CN119413660A - A method for quantitatively evaluating the diffusion capacity of gas in rocks - Google Patents
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- 238000009792 diffusion process Methods 0.000 title claims abstract description 285
- 239000011435 rock Substances 0.000 title claims abstract description 70
- 238000000034 method Methods 0.000 title claims abstract description 49
- 230000008859 change Effects 0.000 claims abstract description 9
- 230000004907 flux Effects 0.000 claims description 8
- 238000012360 testing method Methods 0.000 claims description 7
- 239000000126 substance Substances 0.000 claims description 6
- 238000011156 evaluation Methods 0.000 abstract description 9
- 238000007789 sealing Methods 0.000 abstract 1
- 239000007789 gas Substances 0.000 description 219
- 238000002474 experimental method Methods 0.000 description 14
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 12
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 10
- 239000001257 hydrogen Substances 0.000 description 9
- 229910052739 hydrogen Inorganic materials 0.000 description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 229910052786 argon Inorganic materials 0.000 description 5
- 238000001514 detection method Methods 0.000 description 5
- 150000002431 hydrogen Chemical class 0.000 description 5
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000005755 formation reaction Methods 0.000 description 4
- 239000001307 helium Substances 0.000 description 4
- 229910052734 helium Inorganic materials 0.000 description 4
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 4
- 230000007246 mechanism Effects 0.000 description 4
- 239000004215 Carbon black (E152) Substances 0.000 description 3
- 229930195733 hydrocarbon Natural products 0.000 description 3
- 150000002430 hydrocarbons Chemical class 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000003345 natural gas Substances 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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- 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
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- 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
- 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
本发明涉及地质勘测的技术领域，提供一种定量评价气体在岩石中扩散能力的方法，包括以下步骤：在目标温度和压力条件下，向位于岩石样品一侧的第一扩散室内通入预设摩尔量的气体a，另一侧的第二扩散室内通入预设摩尔量的气体b，气体a和气体b中的至少一者为待测气体；每隔设定的时间间隔，检测扩散至第一扩散室内的气体b的摩尔量以及扩散至第二扩散室内的气体a的摩尔量；基于预先构建的扩散指数模型以及第一扩散室和第二扩散室间气体a和气体b的摩尔浓度变化情况确定待测气体的扩散指数。通过上述的技术方案，能够更加客观科学地定量表征气体在岩石中的扩散能力，为资源类气藏中盖层的封闭性及储气库介质评价提供可靠的地质理论数据。
The present invention relates to the technical field of geological survey, and provides a method for quantitatively evaluating the diffusion capacity of gas in rock, comprising the following steps: under target temperature and pressure conditions, a preset molar amount of gas a is introduced into a first diffusion chamber located on one side of a rock sample, and a preset molar amount of gas b is introduced into a second diffusion chamber on the other side, wherein at least one of gas a and gas b is the gas to be tested; at set time intervals, the molar amount of gas b diffused into the first diffusion chamber and the molar amount of gas a diffused into the second diffusion chamber are detected; based on a pre-constructed diffusion index model and the change in the molar concentration of gas a and gas b between the first diffusion chamber and the second diffusion chamber, the diffusion index of the gas to be tested is determined. Through the above technical scheme, the diffusion capacity of gas in rock can be more objectively and scientifically quantitatively characterized, and reliable geological theoretical data can be provided for the sealing of caprocks in resource-type gas reservoirs and the evaluation of gas storage media.
Description
Technical Field
The invention relates to the technical field of geological survey, in particular to a method for quantitatively evaluating the diffusion capability of gas in rock.
Background
Either conventional natural gas or green low carbon natural hydrogen resources, or rare helium resources, are energy-like resources that have been concentrated in subterranean formations over a lengthy geological history. In the search for such resources, it is necessary to evaluate the rock that is capping these gases, and the ability to quantitatively characterize the gas diffusion in the formation is an important parameter in the evaluation of the gas reservoir cap layer plugging properties, gas storage conditions, and gas resource potential.
