CN115494163B - System and method for determining gas-gas diffusion coefficient in gas reservoir - Google Patents
System and method for determining gas-gas diffusion coefficient in gas reservoir Download PDFInfo
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- CN115494163B CN115494163B CN202110675225.7A CN202110675225A CN115494163B CN 115494163 B CN115494163 B CN 115494163B CN 202110675225 A CN202110675225 A CN 202110675225A CN 115494163 B CN115494163 B CN 115494163B
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- 238000009792 diffusion process Methods 0.000 title claims abstract description 88
- 238000000034 method Methods 0.000 title claims abstract description 41
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 43
- 239000007924 injection Substances 0.000 claims abstract description 26
- 238000002347 injection Methods 0.000 claims abstract description 26
- 239000008398 formation water Substances 0.000 claims abstract description 22
- 238000004458 analytical method Methods 0.000 claims abstract description 19
- 238000005070 sampling Methods 0.000 claims abstract description 17
- 229920006395 saturated elastomer Polymers 0.000 claims abstract description 16
- 238000005259 measurement Methods 0.000 claims abstract description 12
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 4
- 238000004090 dissolution Methods 0.000 description 4
- 230000009545 invasion Effects 0.000 description 4
- 239000003345 natural gas Substances 0.000 description 4
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- 238000012544 monitoring process Methods 0.000 description 3
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- 229910002092 carbon dioxide Inorganic materials 0.000 description 2
- 239000001569 carbon dioxide Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
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- 238000011161 development Methods 0.000 description 1
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- 229920001971 elastomer Polymers 0.000 description 1
- 239000003546 flue gas Substances 0.000 description 1
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- 238000006703 hydration reaction Methods 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
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/04—Preparation or injection of sample to be analysed
- G01N30/06—Preparation
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Abstract
The invention belongs to the technical field of diffusion coefficient measurement, and discloses a system and a method for measuring a gas-gas diffusion coefficient in a gas reservoir. The system comprises two core holders, an incubator, a vacuumizing device, two gas supply subsystems, a confining pressure subsystem, a gas sampling component analysis subsystem and a saturated stratum water injection subsystem; the two core holders are arranged in the incubator and are connected with each other; the two gas supply subsystems are used for injecting gas into the two core holders respectively; the confining pressure subsystem is used for loading confining pressures on core samples in the two core holders; the gas sampling component analysis subsystem is used for determining the gas component concentration of the non-connecting ends of the two core holders; the saturated formation water injection subsystem is used for injecting formation water into the two core holders. The system and the method can be used for measuring the gas-gas diffusion coefficient of the water-containing porous medium in the gas reservoir under different set fluid pressure values and different water saturation conditions.
Description
Technical Field
The invention belongs to the technical field of diffusion coefficient measurement, and particularly relates to a system and a method for measuring a gas-gas diffusion coefficient in a gas reservoir.
Background
In the failure production process of the side bottom water and gas reservoir, the side bottom water can selectively invade under the influence of reservoir heterogeneity to form various water seal gases, so that reserve loss is caused, and the development effect of the gas reservoir is seriously influenced. When water invasion occurs in the gas reservoir, gas-water two-phase flow occurs in the stratum in the water invasion area, and the two-phase flow increases gas phase seepage resistance, so that the waste pressure of the gas reservoir is increased. For the side water and gas reservoirs with more active water bodies, the water outlet phenomenon occurs in the morning and evening during the production of a gas well. After water invades the gas producing interval, the relative permeability of the gas phase is reduced, and the productivity of the gas well is greatly reduced. After the gas well is discharged, the density of fluid in the well bore is increased, the lifting pressure loss of the well bore is increased, and the gas well is stopped when serious.
