Device and method for measuring diffusion coefficient of gas in rock

Abstract

The invention discloses a device and a method for determining a gas diffusion coefficient in rock, and belongs to the technical field of rock performance determination. The device comprises a core holder, sampling mechanisms, a gas analyzer, a gas source and a pressure gauge, a rock sample is clamped in the middle of the core holder, the two sampling mechanisms are symmetrically arranged at the two ends of the rock sample respectively, and each sampling mechanism comprises a first blind pipe, a cylinder, a second blind pipe and a sampling cavity. The opening end of the first blind pipe directly faces the rock sample and is hermetically connected with the end face of the rock sample to form a diffusion chamber. According to the device for measuring the diffusion coefficient of the gas in the rock, the single sampling cavity can be isolated from the diffusion chamber, the pressure of the diffusion chamber is not influenced in the isolation process, undisturbed sampling can be realized, the influence on the pressure of the diffusion chamber is reduced, and the accuracy of a test result is improved.

Description

Technical Field

[0001] The invention relates to the technical field of rock property measurement, and in particular to a device and method for measuring gas diffusion coefficient in rock. Background Art

[0002] The gas diffusion coefficient in rocks can not only reveal the diffusion behavior of gas in reservoirs, but also provide important kinetic characteristic data for multi-component gases in projects such as gas injection and recovery, carbon dioxide storage, well shut-in, and multi-cycle injection and production in gas storage. It is a key parameter for studying gas migration laws, optimizing injection and production strategies, and evaluating reservoir performance.

[0003] At present, the determination of gas diffusion coefficient in rock mainly adopts non-steady-state method. The standard method of testing is disclosed in SY / T6129-2016 "Method for Determining Diffusion Coefficient of Hydrocarbon Gas in Rock", which puts the core in the middle of the core holder, fills the diffusion chambers at both ends of the rock sample with different gases, and tests the composition of hydrocarbon gas in the two diffusion chambers at different time points to obtain the diffusion coefficient of hydrocarbon gas in rock. At least two samplings are required during the test process, and each sampling requires extracting part of the gas from the diffusion chamber for detection, which will disturb the pressure in the diffusion chamber, form a sudden change in pressure difference between the two diffusion chambers, and cause abnormal fluctuations in the diffusion rate of gas molecules, resulting in poor repeatability of experimental data and increased errors. Summary of the invention

[0004] In view of the above technical problems, the object of the present invention is to provide a device and method for measuring the gas diffusion coefficient in rocks, which can reduce or even eliminate the disturbance of the gas pressure in the diffusion chamber during the sampling process, thereby improving the accuracy of the measurement results.

[0005] In order to achieve the above object, the technical solution provided by the present invention is as follows: A device for measuring gas diffusion coefficient in rock, comprising: A core holder for holding the rock sample in the middle; Two sampling mechanisms are arranged at both ends of the rock sample, including: A first blind pipe, the opening end of which faces the rock sample and is sealedly connected to the end face of the rock sample to form a diffusion chamber; At least two enclosed sampling chambers; One end of the cylinder penetrates through each sampling cavity in sequence and extends into the diffusion chamber, and a connecting hole is provided in the cylinder wall corresponding to each sampling cavity; A second blind tube is coaxially sleeved in the cylinder and spaced a certain distance therefrom, with its closed end facing the diffusion chamber and its open end rotating and sealingly connected to the cylinder, thereby forming an annular cavity connected to the diffusion chamber between the cylinder and the second blind tube; an open ring-shaped sealing strip corresponding to the connecting hole and a sampling hole penetrating the tube wall and the sealing strip are provided on the outer wall of the second blind tube; when the second blind tube rotates relative to the cylinder, the connecting hole will be converted in the order of diffusion state, sampling state and isolation state, the diffusion state refers to the state in which the connecting hole faces the opening of the sealing strip, the sampling state refers to the state in which the connecting hole is connected to the sampling hole, and the isolation state refers to the state in which the connecting hole faces the outer wall of the sealing strip and is closed; the sampling holes are staggered along the circumference, so that when the second blind tube is rotated, each connecting hole is connected with the corresponding sampling hole in turn for sampling; a gas analyzer connected to the open end of the second blind tube; a gas source in communication with the diffusion chamber; Pressure gauge for measuring diffusion chamber pressure.

