CN118150407A

CN118150407A - Method for quantitatively representing wettability of sandstone based on three-dimensional digital rock core

Info

Publication number: CN118150407A
Application number: CN202410584912.1A
Authority: CN
Inventors: 王珂; 孙骞; 王建鹏; 王焱伟
Original assignee: Sanya Offshore Oil And Gas Research Institute Of Northeast Petroleum University; China University of Geosciences Beijing
Current assignee: Sanya Offshore Oil And Gas Research Institute Of Northeast Petroleum University; China University of Geosciences Beijing
Priority date: 2024-05-11
Filing date: 2024-05-11
Publication date: 2024-06-07
Anticipated expiration: 2044-05-11
Also published as: CN118150407B

Abstract

The embodiment of the application provides a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital rock core, which comprises the following steps: preparing a sandstone sample to be tested; applying confining pressure to the sandstone sample to be detected, slowly injecting potassium iodide solution into the sandstone sample to be detected, and simultaneously continuously scanning the sandstone sample to be detected by X rays until the sandstone sample to be detected is completely saturated; injecting a second fluid into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected until the potassium iodide solution is completely displaced; acquiring a three-dimensional image, and acquiring a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of a second fluid according to the three-dimensional image; the first volume fraction and the second volume fraction are compared for wettability characterization. By the technical scheme of the application, the influence of different fluids, especially gas, on the wettability of the rock can be tested, and the sample preparation is simple, the testing speed is high, and the precision is high.

Description

Method for quantitatively representing wettability of sandstone based on three-dimensional digital rock core

Technical Field

The application relates to the technical field of underground energy storage, in particular to a method and a device for quantitatively characterizing wettability of sandstone based on a three-dimensional digital rock core and a method for selecting an underground reservoir.

Background

Sandstone is one of the important reservoirs of fluids in the subsurface, the wettability of which affects the distribution, displacement, and injection and production processes of the fluids. Common methods for researching wettability include a wetting angle direct measurement method, a self-absorption method, a nuclear magnetic resonance method, a relative permeability curve method, a conventional well logging information method and the like, the methods are mainly aimed at liquids, some test results are macroscopically influenced by sample preparation and fluid infiltration depth, accuracy is relatively low, besides the liquids, various gases such as methane in shale gas reservoirs, carbon dioxide injected in carbon sequestration processes, hydrogen in underground hydrogen reservoirs and mixed bedding gases can exist in underground reservoirs, and the influence of the gases on rock wettability is difficult to judge by the conventional wettability test methods.

The choice of subsurface reservoir requires a combination of factors in addition to the wettability of the sandstone.

Disclosure of Invention

The embodiment of the application provides a method and a device for quantitatively characterizing sandstone wettability based on a three-dimensional digital rock core and a method for selecting a subsurface reservoir.

According to a first aspect of the embodiment of the application, a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital rock core is provided, and a sandstone sample to be tested is prepared; applying confining pressure to the sandstone sample to be detected, slowly injecting potassium iodide solution into the sandstone sample to be detected, and simultaneously continuously scanning the sandstone sample to be detected by X rays until the sandstone sample to be detected is completely saturated; injecting a second fluid into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected until the potassium iodide solution is completely displaced; acquiring a three-dimensional image, and acquiring a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of a second fluid according to the three-dimensional image; the first volume fraction and the second volume fraction are compared for wettability characterization.

According to the method for quantitatively characterizing the wettability of sandstone based on the three-dimensional digital rock core, firstly, a sandstone sample to be tested is prepared. Then applying confining pressure to the sandstone sample to be detected, slowly injecting potassium iodide solution and simultaneously carrying out X-ray continuous scanning until the sample is completely saturated. And (3) injecting a second fluid into the sandstone sample to be tested, and continuously scanning by X rays until the potassium iodide solution is completely displaced. And finally, obtaining a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of the second fluid according to the three-dimensional image, and comparing the first volume fraction with the second volume fraction for wettability characterization, so that the influence of different fluids, particularly gases, on rock wettability can be tested. And the rock is not required to be replaced, so that the influence of heterogeneity is avoided, the sample preparation is simple, the test speed is high, the precision is high, the method can be used for batch rock test, the wettability characteristics of the rock under different deposition environments or geological backgrounds are compared, and important basis is provided for injection and production scheme design and underground reservoir selection.

In an optional embodiment of the present application, the applying a confining pressure to the sandstone sample to be measured, slowly injecting a potassium iodide solution into the sandstone sample to be measured, and continuously scanning the sandstone sample to be measured by X-rays until the sandstone sample to be measured is completely saturated, specifically includes:

Applying confining pressure to the sandstone sample to be tested;

Slowly injecting potassium iodide solution into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected to obtain a three-dimensional digital core;

And quantitatively dividing the three-dimensional digital rock core until the saturation value of the sandstone sample to be detected is unchanged.

In an optional embodiment of the present application, the quantitatively dividing the three-dimensional digital core until the saturation value of the sandstone sample to be measured does not change specifically includes:

quantitatively dividing the three-dimensional digital rock core to obtain a saturation value of the sandstone sample to be detected;

judging whether the saturation value changes or not;

if not, the sandstone sample to be detected is completely saturated, and the injection of the potassium iodide solution is stopped.

In an alternative embodiment of the present application, the injecting the second fluid into the sandstone sample to be tested, and simultaneously performing continuous X-ray scanning on the sandstone sample to be tested until the potassium iodide solution is completely displaced, specifically includes:

Injecting a second fluid into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected to obtain a two-dimensional X-ray image and a three-dimensional digital rock core;

Judging whether the potassium iodide solution is completely discharged out of the sandstone sample to be tested according to the two-dimensional X-ray image;

if yes, quantitatively dividing the three-dimensional digital rock core to confirm that the displacement of the second fluid is completed.

In an optional embodiment of the present application, the acquiring a three-dimensional image, and obtaining a first volume fraction saturated with potassium iodide and a second volume fraction fully filled with the second fluid according to the three-dimensional image specifically includes:

acquiring a first three-dimensional image of the sandstone sample to be detected after being completely saturated, and carrying out filtering and position alignment on the first three-dimensional image to obtain a first image gray level difference;

obtaining original porosity and residual porosity after filling potassium iodide according to the gray level difference of the first image;

and obtaining a first volume fraction after potassium iodide saturation according to the difference between the original porosity and the residual porosity.

In an optional embodiment of the application, the acquiring a three-dimensional image, obtaining a first volume fraction saturated with potassium iodide and a second volume fraction fully filled with the second fluid according to the three-dimensional image, further includes:

Acquiring a second three-dimensional image after the potassium iodide solution is completely displaced, and filtering and aligning the second three-dimensional image to obtain a second image gray level difference;

and dividing according to the gray level difference of the second image to obtain a second volume fraction of the second fluid after the second fluid is completely filled.

