CN115508250B - Porous medium gas adsorption capacity evaluation system and method considering water rock effect - Google Patents
Porous medium gas adsorption capacity evaluation system and method considering water rock effect Download PDFInfo
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- 239000011435 rock Substances 0.000 title claims abstract description 177
- 238000001179 sorption measurement Methods 0.000 title claims abstract description 94
- 238000000034 method Methods 0.000 title claims abstract description 62
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 58
- 238000011156 evaluation Methods 0.000 title claims abstract description 15
- 230000000694 effects Effects 0.000 title description 3
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 175
- 239000007789 gas Substances 0.000 claims abstract description 128
- 238000005070 sampling Methods 0.000 claims abstract description 101
- 239000003345 natural gas Substances 0.000 claims abstract description 80
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 18
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 103
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 40
- 239000001569 carbon dioxide Substances 0.000 claims description 36
- 238000009792 diffusion process Methods 0.000 claims description 24
- 229920006395 saturated elastomer Polymers 0.000 claims description 18
- 239000008398 formation water Substances 0.000 claims description 15
- 239000001307 helium Substances 0.000 claims description 13
- 229910052734 helium Inorganic materials 0.000 claims description 13
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 claims description 13
- 238000004458 analytical method Methods 0.000 claims description 11
- 238000002347 injection Methods 0.000 claims description 11
- 239000007924 injection Substances 0.000 claims description 11
- 239000007788 liquid Substances 0.000 claims description 11
- 238000005086 pumping Methods 0.000 claims description 10
- 238000005481 NMR spectroscopy Methods 0.000 claims description 8
- 230000006835 compression Effects 0.000 claims description 8
- 238000007906 compression Methods 0.000 claims description 8
- 238000000926 separation method Methods 0.000 claims description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 7
- 239000011148 porous material Substances 0.000 claims description 7
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 claims description 6
- 239000003245 coal Substances 0.000 claims description 4
- 238000001228 spectrum Methods 0.000 claims description 4
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 3
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 claims description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 3
- 239000001273 butane Substances 0.000 claims description 3
- 239000001257 hydrogen Substances 0.000 claims description 3
- 229910052739 hydrogen Inorganic materials 0.000 claims description 3
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 claims description 3
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 claims description 3
- 239000001294 propane Substances 0.000 claims description 3
- 238000002336 sorption--desorption measurement Methods 0.000 claims description 3
- 230000003595 spectral effect Effects 0.000 claims description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 claims 8
- 238000001514 detection method Methods 0.000 abstract description 2
- 238000010997 low field NMR spectroscopy Methods 0.000 description 6
- 230000002860 competitive effect Effects 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 239000004215 Carbon black (E152) Substances 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000003795 desorption Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
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- 229910001872 inorganic gas Inorganic materials 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
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
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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
- G01N7/02—Analysing materials by measuring the pressure or volume of a gas or vapour by absorption, adsorption, or combustion of components and measurement of the change in pressure or volume of the remainder
- G01N7/04—Analysing materials by measuring the pressure or volume of a gas or vapour by absorption, adsorption, or combustion of components and measurement of the change in pressure or volume of the remainder by absorption or adsorption alone
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N13/00—Investigating surface or boundary effects, e.g. wetting power; Investigating diffusion effects; Analysing materials by determining surface, boundary, or diffusion effects
- G01N2013/003—Diffusion; diffusivity between liquids
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Abstract
The invention relates to the technical field of natural gas exploitation and discloses a porous medium gas adsorption capacity evaluation system and method considering the action of water rock. The system comprises a rock sample holder, wherein the upstream of the rock sample holder is respectively connected with a reference kettle, an intermediate container group and a vacuumizing assembly through six-way valves, a first pressure gauge is arranged between the rock sample holder and the six-way valves, a second pressure gauge and a first sampling point are sequentially arranged on the downstream of the rock sample holder, two circuits are arranged between the reference kettle and the six-way valves, the first circuit is provided with two three-way valves at the inlet of the reference kettle, the two three-way valves are connected with an air source mechanism through pipelines, the second circuit is provided with a first valve at the inlet of the reference kettle, the pipeline between the first valve and the six-way valves forms an intermediate sampling area, and one valve of the six-way valves is a second sampling point valve. The invention can realize the detection of the gas adsorption information in the porous medium after the water rock acts.
Description
Technical Field
The invention relates to the technical field of natural gas exploitation, in particular to a porous medium gas adsorption capacity evaluation system and method considering the action of water rock.
Background
Natural gas refers to a mixture of hydrocarbon and non-hydrocarbon gases that are deposited in a formation. After twenty-first century, the national economy of China has grown rapidly, and the demand for natural gas has been increasing gradually. Currently, unconventional natural gas with commercial value is mainly natural gas which exists in the forms of shale gas, coal bed gas, compact sandstone gas, natural gas hydrate, water-soluble gas, inorganic gas, shallow biological gas and the like. Among them, the shale gas resources in China have huge potential, and are one of the energy sources which need to be developed urgently.
Considering that the adsorption capacity of shale to carbon dioxide is greater than that of methane, in the related art, adsorption-state methane in shale can be replaced by introducing carbon dioxide into a shale reservoir to perform competitive adsorption with methane (CH 4).
However, CO 2 is an active gas which, when injected into the ground, is very reactive with rock and formation water in surrounding reservoirs as compared to geological fluids such as oil and gas, and which dissolves in the formation water to form carbonic acid, and the reservoir is highly soluble under temperature and pressure conditions, so that the liquid is highly acidic and can cause changes in physical and chemical properties of the reservoir, and thus research on the gas adsorption capacity of porous media considering water-rock action is a highly desirable problem.
Disclosure of Invention
The invention aims to solve the problem that the prior art does not consider the water rock reaction when researching the adsorption capacity of a reservoir to gas, and provides a porous medium gas adsorption capacity evaluation system and method considering the water rock action. The invention can realize the research of the gas adsorption capacity of the porous medium in the constant-current constant-pressure seepage process of the near-well CO 2 and the research of the gas adsorption capacity of the porous medium in the variable-pressure free diffusion seepage process of the far-well CO 2 by reasonably designing the evaluation system.
