Shale gas reservoir characteristic sampling equipment and use method thereof

Abstract

The invention belongs to the technical field of geological exploration sampling equipment, and particularly relates to shale gas reservoir feature sampling equipment and a using method thereof.The shale gas reservoir feature sampling equipment comprises a sampling pipe, the sampling pipe is installed in an inner cavity of a drill rod and an inner cavity of a drill bit, and the sampling pipe is used for storing rock core samples; the shale gas sampling device further comprises a variable-capacity sealing mechanism, the variable-capacity sealing mechanism is installed on the sampling pipe, and the variable-capacity sealing mechanism improves the sealing sampling effect on shale gas by changing the storage space of a rock core sample. By arranging the variable-volume sealing mechanism, in the opening and transporting process of the rock core sample, the difference between the internal pressure and the external pressure of the rock core sample storage space is effectively reduced through the variability of the volume of the rock core sample storage space in the process of reducing the external pressure, and then the rock core sample is sealed and stored in cooperation with the cutting piece; meanwhile, the varactor is separated from the rock core sample by utilizing the expansion of the varactor, and the difficulty in taking out the rock core sample is effectively reduced by matching with the elastic characteristic of the varactor.

Description

Technical Field

[0001] The present invention belongs to the technical field of geological exploration sampling equipment, and specifically relates to a shale gas reservoir characteristic sampling equipment and its usage method. Background Art

[0002] Shale gas refers to unconventional natural gas stored in reservoir rock series mainly composed of organic-rich shale. It is characterized by large reserves and wide distribution, and has important strategic significance for the growing energy demand, optimizing the energy structure, and promoting the development of clean energy. As a typical unconventional oil and gas resource, shale gas has been initially industrialized in China.

[0003] In the initial stage of shale gas industrial development, it is necessary to explore and evaluate the shale gas reservoir to find out the reserves and mining difficulties of shale gas resources, provide guidance for subsequent mining activities, and thus improve the efficiency and economic benefits of shale gas mining. When evaluating the shale gas reservoir, the method of drilling and coring is usually adopted to obtain core samples, and then the core samples are subjected to thermal desorption and the desorbed gas is collected. Finally, by measuring the content of residual gas and desorbed gas, the total gas content of the core is obtained. During this process, the escape of shale gas to the outside will directly affect the calculation of the total gas content of the core. In order to reduce the degree of gas escape during the process from core sampling to thermal desorption, the method of closed sampling is mostly used for core sampling in related technologies.

[0004] For example, the shale gas and core pressure-holding and sealing sampling device and method disclosed in the related technology, with the application number CN2021104224548. In this scheme, the core is sampled and sealed underground. After the shale sample is intercepted, it is stored in the accommodation cavity of the inner cylinder and the accommodation cavity is sealed underground, so that the obtained core sample is always under the pressure at the sampling site, avoiding the influence of the huge pressure difference between underground and the ground on the core sample when the core sample is taken out of the well, and also avoiding the escape of shale gas in the core during the sampling process. However, it is found in the actual application process that although the sampling pipe seals the core sample effectively, which can reduce the escape of shale gas during mining, due to the high-pressure state always presented in the accommodation cavity, when the external environment returns to normal pressure, a high sealing effect is required. Therefore, when the sealing effect cannot meet the requirements, it is easy to cause the escape of core gas, resulting in an increase in the proportion of lost gas in the total gas content of the core sample and an increase in the probability of data distortion. At the same time, after the accommodation cavity is opened, the internal pressure returns to normal pressure, resulting in a relatively tight combination between the core and the accommodation cavity, so it is difficult to take out the core.

[0005] In view of this, the present invention proposes a shale gas reservoir characteristic sampling equipment and its usage method to solve the above technical problems. Summary of the Invention

[0006] In order to make up for the deficiencies of the prior art and solve the above technical problems, the present invention proposes a shale gas reservoir characteristic sampling device and its usage method.