In an alternative embodiment of the present application, the comparing the first volume fraction and the second volume fraction for wettability characterization specifically includes:

and calculating according to the first volume fraction and the second volume fraction to obtain a wettability index.

In an alternative embodiment of the application, hydrophilic is represented when the wettability index is greater than a preset value and hydrophobic is represented when the wettability index is less than a preset value.

In a second aspect of the embodiment of the present application, there is provided a system for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, including:

a preparation module (110) for preparing a sandstone sample to be tested;

the potassium iodide injection module (120) is used for applying confining pressure to the sandstone sample to be detected, slowly injecting potassium iodide solution into the sandstone sample to be detected, and simultaneously continuously scanning X-rays on the sandstone sample to be detected until the sandstone sample to be detected is completely saturated;

a displacement module (130) for injecting a second fluid into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected until the potassium iodide solution is completely displaced;

An acquisition module (140) for acquiring a three-dimensional image, and acquiring a first volume fraction saturated with potassium iodide and a second volume fraction fully filled with a second fluid according to the three-dimensional image;

a contrast module (150) for comparing the first volume fraction and the second volume fraction for wettability characterization.

In a third aspect of the embodiments of the present application, there is provided a method for selecting a subsurface reservoir, comprising the steps of the method for quantitatively characterizing sandstone wettability based on a three-dimensional digital core, further comprising:

Preparing a rock sample;

placing the rock sample in a rock core holder capable of transmitting X rays, and applying pressure to simulate formation confining pressure to perform initial rock structure scanning;

injecting a fluid into the rock sample and performing continuous X-ray scanning to obtain a three-dimensional gray scale image;

Extracting rock fracture structure information under the continuous action of the fluid in the three-dimensional gray level image to realize quantitative characterization, wherein the fluid comprises fluids in different phases;

The subsurface reservoir is selected based on sandstone wettability and rock fracture structure.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute a limitation on the application. In the drawings:

FIG. 1 is a flow chart of the steps of a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, according to one embodiment of the present application;

FIG. 2 is a flow chart illustrating steps of a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, according to one embodiment of the present application;

FIG. 3 is a flow chart illustrating steps of a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, according to one embodiment of the present application;

FIG. 4 is a flow chart illustrating steps of a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, according to one embodiment of the present application;

FIG. 5 is a flow chart illustrating steps of a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, according to one embodiment of the present application;

FIG. 6 is a flow chart illustrating steps of a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, according to one embodiment of the present application;

FIG. 7 is a flow chart illustrating steps of a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, according to one embodiment of the present application;

FIG. 8 is a block diagram of a system for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, according to one embodiment of the present application;

FIG. 9 is a flow chart illustrating steps of a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, according to one embodiment of the present application;

FIG. 10 is a three-dimensional image of a sandstone sample to be tested at a confining pressure of 10MPa, according to one embodiment of the application;

FIG. 11 is a three-dimensional image of a sandstone sample to be tested, after saturation with a potassium iodide solution, according to one embodiment of the present application;

FIG. 12 is a three-dimensional image of a sandstone sample to be tested after complete CO2 filling, according to one embodiment of the present application.

The correspondence between the reference numerals and the component names in fig. 8 is:

10: a system for quantitatively characterizing wettability of sandstone based on the three-dimensional digital core; 110: preparing a module; 120: a potassium iodide injection module; 130: a displacement module; 140: an acquisition module; 150: and a comparison module.

Detailed Description

In order that the above-recited objects, features and advantages of the present application will be more clearly understood, a more particular description of the application will be rendered by reference to the appended drawings and appended detailed description. It should be noted that, without conflict, the embodiments of the present application and features in the embodiments may be combined with each other.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application, but the present application may be practiced in other ways than those described herein, and therefore the scope of the present application is not limited to the specific embodiments disclosed below.

Methods, apparatus, methods of selecting subsurface reservoirs for characterizing sandstone wettability based on three-dimensional digital cores, according to some embodiments of the present application, are described below with reference to fig. 1-12.

As shown in fig. 1, an embodiment of the present application provides a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, comprising the following steps:

step S102: preparing a sandstone sample to be tested;

Step S104: applying confining pressure to the sandstone sample to be detected, slowly injecting potassium iodide solution into the sandstone sample to be detected, and simultaneously continuously scanning the sandstone sample to be detected by X rays until the sandstone sample to be detected is completely saturated;

Step S106: injecting a second fluid into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected until the potassium iodide solution is completely displaced;

Step S108: acquiring a three-dimensional image, and acquiring a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of a second fluid according to the three-dimensional image;

Step S110: the first volume fraction and the second volume fraction are compared for wettability characterization.

According to the method for characterizing the wettability of sandstone, firstly, a sandstone sample to be tested is prepared. Then applying confining pressure to the sandstone sample to be detected, slowly injecting potassium iodide solution and simultaneously carrying out X-ray continuous scanning until the sample is completely saturated. And (3) injecting a second fluid into the sandstone sample to be tested, and continuously scanning by X rays until the potassium iodide solution is completely displaced. And finally, obtaining a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of the second fluid according to the three-dimensional image, and comparing the first volume fraction with the second volume fraction for wettability characterization, so that the influence of different fluids, particularly gases, on rock wettability can be tested. And the rock is not required to be replaced, so that the influence of heterogeneity is avoided, the sample preparation is simple, the test speed is high, the precision is high, the method can be used for batch rock test, the wettability characteristics of the rock under different deposition environments or geological backgrounds are compared, and important basis is provided for injection and production scheme design and underground reservoir selection.

As shown in fig. 2, according to a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core according to an embodiment of the present application, a confining pressure is applied to a sandstone sample to be tested, and a potassium iodide solution is slowly injected into the sandstone sample to be tested, and at the same time, an X-ray continuous scan is performed on the sandstone sample to be tested until the sandstone sample to be tested is completely saturated, which specifically includes the following steps:

step S202: applying confining pressure to a sandstone sample to be tested;

Step S204: slowly injecting potassium iodide solution into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected to obtain a three-dimensional digital core;

step S206: and quantitatively dividing the three-dimensional digital rock core until the saturation value of the sandstone sample to be measured is unchanged.

In the embodiment, the confining pressure is applied to the sandstone sample to be measured, the potassium iodide solution is slowly injected into the sandstone sample to be measured, and meanwhile, the X-ray continuous scanning is carried out on the sandstone sample to be measured until the sandstone sample to be measured is completely saturated, specifically, the confining pressure is firstly applied to the sandstone sample to be measured. And then slowly injecting potassium iodide solution into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected to obtain the three-dimensional digital core. And quantitatively dividing the three-dimensional digital rock core until the saturation value of the sandstone sample to be measured is unchanged. The quantitative segmentation is carried out through the three-dimensional digital rock core, so that the dynamic wetting characteristic of the fluid in the sandstone can be understood from a three-dimensional angle, and the method has important significance in researching the reservoir and exploitation of oil gas and underground gas storage.

