2 is the pressure value of the bottom hole flow pressure changing along with time, the dynamic change of the instantaneous permeability Kt along with time is recorded, the indication S1 in the unit time of the liquid flowmeter in the permeability test device before gas is not produced is recorded, the indication S1 in the unit time of the liquid flowmeter in the single-phase water flow stage is the water yield changing along with time, the indication S2 and the total indication Q in the unit time of the gas flowmeter in the wellhead device simulation device after gas production are recorded, and the indication S2 and the total indication Q are the unit time gas yield and the total gas yield changing along with time in the gas-water two-phase flow stage respectively;
S5, data analysis, namely after the step S4 is completed, performing comparison analysis on all data recorded in the experimental process, and determining the influence of the discharge stopping stage, the discharge stopping times and the discharge stopping time on the productivity in discontinuous discharge and mining;
and S6, after the test is finished, releasing pressure, discharging all water in the device, closing all switches in the device, and treating the gas collected in the experimental process.
2. The method for testing the coalbed methane productivity change simulation testing device based on discontinuous drainage according to claim 1, wherein the method comprises the following steps: the experiment detection cavity, the experiment drive cavity and the control cavity are corresponding to the experiment cabinet, the front end face and the rear end face of the experiment cabinet are respectively provided with an operation door, the experiment detection cavity is located at the center of the experiment cabinet, the experiment drive cavity and the control cavity are uniformly distributed around the experiment detection cavity, the control cavity is located under the experiment detection cavity, and the upper end face of the partition board at the bottom of the control cavity is provided with at least two guide slide rails and electrically connected with the data acquisition and processing device through the guide slide rails.
3. The method for testing the coalbed methane productivity change simulation testing device based on discontinuous drainage according to claim 1, wherein the method comprises the following steps: the data acquisition and processing device comprises at least one driving circuit based on an industrial computer and at least one data control platform based on a PC computer.
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