In order to achieve the above object, according to one aspect of the present invention, there is provided a porous medium gas adsorption capacity evaluation system considering the actions of water and rock, the system comprising a rock sample holder, upstream of which a reference tank, an intermediate container group and a vacuumizing assembly are connected respectively through six-way valves; a first pressure gauge is arranged between the rock sample holder and the six-way valve, and a second pressure gauge and a first sampling point are sequentially arranged at the downstream of the rock sample holder; the gas source mechanism and the gas booster pump are sequentially arranged on the upstream of the reference kettle along the gas flow direction, two lines are arranged between the reference kettle and the six-way valve, the first line is provided with two three-way valves at the inlet of the reference kettle, the two three-way valves are connected with the gas booster pump through pipelines, the second line is provided with a first valve at the inlet of the reference kettle, a middle sampling area is formed by the pipeline between the first valve and the six-way valve, one valve of the six-way valves is a second sampling point valve, and the reference kettle is connected with a third pressure gauge; the middle container group comprises a carbonic acid container, a stratum water container, a natural gas container and a carbon dioxide container, and a plunger pump is arranged at the upstream of the middle container group.
Preferably, a first flow control device is arranged between the rock sample holder and the first pressure gauge, and a second flow control device is arranged between the second pressure gauge and the first sampling point.
Preferably, a gas-liquid separation device is arranged between the second pressure gauge and the second flow control device.
Preferably, a third valve and a fourth valve are arranged between the second flow control device and the first sampling point, the third valve is opened for exhausting, and the fourth valve is opened for sampling.
Preferably, a fourth pressure gauge is arranged between the intermediate container group and the six-way valve.
Preferably, the carbonic acid container, the formation water container, the natural gas container and the carbon dioxide container are connected in parallel, and the outlets and inlets of the carbonic acid container, the formation water container, the natural gas container and the carbon dioxide container are all provided with switch valves.
Preferably, the reference kettle and the intermediate container group are both arranged in a constant temperature control device.
Preferably, the rock sample holder is placed in a low field nuclear magnetic resonance apparatus, to which a first industrial computer is connected.
Preferably, the first pressure gauge and the second pressure gauge are both connected with the first industrial control computer.
Preferably, the gas source mechanism comprises a natural gas supply unit, a carbon dioxide supply unit and a helium supply unit, and the tops of the natural gas supply unit, the carbon dioxide supply unit and the helium supply unit are respectively provided with a switch valve.
Preferably, the third pressure gauge is connected with a second industrial control computer.
In a second aspect, the present invention provides a method for evaluating the gas adsorption capacity of a porous medium taking into account the action of water and rock, the method being implemented in a system as described hereinbefore,
The method comprises the following steps:
S1, placing a porous medium in the rock sample holder, vacuumizing the system, and measuring the free space volume in the rock sample holder;
S2, vacuumizing the system, injecting natural gas into a porous medium through the plunger pump, performing saturated adsorption, injecting CO 2 at constant pressure and constant flow, collecting gas at the outlet end of the rock sample holder at different times for component analysis, and recording the gas pressure, instantaneous flow and accumulated flow at the two ends of the rock sample holder in real time;
s3, stopping injecting CO 2 after the porous medium is saturated to adsorb CO 2, calculating the adsorption capacity of the porous medium CO 2 according to the formula (I),
Wherein P in、Pi and P p are respectively the CO 2 injection pressure at the inlet end of the rock sample holder, the instantaneous pressure at the outlet end of the rock sample holder and the free space pressure in a porous medium at different moments for collecting and sampling, and the unit is MPa; z in、Zi、Zp is the gas compression factor for pressures P in、Pi and P p, respectively; v in and V i are respectively the CO 2 injection amount at the inlet end of the rock sample holder and the collection amount at the outlet end during collection and sampling at different times, and the unit is mL; v p is the free space volume of the rock sample holder in mL; x i is the volume ratio of CO 2 in the gas at the outlet end of the rock sample holder when collecting and sampling at different moments, and the unit is; i is the sampling times; n Adsorption of is mol;
S4, vacuum pumping is carried out to desorb the porous medium, stratum water is injected into the porous medium to be saturated through the plunger pump, and carbonic acid is injected into the porous medium through the plunger pump to carry out water-rock reaction;
S5, repeating the steps S1 to S3, measuring the adsorption capacity of the porous medium CO 2 after the water-rock reaction, and evaluating the influence of the water-rock reaction on the adsorption capacity of the porous medium.
In a third aspect, the present invention provides a method for evaluating the gas adsorption capacity of a porous medium taking into account the action of water and rock, the method being implemented in a system as described hereinbefore,
The method comprises the following steps:
1) Placing a porous medium in the rock sample holder, then evacuating the system and determining the free space volume in the rock sample holder;
2) The system is vacuumized, natural gas and CO 2 are introduced into the reference kettle, mixed gas of the natural gas and CO 2 with the pressure ratio of K 1 is prepared, the reference kettle and the rock sample holder are communicated, the mixed gas is introduced into a porous medium to be adsorbed to be stable, and the pretreatment of the porous medium is completed;
3) The system is vacuumized, natural gas and CO 2 are introduced into the reference kettle, and mixed gas with the pressure ratio of the natural gas to CO 2 being K 2 is prepared, wherein K 2 and K 1 are the same or different;
4) The reference kettle and the rock sample holder are communicated, so that the mixed gas diffuses into a porous medium, after the intermediate sampling area has diffusion pressure, the first valve is closed until the adsorption of the porous medium is stable, then the six-way valve is closed, the second sampling point valve is opened to sample gas components from the intermediate sampling area for analysis, and the balance pressure of the sampling area at the moment is measured through the first pressure gauge;
5) Repeating the step 4), wherein the diffusion pressure of the intermediate sampling area is different when the operation is repeated, and the adsorption capacity of the porous medium CO 2 under different diffusion pressures is calculated according to the formula (II),
Wherein M i and N i are respectively the equilibrium pressure of the reference kettle and the equilibrium pressure of the sampling area in MPa during each sampling; a i and b i are the volume ratio of CO 2 in the reference kettle gas during each sampling, and the unit is; s L and S p are the volume of the intermediate sampling region and the free space volume of the rock sample holder, respectively, in mL; t i is the gas compression factor corresponding to pressure N i; i is the sampling times; m Adsorption of is mol;
6) Vacuum pumping is carried out to desorb the porous medium, stratum water is injected into the porous medium to be saturated through the plunger pump, and carbonic acid is injected into the porous medium through the plunger pump to carry out water-rock reaction;
7) And (3) repeating the steps 1) to 6), measuring the adsorption capacity of the porous medium CO 2 under different diffusion pressures after the water-rock reaction, and evaluating the influence of the water-rock reaction on the adsorption capacity of the porous medium.