As shown in fig. 3, according to a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core according to an embodiment of the present application, quantitative segmentation is performed on the three-dimensional digital core until saturation values of sandstone samples to be tested do not change, and the method specifically includes the following steps:

Step S302: quantitatively dividing the three-dimensional digital rock core to obtain a saturation value of a sandstone sample to be measured;

step S304: judging whether the saturation value changes or not;

Step S306: if not, the sandstone sample to be detected is completely saturated, and the injection of the potassium iodide solution is stopped.

In this embodiment, the three-dimensional digital core is quantitatively segmented until the saturation value of the sandstone sample to be measured does not change, and specifically, the three-dimensional digital core is quantitatively segmented to obtain the saturation value of the sandstone sample to be measured. And judging whether the saturation value changes or not. And if the saturation value is unchanged, the sandstone sample to be detected is completely saturated, and the injection of the potassium iodide solution is stopped. It can be understood that the method for judging whether the sample is fully saturated with the potassium iodide solution is to quantitatively divide the three-dimensional digital core under different potassium iodide injection stages until the obtained saturation value is basically unchanged, and then the sample can be judged to be fully saturated.

As shown in fig. 4, according to a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core according to an embodiment of the present application, a second fluid is injected into a sandstone sample to be tested, and at the same time, X-ray continuous scanning is performed on the sandstone sample to be tested until a potassium iodide solution is completely displaced, which specifically includes the following steps:

step S402: injecting a second fluid into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected to obtain a two-dimensional X-ray image and a three-dimensional digital rock core;

Step S404: judging whether the potassium iodide solution is completely discharged out of the sandstone sample to be tested according to the two-dimensional X-ray image;

Step S406: if yes, quantitatively dividing the three-dimensional digital rock core to confirm that the second fluid is completely displaced.

In this embodiment, the second fluid is injected into the sandstone sample to be measured, and at the same time, the sandstone sample to be measured is continuously scanned by X-rays until the potassium iodide solution is completely displaced, specifically, the second fluid is injected into the sandstone sample to be measured first, and at the same time, the sandstone sample to be measured is continuously scanned by X-rays, so as to obtain a two-dimensional X-ray image and a three-dimensional digital core. And judging whether the potassium iodide solution is completely discharged out of the sandstone sample to be tested according to the two-dimensional X-ray image. If yes, quantitatively dividing the three-dimensional digital rock core to confirm that the second fluid is completely displaced. It can be understood that the method for judging whether the sample is completely saturated with the second fluid is to preliminarily judge whether the potassium iodide solution is completely discharged from the sample through the two-dimensional X-ray image, and then quantitatively divide the sample through the three-dimensional digital core to confirm that the second fluid is completely displaced.

As shown in fig. 5, according to a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core according to an embodiment of the present application, a three-dimensional image is obtained, and a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of a second fluid are obtained according to the three-dimensional image, which specifically includes the following steps:

Step S502: acquiring a first three-dimensional image of a sandstone sample to be detected after full saturation, and filtering and aligning the first three-dimensional image to obtain a first image gray level difference;

Step S504: obtaining original porosity and residual porosity after filling potassium iodide according to the gray level difference of the first image;

step S506: and obtaining a first volume fraction after potassium iodide saturation according to the difference between the original porosity and the residual porosity.

In the embodiment, a three-dimensional image is acquired, a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of a second fluid are obtained according to the three-dimensional image, specifically, the first three-dimensional image is acquired first, filtering and position alignment are carried out on the first three-dimensional image, and original porosity and residual porosity after filling of potassium iodide are obtained according to the gray level difference of the image. And then, according to the original porosity and the residual porosity, obtaining the first volume fraction of saturated potassium iodide by differencing.

As shown in fig. 6, according to a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core according to an embodiment of the present application, a three-dimensional image is obtained, and a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of a second fluid are obtained according to the three-dimensional image, and further including the following steps:

Step S602: obtaining a second three-dimensional image after the potassium iodide solution is completely displaced, and filtering and aligning the second three-dimensional image to obtain a second image gray level difference;

Step S604: and obtaining a second volume fraction of the second fluid after the second fluid is completely filled according to the gray level difference segmentation of the second image.

In the embodiment, a three-dimensional image is obtained, a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of a second fluid are obtained according to the three-dimensional image, the method further comprises the steps of obtaining a second three-dimensional image, filtering and aligning the second three-dimensional image, and dividing according to the gray level difference of the image to obtain the second volume fraction after complete filling of the second fluid. Wettability characterization can be performed by comparing the first volume fraction, the second volume fraction.

As shown in fig. 7, a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core according to one embodiment of the present application, by comparing a first volume fraction and a second volume fraction, specifically includes the following steps:

Step S702: and calculating according to the first volume fraction and the second volume fraction to obtain the wettability index.

In this embodiment, the first volume fraction and the second volume fraction are compared for wettability characterization, in particular calculated from the first volume fraction and the second volume fraction, resulting in a wettability index. Whether sandstone is hydrophilic or hydrophobic can be determined by the wettability index.

In the above embodiment, when the wettability index is greater than a preset value, it represents hydrophilicity, and when the wettability index is less than the preset value, it represents hydrophobicity. The preset value ranges from 0.9 to 1.1. Wherein the preset value may be 1.

In some embodiments, the wettability is characterized by the formula:

；

Wherein, Is wettability index,/>Is the original porosity,/>To residual porosity after filling with Potassium iodide,/>A second volume fraction of the second fluid after being completely filled. The wettability index can be calculated from the original porosity, the residual porosity after filling with potassium iodide, and the second volume fraction after complete filling with the second fluid.

In some embodiments, the sandstone sample to be tested comprises a cylindrical sandstone sample. The diameter of the cylindrical sandstone sample may be 3mm. The height of the cylindrical sandstone sample may be 1.5mm.

In the above embodiment, the confining pressure is applied to be 10MPa, and the X-rays are synchrotron radiation X-rays.

In some embodiments, the second fluid is a fluid that has an effect on the wettability of the sandstone under actual geological conditions, and may be a liquid or a gas. Wherein the second fluid may be carbon dioxide.

As shown in fig. 8, an embodiment of the present application provides a system 10 for characterizing sandstone wettability, comprising: a preparation module 110 for preparing a sandstone sample to be tested; the potassium iodide injection module 120 is used for applying confining pressure to the sandstone sample to be detected, slowly injecting a potassium iodide solution into the sandstone sample to be detected, and simultaneously continuously scanning the sandstone sample to be detected by X rays until the sandstone sample to be detected is completely saturated; the displacement module 130 is used for injecting a second fluid into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected until the potassium iodide solution is completely displaced; an obtaining module 140, configured to obtain a three-dimensional image, and obtain a first volume fraction saturated with potassium iodide and a second volume fraction fully filled with a second fluid according to the three-dimensional image; a contrast module 150 for comparing the first volume fraction and the second volume fraction for wettability characterization.

