Device and method for measuring gas diffusion coefficient in rock

Abstract

The present invention discloses a device and method for measuring the gas diffusion coefficient in rock, belonging to the technical field of rock property measurement. The device for measuring the gas diffusion coefficient in rock of the present invention includes a core holder, a sampling mechanism, a gas analyzer, a gas source and a pressure gauge. The core sample is clamped in the middle of the core holder. There are two sampling mechanisms, symmetrically arranged at both ends of the core sample respectively. Each sampling mechanism includes a first blind tube, a cylinder body, a second blind tube and a sampling chamber. The opening end of the first blind tube faces the core sample and is hermetically connected to the end face of the core sample to form a diffusion chamber. The device for measuring the gas diffusion coefficient in rock of the present invention can isolate a single sampling chamber from the diffusion chamber, and the pressure of the diffusion chamber is not affected during the isolation process, enabling non-disturbed sampling, reducing the influence on the pressure of the diffusion chamber, and improving the accuracy of the test results.

Description

Technical Field

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

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

[0003] Currently, the measurement of the gas diffusion coefficient in rocks mainly adopts the unsteady-state method. The SY / T6129-2016 "Method for Measuring the Diffusion Coefficient of Hydrocarbon Gases in Rocks" discloses the standard method for testing. In this method, the core is placed in the middle of the core holder, and different gases are filled into the diffusion chambers at both ends of the rock sample. By measuring the composition of hydrocarbon gases in the two diffusion chambers at different time points, the diffusion coefficient of hydrocarbon gases in the rock can be obtained. During the test process, at least two samplings are required. Each sampling needs to extract part of the gas from the diffusion chamber for detection, which will disturb the pressure in the diffusion chamber, form a sudden change in the pressure difference between the two diffusion chambers, and cause abnormal fluctuations in the gas molecule diffusion rate, resulting in poor repeatability of experimental data and increased errors. Summary of the Invention

[0004] In view of the above technical problems, the purpose 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] To achieve the above purpose, the technical solution provided by the present invention is as follows:

[0006] A device for measuring the gas diffusion coefficient in rocks, comprising:

[0007] A core holder for clamping the rock sample in the middle;

[0008] Two sampling mechanisms respectively arranged at both ends of the rock sample, comprising:

[0009] A first blind tube, whose opening end faces the rock sample and is hermetically connected to the end face of the rock sample to form a diffusion chamber;

[0010] At least two closed sampling chambers;

[0011] A cylinder body that penetrates through each sampling chamber in sequence at one end and extends into the diffusion chamber, and communication holes are provided on the cylinder wall corresponding to each sampling chamber;

[0012] A second blind tube coaxially sleeved inside the cylinder and spaced apart from it by a certain distance, with its closed end facing the diffusion chamber and its open end rotatably and sealingly connected to the cylinder, thereby forming an annular cavity communicating with the diffusion chamber between the cylinder and the second blind tube; an annular sealing strip corresponding to the communication hole is provided on the outer wall of the second blind tube, and a sampling hole penetrating through the tube wall and the sealing strip; when the second blind tube rotates relative to the cylinder, the communication hole will sequentially switch in the order of diffusion state, sampling state, and isolation state. The diffusion state refers to the state where the communication hole faces the opening of the sealing strip, the sampling state refers to the state where the communication hole communicates with the sampling hole, and the isolation state refers to the state where the communication hole faces the outer wall of the sealing strip and is closed; the sampling holes are arranged in a circumferential dislocation manner, so that when the second blind tube rotates, each communication hole sequentially communicates with the corresponding sampling hole for sampling;

[0013] A gas analyzer communicating with the open end of the second blind tube;

[0014] A gas source communicating with the diffusion chamber;

[0015] A pressure gauge for measuring the pressure in the diffusion chamber.

[0016] As a specific embodiment of the present invention, a vacuum pump is further included for evacuating the diffusion chamber and the sampling chamber.

[0017] As a specific embodiment of the present invention, a differential pressure gauge is further included for measuring the pressure difference between two diffusion chambers.

[0018] As a specific embodiment of the present invention, the gas source communicates with the sampling chamber.

[0019] As a specific embodiment 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 through the elastic layer.

[0020] As a specific embodiment of the present invention, temperature controllers are respectively provided on both sides of the core holder for independently controlling the temperatures of the two diffusion chambers.

[0021] As a specific embodiment of the present invention, there are multiple gas sources. After the multiple gas sources are connected in parallel, they communicate with two intermediate containers. The two intermediate containers respectively communicate with the two diffusion chambers. Each intermediate container is provided with a piston, and a displacement pump communicates with the two intermediate containers for pushing the piston to move in the intermediate container, thereby sending gas into the diffusion chamber.

[0022] The present invention also discloses a method for measuring the gas diffusion coefficient in rock, which is measured by using the above-mentioned measuring device, and includes the following steps:

[0023] S1. Connect the device to adjust each communication hole to face the opening of the sealing strip, and then perform airtightness and replacement;

[0024] S2. Fill the sampling chamber and the diffusion chamber with the target gas. After adjusting the pressures of the two diffusion chambers to be equal, cut off the gas source.