At present, the diffusion capacity of gas in rock is evaluated at home and abroad by utilizing the volume content change of gas diffusion in an isobaric diffusion experiment to obtain the diffusion coefficient of the gas, namely, the volume concentrations of the gas to be detected in two diffusion chambers are measured by utilizing a gas chromatograph, and the measured concentrations are calculated by utilizing the Phak law.
However, with the above-described related art, the gas diffusion coefficient obtained by the method is equal regardless of which two gases are subjected to isobaric diffusion, and such a calculation result cannot truly reflect the gas diffusion capability, and thus affects the evaluation result.
Therefore, how to objectively and scientifically quantitatively characterize the gas diffusion capacity is an important subject to be solved at present.
Disclosure of Invention
The invention provides a method for quantitatively evaluating the gas diffusion capacity in rock, which is used for solving the problem of inaccurate gas diffusion coefficient measured by using an isobaric diffusion experiment in the prior art, and can quantitatively characterize the gas diffusion capacity in rock more objectively and scientifically.
The invention provides a method for quantitatively evaluating the diffusion capability of gas in rock, which is characterized by comprising the following steps:
Under the conditions of target temperature and pressure, introducing a preset molar quantity of gas a into a first diffusion chamber positioned at one side of a rock sample, and introducing a preset molar quantity of gas b into a second diffusion chamber positioned at the other side of the rock sample, wherein at least one of the gas a and the gas b is a gas to be detected;
Detecting the molar amount of the gas b diffused into the first diffusion chamber and the molar amount of the gas a diffused into the second diffusion chamber at set time intervals;
And determining the diffusion index I of the gas to be detected based on a pre-constructed diffusion index model and the molar concentration change condition of the gas a and the gas b between the first diffusion chamber and the second diffusion chamber.
According to the method for quantitatively evaluating the gas diffusion capacity in the rock, the diffusion index model is constructed based on the mass flux and the molar concentration gradient of substances of the gas to be tested and combined with the Fick first law.
According to the method for quantitatively evaluating the gas diffusion capacity in the rock, which is provided by the invention, the diffusion index model is as follows:
;
Wherein, The molar concentration difference of the gas to be measured at the initial moment is the molar concentration difference of the gas to be measured in the first diffusion chamber and the second diffusion chamber; the first diffusion chamber and the second diffusion chamber are arranged in The molar concentration difference of the gas to be measured at the moment; a volume for the first diffusion chamber; a volume of the second diffusion chamber; S is the cross-sectional area of the rock sample to be measured, and H is the length of the rock sample to be measured.
According to the method for quantitatively evaluating the gas diffusion capacity in the rock, in the diffusion index model, the volume of the first diffusion chamberAnd the volume of the second diffusion chamberIs a fixed value.
According to the method for quantitatively evaluating the gas diffusion capacity in the rock, provided by the invention, the initial time is set to be 0, the molar quantity of the gas to be measured at the initial time in the diffusion chamber at the other side is set to be 0, and then the diffusion index model is as follows:
;
Wherein, An initial molar quantity of the gas to be measured; For the gas to be measured Molar mass of moment diffusion.
According to the method for quantitatively evaluating the gas diffusion capacity in the rock, in the diffusion index model, the volume of a first diffusion chamberAnd the volume of the second diffusion chamberEqual.
According to the method for quantitatively evaluating the gas diffusion capacity in the rock, which is provided by the invention, the diffusion index model is as follows:
;
Wherein V is the volume of the first diffusion chamber and the second diffusion chamber.
According to the method for quantitatively evaluating the diffusion capacity of the gas in the rock, the method for determining the diffusion index of the gas to be measured based on a pre-constructed diffusion index model and the molar concentration change condition of the gas a and the gas b in the first diffusion chamber and the second diffusion chamber comprises the following steps:
determining the linear relation between C and t based on the diffusion molar quantity and the diffusion index model of the gas to be detected at different moments;
And obtaining a final diffusion index I through fitting based on the linear relation between C and t.
According to the method for quantitatively evaluating the diffusion capability of the gas in the rock, the molar quantity of the gas to be measured is obtained by the volume fraction of the gas to be measured by a gas chromatograph.