The gas injection and water control refers to injecting gases such as CO 2、N2, flue gas and the like to a specific position of the oil and gas reservoir, so as to inhibit water invasion. Under the high-temperature and high-pressure condition of the oil reservoir, the phase state of the injected gas can be changed to form a supercritical state. The supercritical state is between the gas and the liquid, and has the dual characteristics of the gas and the liquid, namely, the density is close to that of the liquid, the viscosity is similar to that of the gas, the diffusion coefficient is 10-100 times that of the liquid, and the supercritical state has good mass transfer characteristics, strong dissolution capacity and good flow and transport performance. Supercritical fluids are highly compressible but do not produce a liquid phase when compressed, but only increase their density, and in addition, supercritical fluids have near zero tension and excellent mass transfer properties, making their osmotic diffusion into porous media easier.
Key to gas injection control of water is the diffusion capacity of CO 2 in water-immersed gas reservoirs. The diffusion rate of CO 2 in porous rock media of varying water saturation and natural gas content is crucial for CO 2 injection to inhibit water invasion. In addition, the gas injection and water control can realize geological sequestration of carbon dioxide at the same time, and in the process, CO 2 is in a dynamic diffusion state until equilibrium is reached. In order to evaluate the feasibility, effectiveness and safety of gas injection and water control, the diffusion coefficient of carbon dioxide into natural gas in a water-gas reservoir of a stratum needs to be measured.
The current literature relates to methods for determining the diffusion coefficient of supercritical CO 2 in natural gas-containing porous media, which are generally divided into two categories: direct and indirect processes. Direct assays determine the diffusion coefficient based on monitoring the change over time of the diffusion component in the core, most of which require component analysis. The indirect measurement method mainly obtains the diffusion coefficient by monitoring the corresponding change of certain parameters caused by the dissolution and diffusion process of the gas in the system, and does not need to analyze the components. These parameters include the moving speed of the gas-liquid interface, the injection rate of the gas, the dropping rate of the pressure, etc.
In the prior art, because the diffusion between gas and liquid is slow, the diffusion coefficient between gas and liquid is usually measured by an indirect method under a low pressure condition. The accurate pressure monitoring of the gas-gas diffusion coefficient by the indirect method is very difficult, especially under the supercritical condition, and the gas-gas diffusion coefficient cannot be accurately calculated if the pressure drop data can not be accurately measured during diffusion.
Patent CN104897525A discloses a system and method for testing diffusion coefficient and isothermal/desorption curve of shale gas. Patent CN105092419a discloses an apparatus and a method for automatically detecting the diffusion coefficient of hydrocarbons in rock at high temperature and high pressure. Both patents measure the diffusion coefficient by detecting the gas concentration at both ends of the core at different times and by the feik's second law. However, the gas diffusion chambers designed by the two methods are all in bulk phase condition, are basically in bulk phase condition gas diffusion process into the porous medium, and do not conform to the actual gas diffusion process of the gas in the porous medium into the porous medium in the gas reservoir. Thus, the above method has a limitation in determining the gas-gas diffusion coefficient in the porous medium.
Therefore, currently, in order to determine the gas-gas diffusion coefficient of an aqueous porous medium in a gas reservoir, a system and a method for determining the gas-gas diffusion coefficient in a gas reservoir are needed.
Disclosure of Invention
The object of the present invention is to address the deficiencies of the prior art and to propose a system and a method for determining the gas-gas diffusion coefficient in a gas reservoir. The system and the method can be used for measuring the gas-gas diffusion coefficient of the water-containing porous medium in the gas reservoir under different set fluid pressure values and different water saturation conditions.
To achieve the above object, in one aspect, the present invention provides a system for determining a gas-gas diffusion coefficient in a gas reservoir, the system comprising a first core holder, a second core holder, an incubator, a vacuum apparatus, a first gas supply subsystem, a second gas supply subsystem, a confining pressure subsystem, a gas sampling composition analysis subsystem, and a saturated formation water injection subsystem;
the first core holder and the second core holder are both arranged in the incubator and are connected with each other through a first knob valve;
The vacuumizing device, the first gas supply subsystem, the second gas supply subsystem, the confining pressure subsystem, the gas sampling component analysis subsystem and the saturated formation water injection subsystem are respectively connected with the first core holder and the second core holder;
The first gas supply subsystem and the second gas supply subsystem are used for injecting gas into the first core holder and the second core holder respectively;
The confining pressure subsystem is used for loading confining pressure to the core samples in the first core holder and the second core holder;
the gas sampling component analysis subsystem is used for measuring the gas component concentration of the non-connecting ends of the first core holder and the second core holder;
The saturated formation water injection subsystem is used for injecting formation water into the first core holder and the second core holder.