The system 10 for characterizing sandstone wettability provided in accordance with the present embodiment includes a preparation module 110, a potassium iodide injection module 120, a displacement module 130, an acquisition module 140, and a comparison module 150. Wherein, the preparation module 110 is used for preparing the sandstone sample to be tested. The potassium iodide injection module 120 is used for applying confining pressure to the sandstone sample to be tested, slowly injecting potassium iodide solution into the sandstone sample to be tested, and continuously scanning X-rays on the sandstone sample to be tested until the sandstone sample to be tested is completely saturated. The displacement module 130 is used for injecting a second fluid into the sandstone sample to be detected, and simultaneously, continuously scanning X rays on the sandstone sample to be detected until the potassium iodide solution is completely displaced. The acquisition module 140 is configured to acquire a three-dimensional image, and obtain a first volume fraction saturated with potassium iodide and a second volume fraction fully filled with the second fluid according to the three-dimensional image. The contrast module 150 is configured to compare the first volume fraction to the second volume fraction for wettability characterization. By means of the system 10 for characterizing the wettability of sandstone according to the application, it is possible to test the effect of different fluids, in particular gases, on the wettability of rock. And the rock is not required to be replaced, so that the influence of heterogeneity is avoided, the sample preparation is simple, the test speed is high, the precision is high, the method can be used for batch rock test, the wettability characteristics of the rock under different deposition environments or geological backgrounds are compared, and important basis is provided for injection and production scheme design and underground reservoir selection.

As shown in fig. 9, 10, 11 and 12, a method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core according to a specific embodiment provided by the application comprises the following steps:

s1: and preparing a sandstone sample to be tested.

S2: and (3) applying confining pressure to sandstone to be detected, slowly injecting potassium iodide solution, and simultaneously carrying out X-ray continuous scanning until the sample is completely saturated.

S3: and (3) injecting a second fluid into the sandstone to be tested, and continuously scanning by X rays until the potassium iodide solution is completely displaced.

S4: and obtaining the volume fraction of the saturated potassium iodide and the volume fraction of the second fluid after the second fluid is completely filled according to the three-dimensional image.

S5: the potassium iodide volume fraction was compared to the second fluid volume fraction for wettability characterization.

In this example, the sandstone sample to be tested was prepared as a cylinder with a diameter of 3mm and a height of 1.5 mm. The confining pressure is applied to be 10MPa, synchronous radiation X-rays are used for scanning, and the original three-dimensional image of the rock is shown in figure 2. The method for judging whether the sample is fully saturated with potassium iodide (potassium iodide) solution is to quantitatively divide three-dimensional digital rock cores in different potassium iodide injection stages until the obtained saturation value basically changes, and then the sample is judged to be fully saturated, and the rock after the potassium iodide is saturated is shown in figure 3. The second fluid is CO ₂ gas. The method for judging whether the sample is fully saturated with CO ₂ is to preliminarily judge that the interior of the rock is changed from black gray to transparent through a two-dimensional X-ray image, and then quantitatively divide through a three-dimensional digital rock core to confirm that the distribution of CO ₂ is basically unchanged, wherein the rock after the CO ₂ filling is completed is shown in fig. 4. And carrying out non-local mean filtering on the three-dimensional image, carrying out translational rotation for position alignment, and dividing according to the gray level difference of the image to obtain the original porosity of 1.95%, the residual porosity of 0.34%, and the volume fraction of the fully filled CO ₂ of 1.01%.

Based on the above formula, the following formula is further adopted:

In the middle of Refer to original porosity,/>Refers to residual porosity after filling potassium iodide,/>Refers to the volume fraction of CO ₂. When I is greater than 1, it represents hydrophilic, and when I is less than 1, it represents hydrophobic, and the sandstone wettability index of this example is 1.59, indicating that the sandstone has hydrophilic properties.

From the above description, it can be seen that this embodiment has the following technical effects: the rock wettability characterization under the condition of stratum confining pressure is realized, errors caused by sample preparation problems or difficult complete wetting of the surface of a sample during spontaneous imbibition can be eliminated, and the rock wettability can be characterized under the action of liquid phase and gas phase. This embodiment is also suitable for studying dynamic wetting of fluids in sandstone reservoirs, where oil or gas is difficult to drain from the sandstone if the surface tension of the sandstone pores is high, and where these fluids are more easily released if the surface tension is low. Therefore, the method provided by the embodiment can understand the dynamic wetting characteristic of the fluid in the sandstone from a three-dimensional angle, and has important significance for researching the reservoir and exploitation of oil gas and underground gas storage.

The method for selecting a subsurface reservoir provided according to the present application comprises the steps of the method for quantitatively characterizing sandstone wettability based on a three-dimensional digital core, and further comprises:

Preparing a rock sample;

The subsurface reservoir is selected according to sandstone wettability and rock fracture structure, i.e., among a plurality of subsurface reservoirs to be selected for which the rock wettability is hydrophilic, the fracture structure of the rock is selected to be the subsurface reservoir to be selected for which the length, width, and volume of the rock fracture structure are least changed when the gas phase state of the gas to be stored is changed.

In an embodiment of the application, the step of injecting a fluid into the rock sample and performing a continuous X-ray scan to obtain a three-dimensional gray scale image is preceded by the steps of: environmental conditions are configured to be compatible with the phase inversion of the fluid to enable the fluid to be inverted between different phases, the fluid including CO ₂ of different phases. The environmental conditions include temperature conditions and pressure conditions that are compatible with the phase inversion of the fluid. The step of extracting rock fracture structure information under the continuous action of the fluid in the three-dimensional gray level image to realize quantitative characterization comprises the following steps: importing the three-dimensional gray scale image into an imaging data analysis device; extracting a rock fracture structure of the same rock fracture under the action of different phase fluids; and quantitatively characterizing the rock fracture structure under the action of different phase fluids. The step of preparing a rock sample specifically comprises the following steps: and preparing the rock sample into a rock sample which meets the preset scanning resolution and meets the size requirement of the core holder. The rock sample prepared comprises at least one of the following: a cylindrical rock sample, a rectangular rock sample, and a square rock sample. The step of injecting a fluid into the rock sample and performing a continuous X-ray scan to obtain a three-dimensional gray scale image comprises: the fluid is injected into the rock sample and subjected to continuous synchrotron radiation X-ray scanning to obtain a three-dimensional gray scale image. The step of placing the rock sample in an X-ray transparent core holder and applying pressure to simulate formation confining pressure to perform initial rock structure scanning comprises the following steps: placing the rock sample in a rock core holder capable of transmitting X rays, and continuously injecting water into the rock core holder until the pressure generated by the rock core holder reaches the preset stratum confining pressure; and performing initial rock structure scanning based on the pressure generated by the core holder reaching the preset stratum confining pressure. The step of continuously injecting water into the core holder until the pressure generated by the core holder reaches the preset formation confining pressure comprises the following steps: and continuously injecting water into the core holder through a plunger pump until the pressure generated by the core holder reaches the preset formation confining pressure. The step of injecting a fluid into the rock sample and performing a continuous X-ray scan is preceded by the step of: and (5) carrying out saturation treatment on the rock sample by brine.