According to the method for quantitatively evaluating the gas diffusion capability in the rock, under the condition of physical gas, the volume fraction and the molar quantity meet the following relation:
;
Wherein, Is thatThe volume fraction of the gas a in the first diffusion chamber at the moment; Is that The volume fraction of the gas a in the second diffusion chamber at the moment; The molar quantity of the gas a in the first diffusion chamber is the initial moment; Is that A molar amount of gas a diffused into the second diffusion chamber at the moment; The molar quantity of the gas b in the second diffusion chamber is the initial moment; Is that The molar quantity of gas b diffused into the first diffusion chamber at the moment.
Compared with the volume concentration, the molar concentration is taken as a dimensional physical quantity, the method for quantitatively evaluating the gas diffusion capacity in the rock can reflect the gas diffusion flux in the rock more intuitively and accurately, so that the gas diffusion capacity in the rock can be quantitatively represented more objectively and scientifically, reliable geological theory data are provided for the closure of a cover layer in a resource gas reservoir and the evaluation of a gas storage medium, and the method has important significance for researching the mechanism of the resource gas reservoir.
Drawings
In order to more clearly illustrate the invention or the technical solutions of the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are some embodiments of the invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for quantitatively evaluating the gas diffusion capacity in rock according to an embodiment of the present invention.
Fig. 2 is a plot of C versus time t for a hydrogen and argon diffusion experiment provided by an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is apparent that the described embodiments are some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order to facilitate understanding of the method for quantitatively evaluating the gas diffusion capability in the rock, the application background is introduced first, and for gas resources such as natural gas, natural hydrogen, helium and the like which are hidden in the stratum, the quantitative characterization of the gas diffusion capability in the stratum is an important parameter for evaluating the plugging performance of a gas reservoir cover layer, the gas preservation condition and the potential of the gas resources.
In the related technology, the diffusion capacity of gas in rock is evaluated at home and abroad, the diffusion coefficient of gas is obtained by utilizing the volume content change of gas diffusion in an isobaric diffusion experiment (specific reference can be made to the existing industry standard SY/T6129-2016, the method for measuring the diffusion coefficient of hydrocarbon gas in rock).
In the experiment, a diffusion cavity is arranged in the isobaric gas device, and the rock to be tested divides the diffusion cavity into two gas chambersAndAt a specific temperature and pressure, toIntroducing a gas a such as methane, hydrogen, etc. into the gas chamberIntroducing gas b, such as nitrogen or argon, with stable chemical properties, collecting and diffusing into the container at set time intervals by gas chromatographThe volume concentration of the medium gas b and diffusion toThe volume concentration of the medium gas a is based on the volume concentration change and the diffusion coefficient of the gas to be measured is obtained by combining the Fick first law.
However, the inventors found in practical experiments that by the above-described test method, the gas diffusion coefficient obtained by the method was equal regardless of which two gases were used for isobaric diffusion, and the gas chamber was set at the initial timeThe volume content of the medium gas a is 100%, and the air chamberThe volume content of the gas b is 100%, and at a certain moment, the gas chamber is measured by using a chromatographThe content of the gas b in the gas chamber is x percentThe content of the gas a in the gas chamber is y percentThe content of the gas a in the gas chamber is (100-x)%, and the gas chamberThe content of the gas b is (100-y)%, the concentration difference of the gas a in the two air chambers is calculated to be (100-x-y)%, the concentration difference of the gas b is calculated to be (100-x-y)%, and the concentration differences of the gas a and the gas b between the two air chambers are equal.