[0006] As a specific embodiment of the present invention, it also includes a vacuum pump for evacuating the diffusion chamber and the sampling chamber.

[0007] As a specific embodiment of the present invention, a differential pressure gauge is also included to measure the pressure difference between the two diffusion chambers.

[0008] As a specific implementation of the present invention, the gas source is communicated with the sampling chamber.

[0009] As a specific implementation of the present invention, an elastic layer is provided on the outer wall of the sealing strip to enhance the sealing performance, and the sampling hole penetrates the elastic layer.

[0010] As a specific implementation of the present invention, temperature controllers are respectively arranged on both sides of the core holder to independently control the temperatures of the two diffusion chambers.

[0011] As a specific embodiment of the present invention, there are multiple gas sources, which are connected in parallel to two intermediate containers, and the two intermediate containers are respectively connected to two diffusion chambers. Each intermediate container is provided with a piston, and a displacement pump is connected to the two intermediate containers to push the piston to move in the intermediate container, thereby delivering the gas into the diffusion chamber.

[0012] The present invention also discloses a method for measuring the gas diffusion coefficient in rock, which uses the above-mentioned measuring device to perform measurement, and comprises the following steps: S1. The connecting device adjusts each connecting hole to face the opening of the sealing strip, and then performs airtightness and replacement; S2, fill the sampling cavity and the diffusion chamber with the target gas, adjust the pressure of the two diffusion chambers to be equal, and then cut off the gas source; S3. Start the test. After a certain period of time, rotate the second blind tube to separate the single sampling cavity from the diffusion chamber. Then take samples to analyze the gas components and calculate the diffusion coefficient of the gas.

[0013] The beneficial effects of the present invention are as follows: The gas diffusion coefficient determination device in rock of the present invention can isolate a single sampling cavity from a diffusion chamber, and the pressure of the diffusion chamber is not affected during the isolation process, so that undisturbed sampling can be achieved, the influence on the pressure of the diffusion chamber is reduced, and the accuracy of the determination result is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the overall structure of an embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of the overall structure of the sampling mechanism; Figure 3 for Figure 2 A cross-sectional view of the combined structure of the middle cylinder and the second blind tube; Figure 4 yes Figure 2 Assembly drawing of the combined structure of the middle cylinder and the second blind tube; Figure 5 yes Figure 4 A stereogram of the second blind tube; Figure 6 It is a schematic diagram of the overall structure of another embodiment of the present invention.

[0015] In the figure, core holder 100; rock sample 200; gas source 400; vacuum pump 600; intermediate container 700; displacement pump 800; hollow plug 900; Gas analyzer 310; pressure gauge 320; differential pressure gauge 330; first blind tube 510; cylinder 520; second blind tube 530; diffusion chamber 540; sampling chamber 550; Communication hole 501; annular cavity 502; sealing strip 503; sampling hole 504; air inlet hole 505. DETAILED DESCRIPTION