A method for selecting a subsurface reservoir provided according to the present application further comprises:

Preparing a rock sample;

Performing X-ray scanning on the rock sample to obtain an initial three-dimensional structural image of the rock sample;

applying different confining pressures to the rock sample, and performing continuous in-situ X-ray scanning to obtain three-dimensional structure images of the rock sample in different time and different deformation states;

Post-processing the initial three-dimensional structure image and the three-dimensional structure image of the rock sample under different deformation states at different times to obtain a gray level image for strain calculation;

And determining the strain and distribution mode of the rock sample under different surrounding pressures based on the gray level image so as to realize the representation of rock continuous strain and select a subsurface reservoir according to sandstone wettability, rock fracture structure and rock continuous strain.

In an embodiment of the present application, the step of determining the strain and distribution pattern of the rock sample under different surrounding pressures based on the gray level image specifically includes: and calculating a strain field of the rock sample subjected to stress deformation relative to the previous moment based on the gray level image so as to determine the strain and distribution modes of the rock sample under different surrounding pressures. The step of calculating the strain field of the rock sample deformed by stress relative to the previous moment based on the gray level image specifically comprises the following steps: and calculating the strain field of the rock sample deformed by stress relative to the previous moment by adopting a digital correlation method based on the gray level image. The step of calculating the strain field of the rock sample deformed by stress relative to the previous moment by adopting a digital correlation method based on the gray level image specifically comprises the following steps: importing the gray scale image into an imaging data analysis device; dividing the three-dimensional structure image of the rock sample deformed under different confining pressures and the three-dimensional structure image of the rock sample at the previous moment into a plurality of subvolumes; matching a plurality of said sub-volumes by correlation, the center of each of said sub-volumes being used to estimate and map a displacement field; the displacement field is converted to the strain field by a central finite difference. The steps of applying different confining pressures to the rock sample and performing continuous in-situ X-ray scanning specifically comprise: the rock sample was placed in an X-ray transparent core holder and successive in situ X-ray scans were performed with different confining pressures applied. The rock sample is placed in a rock core holder capable of transmitting X rays, and different confining pressures are applied to perform continuous in-situ X ray scanning, and the method specifically comprises the following steps of: the rock sample is placed in an X-ray transparent core holder, water is continuously injected into the core holder, and continuous in-situ X-ray scanning is performed. The step of post-processing the initial three-dimensional structure image and the three-dimensional structure image of the rock sample under different deformation states at different times specifically comprises the following steps: and carrying out image registration and noise removal processing on the initial three-dimensional structure image and the three-dimensional structure image of the rock sample under different deformation states at different times. Before the steps of performing image registration and noise removal processing on the initial three-dimensional structure image and the three-dimensional structure image of the rock sample under different deformation states at different times, the method further comprises: and pre-registering the initial three-dimensional structure image and the three-dimensional structure image of the rock sample under different deformation states at different times through aligning centers or aligning principal coordinate axes. The noise removal includes non-local mean filtering, gaussian filtering, and median filtering. The rock sample prepared comprises at least one of the following: a cylindrical rock sample, a rectangular rock sample, and a square rock sample. The step of X-ray scanning the rock sample is preceded by: the rock sample is placed in the range of an X-ray scanning view. The step of performing X-ray scanning on the rock sample to obtain an initial three-dimensional structural image of the rock sample specifically includes: and carrying out continuous synchrotron radiation X-ray scanning on the rock sample to obtain a high-resolution initial three-dimensional structure image of the rock sample. The step of X-ray scanning the rock sample to obtain an initial three-dimensional structural image of the rock sample is preceded by: fluid is injected into the rock sample. The fluid comprises fluids of different phases.

Scanning the rock sample to obtain a rock structure image;

Constructing a rock pore network model according to the rock structure image;

And constructing a gas mutual flooding model of the rock according to the rock pore network model, wherein the gas mutual flooding model is used for determining the gas mutual flooding characteristic of the rock so as to select a subsurface reservoir according to the wettability of sandstone, the rock fracture structure, the rock continuous strain and the gas mutual flooding characteristic of the rock.

In an embodiment of the application, said constructing a pore network model from said rock structure image comprises: dividing the rock structure image to obtain a rock pore distribution image; and constructing the rock pore network model according to the rock pore distribution image. The constructing the rock pore network model according to the rock pore distribution image comprises the following steps: separating the rock pore distribution image to obtain a rock pore phase model; and constructing the rock pore network model according to the rock pore phase model. The step of separating the rock pore distribution image to obtain a rock pore phase model comprises the following steps: and separating the rock pore distribution image according to the pixel value to obtain the rock pore phase model. The constructing a gas mutual flooding model according to the rock pore network model comprises the following steps: optimizing the rock pore network model to obtain a rock grid structure model; and constructing a rock gas mutual driving model according to the rock grid structure model. The optimizing the rock pore network model to obtain a rock grid structure model comprises the following steps: converting the rock pore network model into a rock three-dimensional structure model; and carrying out optimization treatment on the rock three-dimensional structure model to obtain a rock grid structure model. The optimizing the rock three-dimensional structure model to obtain a rock grid structure model comprises the following steps: converting the rock three-dimensional structure model into a first grid model according to the first grid density; and carrying out optimization treatment on the first grid model to obtain the rock grid structure model. The optimization processing at least comprises overlapping grid removing processing, grid hole filling processing and special-shaped grid adjusting processing. The building of the rock gas mutual driving model according to the rock grid structure model comprises the following steps: and training the rock grid structure model according to a sample data set to obtain the rock gas mutual flooding model. The sample data set includes at least a training data set and a test data set. The scanning of the rock to obtain the rock structure image comprises the following steps: and carrying out X-ray scanning on the rock to obtain the rock structure image. The rock structure image is a gray image with preset storage capacity.