Specifically, taking methane and nitrogen as examples, the detection results of the method for measuring the diffusion coefficient of hydrocarbon gas in rock by using SY/T6129-2016 are shown in the following table:
Table 1, one of the diffusion coefficient detection reports;
table 2, second diffusion coefficient detection report;
It is clear from the above two sets of detection results that the concentration differences of the two gases in the two diffusion chambers are equal at any time, so that the diffusion coefficients of the two gases calculated according to SY/T6129-2016, the method for measuring the diffusion coefficient of hydrocarbon gas in rock are equal, and the two diffusion chambers are two completely different gases, the diffusion coefficients of any two completely different gases in a rock sample are obviously unreasonable, in other words, the experimental method is accurate only when the diffusion coefficients of the two gases in the rock sample are equal or very close, but obviously, the diffusion coefficients of the two gases in the rock sample are unknown.
In addition, in the actual test, since the gas to be tested (such as methane, hydrogen, helium, etc.) is the resource gas actually buried in the ground, and the evaluation of the rock covering these gases is the main objective of the experiment, researchers generally only pay attention to the concentration difference and diffusion coefficient of the gas to be tested, so as to measure the diffusion capacity of the resource gas in the cover rock layer, while another gas is used as an aid, the relationship between the concentration difference, diffusion coefficient and the diffusion coefficient thereof and the diffusion coefficient of the gas to be tested is often ignored, so that the calculation result cannot truly reflect the diffusion capacity of the gas, and further influence the evaluation result.
Therefore, how to objectively and scientifically quantitatively characterize the gas diffusion capacity is an important topic to be solved currently.
Based on the technical problems and findings, the invention provides a method for quantitatively evaluating the gas diffusion capability in the rock, which can quantitatively characterize the gas diffusion capability in the rock more objectively and scientifically, provides reliable geological theory data for the closure of a cover layer in a resource gas reservoir and the evaluation of a gas storage medium, and has important significance for researching the mechanism of resource gas reservoir formation.
The method of quantitatively evaluating the ability of a gas to diffuse in rock according to the present invention is described below with reference to fig. 1-2.
Referring to fig. 1, a method for quantitatively evaluating the ability of a gas to diffuse in rock, comprising the steps of:
And 101, introducing a preset molar quantity of gas a into a first diffusion chamber positioned at one side of the rock sample under the condition of target temperature and pressure, and introducing a preset molar quantity of gas b into a second diffusion chamber positioned at the other side, wherein at least one of the gas a and the gas b is the gas to be detected.
Step 102, detecting the molar amount of the gas b diffused into the first diffusion chamber and the molar amount of the gas a diffused into the second diffusion chamber at predetermined time intervals.
And step 103, determining the diffusion index of the gas to be measured based on a pre-constructed diffusion index model and the molar concentration change condition of the gas a and the gas b between the first diffusion chamber and the second diffusion chamber.
Specifically, when the test is actually performed, a rock sample is placed in a diffusion chamber of an isobaric gas device, the rock sample divides the diffusion chamber of the isobaric gas device into the first diffusion chamber and the second diffusion chamber, a gas a, for example, a resource gas such as hydrogen, methane, helium and the like is introduced into the first diffusion chamber, a gas b, for example, a chemically stable gas such as nitrogen, argon and the like is introduced into the diffusion chamber at the other side, the molar amount of the gas b diffused into the first diffusion chamber and the molar amount of the gas a diffused into the second diffusion chamber are detected at preset intervals, and a diffusion index is obtained according to a molar concentration gradient of the gas a and the gas b between the first diffusion chamber and the second diffusion chamber and a diffusion index model constructed in advance.
At the initial time, the molar concentration of the gas a in the first diffusion chamber isWherein, the method comprises the steps of, wherein,In terms of the molar amount of the gas a,The molar concentration of the gas b in the second diffusion chamber is equal to the volume of the first diffusion chamberWherein, the method comprises the steps of, wherein,In terms of the molar amount of the gas b,Is the volume of the second diffusion chamber.
At a certain time, when the molar amount of the gas a diffused into the second diffusion from the first diffusion chamber is x and the molar amount of the gas b diffused into the first diffusion from the second diffusion chamber is y, the molar concentration of the gas a in the first diffusion chamber isThe molar concentration of the gas a in the second diffusion chamber isThe molar concentration of the gas b in the second diffusion chamber isThe molar concentration of the gas b in the first diffusion chamber isThe molar concentration difference of the gas a between the first diffusion chamber and the second diffusion chamber is-And the molar concentration difference of the gas b between the first diffusion chamber and the second diffusion chamber isThe diffusion index is obtained according to the molar concentration variation and the diffusion index model.
