Coal sample deformation behavior monitoring experiment system and method based on nuclear magnetic resonance

Abstract

The invention relates to the technical field of coal bed gas development, and discloses a nuclear magnetic resonance-based coal sample deformation behavior monitoring experiment system and method, and the system comprises a gas injection system which comprises a first gas cylinder; the nuclear magnetic resonance adsorption and desorption system comprises a first core holder, a second core holder and a nuclear magnetic resonance unit, the first core holder and the second core holder are respectively communicated with the first gas cylinder through a first gas injection branch, and the second core holder can be detachably connected with the nuclear magnetic resonance unit; and when the second core holder is located in the nuclear magnetic resonance unit, the strain monitoring system is connected with the second core holder. The dynamic change of the methane state of the coal sample in the adsorption and desorption process can be captured in real time through the transverse relaxation time signal change of nuclear magnetic resonance and the strain monitoring data, and more accurate data support is provided for coal reservoir permeability evolution prediction and coal mine safety production.

Description

Technical Field

[0001] The present invention relates to the technical field of coalbed methane development, and particularly to an experimental system and method for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance. Background Art

[0002] As an important unconventional natural gas resource, coalbed methane is widely distributed around the world. Its development and utilization are of great significance for alleviating energy shortages and improving environmental quality. During the development of coalbed methane, the adsorption and desorption of methane cause the coal body to expand and contract, changing the mechanical properties of the coal body, which in turn leads to changes in the permeability of coal and rock, affecting the occurrence and flow of methane in the coal body. At present, there are many ways and methods for studying the deformation behavior of coal samples, but none of them can achieve the function of both real-time monitoring of the deformation behavior during the adsorption / desorption process of coal samples and calculating the corresponding adsorbed gas and free gas contents. Therefore, developing a method for monitoring the deformation behavior of coal samples under the coupling action of multiple fields combined with nuclear magnetic resonance technology is of great significance for studying the ratio of adsorbed / free gas and the influence of coal body adsorption and desorption deformation on improving the deep coalbed methane extraction efficiency in the actual development process.

[0003] In the current experimental devices, there is a lack of a device that can complete the above two detections with high precision at the same time. For example, in the patent CN209745750U "Deformation amount-adsorption amount synchronous test device for the process of coal body adsorbing gas" and the patent CN111521516A "A coal body gas adsorption and strain test system", only the isothermal adsorption experiment is used to test the adsorbed gas content and the strain of the coal body. The disadvantage is that the free gas content cannot be tested simultaneously.

[0004] Therefore, there is an urgent need for an experimental system and method for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide an experimental system and method for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance to solve the problems existing in the above prior art.

[0006] To achieve the above purpose, the present invention provides the following solution: The present invention provides an experimental system for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance, including:

[0007] A gas injection system, including a first gas cylinder;

[0008] A nuclear magnetic resonance adsorption and desorption system, including a first core holder, a second core holder and a nuclear magnetic resonance unit. The first core holder and the second core holder are respectively connected to the first gas cylinder through a first gas injection branch, wherein the second core holder is detachably connected to the nuclear magnetic resonance unit;

[0009] A temperature regulating member, wherein the first core holder and the second core holder respectively regulate the temperature through the temperature regulating member;

[0010] A strain monitoring system, when the second core holder is located within the nuclear magnetic resonance unit, the strain monitoring system is connected to the second core holder.

[0011] According to an experimental system for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance provided by the present invention, the nuclear magnetic resonance unit includes a nuclear magnetic coil interlayer, and the second core holder is located within the nuclear magnetic coil interlayer.

[0012] According to an experimental system for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance provided by the present invention, the strain monitoring system includes a strain monitor and a strain receiver. The strain monitor is connected to the second core holder, the strain receiver is connected to the strain monitor, and the strain receiver is connected to a computer.

[0013] According to an experimental system for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance provided by the present invention, the first gas injection branch includes a pipeline. The first core holder and the second core holder are respectively connected to a first gas cylinder through the pipeline. A first pressure gauge, a first valve, and a second valve are sequentially installed on the pipeline along the gas transmission direction. A third valve is installed between the first core holder and the pipeline, and a fourth valve is installed between the second core holder and the pipeline.

[0014] According to an experimental system for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance provided by the present invention, a booster pump is connected to the pipeline, and the booster pump is connected to an air compressor.

[0015] According to an experimental system for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance provided by the present invention, a vacuum pump is connected to the pipeline. The vacuum pump is connected to a gas recovery tank, and a flow meter is provided between the vacuum pump and the gas recovery tank.

[0016] According to an experimental system for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance provided by the present invention, the temperature regulating member includes a first temperature control box and a second temperature control box. The first core holder is placed within the first temperature control box, the second core holder is placed within the second temperature control box, and the second core holder can be removed from the second temperature control box and transferred to the nuclear magnetic coil interlayer.