[0025] S3. Start the test. After a certain interval of time, rotate the second blind tube to separate a single sampling chamber from the diffusion chamber, and then take a sample to analyze the gas components, and further calculate the diffusion coefficient of the gas.

[0026] The beneficial effects of the present invention are as follows:

[0027] The device for measuring the gas diffusion coefficient in rock of the present invention can isolate a single sampling chamber from the diffusion chamber, and the pressure of the diffusion chamber is not affected during the isolation process, enabling non-disturbed sampling, reducing the impact on the pressure of the diffusion chamber, and improving the accuracy of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of the overall structure of an embodiment of the present invention;

[0029] Figure 2 is Figure 1 a schematic diagram of the overall structure of the sampling mechanism in

[0030] Figure 3 is Figure 2 a sectional view of the combined structure of the cylinder and the second blind tube in

[0031] Figure 4 is Figure 2 an assembly drawing of the combined structure of the cylinder and the second blind tube in

[0032] Figure 5 is Figure 4 a three-dimensional view of the second blind tube in

[0033] Figure 6 is a schematic diagram of the overall structure of another embodiment of the present invention.

[0034] In the figure, core holder 100; rock sample 200; gas source 400; vacuum pump 600; intermediate container 700; displacement pump 800; hollow plug 900;

[0035] 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;

[0036] communication hole 501; annular cavity 502; sealing strip 503; sampling hole 504; air inlet hole 505. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] Next, in combination with the accompanying drawings and specific embodiments, the present invention will be further described. It should be noted that, on the premise of no conflict, any combination can be formed between the following described embodiments or technical features to form a new embodiment.

[0038] Please refer to Figures 1 to 6 , which shows a schematic structural diagram of two specific embodiments of the device for measuring the gas diffusion coefficient in rock of the present invention. The device for measuring the gas diffusion coefficient 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. A rock sample 200 is clamped in the middle of the core holder 100. There are two sampling mechanisms, which are symmetrically arranged at both ends of the rock sample 200 respectively. Each sampling mechanism includes a first blind tube 510, a cylinder 520, a second blind tube 530, and a sampling chamber 550. The opening end of the first blind tube 510 faces the rock sample 200 and is hermetically connected to the end face of the rock sample 200 to form a diffusion chamber 540. In some embodiments, the annular pressure of the core holder 100 can be controlled so that the inner wall (rubber cylinder) of the core holder 100 presses against the outer wall of the opening end of the first blind tube 510, thereby achieving sealing. There are at least two sampling chambers 550. Of course, the specific number of sampling chambers 550 can be designed according to the number of samplings during the experiment. Each sampling chamber 550 corresponds to a non-disturbed sampling process. Increasing the number of sampling chambers 550 can perform more non-disturbed samplings. Each sampling chamber 550 is arranged along the axial direction of the core holder 100. Each sampling chamber 550 can be spaced at a certain distance. Of course, it can also be like Figure 2As shown, the sampling chambers 550 are connected in series in a butting manner, which can reduce the number of partition plates of the sampling chambers 550 and is beneficial to reducing the manufacturing cost. One end of the cylinder body 520 penetrates through each sampling chamber 550 in sequence and extends into the diffusion chamber 540. Communication holes 501 are opened in the cylinder wall corresponding to each sampling chamber 550. Therefore, each sampling chamber 550 can be communicated with the inside of the cylinder body 520 through the corresponding communication hole 501. The second blind tube 530 is coaxially sleeved in the cylinder body 520 and is spaced from it by a certain distance. The closed end of the second blind tube 530 faces the diffusion chamber 540, and the open end is rotationally and sealingly connected to the cylinder body 520, thereby forming an annular cavity 502 communicated with the diffusion chamber 540 between the cylinder body 520 and the second blind tube 530. An annular sealing strip 503 corresponding to the communication hole 501 and a sampling hole 504 penetrating through the tube wall and the sealing strip 503 are provided on the tube wall of the second blind tube 530. The open end of the second blind tube 530 is communicated with the gas analyzer 310, so as to send the sample gas flowing into through the sampling hole 504 into the gas analyzer 310 for component analysis. When the second blind tube 530 is rotated in the same direction to rotate relative to the cylinder body 520, the communication hole 501 is in three states in sequence, namely the diffusion state, the sampling state, and the isolation state. Among them, the diffusion state refers to the state where the communication hole 501 faces the opening of the sealing strip 503. At this time, the sampling chamber 550 corresponding to the communication hole 501 is communicated with the annular cavity 502, and then is integrated with the diffusion chamber 540. The gas in the sampling chamber 550 participates in the gas diffusion process of the rock sample, and the gas components will change with the progress of diffusion. The sampling state refers to the state where the communication hole 501 faces the sampling hole 504. At this time, the sampling chamber 550 corresponding to the communication hole 501 is communicated with the second blind tube 530, so that the gas in the sampling chamber 550 can be transported to the gas analyzer 310 for component analysis. Since the gas is separated from the diffusion chamber 540, the gas components do not change during the sampling process. At the same time, the reduction of the gas in the sampling chamber 550 will not affect the pressure of the diffusion chamber 540, thus realizing non-disturbing sampling. The isolation state refers to the state where the communication hole 501 faces the outer wall of the sealing strip 503. At this time, the communication hole 501 is closed by the outer wall of the sealing strip 503, and the corresponding sampling chamber 550 is isolated, neither disturbing the pressure of the diffusion chamber 540 nor disturbing the gas components in the second blind tube 530. The present invention has a plurality of sampling holes 504, and the sampling holes 504 are arranged in a circumferential dislocation manner. When the second blind tube 530 is rotated, the communication holes 501 are sequentially communicated with the corresponding sampling holes 504, so as to sample the gas in each sampling chamber 550 in sequence. In this way, the non-sampled communication holes 501 are always in the diffusion state, and the communication holes 501 that have completed sampling are always in the isolation state until all the sampling holes 504 have completed sampling. The gas source 400 is communicated with the diffusion chamber 540 and is used to supply gas to the diffusion chamber 540. The pressure gauge 320 is used to measure the gas pressure in the diffusion chamber 540.