Preferably, the method further comprises measuring the T 2 spectrum of the porous medium by the low-field nmr analyzer, analyzing the spectral peak area variations and the gas adsorption-desorption behavior in the pores of the different porous medium.
Preferably, the natural gas contains one or more of methane, ethane, propane, butane and hydrogen.
Preferably, the porous medium is shale, coal, activated carbon, sandstone or carbonate.
The system provided by the invention can be used for exploring the difference of the adsorption capacity of the porous medium before and after the action of water rock in the near-well CO 2 constant-current constant-pressure seepage process and the difference of the adsorption capacity of the porous medium before and after the action of water rock in the far-well CO 2 free diffusion seepage process by matching with a specific method, so that the detection of gas adsorption information in the porous medium after the action of water rock is realized, and the efficient exploitation of shale gas and the carbon burying of a shale reservoir can be reasonably guided.
Drawings
FIG. 1 is a diagram of a porous media gas adsorption capacity evaluation system taking into account the action of water rock according to the present invention.
FIG. 2 is a graph showing the change in the adsorption amount before and after the water-rock reaction in example 1.
FIG. 3 is a graph showing the change in the adsorption amount before and after the water-rock reaction in example 2.
FIG. 4 is a graph showing the T2 curve before and after the water rock action in the embodiment 2.
Description of the reference numerals
1A rock sample holder; 2, referring to a kettle; 3 an intermediate container group; a 31 carbonic acid container; a 32 formation water container; 33 natural gas vessel; 34 carbon dioxide vessel; 35 plunger pump; 4, vacuumizing the assembly; 5, a first pressure gauge; 6, a second pressure gauge; 7, a first sampling point; 8 air source mechanism; 81 a natural gas supply unit; 82 a carbon dioxide supply unit; 83 helium gas supply unit; 9 three-way valve; 10 a first valve; 12a second sampling point valve; 13 a third pressure gauge; 14 a first flow control device; 15 second flow control means; 16 a gas-liquid separation device; 17 a third valve; 18 a fourth valve; 19 a fourth pressure gauge; a first industrial control computer; a second industrial control computer 21; a six-way valve; b, a booster pump; c a constant temperature control device; 101 low field nmr.
Detailed Description
The following describes specific embodiments of the present invention in detail with reference to the drawings. It should be understood that the detailed description and specific examples, while indicating and illustrating the invention, are not intended to limit the invention.
The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.
In the present invention, unless otherwise stated, the "upstream" refers to the direction of origin of the gas, and the "downstream" refers to the direction of the gas, and in fig. 1, the left side is "upstream" and the right side is "downstream".
On one hand, the invention provides a porous medium gas adsorption capacity evaluation system considering the action of water and rock, as shown in fig. 1, the system comprises a rock sample holder 1, wherein the upstream of the rock sample holder 1 is respectively connected with a reference kettle 2, an intermediate container group 3 and a vacuumizing assembly 4 through a six-way valve A; a first pressure gauge 5 is arranged between the rock sample holder 1 and the six-way valve A, and a second pressure gauge 6 and a first sampling point 7 are sequentially arranged at the downstream of the rock sample holder 1; an air source mechanism 8 and an air booster pump B are sequentially arranged on the upstream of the reference kettle 3 along the air flow direction, two lines are arranged between the reference kettle 3 and the six-way valve A, a first line is provided with two three-way valves 9 at the inlet of the reference kettle 3, the two three-way valves 9 are connected with the air booster pump B through pipelines, a first valve 10 is arranged at the inlet of the reference kettle 3 through a second line, a pipeline between the first valve 10 and the six-way valve A forms an intermediate sampling area 11, one valve of the six-way valves A is a second sampling point valve 12, and the reference kettle is connected with a third pressure gauge 13; the intermediate container group 3 comprises a carbonic acid container 31, a stratum water container 32, a natural gas container 33 and a carbon dioxide container 34, and a plunger pump 35 is arranged at the upstream of the intermediate container group 3.
In the system of the invention, the gas provided by the gas source mechanism 8 can be directly transmitted to the six-way valve A through a first line without entering the reference kettle 3 by controlling the opening and closing of the two three-way valves 9, then the six-way valve A is controlled to enable the gas to be respectively transmitted to the natural gas container 33 and the carbon dioxide container 34 in the middle container group 3, the liquid in the carbonic acid container 31 and the stratum water container 32 can be directly filled in advance, and then the natural gas, the carbon dioxide, the carbonic acid or the stratum water in the natural gas container 33, the carbon dioxide container 34, the carbonic acid container 31 or the stratum water container 32 is transmitted to the rock sample holder 1 through the six-way valve A through the plunger pump 35. In the system of the invention, the gas provided by the gas source mechanism 8 can enter the reference kettle 3 through a second line to reach the six-way valve A by controlling the switch of the two three-way valves 9, and then the gas can directly enter the rock sample holder 1 by controlling the six-way valve A. After the natural gas and the carbon dioxide enter the reference kettle 3, the reference kettle 3 can be used for preparing natural gas and carbon dioxide mixed gas with different proportions. The vacuumizing assembly 4 is used for vacuumizing the whole system. The gas booster pump B is used for pumping out the gas provided by the gas source mechanism 8, and then pumping the gas with the specified pressure into the reference kettle 3 or pumping the gas with the specified pressure into the six-way valve A.
In a specific embodiment, the rock sample holder 1 is further connected via a connecting line to means for generating confining pressure and high temperature and high pressure in the rock sample holder 1, which means serve to provide the sample in the rock sample holder 1 with temperature and pressure conditions approximating the formation environment.
In a preferred embodiment, a first flow control device 14 is arranged between the rock sample holder 1 and the first pressure gauge 5, and a second flow control device 15 is arranged between the second pressure gauge 6 and the first sampling point 7. The first flow control means 14 and the second flow control means 15 may be used to control the flow of gas through a porous medium placed in the rock sample holder 1.