In another aspect, the present invention provides a method for determining the gas-gas diffusion coefficient in a gas reservoir, the method employing the system for determining the gas-gas diffusion coefficient in a gas reservoir, comprising the steps of:
S1: respectively placing two columnar core samples with the same specification into the first core holder and the second core holder; loading confining pressure to the two columnar core samples with the same specification; adjusting the temperature of the incubator to a set value;
S2: vacuumizing the two core holders in the step S1, and simultaneously injecting stratum water into the two core holders in the step S1 until the water saturation of the columnar core samples with the same specification is achieved;
s3: starting the first gas supply subsystem and the second gas supply subsystem, and respectively injecting two different gases into the two core holders in the step S2 until the fluid pressure values in the two core holders in the step S2 reach the set fluid pressure values, and closing the first gas supply subsystem and the second gas supply subsystem; adjusting the confining pressure of the two columnar core samples with the same specification to reach a set confining pressure value so as to keep the fluid pressure value in the two core holders constant as the set fluid pressure value;
S4: and (3) opening the first knob valve, performing a gas-gas diffusion coefficient measurement experiment, obtaining gas component concentration difference data of the non-connecting ends of the two core holders in step S3 at different time points, and calculating the gas-gas diffusion coefficient in the gas reservoir by combining with the Fick second law.
The technical scheme of the invention has the following beneficial effects:
(1) The system for measuring the gas-gas diffusion coefficient in the gas reservoir can simply and easily measure the gas-gas diffusion coefficient of the water-containing porous medium in the gas reservoir.
(2) The invention is different from the diffusion experiment of the gas in the bulk diffusion chamber to the porous medium (core) in the prior art, and the invention is the diffusion of the gas in the porous medium to the gas in the porous medium, namely, the gas-gas diffusion under the condition of the full porous medium is realized, and the invention is more in line with the actual condition of stratum.
(3) According to the invention, through selecting two rock core samples with the same specification and different water saturation, and setting different fluid pressure values, the gas-gas diffusion coefficients of porous media under different set fluid pressure values and different water saturation conditions can be determined.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular descriptions of exemplary embodiments of the invention as illustrated in the accompanying drawings wherein like reference numbers generally represent like parts throughout the exemplary embodiments of the invention.
Fig. 1 shows a schematic diagram of a system for determining gas-gas diffusion coefficient in a gas reservoir according to embodiment 1 of the present invention.
The reference numerals are explained as follows:
1. A first gas cylinder, a fourth knob valve, a first intermediate container, a first ISCO pump, a second knob valve, a first core holder, a precise differential pressure sensor, a second core holder, a first knob valve, a three-way flow dividing valve and a gas chromatograph, wherein the first knob valve, the three-way flow dividing valve and the gas chromatograph are respectively arranged at the bottom of the core holder and the top of the core holder respectively, the system comprises a data analyzer, a third knob valve, a second intermediate container, a second ISCO pump, a fifth knob valve, a second gas cylinder, a surrounding pressure pump, a constant temperature box, a first inlet end, a second inlet end and an outlet end.
Detailed Description
Preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention are described below, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
In one aspect, the invention provides a system for determining a gas-gas diffusion coefficient in a gas reservoir, the system comprising a first core holder, a second core holder, an incubator, a vacuumizing device, a first gas supply subsystem, a second gas supply subsystem, a confining pressure subsystem, a gas sampling composition analysis subsystem and a saturated formation water injection subsystem;
the first core holder and the second core holder are both arranged in the incubator and are connected with each other through a first knob valve;
The vacuumizing device, the first gas supply subsystem, the second gas supply subsystem, the confining pressure subsystem, the gas sampling component analysis subsystem and the saturated formation water injection subsystem are respectively connected with the first core holder and the second core holder;
The first gas supply subsystem and the second gas supply subsystem are used for injecting gas into the first core holder and the second core holder respectively;
The confining pressure subsystem is used for loading confining pressure to the core samples in the first core holder and the second core holder;
the gas sampling component analysis subsystem is used for measuring the gas component concentration of the non-connecting ends of the first core holder and the second core holder;
The saturated formation water injection subsystem is used for injecting formation water into the first core holder and the second core holder.