Compared with the volume concentration, the molar concentration is taken as a dimensional physical quantity, the diffusion flux of the gas in the rock can be reflected more intuitively and accurately, so that the diffusion capacity of the gas in the rock can be quantitatively represented more objectively and scientifically, reliable geological theory data are provided for the closure of a cover layer in a resource gas reservoir and the evaluation of a gas storage medium, and the method has important significance for researching the mechanism of the reservoir formation of the resource gas.
In one embodiment of the invention, the diffusion index model is constructed based on the mass flux and molar concentration gradient of the substance of the gas to be measured in combination with the Fick first law.
Specifically, the construction of the diffusion index model includes the following steps.
The rock sample is cut into a cylinder with the bottom surface section area S and the height H, the gas diffusion quantity passing through the rock sample in a certain time is measured in two diffusion chambers, and then the gas diffusion index is obtained according to the Fick first law by the measured values. According to Fick's first law, the flux from the high concentration region to the low concentration stream is proportional to the concentration gradient, and for one-dimensional diffusion, the flux of a substance in the x (i.e. the height direction of the rock to be measured) direction can be considered to be proportional to the concentration gradient there, and the specific formula is as follows (it is to be noted that the units in the formula are all determined according to the experimental practical conditions):
Wherein N is the quantity of a substance diffusing gas, mol, S is the bottom surface sectional area of a rock sample, cm 3, t is the duration of a diffusion test, S, I is the gas diffusion index, cm 2/S; h is the height of the rock sample, i.e. the diffusion distance of the diffusion gas, cm.
Setting the volume of the first diffusion chamber asThe volume of the second diffusion chamber isAfter t time diffusion, the molar concentrations of the gases to be detected in the first diffusion chamber and the second diffusion chamber are respectivelyAndNamely there is。
As is known from the principle of conservation of mass,Substitution simplification can be obtained:
Setting initial time, wherein the molar concentration difference of the gas to be measured between the first diffusion chamber and the second diffusion chamber is as follows Through the process ofAfter time diffusion, the molar concentration difference of the gas to be measured between the first diffusion chamber and the second diffusion chamber isThe integral of the above formula can be obtained:
Then 。
The relation between the molar concentration variation of the gas to be measured between two diffusion chambers and the test time can be measured through the diffusion index model.
In one embodiment of the present invention, in the diffusion test, the pressure between the first diffusion chamber and the second diffusion chamber is equal in an ideal state, however, due to the difference of the diffusion capacities of the gas a and the gas b, a tiny pressure difference is necessarily generated in the first diffusion chamber and the second diffusion chamber along with the progress of the experiment, so that the volumes of the first diffusion chamber and the second diffusion chamber can be adjusted along with the progress of the experiment in an ideal state, and the diffusion chambers on two sides are ensured to be in an isobaric state.
However, the above method can certainly increase the difficulty of the experiment, considering that the pressure difference between the two diffusion chambers is small and the effect on the result of the diffusion experiment is limited, thus, in the diffusion index model, the volume of the first diffusion chamberAnd the volume of the second diffusion chamberIs a fixed value.
In one embodiment of the present invention, the initial time is set to 0, and the molar quantity of the gas to be measured in the diffusion chamber at the other side at the initial time is set to 0, and then the diffusion index model is as follows:
。
Wherein, For the initial molar amount of the gas to be measured,For the gas to be measuredMolar mass of moment diffusion.
Through the diffusion index model, the relation between the change of the molar quantity of the gas to be detected between the two diffusion chambers and the test time can be measured.
In one embodiment of the present invention, in order to further improve the convenience of the experiment, in the diffusion index model, the volume of the first diffusion chamberVolume with the second diffusion chamberEqual, the diffusion index model is:
wherein V is the volume of the first diffusion chamber and the second diffusion chamber, and C is 。
By measuringThe molar quantity of gas diffusion to be measured at any time can be obtainedThe value of the gas C to be measured at the moment.