Preparing a rock sample, and determining a marker corresponding to an organic matter to be detected on the rock sample;

determining first position information of the organic matter to be detected through a nano infrared spectrometer and the marker;

determining second position information of the organic matter to be detected through the atomic force probe of the nanometer infrared spectrometer and the first position information;

Based on the second position information, acquiring infrared spectrums of the organic matters to be detected through the nanometer infrared spectrometer;

And determining the gas adsorption capacity of the organic matter to be detected according to the infrared spectrum, and taking the gas adsorption capacity as the adsorption capacity of the rock to gas, so as to select the underground reservoir according to the wettability of sandstone, the crack structure of the rock, the continuous strain of the rock, the gas mutual driving characteristic of the rock and the adsorption capacity of the rock to gas.

In an embodiment of the present application, the determining, by using a nano infrared spectrometer and the marker, the first position information of the organic matter to be detected specifically includes: and observing the marker through an optical microscope in the nanometer infrared spectrometer, and determining the first position information of the organic matter to be detected. The determining, by the atomic force probe of the nano infrared spectrometer and the first position information, the second position information of the organic matter to be detected specifically includes: according to the first position information, controlling the atomic force probe to be close to the organic matter to be detected, and determining third position information of the atomic force probe; and determining the second position information of the organic matter to be detected according to the third position information. And controlling the atomic force probe to be close to the organic matter to be detected according to the first position information, and determining third position information of the atomic force probe, wherein the method specifically comprises the following steps of: setting a test distance between the surface of the rock sample and the atomic force probe based on the first position information; and according to the test distance, enabling the atomic force probe to approach the organic matter to be tested, and determining the third position information. Based on the second position information, the infrared spectrum of the organic matter to be detected is collected through the nanometer infrared spectrometer, and the method specifically comprises the following steps: determining a laser position of the nano infrared spectrometer according to the second position information, wherein the laser position maximizes a light spot in a sample surface contact area; and acquiring the infrared spectrum of the organic matter to be detected according to the laser position. The determining the laser position of the nanometer infrared spectrometer according to the second position information specifically includes: according to the second position information, determining a plurality of target wave numbers of laser emitted by the nanometer infrared spectrometer; and carrying out position calibration on laser emitted by the nanometer infrared spectrometer according to the plurality of target wave numbers so as to obtain the laser position. The step of collecting the infrared spectrum of the organic matter to be detected according to the laser position specifically comprises the following steps: determining a plurality of target wave bands corresponding to the nanometer infrared spectrometer according to the laser positions; and based on the target wave bands, carrying out spectrum acquisition on the organic matter to be detected to obtain the infrared spectrum. The determining the gas adsorption capacity of the organic matter to be detected according to the infrared spectrum specifically comprises the following steps: according to the infrared spectrum, the original adsorption capacity and humidity influence coefficient of the organic matters to be detected are truly determined; and determining the gas adsorption capacity according to the original adsorption capacity and the humidity influence coefficient. The method for determining the original adsorption capacity of the organic matter to be detected according to the infrared spectrum specifically comprises the following steps: determining a plurality of absorption intensities corresponding to the organic matter to be detected according to the infrared spectrum; and determining the original adsorption capacity according to the plurality of absorption intensities. The method for determining the humidity influence coefficient of the organic matter to be detected according to the infrared spectrum specifically comprises the following steps: determining a plurality of absorption intensities corresponding to the organic matter to be detected according to the infrared spectrum; and determining the humidity influence coefficient according to the plurality of absorption intensities. The method for determining the gas adsorption capacity according to the original adsorption capacity and the humidity influence coefficient specifically comprises the following steps: and carrying out numerical correction on the original adsorption capacity according to the humidity influence coefficient to obtain the gas adsorption capacity. The determining of the marker corresponding to the organic matter to be detected on the rock sample specifically comprises the following steps: and observing the organic matter to be detected on the rock sample through an optical instrument, and determining the marker corresponding to the organic matter to be detected. The markers are mineral particles on the rock sample. The markers are markings engraved on the rock sample. After the first position information of the organic matter to be detected is determined, the method further comprises the following steps: collecting a plurality of spectral background values of the nano infrared spectrometer; and removing the measurement error of the nanometer infrared spectrometer through the plurality of spectrum background values. The gas adsorption capacity is the adsorption capacity of functional groups such as hydroxyl, aromatic ring, carboxyl, carbonyl and the like in the organic matter to be detected on gas substances.

acquiring a rock sample to be tested; wherein the rock sample to be tested is taken from organic shale;

obtaining the distribution position of kerogen in the rock sample to be detected by using a first scanning instrument;

obtaining the surface morphology features of each kerogen in the rock sample to be detected by using a second scanning instrument based on the distribution positions of the kerogen in the rock sample to be detected; wherein the surface topography features comprise at least: surface relief and roughness;

Carrying out spectrum test on each kerogen in the rock sample to be tested by utilizing a spectrum test instrument based on the distribution position of the kerogen in the rock sample to be tested to obtain the surface molecular structural characteristics of each kerogen in the rock sample to be tested;

And determining the storage capacity of each kerogen in the rock sample to be tested to the target gas according to the surface morphology features and the surface molecular structure features of each kerogen in the rock sample to be tested, so as to select a subsurface reservoir according to the wettability of sandstone, the rock fracture structure, the rock continuous strain, the gas mutual driving characteristics of the rock, the adsorption capacity of the rock to the gas and the storage capacity of each kerogen in the rock sample to the target gas.