In the present invention, the saturated formation water injection subsystem is a well known system device for injecting formation water into the first core holder and the second core holder.
According to the invention, preferably, the confining pressure subsystem comprises a precision differential pressure sensor and a confining pressure pump; and two ends of the confining pressure pump are respectively connected with the side wall of the box body of the first core holder and the side wall of the box body of the second core holder.
According to the present invention, preferably, the gas sampling component analysis subsystem includes a three-way diverter valve, a gas chromatograph, and a data recorder; the three-way diverter valve includes a first inlet end, a second inlet end, and an outlet end; the outlet end is connected with the gas chromatograph and the data recorder in sequence.
According to the present invention, preferably, the outlet end of the first core holder is connected to the outlet end of the second core holder through the first knob valve.
According to the invention, preferably, the system further comprises a second knob valve and a third knob valve.
According to the present invention, preferably, one end of the second knob valve, one end of the first inlet port and one end of the precision differential pressure sensor are all connected to the inlet port of the first core holder.
According to the present invention, preferably, one end of the third knob valve, the second inlet end, and the other end of the precision differential pressure sensor are all connected to the inlet end of the second core holder.
In the present invention, the precision differential pressure sensor is used to monitor the differential pressure across the unconnected ends of the first core holder and the second core holder.
According to the present invention, preferably, the first gas supply subsystem includes a fourth knob valve, a first gas cylinder, a first intermediate container, and a first ISCO pump; the other ends of the first gas cylinder, the fourth knob valve, the first intermediate container and the second knob valve are sequentially connected; the first intermediate container is also connected to the first ISCO pump.
According to the present invention, preferably, the second gas supply subsystem includes a fifth knob valve, a second gas cylinder, a second intermediate container, and a second ISCO pump; the other ends of the second gas cylinder, the fifth knob valve, the second intermediate container and the third knob valve are sequentially connected; the second intermediate container is also connected to the second ISCO pump.
In another aspect, the present invention provides a method for determining the gas-gas diffusion coefficient in a gas reservoir, the method employing the system for determining the gas-gas diffusion coefficient in a gas reservoir, comprising the steps of:
S1: respectively placing two columnar core samples with the same specification into the first core holder and the second core holder; loading confining pressure to the two columnar core samples with the same specification; adjusting the temperature of the incubator to a set value;
S2: vacuumizing the two core holders in the step S1, and simultaneously injecting stratum water into the two core holders in the step S1 until the water saturation of the columnar core samples with the same specification is achieved;
s3: starting the first gas supply subsystem and the second gas supply subsystem, and respectively injecting two different gases into the two core holders in the step S2 until the fluid pressure values in the two core holders in the step S2 reach the set fluid pressure values, and closing the first gas supply subsystem and the second gas supply subsystem; adjusting the confining pressure of the two columnar core samples with the same specification to reach a set confining pressure value so as to keep the fluid pressure value in the two core holders constant as the set fluid pressure value;
S4: and (3) opening the first knob valve, performing a gas-gas diffusion coefficient measurement experiment, obtaining gas component concentration difference data of the non-connecting ends of the two core holders in step S3 at different time points, and calculating the gas-gas diffusion coefficient in the gas reservoir by combining with the Fick second law.
In the invention, the two columnar core samples with the same specification refer to the two columnar core samples with the same water saturation.
In the present invention, in step S1, the purpose of loading confining pressure on the two columnar core samples with the same specification is to make the rubber cylinder in the core holder wrap the core sample.
According to the invention, preferably, the set value of the temperature of the incubator is determined according to the gas reservoir temperature, and the constant temperature time of the incubator is 2-2.5h.
According to the present invention, it is preferable that the difference between the fluid pressure values in the two core holders of step S2 is kept less than 0.1KPa during the injection of the two different gases into the two core holders of step S2, respectively.