In a preferred embodiment, a gas-liquid separation device 16 is provided between the second pressure gauge 6 and the second flow control device 15. In the evaluation method, after the formation water and the carbonated water are added, the outlet end of the rock sample holder 1 can produce liquid, and the gas-liquid separation device 16 is used for separation so as to collect a gas sample.
In a preferred embodiment, a third valve 17 and a fourth valve 18 are arranged between the second flow control device 15 and the first sampling point 7, the third valve 17 being open for exhaust gas and the fourth valve 18 being open for sampling.
In a preferred embodiment, a fourth pressure gauge 19 is provided between the intermediate container group 3 and the six-way valve a. The fourth pressure gauge 19 serves to define the gas pressure in the intermediate container group 3.
In a preferred embodiment, the carbonic acid container 31, the formation water container 32, the natural gas container 33 and the carbon dioxide container 34 are connected in parallel, and the outlets and inlets of the carbonic acid container 31, the formation water container 32, the natural gas container 33 and the carbon dioxide container 34 are provided with on-off valves. In actual operation, the individual use of each of carbonic acid, formation water, natural gas and carbon dioxide can be achieved by controlling the on-off valve of each container.
In a preferred embodiment, the reference tank 2 and the intermediate container group 3 are both placed in a thermostatic control device C, so that the temperature of the gas entering the reference tank and the gas and liquid in the intermediate container group 3 are consistent with the temperature of the porous medium placed in the rock sample holder 1, simulating the formation environment.
In a preferred embodiment, the rock sample holder 1 is placed in a low field nmr apparatus 101, the low field nmr apparatus 101 being connected to a first industrial computer 20. The low field nmr 2 may measure the transverse relaxation time of the natural gas and display the results via the first industrial computer 20.
In a preferred embodiment, the first pressure gauge 5 and the second pressure gauge 6 are both connected to the first industrial personal computer 20. The first industrial control computer 20 can record pressure change data of the inlet and outlet of the rock sample holder 1 in real time.
In a preferred embodiment, the gas source mechanism 8 includes a natural gas supply unit 81, a carbon dioxide supply unit 82, and a helium supply unit 83, and the natural gas supply unit 81, the carbon dioxide supply unit 82, and the helium supply unit 83 are each provided with an on-off valve at the top thereof. The natural gas, carbon dioxide and helium supplied from the natural gas supply unit 81, the carbon dioxide supply unit 82 and the helium supply unit 83 may be used singly or simultaneously. The helium gas may be used to determine the free space volume of the rock sample holder 1.
In a preferred embodiment, the third pressure gauge 13 is connected to a second industrial personal computer 21. The second industrial control computer 21 may be used to record the pressure in the reference tank 3 in real time.
In a second aspect, the present invention provides a method for evaluating the gas adsorption capacity of a porous medium taking into account the action of water and rock, the method being implemented in a system as described hereinbefore,
The method comprises the following steps:
s1, placing a porous medium in the rock sample holder 1, vacuumizing the system, and measuring the free space volume in the rock sample holder 1;
S2, vacuumizing the system, injecting natural gas into a porous medium through the plunger pump 35, performing saturated adsorption, injecting CO 2 at constant pressure and constant flow, collecting gas at the outlet end of the rock sample holder 1 at different moments for component analysis, and recording the gas pressure, the instantaneous flow and the accumulated flow at the two ends of the rock sample holder 1 in real time;
s3, stopping injecting CO 2 after the porous medium is saturated to adsorb CO 2, calculating the adsorption capacity of the porous medium CO 2 according to the formula (I),
Wherein P in、Pi and P p are respectively the CO 2 injection pressure at the inlet end of the rock sample holder 1, the instantaneous pressure at the outlet end of the rock sample holder 1 during collecting and sampling at different times and the free space pressure in a porous medium, and the unit is MPa; z in、Zi、Zp is the gas compression factor for pressures P in、Pi and P p, respectively; v in and V i are respectively the CO 2 injection amount at the inlet end of the rock sample holder 1 and the collection amount at the outlet end during collection and sampling at different times, and the unit is mL; v p is the free space volume of the rock sample holder 1 in mL; x i is the volume ratio of CO 2 in the gas at the outlet end of the rock sample holder 1 when collecting and sampling at different moments, and the unit is; i is the sampling times; n Adsorption of is mol;
s4, vacuum pumping is carried out to desorb the porous medium, stratum water is injected into the porous medium to be saturated through the plunger pump 35, and carbonic acid is injected into the porous medium through the plunger pump 35 to carry out water-rock reaction;
S5, repeating the steps S1 to S3, measuring the adsorption capacity of the porous medium CO 2 after the water-rock reaction, and evaluating the influence of the water-rock reaction on the adsorption capacity of the porous medium.
The method provided by the second aspect of the invention can be used for exploring the difference of the adsorption capacity of the porous medium before and after the action of water rock in the process of constant-current constant-pressure seepage of near-well CO 2. The method comprises the following specific operation processes: after the system is installed, namely after the preparation work is finished, the free space volume in the rock sample holder 1 is measured after the system is vacuumized, natural gas is injected into a porous medium through a plunger pump 35 and is subjected to saturated adsorption, the adsorption behavior of the original natural gas in a reservoir is simulated, CO 2 is then injected into the porous medium at a constant pressure and constant flow, the natural gas is replaced through competitive adsorption and the adsorption capacity of the CO 3725 is evaluated, the injection pressure and the injection flow of the CO 2 are monitored through a first pressure gauge 5 and a first flow control device 14, the gas at the outlet end of the rock sample holder 1 is collected from a first sampling point 7 at intervals of time, the component analysis is performed, then the adsorption capacity of the porous medium is calculated according to a formula (I), the porous medium is desorbed by vacuumizing, the porous medium is injected with water to saturation through the plunger pump 35, then the porous medium is injected with carbonic acid for water rock reaction, the CO 2 is simulated to be injected into the reservoir, the condition that CO 2 reacts with rock and rock in the surrounding reservoir is carried out, the step S3 is repeated, and the adsorption capacity of the porous medium is evaluated, and the adsorption capacity of the porous medium is measured after the step S3 is repeated, and the adsorption capacity of the porous medium is measured.