In an embodiment of the present application, the obtaining a rock sample to be measured includes: obtaining a rock sample from the shale rich in organic matter; preparing the rock sample into a rock sample to be polished with a preset size and a preset shape; and polishing the rock sample to be polished to obtain the rock sample to be polished. The first scanning instrument is a scanning electron microscope, and the obtaining of the distribution position of kerogen in the rock sample to be detected by using the first scanning instrument comprises the following steps: scanning the rock sample to be detected by using the scanning electron microscope under a preset condition to obtain the distribution position of kerogen in the rock sample to be detected; wherein the preset conditions at least comprise a low vacuum condition. The second scanning instrument is an atomic force microscope, and based on the distribution position of the kerogen in the rock sample to be detected, the surface topography features of each kerogen in the rock sample to be detected are obtained by using the second scanning instrument, and the method comprises the following steps: scanning each kerogen in the rock sample to be detected by utilizing the atomic force microscope based on the distribution position of the kerogen in the rock sample to be detected, so as to obtain a scanning image of each kerogen in the rock sample to be detected; and determining the surface morphology features of each kerogen in the rock sample to be detected according to the scanning images of each kerogen in the rock sample to be detected. The determining the surface topography features of each kerogen in the rock sample to be tested according to the scanned images of each kerogen in the rock sample to be tested comprises the following steps: determining the highest point and the lowest point of the surface of each kerogen in the rock sample to be tested according to the scanned image of each kerogen in the rock sample to be tested; and obtaining the surface waviness of each kerogen in the rock sample to be tested according to the distance between the highest point and the lowest point of the surface of each kerogen in the rock sample to be tested. The determining the surface topography features of each kerogen in the rock sample to be tested according to the scanned images of each kerogen in the rock sample to be tested comprises the following steps: the roughness of each kerogen in the rock sample to be measured was calculated using the following formula: ; wherein R _a is the roughness average of kerogen; n _x and N _y represent the number of data points scanned in the X and Y coordinate axis directions, respectively, and Z (i, j) represents the height of the data point scanned; z _mean represents the average height of the baseline of the scanned data points. The surface molecular structure characteristics of the kerogen include the relative absorption intensity of the characteristic functional groups on the surface of the kerogen to infrared light of a preset wave band, and the spectral test is performed on each kerogen in the rock sample to be tested by utilizing a spectral test instrument based on the distribution position of the kerogen in the rock sample to be tested to obtain the surface molecular structure characteristics of each kerogen in the rock sample to be tested, and the method comprises the following steps: based on the distribution position of kerogen in the rock sample to be tested, carrying out atomic force-based nanometer infrared spectrum test on each kerogen in the rock sample to be tested by utilizing a spectrum test instrument to obtain the relative absorption intensity of various characteristic functional groups on the surfaces of each kerogen in the rock sample to be tested on infrared light of the preset wave band; the absorption intensity of the characteristic functional group to the infrared light of the preset wave band is related to the absorption capacity of the characteristic functional group to target gas. The determining the storage capacity of each kerogen in the rock sample to be tested to the target gas according to the surface morphology feature and the surface molecular structure feature of each kerogen in the rock sample to be tested comprises the following steps: for each kerogen in the rock sample to be tested, the following steps are performed: determining the surface area of the kerogen available for adsorbing gas according to the surface waviness and roughness of the kerogen; determining the adsorption capacity of the kerogen to the target gas according to the relative absorption intensity of various characteristic functional groups on the surface of the kerogen to the infrared light of the preset wave band; the storage capacity of the kerogen for the target gas is determined based on the amount of surface area of the kerogen available for adsorption of gas and the amount of adsorption capacity of the kerogen for the target gas.

preparing a rock sample to be tested;

carrying out X-ray scanning on a rock sample to be detected to obtain a three-dimensional structure image;

determining a gridding image for flow simulation according to the three-dimensional structure image;

performing fluid flow simulation on the gridded image;

The fluid flow characteristics of the different rock samples are compared for evaluation of the rock micro-pore structure to select a subsurface reservoir based on sandstone wettability, rock fracture structure, rock continuous strain, gas mutual drive characteristics of the rock, adsorption capacity of the rock to gas, storage capacity of the respective kerogen in the rock sample to target gas, and the rock micro-pore structure.

In an embodiment of the present application, determining a gridded image for flow simulation from a three-dimensional structure image specifically includes: noise removing is carried out on the three-dimensional structure image; carrying out pore segmentation on the denoised image according to the gray value; the segmented pores are extracted, and a tetrahedron grid is generated through edge overturning, edge folding and vertex translation and is used as a gridding image for flow simulation. Performing fluid flow simulation on the gridded image, specifically including: introducing the pores of the gridding image into a multiphase flow model; the same fluid is injected into the pores of the gridding image according to the same flow velocity under the same temperature and pressure condition in the multiphase flow model. The evaluation of the rock micro-pore structure specifically comprises the following steps: and selecting the highest flow velocity point in the pore as a key node, and calculating the average pressure difference of the flow velocity according to the key node to judge the complexity of the microscopic pore throat.

preparing a rock sample to be detected, wherein the rock is shale;

identifying target organic matters in a rock sample to be detected;

acquiring the surface morphology, elastic modulus characteristics and surface components of the target organic matter;

The surface morphology, elastic modulus characteristics and surface composition of the target organic matter determine the microstructure of the target organic matter to select a subsurface reservoir based on sandstone wettability, rock fracture structure, rock continuous strain, gas mutual drive characteristics of the rock, adsorption capacity of the rock to gas, storage capacity of each kerogen in the rock sample to the target gas, rock micro-pore structure and microstructure of the organic matter in the rock.

In the embodiment of the application, the target organic matter is identified by observing the rock sample to be detected through an optical microscope and a scanning electron microscope, wherein the optical microscope adopts reflected light for observation, and the scanning electron microscope adopts a low vacuum condition for observation. The obtaining the surface morphology and the elastic modulus of the target organic matter comprises the following steps: testing the root mean square roughness of a target organic matter by an atomic force microscope and taking the root mean square roughness as the surface morphology of the target organic matter; the elastic modulus of the target organic material was tested by the Derjaguar-Muller-Toporov model of an atomic force microscope, which is a model used to describe the interaction between the sample and the probe. The obtaining the surface component of the target organic matter comprises the following steps: and testing the surface components of the target organic matters by utilizing an atomic force infrared combined system based on a photo-thermal induced nano infrared technology. Before testing the surface composition of the target organic matter, the method further comprises: the atomic force infrared combined system is 1450-1460、1600-1620And 2920-2930The wavenumber is laser calibrated. The method for determining the microstructure of the organic matter according to the surface morphology, the elastic modulus and the surface composition of the target organic matter, as the characteristic of the organic matter, comprises the following steps: determining the reduction degree of the fatty chain according to the surface component of the target organic matter, wherein the reduction degree of the fatty chain is the ratio of methyl to methylene content in an infrared spectrogram; comparing the root mean square roughness, the elastic modulus and the fatty chain reduction degree of the first rock sample to be tested and the second rock sample to be tested; under the condition that the root mean square roughness of the first rock sample to be measured is larger than that of the second rock sample to be measured, the elastic modulus of the first rock sample to be measured is larger than that of the second rock sample to be measured, and the reduction degree of the fatty chain of the first rock sample to be measured is smaller than that of the second rock sample to be measured, the hydrocarbon generation and emission potential of the first rock sample to be measured is larger than that of the second rock sample to be measured.

In an embodiment of the application, the subsurface reservoir is selected to include two application scenarios: first, a target subsurface reservoir is selected from a plurality of subsurface reservoirs based on the gas to be stored, and second, a reservoir gas adapted to the subsurface reservoir is selected from a plurality of reservoir gases based on characteristics of the rock in the subsurface reservoir, wherein the characteristics of the rock include, but are not limited to, fracture structure of the rock, strain of the rock, gas mutual drive characteristics in the rock, adsorption capacity of the rock to gas, wettability of the rock, gas storage capacity of kerogen in the rock, micro-pore structure of the rock, microstructure of the rock organic matter, and in selecting the subsurface reservoir, the fracture structure of the rock, strain of the rock, gas mutual drive characteristics in the rock, adsorption capacity of the rock to gas, wettability of the rock, gas storage capacity of kerogen in the rock, microstructure of the rock, characteristics of at least 2 of the rock in microstructure of the rock, including, but not limited to carbon dioxide, hydrogen, natural gas, can be combined.