In the present invention, in step S3, the present invention can determine the gas-gas diffusion coefficient of the porous medium under the conditions of different set fluid pressure values by setting the different fluid pressure values. The method comprises the following steps:
And if the set fluid pressure values of the two core holders are smaller than or equal to 0.2MPa, adjusting the confining pressure of the columnar core samples with the same specification to 3MPa so as to keep the fluid pressure values in the two core holders constant as the set fluid pressure values.
If the set fluid pressure value of the two core holders is greater than 0.2MPa and less than or equal to 15MPa, the effective stress of the two columnar core samples with the same specification is set to be 3MPa by utilizing the surrounding pressure subsystem so as to keep the fluid pressure values in the two core holders constant as the set fluid pressure value.
If the set fluid pressure value of the two core holders is greater than 15MPa, the effective stress of the two columnar core samples with the same specification is set to be 20% of the set fluid pressure value by utilizing the surrounding pressure subsystem, so that the fluid pressure values in the two core holders are kept constant to be the set fluid pressure value.
Wherein effective stress = overburden formation pressure-fluid pressure, in the present invention the overburden formation pressure is provided in accordance with the confining pressure subsystem.
That is, when the fluid pressure value set by the two core holders is less than or equal to 0.2MPa, the set confining pressure value is the confining pressure of the two columnar core samples with the same specification; when the set fluid pressure value of the two core holders is larger than 0.2MPa, the set confining pressure value is determined according to the effective stress of the two columnar core samples with the same specification.
According to the present invention, preferably, the step of the gas-gas diffusion coefficient measurement experiment includes: and (3) measuring the gas component concentrations of the non-connecting ends of the two core holders in the step (S3) by utilizing a gas chromatography at different time points, and stopping the gas-gas diffusion coefficient measurement experiment when the gas component concentrations of the non-connecting ends of the two core holders in the step (S3) are the same or the gas component concentrations of at least 10 groups are obtained at equal time intervals.
In the present invention, the gas chromatography refers to a composition analysis gas chromatography of GB/T13610-2014 natural gas.
According to the invention, the time interval of the different time points is preferably 2-12h.
According to the invention, preferably, the method further comprises selecting two columnar core samples with the same specification and different water saturation, repeating the steps S1-S4, and determining the gas-gas diffusion coefficient in the gas reservoir under different water saturation conditions.
The present invention is specifically illustrated by the following examples.
Example 1
The present embodiment provides a system for determining gas-gas diffusion coefficient in a gas reservoir, as shown in fig. 1, the system includes a first core holder 6, a second core holder 8, an incubator 19, a vacuum pumping device (not shown), a first gas supply subsystem, a second gas supply subsystem, a confining pressure subsystem, a gas sampling composition analysis subsystem, and a saturated formation water injection subsystem (not shown);
The first core holder 6 and the second core holder 8 are both arranged in the incubator 19, and the outlet end of the first core holder 6 is connected with the outlet end of the second core holder 8 through the first knob valve 9;
the vacuumizing device (not shown), the first gas supply subsystem, the second gas supply subsystem, the confining pressure subsystem, the gas sampling composition analysis subsystem and the saturated formation water injection subsystem (not shown) are respectively connected with the first core holder 6 and the second core holder 8;
The confining pressure subsystem is used for loading confining pressures on core samples in the first core holder 6 and the second core holder 8; the confining pressure subsystem comprises a precise differential pressure sensor 7 and a confining pressure pump 18; and two ends of the confining pressure pump 18 are respectively connected with the box side wall of the first core holder 6 and the box side wall of the second core holder 8.
The gas sampling component analysis subsystem is used for measuring the gas component concentration of the non-connecting ends of the first core holder 6 and the second core holder 8; the gas sampling component analysis subsystem comprises a three-way diverter valve 10, a gas chromatograph 11 and a data recorder 12; the three-way diverter valve 10 includes a first inlet end 20, a second inlet end 21, and an outlet end 22; the outlet end 22 is connected with the gas chromatograph 11 and the data recorder 12 in sequence.