In a third aspect, the present invention provides a method for evaluating the gas adsorption capacity of a porous medium taking into account the action of water and rock, the method being implemented in a system as described hereinbefore,
The method comprises the following steps:
1) Placing a porous medium in the rock sample holder 1, then evacuating the system and determining the free space volume in the rock sample holder 1;
2) The system is vacuumized, natural gas and CO 2 are introduced into the reference kettle 2, mixed gas with the pressure ratio of the natural gas to the CO 2 being K 1 is prepared, the reference kettle 2 and the rock sample holder 1 are communicated, the mixed gas is introduced into a porous medium to be adsorbed to be stable, and the pretreatment of the porous medium is completed;
3) The system is vacuumized, natural gas and CO 2 are introduced into the reference kettle 2, and mixed gas with the pressure ratio of the natural gas to the CO 2 of K 2 is prepared, wherein K 2 and K 1 are the same or different;
4) The reference kettle 2 and the rock sample holder 1 are communicated, so that the mixed gas diffuses into a porous medium, after the intermediate sampling area 11 has diffusion pressure, the first valve 10 is closed until the adsorption of the porous medium is stable, then the six-way valve A is closed, the second sampling point valve 12 is opened to sample the gas from the intermediate sampling area 11 for gas component analysis, and the balance pressure of the sampling area 11 at the moment is measured through the first pressure gauge 5;
5) Repeating the step 4), wherein the intermediate sampling area 11 has different diffusion pressures each time the operation is repeated, and calculating the adsorption capacity of the porous medium CO 2 under different diffusion pressures according to the formula (II),
Wherein M i and N i are respectively the equilibrium pressure of the reference kettle 2 and the equilibrium pressure of the sampling area 11 during each sampling, and the unit is MPa; a i and b i are the volume ratio of CO 2 in the gas of the reference kettle 2 in unit of each sampling; s L and S p are the volume of the intermediate sampling region 11 and the free space volume of the rock sample holder 1, respectively, in mL; t i is the gas compression factor corresponding to pressure N i; i is the sampling times; m Adsorption of is mol;
6) Vacuum is pumped to desorb the porous medium, stratum water is injected into the porous medium to be saturated through the plunger pump 35, and carbonic acid is injected into the porous medium through the plunger pump 35 to carry out water-rock reaction;
7) And (3) repeating the steps 1) to 6), measuring the adsorption capacity of the porous medium CO 2 under different diffusion pressures after the water-rock reaction, and evaluating the influence of the water-rock reaction on the adsorption capacity of the porous medium.
The method provided by the third aspect of the invention is used for researching the difference of the adsorption capacities of the porous medium before and after the action of the water rock in the process of free diffusion and seepage of the far well CO 2. the method comprises the following specific operations: after the system is installed, namely after the preparation work is finished, the system is vacuumized, the free space volume in the rock sample holder 1 is measured, then natural gas and CO 2 are introduced into the reference kettle 2, the mixed gas of the natural gas and CO 2 with the pressure ratio of K 1 is prepared, Connecting the reference kettle 2 and the rock sample holder 1, introducing the mixed gas into a porous medium to be adsorbed to be stable, completing pretreatment of the porous medium, wherein the pretreatment aims at simulating initial adsorption states of natural gas and CO 2 with different proportions in a natural gas reservoir, vacuumizing again, introducing the natural gas and CO 2 into the reference kettle 2, preparing the mixed gas with the pressure ratio of the natural gas and CO 2 being K 2, K 2 and K 1 can be the same or different, the reference kettle 2 and the rock sample holder 1 are communicated to diffuse the mixed gas into the porous medium, the first valve 10 is closed after the intermediate sampling area 11 has a certain diffusion pressure until the porous medium is adsorbed stably, then the six-way valve A is closed, the second sampling point valve 12 is opened to sample the gas from the intermediate sampling area 11 for gas component analysis, and the equilibrium pressure of the sampling area 11 is measured by the first pressure gauge 5, the operation is repeated, except that after the mixed gas is diffused into the porous medium each time by connecting the reference kettle 2 and the rock sample holder 1, the diffusion pressure of the middle sampling area 11 is different, then the adsorption capacity of the porous medium CO 2 under different diffusion pressures is calculated according to the formula (II), then the porous medium is desorbed by vacuumizing, the stratum water is injected into the porous medium to saturation by the plunger pump 35, Then injecting carbonic acid into the porous medium through the plunger pump 35 to perform water-rock reaction, simulating the situation that CO 2 is injected into a reservoir, CO 2 reacts with rocks in surrounding reservoirs and stratum water, repeating the steps 1) to 6), measuring the adsorption capacity of the porous medium CO 2 under different diffusion pressures after the water-rock reaction, The effect of the water rock reaction on the adsorption capacity of the porous media was evaluated.
The methods provided in the second and third aspects of the present invention further comprise measuring the T 2 spectrum of the porous medium by the low-field nmr apparatus 101, analyzing the spectral peak area variation and the gas adsorption-desorption behavior in the pores of the different porous medium. Specifically, the T 2 spectrum can obtain the adsorption characteristics of natural gas in pores with different sizes, analyze the competitive adsorption of injected CO 2 in the pores and influence on the desorption behavior of the natural gas, and compare the change characteristics of the competitive adsorption behavior of the natural gas and CO 2 before and after the water rock reaction.
In the method provided by the second and third aspects of the present invention, the natural gas contains one or more of methane, ethane, propane, butane and hydrogen.
In the methods provided by the second and third aspects of the invention, the porous medium is shale, coal, activated carbon, sandstone or carbonate.
The present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.