[0016] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0017] Please refer to Figure 1 to Figure 6, which shows a schematic diagram of the structure of two specific embodiments of the gas diffusion coefficient determination device in rock of the present invention. The gas diffusion coefficient determination device in rock of the present invention includes a core holder 100, a sampling mechanism, a gas analyzer 310, a gas source 400 and a pressure gauge 320. The middle part of the core holder 100 clamps the rock sample 200. There are two sampling mechanisms, which are symmetrically arranged at both ends of the rock sample 200. Each sampling mechanism includes a first blind tube 510, a cylinder 520, a second blind tube 530 and a sampling cavity 550. The opening end of the first blind tube 510 faces the rock sample 200 and is sealed and connected to the end face of the rock sample 200 to form a diffusion chamber 540. In some embodiments, the diffusion chamber 540 can be controlled by The ring pressure of the core holder 100 is controlled so that the inner wall (rubber tube) of the core holder 100 is pressed against the outer wall of the open end of the first blind tube 510, thereby achieving sealing; there are at least two sampling chambers 550, and of course the specific number of sampling chambers 550 can be designed according to the number of sampling times during the experiment. Each sampling chamber 550 corresponds to one undisturbed sampling process, and increasing the number of sampling chambers 550 can perform more undisturbed sampling; each sampling chamber 550 is arranged along the axial direction of the core holder 100, and each sampling chamber 550 can be spaced a certain distance apart, and of course, it can also be as Figure 2As shown, each sampling cavity 550 is connected in series in an abutting manner, which can reduce the number of baffles of the sampling cavity 550 and help reduce manufacturing costs; one end of the cylinder 520 sequentially penetrates each sampling cavity 550 and extends into the diffusion chamber 540, and its cylinder wall is provided with a connecting hole 501 corresponding to each sampling cavity 550, so that each sampling cavity 550 can be connected to the interior of the cylinder 520 through the corresponding connecting hole 501; the second blind tube 530 is coaxially sleeved in the cylinder 520 and spaced a certain distance therefrom, the closed end of the second blind tube 530 is directly opposite to the diffusion chamber 540, and the open end is rotatably sealed and connected to the cylinder 520, thereby forming a diffusion chamber 540 between the cylinder 520 and the second blind tube 530. The annular cavity 502 is connected to the chamber 540; the wall of the second blind tube 530 is provided with an open ring-shaped sealing strip 503 corresponding to the connecting hole 501 and a sampling hole 504 penetrating the tube wall and the sealing strip 503, and the open end of the second blind tube 530 is connected to the gas analyzer 310, so that the sample gas flowing in through the sampling hole 504 is sent to the gas analyzer 310 for component analysis; when the second blind tube 530 is rotated in the same direction so that it rotates relative to the cylinder 520, the connecting hole 501 is in three states in sequence, namely, a diffusion state, a sampling state and an isolation state, wherein the diffusion state refers to the state in which the connecting hole 501 is facing the opening of the sealing strip 503, at this time, the sampling state corresponding to the connecting hole 501 The sample cavity 550 is connected to the annular cavity 502, and further connected to the diffusion chamber 540. The gas in the sampling cavity 550 participates in the gas diffusion process of the rock sample, and the gas composition will change as the diffusion proceeds; the sampling state refers to the state in which the connecting hole 501 is directly opposite to the sampling hole 504. At this time, the sampling cavity 550 corresponding to the connecting hole 501 is connected to the second blind tube 530, so that the gas in the sampling cavity 550 can be transported to the gas analyzer 310 for component analysis. Since the gas is separated from the diffusion chamber 540, the gas composition no longer changes during the sampling process. At the same time, the reduction of gas in the sampling cavity 550 will not affect the pressure of the diffusion chamber 540, thereby achieving disturbance-free sampling; isolation state Refers to the state where the connecting hole 501 is facing the outer wall of the sealing strip 503. At this time, the connecting hole 501 is closed by the outer wall of the sealing strip 503, and the corresponding sampling cavity 550 is isolated, which neither interferes with the pressure of the diffusion chamber 540 nor interferes with the gas components in the second blind tube 530. The present invention has multiple sampling holes 504, each sampling hole 504 is staggered along the circumference, and when the second blind tube 530 is rotated, each connecting hole 501 is connected with the corresponding sampling hole 504 in turn, so that the gas in each sampling cavity 550 is sampled in turn. In this way, the unsampled connecting hole 501 is always in a diffusion state, and the sampled connecting hole 501 is always in an isolated state until all sampling holes 504 complete sampling. The gas source 400 is connected to the diffusion chamber 540 for supplying gas to the diffusion chamber 540, and the pressure gauge 320 is used to measure the gas pressure of the diffusion chamber 540.