[0017] According to an experimental system for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance provided by the present invention, a second pressure gauge is externally connected to the first core holder, and a third pressure gauge and a first thermometer are externally connected to the second core holder.

[0018] According to an experimental system for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance provided by the present invention, the first gas cylinder is a high-pressure resistant gas cylinder, and methane gas is stored in the first gas cylinder.

[0019] A method for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance includes the following steps:

[0020] Place the sample into the first core holder, control the pressures of the first core holder and the second core holder through the gas injection system, and measure the volumes of the first core holder and the second core holder according to the pressures, which are V 1 and V 2 ;

[0021] Place the test item into the second core holder, control the pressures of the first core holder and the second core holder through the gas injection system, and establish the relationship between the T2 peak area and mass of pure methane according to the pressure, Y area = aX mass, and solve for a;

[0022] By changing the temperature and pressure conditions, conduct several groups of experiments to generate coal sample deformation data under different temperature and pressure conditions.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] An experimental system and method for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance provided by the present invention can, through the change of the transverse relaxation time signal of nuclear magnetic resonance and the strain monitoring data, capture the dynamic changes of the methane state during the adsorption and desorption process of coal samples in real time, accurately measure the adsorbed / free gas content and the deformation amount of the coal body during the adsorption and desorption process under different temperature and pressure conditions throughout the process, and provide more accurate data support for the prediction of the evolution of coal reservoir permeability and the safe production of coal mines. It is of great significance for guiding the formulation of development plans, predicting the law of production changes, and evaluating the recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts:

[0026] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0027] Among them, 1. The first gas cylinder; 2. The first pressure gauge; 3. The first valve; 4. The booster pump; 5. The air compressor; 6. The vacuum pump; 7. The flowmeter; 8. The gas recovery tank; 9. The second valve; 10. The third valve; 11. The second pressure gauge; 12. The first core holder; 13. The first temperature control box; 14. The fourth valve; 15. The first thermometer; 16. The third pressure gauge; 17. The second core holder; 18. The second temperature control box; 19. The NMR coil sandwich; 20. The strain monitor; 21. The strain receiver; 22. The computer. Specific embodiments

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0030] Referring to Figure 1 , the present invention provides a coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance, including:

[0031] The gas injection system includes the first gas cylinder 1;

[0032] The nuclear magnetic resonance adsorption and desorption system includes the first core holder 12, the second core holder 17, and the nuclear magnetic resonance unit. The first core holder 12 and the second core holder 17 are respectively connected to the first gas cylinder 1 through the first gas injection branch, and the second core holder 17 can be detachably connected to the nuclear magnetic resonance unit;

[0033] The temperature adjustment member, the first core holder 12 and the second core holder 17 are respectively adjusted in temperature through the temperature adjustment member;

[0034] The strain monitoring system is connected to the second core holder 17 when the second core holder 17 is located in the nuclear magnetic resonance unit.

[0035] In an embodiment of the present invention, when in use, the reference group and the test group are respectively placed in the first core holder 12 and the second core holder 17, and the pressures are controlled through the gas injection system. The second core holder 17 is placed in the nuclear magnetic resonance unit and monitored through the strain monitoring system, so as to realize the ability to calculate the changes in the pore structure and the matrix deformation law of coal and rock under different temperatures and different pressures.

[0036] As an alternative embodiment, the nuclear magnetic resonance unit includes a nuclear magnetic coil sandwich layer 19, and the second core holder 17 is located within the nuclear magnetic coil sandwich layer 19.

[0037] In one embodiment of the present invention, nuclear magnetism is released through the provided nuclear magnetic coil sandwich layer 19.

[0038] As an alternative embodiment, the strain monitoring system includes a strain monitor 20 and a strain receiver 21. The strain monitor 20 is connected to the second core holder 17, the strain receiver 21 is connected to the strain monitor 20, and the strain receiver 21 is connected to the computer 22.

[0039] In one embodiment of the present invention, monitoring is performed through the provided strain monitor 20. Meanwhile, the strain monitor 20 is a disposable product and is replaced after use.

[0040] As an alternative embodiment, the first gas injection branch includes a pipeline. The first core holder 12 and the second core holder 17 are respectively connected to the first gas cylinder 1 through the pipeline. A first pressure gauge 2, a first valve 3, and a second valve 9 are sequentially installed on the pipeline along the gas transportation direction. A third valve 10 is installed between the first core holder 12 and the pipeline, and a fourth valve 14 is installed between the second core holder 17 and the pipeline.

[0041] In one embodiment of the present invention, the transportation of gas is controlled through the provided first gas cylinder 1 and several valves.