The following embodiment is implemented in a porous medium gas adsorption capacity evaluation system taking into account water rock action as shown in fig. 1, the system comprises a rock sample holder 1, wherein the upstream of the rock sample holder 1 is respectively connected with a reference kettle 2, an intermediate container group 3 and a vacuumizing assembly 4 through a six-way valve A, a first pressure gauge 5 is arranged between the rock sample holder 1 and the six-way valve A, a second pressure gauge 6 and a first sampling point 7 are sequentially arranged on the downstream of the rock sample holder 1, a gas source mechanism 8 and a gas booster pump B are sequentially arranged on the upstream of the reference kettle 3 along the gas flow direction, two lines are arranged between the reference kettle 3 and the six-way valve A, the first line is provided with two three-way valves 9 at the inlet of the reference kettle 3, the two three-way valves 9 are connected with the gas booster pump B through pipelines, the second line is provided with a first valve 10 at the inlet of the reference kettle 3, the pipeline between the first valve 10 and the six-way valve A forms an intermediate sampling area 11, one valve of the six-way valve A is a second sampling point valve 12, the reference kettle is connected with a third pressure gauge 13, the intermediate container group 3 comprises a carbonic acid container 31, a stratum water container 32, a natural gas container 33 and a carbon dioxide container 34, a plunger pump 35 is arranged at the upstream of the intermediate container group 3, a first flow control device 14 is arranged between the rock sample holder 1 and the first pressure gauge 5, a second flow control device 15 is arranged between the second pressure gauge 6 and the first sampling point 7, a gas-liquid separation device 16 is arranged between the second pressure gauge 6 and the second flow control device 15, a third valve 17 and a fourth valve 18 are arranged between the second flow control device 15 and the first sampling point 7, the third valve 17 is opened for exhausting, the fourth valve 18 is opened for sampling, the third valve 17 and the fourth valve 18 are arranged between the second flow control device 15 and the first sampling point 7, the third valve 17 is opened for exhausting, the fourth valve 18 is opened for sampling, a fourth pressure gauge 19 is arranged between the middle container group 3 and the six-way valve A, the carbonic acid container 31, the formation water container 32, the natural gas container 33 and the carbon dioxide container 34 are connected in parallel, the carbonic acid container 31, the formation water container 32, the natural gas container 33 and the outlet and the inlet of the carbon dioxide container 34 are respectively provided with a switch valve, the reference kettle 2 and the middle container group 3 are respectively arranged in the constant temperature control device C, the rock sample holder 1 is arranged in the low-field nuclear magnetic resonance instrument 101, the low-field nuclear magnetic resonance instrument 101 is connected with a first industrial control computer 20, the first pressure gauge 5 and the second pressure gauge 6 are respectively connected with the first industrial control computer 20, the carbon dioxide supply unit 8, the natural gas supply unit 82 and the third industrial control unit 81 are respectively provided with a helium supply unit 83, and a natural gas supply unit 81.
The natural gas employed in examples 1 and 2 had a methane composition.
Example 1 was used to explore the difference in adsorption capacity of shale before and after water rock action during constant flow and constant pressure seepage of near well CO 2.
The method comprises the following steps:
s1, placing shale into the rock sample holder 1, vacuumizing the system, and measuring the free space volume in the rock sample holder 1;
S2, vacuumizing the system, injecting natural gas into shale through the plunger pump 35, performing saturated adsorption, injecting CO 2 at constant pressure and constant flow, collecting gas at the outlet end of the rock sample holder 1 at different times for component analysis, and recording the gas pressure, instantaneous flow and accumulated flow at the two ends of the rock sample holder 1 in real time;
S3, stopping injecting CO 2 after the shale is saturated to adsorb CO 2, calculating the adsorption capacity of shale CO 2 according to the formula (I),
Wherein P in、Pi and P p are respectively the CO 2 injection pressure at the inlet end of the rock sample holder 1, the instantaneous pressure at the outlet end of the rock sample holder 1 during collecting and sampling at different times and the free space pressure in shale, and the unit is MPa; z in、Zi、Zp is the gas compression factor for pressures P in、Pi and P p, respectively; v in and V i are respectively the CO 2 injection amount at the inlet end of the rock sample holder 1 and the collection amount at the outlet end during collection and sampling at different times, and the unit is mL; v p is the free space volume of the rock sample holder 1 in mL; x i is the volume ratio of CO 2 in the gas at the outlet end of the rock sample holder 1 when collecting and sampling at different moments, and the unit is; i is the sampling times;
S4, vacuum pumping is carried out to desorb shale, stratum water is injected into the shale to be saturated through the plunger pump 35, and carbonic acid is injected into a porous medium through the plunger pump 35 to carry out water-rock reaction;
S5, repeating the steps S1 to S3, measuring the shale CO 2 adsorption capacity after the water-rock reaction, and evaluating the influence of the water-rock reaction on the shale adsorption capacity.
The change of the adsorption amount before and after the water rock action in this example is shown in fig. 2. As can be seen from fig. 2, the CO2 adsorption rate becomes faster after the water rock is acted, i.e. the saturated adsorption state is reached more quickly, but the total adsorption amount is reduced.
Example 2 was used to explore the difference in adsorption capacity of porous media before and after water rock action during free diffusion and percolation of far well CO 2.
The method comprises the following steps:
1) Placing shale in the rock sample holder 1, then evacuating the system and determining the free space volume in the rock sample holder 1;
2) The system is vacuumized, natural gas and CO 2 are introduced into the reference kettle 2, mixed gas of the natural gas and CO 2 with the pressure ratio of K 1(K1 being 5) is prepared, the reference kettle 2 and the rock sample holder 1 are communicated, the mixed gas is introduced into shale to be adsorbed to be stable, and the pretreatment of a porous medium is completed;
3) The system is vacuumized, natural gas and CO 2 are introduced into the reference kettle 2, and mixed gas of the natural gas and CO 2 with the pressure ratio of K 2(K2 being 0.5) is prepared;
4) The reference kettle 2 and the rock sample holder 1 are communicated, so that the mixed gas diffuses into shale, after a certain diffusion pressure exists in the middle sampling area 11, the first valve 10 is closed until shale adsorption is stable, then the six-way valve A is closed, the second sampling point valve 12 is opened to sample gas from the middle sampling area 11 for gas component analysis, and the balance pressure of the sampling area 11 at the moment is measured through the first pressure gauge 5;
5) Repeating step 4), wherein the intermediate sampling area 11 has different diffusion pressures during each repeated operation, and calculating the adsorption capacity of shale CO 2 under different diffusion pressures according to formula (II),
Wherein M i and N i are respectively the equilibrium pressure of the reference kettle 2 and the equilibrium pressure of the sampling area 11 during each sampling, and the unit is MPa; a i and b i are the volume ratio of CO 2 in the gas of the reference kettle 2 in unit of each sampling; s L and S p are the volume of the intermediate sampling region 11 and the free space volume of the rock sample holder 1, respectively, in mL; t i is the gas compression factor corresponding to pressure N i; i is the number of samplings.
6) Vacuum pumping is carried out to desorb shale, stratum water is injected into the porous medium to be saturated through the plunger pump 35, and carbonic acid is injected into the porous medium through the plunger pump 35 to carry out water-rock reaction;
7) And (3) repeating the steps 1) to 6), measuring the shale CO 2 adsorption capacity under different diffusion pressures after the water-rock reaction, and evaluating the influence of the water-rock reaction on the shale adsorption capacity.