[0018] In some embodiments, the pressures of the two diffusion chambers 540 can be measured separately to determine whether the initial pressures of the two are balanced. However, since the pressure difference has a great influence on the result, in some embodiments, a high-precision pressure difference gauge 330 is provided to measure the pressure difference of the two diffusion chambers 540, so as to more accurately measure the pressure difference. Figure 1 shown.

[0019] In some embodiments, a vacuum pump 600 may be provided to evacuate the diffusion chamber 540 and the sampling chamber 550 to facilitate rapid exhaustion of air in the diffusion system and shorten the experimental time.

[0020] When the present invention is used, the open end of the first blind tube 510 is to be fixed in the core holder 100. For the convenience of fixing, the first blind tube 510 can be fixed in the core holder 100 in a detachable manner. The first blind tube 510 and the sampling chamber 550 can also be integrally formed and fixed in the core holder 100 in a detachable manner. For example, Figure 1 As shown, the integrated structure of the first blind tube 510 and the sampling chamber 550 is placed in the core holder 100 , and the integrated structure is fixed in the core holder 100 by using a hollow plug 900 threadedly connected to the core holder 100 .

[0021] In the present invention, the initial gas compositions in the two diffusion chambers 540 are different. In some embodiments, the gas compositions in the two diffusion chambers 540 may be different. Figure 1 As shown, the two diffusion chambers are connected to different gas sources 400. In other embodiments, Figure 6 As shown, a plurality of gas sources 400 are connected in parallel and are all connected to two diffusion chambers 540 , so that the required gas components can be prepared by adjusting the flow rate of each gas source 400 .

[0022] In some embodiments, the gas can be delivered to the diffusion chamber 540 by using the pressure of the gas source 400 itself. In other embodiments, the gas can also be delivered to the diffusion chamber 540 by an intermediate container 700 including a piston. Figure 6 As shown, the two intermediate containers 700 share a displacement pump 800 , which injects liquid into the intermediate container 700 to drive the piston in the intermediate container 700 to move, and presses the gas at the other end of the intermediate container 700 into the diffusion chamber 540 .

[0023] In some embodiments, an elastic layer is disposed on the outer wall of the sealing strip 503, and the sampling hole 504 passes through the elastic layer to enhance the sealing performance.

[0024] In some embodiments, Figure 6 As shown, the gas source 400 is connected to a sampling chamber 550, so that the gas is sent into the diffusion chamber 540 through the sampling chamber 550. In other embodiments, as shown in FIG. Figure 2As shown, an air inlet 505 is provided on one side of the second blind tube 530 outside the sampling cavity 550, one end of the air inlet 505 is connected to the annular cavity 502, and the other end is connected to the gas source 400. In this way, as long as the volumes of the sampling cavities 550 are equal, the reduction in the volume of the diffused gas is equal each time the sampling is performed, which facilitates the calculation of the volume of the gas involved in the diffusion of the rock sample gas.

[0025] In some embodiments, temperature controllers may be provided on both sides of the core holder 100 to independently control the temperatures of the two diffusion chambers 540. When the temperatures of the two diffusion chambers 540 are controlled differently, the gas diffusion coefficient under the condition of coexistence of temperature gradient and concentration gradient may be simulated.

[0026] The measuring device of the present invention can measure the gas diffusion coefficient in rocks by the following method: S1. The connecting device adjusts each connecting hole 501 to face the opening of the sealing strip 503, and then performs airtightness and replacement; S2, filling the sampling chamber 550 and the diffusion chamber 540 with the target gas, adjusting the pressures of the two diffusion chambers 540 to be equal, and then cutting off the gas source 400; S3, start the test, rotate the second blind tube after a certain period of time to separate the single sampling cavity from the diffusion chamber, then sample and analyze the gas components, and then calculate the diffusion coefficient of the gas.

[0027] In step S3, the gas diffusion coefficient calculation formula in SY / T6129-2016 "Determination Method of Gas Diffusion Coefficient of Hydrocarbons in Rocks" can be used to determine the gas diffusion coefficient in the diffusion process corresponding to two adjacent samplings. When the number of samplings is large, a gas diffusion coefficient can be calculated for all two adjacent sampling processes, and then the average value of all gas diffusion coefficients is taken as the final gas diffusion coefficient.