The system further comprises a second knob valve 5 and a third knob valve 13, wherein one end of the second knob valve 5, the first inlet end 20 and one end of the precision differential pressure sensor 7 are all connected to the inlet end of the first core holder 6; one end of the third knob valve 13, the second inlet end 21 and the other end of the precision differential pressure sensor 7 are all connected to the inlet end of the second core holder 8.
The first and second gas supply subsystems are used for injecting gas into the first and second core holders 6 and 8, respectively; the first gas supply subsystem comprises a fourth knob valve 2, a first gas bottle 1, a first intermediate container 3 and a first ISCO pump 4; the other ends of the first gas cylinder 1, the fourth knob valve 2, the first intermediate container 3 and the second knob valve 5 are sequentially connected; said first intermediate container 3 is also connected to said first ISCO pump 4; the second gas supply subsystem comprises a fifth knob valve 16, a second gas cylinder 17, a second intermediate container 14 and a second ISCO pump 15; the other ends of the second gas cylinder 17, the fifth knob valve 16, the second intermediate container 14 and the third knob valve 13 are sequentially connected; the second intermediate container 14 is also connected to the second ISCO pump 15. In this embodiment, the first gas cylinder 1 is a CO 2 gas cylinder, and the second gas cylinder 17 is a CH 4 gas cylinder.
The saturated formation water injection subsystem is used for injecting formation water into the first core holder 6 and the second core holder 8.
Example 2
This embodiment provides a method for determining the gas-gas diffusion coefficient in a gas reservoir, the method employing the system for determining the gas-gas diffusion coefficient in a gas reservoir of embodiment 1, comprising the steps of:
s1: two columnar core samples with the same specification (the length is 100mm, the diameter is 38mm, the porosity is 0.15, the permeability is 12mD, and the water saturation is 58%) are respectively placed in the first core holder 6 and the second core holder 8; loading confining pressure of 3MPa on the two columnar core samples with the same specification; according to the gas reservoir temperature condition, regulating the temperature of the incubator 19 to a set value of 80 ℃, and keeping the constant temperature for 2-2.5 hours;
s2: vacuumizing the two core holders in the step S1 by using the vacuumizing device, and simultaneously injecting formation water into the two core holders in the step S1 by using the saturated formation water injection subsystem until the water saturation of the columnar core samples reaches 58% of that of the columnar core samples with the same specification;
S3: starting the first gas supply subsystem and the second gas supply subsystem, and respectively injecting CO 2 and CH 4 into the two core holders in the step S2 until the fluid pressure values in the two core holders in the step S2 reach the set fluid pressure value of 10MPa, and closing the first gas supply subsystem and the second gas supply subsystem; the confining pressure of the two columnar core samples with the same specification is adjusted by utilizing the confining pressure subsystem to reach a set confining pressure value of 15Mpa (the effective stress is set to be 3 Mpa) so as to keep the fluid pressure value in the two core holders constant as the set fluid pressure value; during the injection of CO 2 and CH 4 into the two core holders of step S2, respectively, the difference in fluid pressure values in the two core holders of step S2 was kept to be less than 0.1KPa.
S4: and (3) opening the first knob valve, performing a gas-gas diffusion coefficient measurement experiment to obtain gas component concentration difference data of the non-connecting ends of the two core holders in the step S3 at different time points, and calculating the gas-gas diffusion coefficient in the gas reservoir to be 5.89 multiplied by 10 -7m2 s-1 by combining with the Fick second law.
The gas-gas diffusion coefficient determination experiment comprises the following steps: measuring the gas component concentrations of the non-connecting ends of the two core holders in the step S3 by utilizing a gas chromatography at different time points, and stopping the gas-gas diffusion coefficient measurement experiment when 10 groups of gas component concentrations are acquired at equal time intervals; the time interval of the different time points is 12h.
Comparative example
This comparative example provides a method for determining the gas-gas diffusion coefficient in a gas reservoir using the system for determining the gas-gas diffusion coefficient in a gas reservoir described in example 1.