The adsorption amount changes before and after the water rock action in this embodiment are shown in fig. 3, and the abscissa of fig. 3 shows the equilibrium pressure of the sampling area 11 at each sampling analysis. As can be seen from fig. 3, after the water rock is acted, the adsorption amount of CO2 is increased at a low pressure value, and the pressure value required for reaching saturation adsorption is reduced, but the total adsorption amount is reduced.
The T2 curve change before and after the water rock action in the embodiment is shown in fig. 4. As can be seen from fig. 4, the curve area is reduced after CO2 injection before and after the water rock action, which means that CO2 can well displace natural gas before and after the water rock action, but the saturated natural gas amount is reduced after the water rock action, which means that the pore structure is changed, the partial pore size is increased, and the specific surface area is reduced, so that the adsorption total amount is reduced.
The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.
Claims (25)
1. A porous medium gas adsorption capacity evaluation method taking into consideration the action of water rock is characterized in that the method is implemented in a porous medium gas adsorption capacity evaluation system taking into consideration the action of water rock,
The system comprises a rock sample holder (1), wherein the upstream of the rock sample holder (1) is respectively connected with a reference kettle (2), an intermediate container group (3) and a vacuumizing assembly (4) through a six-way valve (A),
A first pressure gauge (5) is arranged between the rock sample holder (1) and the six-way valve (A), a second pressure gauge (6) and a first sampling point (7) are sequentially arranged at the downstream of the rock sample holder (1),
The upstream of the reference kettle (2) is sequentially provided with an air source mechanism (8) and a gas booster pump (B) along the air flow direction, two circuits are arranged between the reference kettle (2) and the six-way valve (A), the first circuit is provided with two three-way valves at the inlet of the reference kettle (2), the two three-way valves are arranged in parallel, the two three-way valves are connected with the gas booster pump (B) through pipelines, the second circuit is provided with a first valve (10) at the inlet of the reference kettle (2), the pipeline between the first valve (10) and the six-way valve (A) forms an intermediate sampling area (11), one valve of the six-way valve (A) is a second sampling point valve (12), the reference kettle is connected with a third pressure gauge (13),
The middle container group (3) comprises a carbonic acid container (31), a stratum water container (32), a natural gas container (33) and a carbon dioxide container (34), and a plunger pump (35) is arranged at the upstream of the middle container group (3);
The method comprises the following steps:
S1, placing a porous medium in the rock sample holder (1), vacuumizing the system, and measuring the free space volume in the rock sample holder (1);
S2, vacuumizing the system, injecting natural gas into a porous medium through the plunger pump (35) and performing saturated adsorption, then injecting CO 2 at constant pressure and constant flow, collecting gas at the outlet end of the rock sample holder (1) at different moments for component analysis, and recording the gas pressure, the instantaneous flow and the accumulated flow at the two ends of the rock sample holder (1) in real time;
S3, stopping injecting CO 2 after the porous medium is saturated to adsorb CO 2, calculating the adsorption capacity of the porous medium CO 2 according to the formula (I),
（I）
Wherein P in、Pi and P p are respectively the CO 2 injection pressure at the inlet end of the rock sample holder (1), the instantaneous pressure at the outlet end of the rock sample holder (1) during collecting and sampling at different times and the free space pressure in a porous medium, and the unit is MPa; z in、Zi、Zp is the gas compression factor for pressures P in、Pi and P p, respectively; v in and V i are respectively the CO 2 injection amount at the inlet end of the rock sample holder (1) and the collection amount at the outlet end during collection and sampling at different moments, wherein the units are mL; v p is the free space volume of the rock sample holder (1), in mL; x i is the volume ratio of CO 2 in the gas at the outlet end of the rock sample holder (1) when collecting and sampling at different moments, and the unit is; i is the sampling times; n Adsorption of is mol;
s4, vacuum pumping is carried out to desorb the porous medium, stratum water is injected into the porous medium to be saturated through the plunger pump (35), and carbonic acid is injected into the porous medium through the plunger pump (35) to carry out water-rock reaction;
And S5, repeating the steps S1-S3, measuring the adsorption capacity of the porous medium CO 2 after the water-rock reaction, and evaluating the influence of the water-rock reaction on the adsorption capacity of the porous medium.
2. Method according to claim 1, characterized in that a first flow control device (14) is arranged between the rock sample holder (1) and the first pressure gauge (5), and a second flow control device (15) is arranged between the second pressure gauge (6) and the first sampling point (7).
3. Method according to claim 2, characterized in that a gas-liquid separation device (16) is arranged between the second pressure gauge (6) and the second flow control device (15).
4. Method according to claim 2, characterized in that a third valve (17) and a fourth valve (18) are arranged between the second flow control device (15) and the first sampling point (7), the third valve (17) being open for exhaust gas and the fourth valve (18) being open for sampling.
5. Method according to claim 1 or 2, characterized in that a fourth pressure gauge (19) is arranged between the intermediate container group (3) and the six-way valve (a).
6. The method according to claim 1 or 2, characterized in that the carbonic acid container (31), the formation water container (32), the natural gas container (33) and the carbon dioxide container (34) are connected in parallel, and that the outlet and inlet of the carbonic acid container (31), the formation water container (32), the natural gas container (33) and the carbon dioxide container (34) are provided with on-off valves.
7. Method according to claim 1 or 2, characterized in that the reference tank (2) and the intermediate container group (3) are both placed in a thermostatic control device (C).
8. The method according to claim 1, characterized in that the rock sample holder (1) is placed in a low field nuclear magnetic resonance apparatus (101), the low field nuclear magnetic resonance apparatus (101) being connected to a first industrial computer (20).
9. The method according to claim 8, characterized in that the first pressure gauge (5) and the second pressure gauge (6) are both connected to the first industrial control computer (20).
10. The method according to claim 1, characterized in that the gas source mechanism (8) comprises a natural gas supply unit (81), a carbon dioxide supply unit (82) and a helium supply unit (83), and that the tops of the natural gas supply unit (81), the carbon dioxide supply unit (82) and the helium supply unit (83) are provided with on-off valves.
11. Method according to claim 1, characterized in that the third pressure gauge (13) is connected to a second industrial control computer (21).