[0007] The technical solution adopted by the present invention to solve its technical problems is as follows: A shale gas reservoir characteristic sampling device described in the present invention includes a sampling pipe. The sampling pipe is a tubular structure with openings at both ends. The sampling pipe is installed in the inner cavity of the drill pipe and the drill bit, and the sampling pipe is used to store core samples.

[0008] It further includes a variable volume sealing mechanism. The variable volume sealing mechanism is installed on the sampling pipe. The variable volume sealing mechanism enhances the sealing sampling effect of shale gas by changing the storage space of the core sample.

[0009] The variable volume sealing mechanism includes:

[0010] An installation ring. The installation ring is installed inside the sampling pipe, and the installation ring is coaxially arranged with the sampling pipe.

[0011] A variable volume pipe. The variable volume pipe is installed on the installation ring. The variable volume pipe is a cylindrical structure made of elastic material, and the variable volume pipe is used to store core samples.

[0012] A cutting member. The cutting member is installed on the installation ring. The cutting member includes an open state and a closed state, and the cutting member is used to cut off the conduction channel between the installation ring and the outside.

[0013] Preferably, the cutting member includes a driving ring and a cutting piece. A closing groove is provided on the installation ring. The driving ring is rotatably installed in the closing groove. A cutting piece is hingedly installed on the side of the closing groove close to the center of the installation ring. The cutting piece is hingedly connected to the driving ring through a connecting rod. A plurality of the cutting pieces are formed by cutting a circular plate.

[0014] Preferably, a driving motor is fixedly installed on the installation ring. The output end of the driving motor extends into the closing groove, and a transmission wheel is fixedly installed at the output end of the driving motor. The transmission wheel is meshed with the driving ring.

[0015] Preferably, the variable volume sealing mechanism further includes a plastic sealing bag. The plastic sealing bag is installed inside the variable volume pipe. The plastic sealing bag is a cylindrical structure with one end open. The diameter and length of the plastic sealing bag are both larger than those of the variable volume pipe. The open end of the plastic sealing bag is detachably and fixedly connected to the installation ring.

[0016] Preferably, the installation ring is composed of a threaded ring and a clamping ring. The threaded ring is threadedly connected to the sampling pipe. The threaded ring and the clamping ring are coaxially arranged. The threaded ring and the clamping ring are bolt-fixed. In the initial state, the open end of the plastic sealing bag is clamped and installed between the threaded ring and the clamping ring.

[0017] Preferably, sealing gaskets are fixedly installed on the sides of the threaded ring and the assembly ring close to each other, and the plastic-sealed bag extends into the gap of the sealing gasket.

[0018] Preferably, it further includes a forced variable volume mechanism for adjusting the volume of the variable volume tube. The forced variable volume mechanism includes:

[0019] Installation rods, the installation ring is detachably and fixedly installed on the installation ring through bolts, and the plurality of installation rods are evenly arranged along the circumferential direction of the installation ring;

[0020] Electric telescopic rods, the installation rods are fixedly installed with electric telescopic rods, one end of the electric telescopic rod away from the installation rod is fixedly installed with a connecting plate, and the connecting plate is fixedly installed on the outer wall of the variable volume tube.

[0021] Preferably, the installation rods are all designed in an inverted L shape, the electric telescopic rods are divided into two groups, and the two groups of electric telescopic rods are respectively perpendicular to the side wall and the top end of the variable volume tube.

[0022] Preferably, in the initial state, the length of the electric telescopic rod is the smallest, after sampling, the length of the electric telescopic rod is the largest, and in the sealed transportation state, the length of the electric telescopic rod gradually decreases.