[0042] As an alternative embodiment, a booster pump 4 is connected to the pipeline, and the booster pump 4 is connected to an air compressor 5.

[0043] In one embodiment of the present invention, the pressure is regulated through the provided booster pump 4.

[0044] As an alternative embodiment, a vacuum pump 6 is connected to the pipeline. The vacuum pump 6 is connected to a gas recovery tank 8, and a flow meter 7 is provided between the vacuum pump 6 and the gas recovery tank 8.

[0045] In one embodiment of the present invention, vacuum pumping is performed through the provided vacuum pump 6.

[0046] As an alternative embodiment, the temperature regulating member includes a first temperature control box 13 and a second temperature control box 18. The first core holder 12 is placed within the first temperature control box 13, and the second core holder 17 is placed within the second temperature control box 18. Moreover, the second core holder 17 can be removed from the second temperature control box 18 and transferred into the nuclear magnetic coil sandwich layer 19.

[0047] In one embodiment of the present invention, the temperature is regulated through the provided first temperature control box 13 and second temperature control box 18.

[0048] As an alternative embodiment, a second pressure gauge 11 is externally connected to the first core holder 12, and a third pressure gauge 16 and a first thermometer 15 are externally connected to the second core holder 17.

[0049] In one embodiment of the present invention, the temperature and pressure are monitored by the provided pressure gauge and thermometer.

[0050] As an alternative embodiment, the first gas cylinder 1 is a high-pressure resistant gas cylinder, and methane gas is stored in the first gas cylinder 1.

[0051] In one embodiment of the present invention, methane gas or other adsorbable gases are transported through the provided first gas cylinder 1.

[0052] A method for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance includes the following steps:

[0053] Place the sample into the first core holder 12, control the pressures of the first core holder 12 and the second core holder 17 through the gas injection system, and measure the volumes of the first core holder 12 and the second core holder 17 according to the pressure, which are V 1 and V 2 ;

[0054] Check the airtightness of the overall system. After checking the airtightness, close all valves, open the first valve 3, the second valve 9, and the third valve 10, and record the pressure reading P 1 of the second pressure gauge 11. Close the first valve 3 and the second valve 9, open the fourth valve 14, and when the pressure readings of the second pressure gauge 11 and the third pressure gauge 16 are balanced and consistent, record the pressure as P 2 ; Use the ideal gas state equation PV = ZnRT to establish the first equation as P 1 V 1 = P 2 (V 1 + V 2 );

[0055] The first core holder 12 is a reference chamber, and the second core holder 17 is a sample chamber. Place a polytetrafluoroethylene column with a known volume of V column into the second core holder 17, open the first valve 3, the second valve 9, and the third valve 10, and record the pressure reading P 3 of the second pressure gauge 11. Close the first valve 3 and the second valve 9, open the fourth valve 14, and when the pressure readings of the second pressure gauge 11 and the third pressure gauge 16 are balanced and consistent, record the pressure as P 4 ; Establish the second equation as P 3 V 1 = P 4 (V 1 + V2 -V 柱 );Solve the first equation and the second equation simultaneously to calculate the reference cavity volume V 1 and the sample cavity volume V 2 ;

[0056] Place the test sample in the second core holder 17, control the pressures of the first core holder 12 and the second core holder 17 through the gas injection system, and establish the relationship between the T2 peak area and mass of pure methane according to the pressure, Y 面积 = aX 质量 , and solve for a;

[0057] Open the first valve 3, the second valve 9 and the fourth valve 14, and record the T 2 spectral peak areas corresponding to different pressure points, and use PV 2 = ZnRT to calculate the methane mass at different pressures, generate a graph with the peak area on the vertical axis and the mass relationship on the horizontal axis, and solve for the coefficient a;

[0058] Conduct a number of experiments by changing the temperature and pressure conditions to generate coal sample deformation data under different temperature and pressure conditions;

[0059] Measure the adsorbed gas and free gas contents and the corresponding deformation amounts under different temperature and pressure conditions:

[0060] Set different pressures: Place the experimental sample inside the second core holder 17, open the first valve 3, the second valve 9, and the third valve 10, and record the pressure reading P of the second pressure gauge 11 1 , close the first valve 3 and the second valve 9, open the fourth valve 14, and when the pressure readings of the second pressure gauge 11 and the third pressure gauge 16 are balanced and consistent, record the pressure to generate the T 2 peak area, and the T 2 peak is divided into an adsorption peak and a free peak according to the relaxation time, record the areas of the adsorption peak and the free peak respectively, and record the data of the strain monitor simultaneously;

[0061] Set the temperature: Adjust the first temperature control box 13 and the second temperature control box 18 to set the temperature required for the experiment;

[0062] Calculate the adsorbed gas content, free gas content and deformation amount: Use the peak area directly given by the experimental device, combined with the solved coefficient a, to obtain the corresponding adsorbed gas and free gas contents;

[0063] Change the conditions to continue the comparative experiment: According to the experimental purpose, for different rock samples, change the experimental temperature, pressure and other conditions, and similarly conduct comparative experiments under other experimental conditions.