12. A porous medium gas adsorption capacity evaluation method taking into consideration the action of water rock is characterized in that the method is implemented in a porous medium gas adsorption capacity evaluation system taking into consideration the action of water rock,
The system comprises a rock sample holder (1), wherein the upstream of the rock sample holder (1) is respectively connected with a reference kettle (2), an intermediate container group (3) and a vacuumizing assembly (4) through a six-way valve (A),
A first pressure gauge (5) is arranged between the rock sample holder (1) and the six-way valve (A), a second pressure gauge (6) and a first sampling point (7) are sequentially arranged at the downstream of the rock sample holder (1),
The upstream of the reference kettle (2) is sequentially provided with an air source mechanism (8) and a gas booster pump (B) along the air flow direction, two circuits are arranged between the reference kettle (2) and the six-way valve (A), the first circuit is provided with two three-way valves at the inlet of the reference kettle (2), the two three-way valves are arranged in parallel, the two three-way valves are connected with the gas booster pump (B) through pipelines, the second circuit is provided with a first valve (10) at the inlet of the reference kettle (2), the pipeline between the first valve (10) and the six-way valve (A) forms an intermediate sampling area (11), one valve of the six-way valve (A) is a second sampling point valve (12), the reference kettle is connected with a third pressure gauge (13),
The middle container group (3) comprises a carbonic acid container (31), a stratum water container (32), a natural gas container (33) and a carbon dioxide container (34), and a plunger pump (35) is arranged at the upstream of the middle container group (3);
The method comprises the following steps:
1) Placing a porous medium in the rock sample holder (1), then evacuating the system and determining the free space volume in the rock sample holder (1);
2) The system is vacuumized, natural gas and CO 2 are introduced into the reference kettle (2), mixed gas with the pressure ratio of the natural gas to the CO 2 being K 1 is prepared, the reference kettle (2) and the rock sample holder (1) are communicated, the mixed gas is introduced into a porous medium to be adsorbed to be stable, and the pretreatment of the porous medium is completed;
3) The system is vacuumized, natural gas and CO 2 are introduced into the reference kettle (2), and mixed gas with the pressure ratio of the natural gas to the CO 2 of K 2 is prepared, wherein K 2 and K 1 are the same or different;
4) The reference kettle (2) and the rock sample holder (1) are communicated, so that mixed gas diffuses into a porous medium, the first valve (10) is closed until the porous medium is adsorbed stably after the intermediate sampling area (11) has diffusion pressure, then the six-way valve (A) is closed, the second sampling point valve (12) is opened to sample the intermediate sampling area (11) for gas component analysis, and the balance pressure of the sampling area (11) at the moment is measured through the first pressure gauge (5);
5) Repeating the step 4), wherein the intermediate sampling area (11) has different diffusion pressures when repeating the operation, and the adsorption capacity of the porous medium CO 2 under different diffusion pressures is calculated according to the formula (II),
（II）
Wherein M i and N i are respectively the equilibrium pressure of the reference kettle (2) and the equilibrium pressure of the sampling area (11) during each sampling, and the unit is MPa; a i and b i are the volume ratio of CO 2 in the gas of the reference kettle (2) when sampling is carried out each time, and the unit is; s L and S p are the volume of the intermediate sampling region (11) and the free space volume of the rock sample holder (1), respectively, in mL; t i is the gas compression factor corresponding to pressure N i; i is the sampling times; m Adsorption of is mol;
6) Vacuum pumping is carried out to desorb the porous medium, stratum water is injected into the porous medium to be saturated through the plunger pump (35), and carbonic acid is injected into the porous medium through the plunger pump (35) to carry out water-rock reaction;
7) And (3) repeating the steps 1) to 6), measuring the adsorption capacity of the porous medium CO 2 under different diffusion pressures after the water-rock reaction, and evaluating the influence of the water-rock reaction on the adsorption capacity of the porous medium.
13. Method according to claim 12, characterized in that a first flow control device (14) is arranged between the rock sample holder (1) and the first pressure gauge (5), and a second flow control device (15) is arranged between the second pressure gauge (6) and the first sampling point (7).
14. Method according to claim 13, characterized in that a gas-liquid separation device (16) is arranged between the second pressure gauge (6) and the second flow control device (15).
15. Method according to claim 13, characterized in that a third valve (17) and a fourth valve (18) are arranged between the second flow control device (15) and the first sampling point (7), the third valve (17) being open for exhaust gas and the fourth valve (18) being open for sampling.
16. Method according to claim 12 or 13, characterized in that a fourth pressure gauge (19) is arranged between the intermediate container group (3) and the six-way valve (a).
17. The method according to claim 12 or 13, characterized in that the carbonic acid container (31), the formation water container (32), the natural gas container (33) and the carbon dioxide container (34) are connected in parallel, and that the outlet and inlet of the carbonic acid container (31), the formation water container (32), the natural gas container (33) and the carbon dioxide container (34) are provided with on-off valves.
18. Method according to claim 12 or 13, characterized in that the reference tank (2) and the intermediate container group (3) are both placed in a thermostatic control device (C).
19. The method according to claim 12, characterized in that the rock sample holder (1) is placed in a low field nuclear magnetic resonance apparatus (101), the low field nuclear magnetic resonance apparatus (101) being connected to a first industrial computer (20).
20. The method according to claim 19, characterized in that the first pressure gauge (5) and the second pressure gauge (6) are both connected to the first industrial control computer (20).
21. The method according to claim 12, characterized in that the gas source mechanism (8) comprises a natural gas supply unit (81), a carbon dioxide supply unit (82) and a helium supply unit (83), and that the tops of the natural gas supply unit (81), the carbon dioxide supply unit (82) and the helium supply unit (83) are provided with on-off valves.
22. Method according to claim 12, characterized in that the third pressure gauge (13) is connected to a second industrial control computer (21).
23. The method according to claim 1 or 12, further comprising measuring the T 2 spectrum of the porous medium by means of a low-field nuclear magnetic resonance apparatus (101), analyzing the spectral peak area variations and the gas adsorption-desorption behaviour in the pores of the different porous medium.
24. The method of claim 1 or 12, wherein the natural gas comprises one or more of methane, ethane, propane, butane, and hydrogen.
25. The method of claim 1 or 12, wherein the porous medium is shale, coal, activated carbon, sandstone or carbonate.
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