The method of this comparative example is different from that of example 2 in that: in the step S2, stratum water is not respectively injected into the two core holders in the step S1;
the method comprises the following steps:
S1: two columnar core samples of the same specification (the length is 100mm, the diameter is 38mm, the porosity is 0.15, the permeability is 12mD, and the water saturation is 0) are respectively placed in the first core holder 6 and the second core holder 8; loading confining pressure of 3MPa on the two columnar core samples with the same specification; according to the gas reservoir temperature condition, regulating the temperature of the incubator 19 to a set value of 80 ℃, and keeping the constant temperature for 2-2.5 hours;
s2: vacuumizing the two core holders in the step S1 by using the vacuumizing device;
S3: starting the first gas supply subsystem and the second gas supply subsystem, and respectively injecting CO 2 and CH 4 into the two core holders in the step S2 until the fluid pressure values in the two core holders in the step S2 reach the set fluid pressure value of 10MPa, and closing the first gas supply subsystem and the second gas supply subsystem; the confining pressure of the two columnar core samples with the same specification is adjusted by the confining pressure subsystem to reach a set confining pressure value of 15MPa (the effective stress is set to be 3 MPa) so as to keep the fluid pressure values in the two core holders constant as the set fluid pressure values; during the injection of CO 2 and CH 4 into the two core holders of step S2, respectively, the difference in fluid pressure values in the two core holders of step S2 was kept to be less than 0.1KPa.
S4: and (3) opening the first knob valve, performing a gas-gas diffusion coefficient measurement experiment to obtain gas component concentration difference data of the non-connecting ends of the two core holders in the step S3 at different time points, and calculating the gas-gas diffusion coefficient in the gas reservoir to be 6.28x10 -8m2 s-1 by combining with the Fick second law.
The gas-gas diffusion coefficient determination experiment comprises the following steps: measuring the gas component concentrations of the non-connecting ends of the two core holders in the step S3 by utilizing a gas chromatography at different time points, and stopping the gas-gas diffusion coefficient measurement experiment when 10 groups of gas component concentrations are acquired at equal time intervals; the time interval of the different time points is 12h.
In the present invention, the purpose of the set control is to:
The difference between the CO 2 gas diffusion coefficients of the dry core and the aqueous core due to the residual water distribution in the core and the dissolution of CO 2, i.e., the conditions of the diffused media change under wet spline conditions, and the diffusion of CO 2 gas is not due solely to the collision of gas molecules in motion, but rather the diffusion of CO 2 gas after dissolution in pore water in the form of gap filling and hydration. According to the test calculation, the diffusion coefficient of the water-containing core is generally 1-2 orders of magnitude larger than that of the dry core.
The foregoing description of embodiments of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the various embodiments described.
Claims (10)
1. A method for measuring gas-gas diffusion coefficient in a gas reservoir, wherein the method adopts a system comprising a first core holder, a second core holder, an incubator, a vacuumizing device, a first gas supply subsystem, a second gas supply subsystem, a confining pressure subsystem, a gas sampling component analysis subsystem and a saturated formation water injection subsystem;
the first core holder and the second core holder are both arranged in the incubator and are connected with each other through a first knob valve;
The vacuumizing device, the first gas supply subsystem, the second gas supply subsystem, the confining pressure subsystem, the gas sampling component analysis subsystem and the saturated formation water injection subsystem are respectively connected with the first core holder and the second core holder;
The first gas supply subsystem and the second gas supply subsystem are used for injecting gas into the first core holder and the second core holder respectively;
The confining pressure subsystem is used for loading confining pressure to the core samples in the first core holder and the second core holder;
the gas sampling component analysis subsystem is used for measuring the gas component concentration of the non-connecting ends of the first core holder and the second core holder;
the saturated formation water injection subsystem is used for injecting formation water into the first core holder and the second core holder;
The method comprises the following steps:
S1: respectively placing two columnar core samples with the same specification into the first core holder and the second core holder; loading confining pressure to the two columnar core samples with the same specification; adjusting the temperature of the incubator to a set value;
S2: vacuumizing the two core holders in the step S1, and simultaneously injecting stratum water into the two core holders in the step S1 until the water saturation of the columnar core samples with the same specification is achieved;
s3: starting the first gas supply subsystem and the second gas supply subsystem, and respectively injecting two different gases into the two core holders in the step S2 until the fluid pressure values in the two core holders in the step S2 reach the set fluid pressure values, and closing the first gas supply subsystem and the second gas supply subsystem; adjusting the confining pressure of the two columnar core samples with the same specification to reach a set confining pressure value so as to keep the fluid pressure value in the two core holders constant as the set fluid pressure value;
S4: and (3) opening the first knob valve, performing a gas-gas diffusion coefficient measurement experiment, obtaining gas component concentration difference data of the non-connecting ends of the two core holders in step S3 at different time points, and calculating the gas-gas diffusion coefficient in the gas reservoir by combining with the Fick second law.