In embodiments of the application, in selecting a subsurface reservoir, the smaller the length, width and volume changes of the rock fracture structure as the gas phase of the gas to be stored changes, the better the fracture structure is to avoid the risk of leakage of the gas to be stored during the storage.

In embodiments of the application, in selecting a subsurface reservoir, the subsurface reservoir rock is subject to significant expansion strain as the gas phase of the gas to be stored changes, if the rock expansion strain is small, the subsurface reservoir is selected, if the expansion strain is large, the rock aperture is easily caused to close significantly, reducing gas storage capacity.

In embodiments of the application, where the gas to be stored is carbon dioxide and methane is present in the rock in the subsurface reservoir, in selecting the subsurface reservoir, the displacement effect of carbon dioxide on methane is determined based on the characteristics of the mutual displacement between carbon dioxide and methane, i.e., the change in the volumetric flow rates of carbon dioxide and methane in the pore structure, the better the displacement effect of carbon dioxide on methane, the greater the probability of selecting the current subsurface reservoir.

In the embodiment of the application, in the case that the gas to be stored is carbon dioxide, in the selective subsurface reservoir, the more the oxygen-containing functional group content is, the more the adsorption capacity of kerogen to carbon dioxide gas can be enhanced, and the greater the probability of selecting the current subsurface reservoir.

In embodiments of the application, where the gas to be stored is carbon dioxide, the blocking capacity of the rock is reduced when the rock wettability is hydrophobic in the selected subsurface reservoir, and the current subsurface reservoir is selected when the rock wettability is hydrophilic.

In an embodiment of the application, where the gas to be stored is carbon dioxide, in selecting the subsurface reservoir, the gas storage capacity of kerogen in the rock is determined by the size of the surface area of kerogen available for adsorption of gas and the size of the capacity of said kerogen for adsorption of carbon dioxide gas, the larger the surface area of kerogen available for adsorption of gas and the larger the capacity of said kerogen for adsorption of carbon dioxide gas, the greater the probability of selecting the current subsurface reservoir.

In embodiments of the present application, the more complex the subsurface reservoir rock micro-pore structure is in selecting a subsurface reservoir, the more resistance to fluid flow is readily produced, and therefore the simpler the subsurface reservoir rock micro-pore structure is, the greater the probability of selecting a current subsurface reservoir.

In embodiments of the present application, in selecting a subsurface reservoir, the microstructure of the rock organic matter is the roughness and elastic modulus of the rock organic matter, the greater the roughness of the subsurface reservoir rock organic matter is, the more advantageous the gas enrichment, the greater the elastic modulus is, the more the shale bulk stiffness can be enhanced, and therefore the greater the roughness and elastic modulus of the subsurface reservoir rock organic matter is, the greater the probability of selecting a current subsurface reservoir.

In the present application, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; the term "plurality" means two or more, unless expressly defined otherwise. The terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; "coupled" may be directly coupled or indirectly coupled through intermediaries. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.

In the description of the present application, it should be understood that the directions or positional relationships indicated by the terms "upper", "lower", "front", "rear", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present application and simplifying the description, and do not indicate or imply that the apparatus or module referred to must have a specific direction, be constructed and operated in a specific direction, and thus should not be construed as limiting the present application.

In the description of the present specification, the terms "one embodiment," "some embodiments," "particular embodiments," and the like, mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The above is only a preferred embodiment of the present application, and is not intended to limit the present application, but various modifications and variations can be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, comprising:

Preparing a sandstone sample to be tested;

Applying confining pressure to the sandstone sample to be detected, injecting potassium iodide solution into the sandstone sample to be detected, and continuously scanning the sandstone sample to be detected by X rays until the sandstone sample to be detected is completely saturated;

injecting a second fluid into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected until the potassium iodide solution is completely displaced;

Acquiring a three-dimensional image, and acquiring a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of a second fluid according to the three-dimensional image;

-comparing the first volume fraction and the second volume fraction for wettability characterization.

2. The method according to claim 1, wherein the applying the confining pressure to the sandstone sample to be tested and injecting the potassium iodide solution into the sandstone sample to be tested simultaneously continuously scans the sandstone sample to be tested by X-rays until the sandstone sample to be tested is completely saturated, specifically comprises:

Applying confining pressure to the sandstone sample to be tested;

Injecting potassium iodide solution into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected to obtain a three-dimensional digital core;

3. The method according to claim 2, wherein the quantitatively segmenting the three-dimensional digital core until the saturation value of the sandstone sample to be measured does not change, specifically comprises:

judging whether the saturation value changes or not;

4. The method according to claim 1, wherein the injecting the second fluid into the sandstone sample to be tested while continuously scanning the sandstone sample to be tested with X-rays until the potassium iodide solution is completely displaced, specifically comprises:

5. The method according to claim 1, wherein the acquiring a three-dimensional image, obtaining a first volume fraction saturated with potassium iodide and a second volume fraction fully filled with a second fluid from the three-dimensional image, specifically comprises:

6. The method of claim 5, wherein the acquiring a three-dimensional image, from which a first volume fraction saturated with potassium iodide and a second volume fraction fully filled with a second fluid are obtained, further comprises:

7. The method according to claim 1, characterized in that said comparing said first volume fraction and said second volume fraction for wettability characterization, in particular comprises:

8. The method of claim 7, wherein the step of determining the position of the probe is performed,

And when the wettability index is larger than a preset value, representing hydrophilicity, and when the wettability index is smaller than the preset value, representing hydrophobicity.

9. A system for quantitatively characterizing wettability of sandstone based on a three-dimensional digital core, comprising:

The preparation module is used for preparing a sandstone sample to be tested;

The potassium iodide injection module is used for applying confining pressure to the sandstone sample to be detected, injecting potassium iodide solution into the sandstone sample to be detected, and simultaneously continuously scanning the sandstone sample to be detected by X rays until the sandstone sample to be detected is completely saturated;

The displacement module is used for injecting a second fluid into the sandstone sample to be detected, and simultaneously carrying out X-ray continuous scanning on the sandstone sample to be detected until the potassium iodide solution is completely displaced;

The acquisition module is used for acquiring a three-dimensional image, and acquiring a first volume fraction after potassium iodide saturation and a second volume fraction after complete filling of a second fluid according to the three-dimensional image;

and the comparison module is used for comparing the first volume fraction with the second volume fraction for wettability characterization.

10. A method for selecting a subsurface reservoir, comprising the steps of the method for quantitatively characterizing sandstone wettability based on a three-dimensional digital core according to any one of claims 1 to 8, further comprising:

Preparing a rock sample;