[0064] The present invention provides an experimental system and method for monitoring the deformation behavior of coal samples based on nuclear magnetic resonance. Through nuclear magnetic resonance technology, it is possible to monitor the changes in the contents of adsorbed gas and free gas in real time, and it is more accurate for calculating the amounts of adsorbed gas, free gas and desorbed gas. Through the strain monitoring device, it is possible to test the deformation amount of the coal body during the adsorption and desorption processes under different temperature and pressure conditions throughout the process. This experimental system and method are of great significance for guiding hydraulic fracturing strategies, predicting the variation law of reservoir permeability and evaluating recovery efficiency.

[0065] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0066] The embodiments described above are only for describing the preferred mode of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solution of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance, characterized in that: include: A gas injection system comprises a first gas cylinder (1); A nuclear magnetic resonance adsorption and desorption system comprises a first core holder (12), a second core holder (17) and a nuclear magnetic resonance unit, wherein the first core holder (12) and the second core holder (17) are respectively connected to the first gas cylinder (1) through a first gas injection branch, wherein the second core holder (17) can be detachably connected to the nuclear magnetic resonance unit; a temperature regulating member, through which the first core holder (12) and the second core holder (17) respectively regulate the temperature; A strain monitoring system is connected to the second core holder (17) when the second core holder (17) is located in the nuclear magnetic resonance unit.

2. The coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance according to claim 1, characterized in that: The nuclear magnetic resonance unit comprises a nuclear magnetic coil sandwich (19), and the second core holder (17) is located in the nuclear magnetic coil sandwich (19).

3. The coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance according to claim 1, characterized in that: The strain monitoring system comprises a strain monitor (20) and a strain receiver (21), wherein the strain monitor (20) is connected to the second core holder (17), the strain receiver (21) is connected to the strain monitor (20), and the strain receiver (21) is connected to a computer (22).

4. The coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance according to claim 1, characterized in that: The first gas injection branch comprises a pipeline, the first core holder (12) and the second core holder (17) are respectively connected to the first gas cylinder (1) through pipelines, a first pressure gauge (2), a first valve (3) and a second valve (9) are sequentially installed on the pipeline along the gas delivery direction, a third valve (10) is installed between the first core holder (12) and the pipeline, and a fourth valve (14) is installed between the second core holder (17) and the pipeline.

5. The coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance according to claim 4 is characterized in that: A booster pump (4) is connected to the pipeline, and the booster pump (4) is in communication with an air compressor (5).

6. The coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance according to claim 4, characterized in that: The pipeline is connected to a vacuum pump (6), the vacuum pump (6) is connected to a gas recovery tank (8), and a flow meter (7) is provided between the vacuum pump (6) and the gas recovery tank (8).

7. The coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance according to claim 2, characterized in that: The temperature regulating component comprises a first temperature control box (13) and a second temperature control box (18); the first core holder (12) is placed in the first temperature control box (13); the second core holder (17) is placed in the second temperature control box (18); and the second core holder (17) can be removed from the second temperature control box (18) and transferred to the nuclear magnetic coil interlayer (19).

8. The coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance according to claim 1, characterized in that: The first core holder (12) is externally connected to a second pressure gauge (11), and the second core holder (17) is externally connected to a third pressure gauge (16) and a first thermometer (15).

9. The coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance according to claim 1, characterized in that: The first gas cylinder (1) is a high-pressure resistant gas cylinder, and methane gas is stored in the first gas cylinder (1).

10. A method for monitoring coal sample deformation behavior based on nuclear magnetic resonance, applicable to the coal sample deformation behavior monitoring experimental system based on nuclear magnetic resonance according to claim 1, characterized in that: The following steps are involved: Putting a sample into the first core holder (12), controlling the pressure of the first core holder (12) and the second core holder (17) by the gas injection system, and measuring the volumes of the first core holder (12) and the second core holder (17) according to the pressure, which are V1 and V2 respectively; The test sample is placed in the second core holder (17), the pressure of the first core holder (12) and the second core holder (17) is controlled by the gas injection system, and the relationship between the peak area and mass of pure methane T2 is established according to the pressure, Y 面积 =aX 质量 , solve for a; By changing the temperature and pressure conditions, several groups of experiments are carried out to generate the deformation data of coal samples under different temperature and pressure conditions.

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