In one embodiment of the present invention, step 103 includes the steps of:
And S1, determining the linear relation between C and t based on the diffusion molar quantity and the diffusion index model of the gas to be detected at different moments.
And S2, fitting based on the linear relation between C and t to obtain a final diffusion index.
Specifically, by measuring differencesThe molar quantity of the gas diffusion to be measured at the moment can be obtained correspondingly to differentAnd fitting the value of the gas C to be measured at the moment by using a least square method to obtain the linear relation between C and t, wherein the slope is the final diffusion index.
In the following, two gases of hydrogen and argon are taken as specific examples, an isobaric diffusion experiment is carried out under the conditions of 3MPa and 25 ℃, the hydrogen diffusion index is calculated as an example, and the acquired data are substituted into a formula to obtain the following table through calculation.
Table 3, diffusion index detection report for hydrogen and argon.
Referring to FIG. 2, a scatter diagram is formed from times t and C, and a slope is obtained by linear fitting using a least square method= 3.78683E-05 (cm 2/s), coefficient of determination=0.9771。
In one embodiment of the present invention, the molar amount of the gas to be measured is obtained by the volume fraction of the gas to be measured by a gas chromatograph.
Setting the initial time, the mole quantity of the gas a in the first diffusion chamber asThe molar amount of the gas b in the second diffusion chamber isPass throughAfter diffusion of time, the molar amount of the gas a entering the second diffusion chamber from the first diffusion chamber isThe molar amount of the gas b entering the first diffusion chamber from the second diffusion chamber isThe volume fraction of the gas a in the first diffusion chamber was measured by gas chromatographThe volume fraction of the gas a in the second diffusion chamber isIn an ideal case, the molar quantity and the volume fraction satisfy the following relationship:
Finally, the molar amount of diffusion of the gas a is obtained as follows: ;
the molar amount of diffusion of gas b is: 。
by adopting the scheme, the molar quantity of the gas diffusion to be detected can be measured by using a gas chromatograph.
It is to be understood that the various embodiments or examples described in this specification and the features of the various embodiments or examples may be combined and combined by persons skilled in the art without contradiction.
By the method for quantitatively evaluating the gas diffusion capability in the rock, provided by the embodiment of the invention, the molar concentration of the gas a in the first diffusion chamber is as follows at the initial momentWherein, the method comprises the steps of, wherein,In terms of the molar amount of the gas a,The molar concentration of the gas b in the second diffusion chamber is equal to the volume of the first diffusion chamberWherein, the method comprises the steps of, wherein,In terms of the molar amount of the gas b,Is the volume of the second diffusion chamber.
At a certain time, when the molar amount of the gas a diffused into the second diffusion from the first diffusion chamber is x and the molar amount of the gas b diffused into the first diffusion from the second diffusion chamber is y, the molar concentration of the gas a in the first diffusion chamber isThe molar concentration of the gas a in the second diffusion chamber isThe molar concentration of the gas b in the second diffusion chamber isThe molar concentration of the gas b in the first diffusion chamber isThe molar concentration difference of the gas a between the first diffusion chamber and the second diffusion chamber is-And the molar concentration difference of the gas b between the first diffusion chamber and the second diffusion chamber isThe diffusion index is obtained according to the molar concentration variation and the diffusion index model, compared with the volume concentration, the molar concentration is taken as a dimensional physical quantity, and the diffusion flux of the gas in the rock can be reflected more intuitively and accurately, so that the diffusion capacity of the gas in the rock can be quantitatively represented more objectively and scientifically, reliable geological theory data is provided for the closure of a cover layer in a resource gas reservoir and the evaluation of a gas storage medium, and the method has important significance for researching the mechanism of the resource gas reservoir.
It should be noted that the above-mentioned embodiments are merely for illustrating the technical solution of the present invention, and not for limiting the same, and although the present invention has been described in detail with reference to the above-mentioned embodiments, it should be understood by those skilled in the art that the technical solution described in the above-mentioned embodiments may be modified or some technical features may be equivalently replaced, and these modifications or substitutions do not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solution of the embodiments of the present invention.