[0039] In some embodiments, the pressures of the two diffusion chambers 540 can be measured separately to determine whether their initial pressures are balanced. However, since the pressure difference has a great influence on the results, in some embodiments, a high-precision differential pressure gauge 330 is provided to measure the pressure difference between the two diffusion chambers 540, which is convenient for more accurate measurement of the pressure difference, as Figure 1 shown.

[0040] In some embodiments, a vacuum pump 600 can be provided to evacuate the diffusion chamber 540 and the sampling chamber 550, which is convenient for quickly discharging the air in the diffusion system and shortening the experimental time.

[0041] When the present invention is used, the open end of the first blind tube 510 should be fixed in the core holder 100. For the convenience of fixing, the first blind tube 510 as a whole can be detachably fixed in the core holder 100, or the first blind tube 510 and the sampling chamber 550 can be integrally formed, and the whole is detachably fixed in the core holder 100. For example Figure 1 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.

[0042] In the present invention, the initial gas compositions in the two diffusion chambers 540 are different. In some embodiments, as Figure 1 shown, the two diffusion chambers are respectively connected to different gas sources 400. In other embodiments, as Figure 6 shown, multiple gas sources 400 are connected in parallel and are all communicated with the two diffusion chambers 540, so that the required gas components can be prepared by adjusting the flow rates of the respective gas sources 400.

[0043] In some embodiments, the gas can be sent into the diffusion chamber 540 by using the pressure of the gas source 400 itself. In other embodiments, the gas can also be transported to the diffusion chamber 540 through an intermediate container 700 containing a piston. As Figure 6 shown, two intermediate containers 700 share a displacement pump 800. The displacement pump 800 injects liquid into the intermediate container 700 to drive the piston in the intermediate container 700 to move, and the gas at the other end of the intermediate container 700 is pressed into the diffusion chamber 540.

[0044] In some embodiments, an elastic layer is provided on the outer wall of the sealing strip 503, and the sampling hole 504 penetrates through the elastic layer to enhance the sealing performance.

[0045] In some embodiments, as Figure 6 shown, the gas source 400 is communicated with a sampling chamber 550, so that the gas is sent into the diffusion chamber 540 through the sampling chamber 550. In other embodiments, as Figure 2As shown, an air inlet hole 505 is provided on one side of the second blind tube 530 outside the sampling chamber 550. One end of the air inlet hole 505 communicates with the annular cavity 502, and the other end communicates with the gas source 400. In this way, as long as the volumes of the sampling chambers 550 are equal, the reduction in the volume of the diffused gas is equal each time a sample is taken, which is convenient for calculating the volume of the gas participating in the gas diffusion of the rock sample.

[0046] In some embodiments, temperature controllers may also be respectively 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 to be different, the gas diffusion coefficient under the coexistence of a temperature gradient and a concentration gradient can be simulated.

[0047] The measuring device of the present invention can measure the gas diffusion coefficient in a rock by the following method:

[0048] S1. Adjust the connecting device so that each communication hole 501 faces the opening of the sealing strip 503, and then perform airtightness and replacement.

[0049] S2. Fill the sampling chamber 550 and the diffusion chamber 540 with the target gas. After adjusting the pressures of the two diffusion chambers 540 to be equal, cut off the gas source 400.

[0050] S3. Start the test. After a certain interval of time, rotate the second blind tube to separate a single sampling chamber from the diffusion chamber, and then take a sample to analyze the gas components, and further calculate the gas diffusion coefficient.

[0051] In step S3, the gas diffusion coefficient calculation formula in SY / T6129-2016 "Determination Method for Gas Diffusion Coefficient of Hydrocarbon Gases in Rocks" can be used to determine the gas diffusion coefficient during the diffusion process corresponding to two adjacent samplings. When the number of samplings is large, a gas diffusion coefficient can be calculated for each of all adjacent sampling processes, and then the average value of all gas diffusion coefficients can be taken as the final gas diffusion coefficient.

[0052] For those skilled in the art, various corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all such 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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