2. The method for determining the gas-gas diffusion coefficient in a gas reservoir of claim 1, wherein the confining pressure subsystem comprises a precision differential pressure sensor and a confining pressure pump; and two ends of the confining pressure pump are respectively connected with the side wall of the box body of the first core holder and the side wall of the box body of the second core holder.
3. The method for determining the gas-gas diffusion coefficient in a gas reservoir of claim 2, wherein the gas sampling composition analysis subsystem comprises a three-way diverter valve, a gas chromatograph, and a data recorder; the three-way diverter valve includes a first inlet end, a second inlet end, and an outlet end; the outlet end is connected with the gas chromatograph and the data recorder in sequence.
4. The method for determining a gas-gas diffusion coefficient in a gas reservoir according to claim 3, wherein,
The outlet end of the first core holder is connected with the outlet end of the second core holder through the first knob valve;
the system further comprises a second knob valve and a third knob valve,
One end of the second knob valve, the first inlet end and one end of the precise differential pressure sensor are all connected to the inlet end of the first core holder;
One end of the third knob valve, the second inlet end and the other end of the precise differential pressure sensor are all connected to the inlet end of the second core holder .
5. The method for determining the gas-gas diffusion coefficient in a gas reservoir of claim 4, wherein said first gas supply subsystem comprises a fourth knob valve, a first gas cylinder, a first intermediate container, and a first ISCO pump; the other ends of the first gas cylinder, the fourth knob valve, the first intermediate container and the second knob valve are sequentially connected; the first intermediate container is also connected to the first ISCO pump;
The second gas supply subsystem comprises a fifth knob valve, a second gas cylinder, a second intermediate container and a second ISCO pump; the other ends of the second gas cylinder, the fifth knob valve, the second intermediate container and the third knob valve are sequentially connected; the second intermediate container is also connected to the second ISCO pump.
6. The method for determining a gas-gas diffusion coefficient in a gas reservoir according to claim 1, wherein the set value of the temperature of the incubator is determined according to the gas reservoir temperature condition, and the constant temperature time of the incubator is 2 to 2.5 hours.
7. The method for determining the gas-gas diffusion coefficient in a gas reservoir according to claim 1, wherein the difference in fluid pressure values in the two core holders of step S2 is kept less than 0.1KPa during the injection of the two different gases into the two core holders of step S2, respectively.
8. The method for determining the gas-gas diffusion coefficient in a gas reservoir according to claim 1, wherein the step of gas-gas diffusion coefficient determination experiments comprises: and (3) measuring the gas component concentrations of the non-connecting ends of the two core holders in the step (S3) by utilizing a gas chromatography at different time points, and stopping the gas-gas diffusion coefficient measurement experiment when the gas component concentrations of the non-connecting ends of the two core holders in the step (S3) are the same or the gas component concentrations of at least 10 groups are obtained at equal time intervals.
9. The method for determining the gas-gas diffusion coefficient in a gas reservoir according to claim 8, wherein the time interval of the different time points is 2-12h.
10. The method for determining the gas-gas diffusion coefficient in a gas reservoir according to any one of claims 1-9, wherein the method further comprises repeating steps S1-S4 with two column-like core samples of the same specification for different water saturation, and determining the gas-gas diffusion coefficient in a gas reservoir under different water saturation conditions.
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