Claims (10)
1. A method for quantitatively evaluating the ability of a gas to diffuse in rock, comprising the steps of:
Under the conditions of target temperature and pressure, introducing a preset molar quantity of gas a into a first diffusion chamber positioned at one side of a rock sample, and introducing a preset molar quantity of gas b into a second diffusion chamber positioned at the other side of the rock sample, wherein at least one of the gas a and the gas b is a gas to be detected;
Detecting the molar amount of the gas b diffused into the first diffusion chamber and the molar amount of the gas a diffused into the second diffusion chamber at set time intervals;
And determining the diffusion index I of the gas to be detected based on a pre-constructed diffusion index model and the molar concentration change condition of the gas a and the gas b between the first diffusion chamber and the second diffusion chamber.
2. The method of quantitatively evaluating the ability of a gas to diffuse in rock according to claim 1, characterized in that the diffusion index model is constructed based on the mass flux and molar concentration gradient of the substance of the gas to be measured in combination with the fick first law.
3. The method of quantitatively evaluating the ability of a gas to diffuse in rock according to claim 2, wherein the diffusion index model is:
;
Wherein, The molar concentration difference of the gas to be measured at the initial moment is the molar concentration difference of the gas to be measured in the first diffusion chamber and the second diffusion chamber; the first diffusion chamber and the second diffusion chamber are used for measuring the molar concentration difference of the gas to be measured at the moment; a volume for the first diffusion chamber; a volume of the second diffusion chamber; s is the cross-sectional area of the rock sample to be measured, and H is the length of the rock sample to be measured.
4. The method of quantitatively evaluating a gas diffusion capacity in rock according to claim 3, wherein in said diffusion index model, the volume of said first diffusion chamberAnd the volume of the second diffusion chamberIs a fixed value.
5. The method for quantitatively evaluating the diffusion capacity of a gas in rock according to claim 4, wherein the diffusion index model is as follows, when the initial time is set to 0 and the molar quantity of the gas to be measured in the diffusion chamber on the other side at the initial time is set to 0:
;
Wherein, An initial molar quantity of the gas to be measured; For the gas to be measured Molar mass of moment diffusion.
6. The method of quantitatively evaluating a gas's ability to diffuse in rock according to claim 5, wherein in the diffusion index model, the volume of the first diffusion chamberAnd the volume of the second diffusion chamberEqual.
7. The method of quantitatively evaluating a gas's ability to diffuse in rock according to claim 6, wherein the diffusion index model is:
;
wherein V is the volume of the first diffusion chamber and the second diffusion chamber, C is 。
8. The method of quantitatively evaluating a gas diffusivity in rock according to claim 7, wherein said determining a diffusivity of a gas under test based on a pre-constructed diffusion index model and the molar concentration variation of gas a and gas b in said first and second diffusion chambers comprises:
determining the linear relation between C and t based on the diffusion molar quantity and the diffusion index model of the gas to be detected at different moments;
And obtaining a final diffusion index I through fitting based on the linear relation between C and t.
9. The method for quantitatively evaluating the ability of a gas to diffuse in rock according to any one of claims 1 to 8, wherein the molar amount of the gas to be measured is obtained by the volume fraction of the gas to be measured by a gas chromatograph.
10. The method of quantitatively evaluating the ability of a gas to diffuse in rock according to claim 9, wherein said volume fraction and said molar amount satisfy the following relationship under physiological gas conditions:
;
Wherein, Is thatThe volume fraction of the gas a in the first diffusion chamber at the moment; Is that The volume fraction of the gas a in the second diffusion chamber at the moment; The molar quantity of the gas a in the first diffusion chamber is the initial moment; Is that A molar amount of gas a diffused into the second diffusion chamber at the moment; The molar quantity of the gas b in the second diffusion chamber is the initial moment; Is that The molar quantity of gas b diffused into the first diffusion chamber at the moment.
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