[0028] For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all of these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A device for measuring gas diffusion coefficient in rock, characterized in that: include: A core holder for holding the rock sample in the middle; Two sampling mechanisms are respectively arranged at two ends of the rock sample, comprising: A first blind pipe, the opening end of which faces the rock sample and is sealedly connected to the end face of the rock sample to form a diffusion chamber; At least two enclosed sampling chambers; A barrel having one end which sequentially penetrates through each of the sampling cavities and extends into the diffusion chamber, and a communicating hole is formed in the barrel wall corresponding to each of the sampling cavities; A second blind tube is coaxially sleeved in the cylinder and spaced a certain distance therefrom, the closed end of which faces the diffusion chamber and the open end is rotatably sealed and connected to the cylinder, so that an annular cavity connected to the diffusion chamber is formed between the cylinder and the second blind tube; the outer wall of the second blind tube is provided with an open ring sealing strip corresponding to the communicating hole and a sampling hole penetrating the tube wall and the sealing strip; when the second blind tube rotates relative to the cylinder, the communicating hole will be converted in the order of diffusion state, sampling state and isolation state, the diffusion state refers to the state in which the communicating hole faces the opening of the sealing strip, the sampling state refers to the state in which the communicating hole is connected with the sampling hole, and the isolation state refers to the state in which the communicating hole faces the outer wall of the sealing strip and is closed; the sampling holes are staggered along the circumference, so that when the second blind tube is rotated, the communicating holes are connected with the corresponding sampling holes in turn for sampling; a gas analyzer in communication with the open end of the second blind tube; a gas source in communication with the diffusion chamber; A pressure gauge for measuring the pressure in the diffusion chamber.

2. The device for measuring gas diffusion coefficient in rock according to claim 1, characterized in that: A vacuum pump is also included, which is used to evacuate the diffusion chamber and the sampling chamber.

3. The device for measuring gas diffusion coefficient in rock according to claim 1, characterized in that: A differential pressure gauge is also included, for measuring the differential pressure between the two diffusion chambers.

4. The device for measuring gas diffusion coefficient in rock according to claim 1, characterized in that: The gas source is communicated with the sampling cavity.

5. The device for measuring gas diffusion coefficient in rock according to claim 1, characterized in that: An air inlet is arranged on one side of the second blind tube outside the sampling cavity, one end of the air inlet is connected with the annular cavity, and the other end of the air inlet is connected with the air source.

6. The device for measuring gas diffusion coefficient in rock according to claim 1, characterized in that: An elastic layer is disposed on the outer wall of the sealing strip, and the sampling hole penetrates through the elastic layer.

7. The device for measuring gas diffusion coefficient in rock according to claim 1, characterized in that: Temperature controllers are respectively arranged on both sides of the core holder to independently control the temperatures of the two diffusion chambers.

8. The device for measuring gas diffusion coefficient in rock according to claim 1, characterized in that: There are multiple gas sources, which are connected in parallel to two intermediate containers, and the two intermediate containers are respectively connected to the two diffusion chambers. Each intermediate container is provided with a piston, and a displacement pump is connected to the two intermediate containers to push the piston to move in the intermediate container, thereby delivering the gas into the diffusion chamber.

9. A method for measuring the gas diffusion coefficient in rock, using the gas diffusion coefficient measuring device in rock according to any one of claims 1 to 8 for measurement, characterized in that: The steps include: S1, the connecting device adjusts each of the communicating holes to face the opening of the sealing strip, and then performs airtightness and replacement; S2, filling the sampling cavity and the diffusion chamber with target gas, adjusting the pressures of the two diffusion chambers to be equal, and then cutting off the gas source; S3, start the test, rotate the second blind tube after a certain period of time to separate the single sampling cavity from the diffusion chamber, then sample and analyze the gas components, and then calculate the diffusion coefficient of the gas.

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