[0023] A method for using a shale gas reservoir characteristic sampling device, the method includes the following steps:

[0024] S1: Before sampling, disassemble the drill bit and the drill pipe, install the sampling device in the drill pipe, and go deep into the well to move forward towards the shale gas reservoir;

[0025] S2: Drive the drill bit to rotate by the drill pipe to drill the shale, the core enters the variable volume sealing mechanism through the central cavity of the drill bit, and after the drilling depth reaches the preset value, stop sampling;

[0026] S3: The forced variable volume mechanism first drives the volume of the variable volume tube to contract, then the cutting part cuts off the conduction channel between the installation ring and the outside, and then the forced variable volume mechanism drives the volume of the variable volume tube to gradually expand;

[0027] S4: Lift the drill pipe, disassemble the drill bit and the drill pipe outside the well, take out the sampling device, and rotate the threaded ring to separate the sampling pipe from the variable volume sealing mechanism;

[0028] S5: Manually tie the open end of the plastic-sealed bag, disassemble the installation ring, obtain the core sealed and wrapped by the plastic-sealed bag, and then directly open the plastic-sealed bag in the pyrolysis desorption device to perform pyrolysis desorption operation.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1. A shale gas reservoir characteristic sampling device and its usage method according to the present invention, by setting a variable volume sealing mechanism, during the opening and transportation of the core sample, through the variability of the volume of the core sample storage space, during the process of the external pressure decreasing, effectively reducing the pressure difference between the inside and outside of the core sample storage space, and then cooperating with the cutting member to achieve the sealed storage of the core sample. At the same time, by the expansion of the variable volume tube, causing the separation of the variable volume tube from the core sample, and cooperating with the elastic characteristics of the variable volume tube, effectively reducing the difficulty of taking out the core sample.

[0031] 2. A shale gas reservoir characteristic sampling device and its usage method according to the present invention, using a plastic sealing bag to cover the core and shale gas, and then cooperating with the variable volume tube to achieve double wrapping of the core sample. On the one hand, when the pressure difference between the inside and outside of the core sample storage space changes, the plastic sealing bag cooperates with the variable volume tube to double cover the shale gas and the shale core, reducing the probability of shale gas escaping. On the other hand, when taking out the sample, taking out the plastic sealing bag and the core sample together, the smooth surface characteristics of the plastic sealing bag can be utilized to reduce the difficulty of taking out the core sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The following further describes the present invention with reference to the drawings.

[0033] Figure 1 is the assembled three-dimensional view of the present invention with the drill pipe and the drill bit;

[0034] Figure 2 is the three-dimensional view of the present invention;

[0035] Figure 3 is the assembled three-dimensional view of the variable volume tube and the forced variable volume mechanism;

[0036] Figure 4 is the three-dimensional view of the mounting ring;

[0037] Figure 5 is the schematic diagram of the cutting member in the closed state;

[0038] Figure 6 is the schematic diagram of the cutting member in the open state;

[0039] Figure 7 is the cross-sectional view of the present invention;

[0040] Figure 8 is Figure 7 the partial enlarged view at A in

[0041] Figure 9 is the method flow chart of the present invention;

[0042] In the figure: 1. Sampling pipe; 11. Drill pipe; 12. Drill bit; 2. Installation ring; 21. Threaded ring; 22. Clamping ring; 23. Sealing gasket; 24. Closing groove; 3. Variable volume pipe; 4. Cutting member; 41. Driving ring; 42. Cutting piece; 43. Connecting rod; 44. Driving motor; 45. Transmission wheel; 5. Plastic sealed bag; 6. Installation rod; 61. Electric telescopic rod; 62. Connecting plate. Detailed implementation mode

[0043] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with the specific implementation modes.

[0044] As Figures 1 to 8 shown, a shale gas reservoir characteristic sampling device according to the present invention includes a sampling pipe 1. The sampling pipe 1 is a tubular structure with openings at both ends. The sampling pipe 1 is installed in the inner cavities of the drill pipe 11 and the drill bit 12, and the sampling pipe 1 is used to store core samples.

[0045] It further includes a variable volume sealing mechanism. The variable volume sealing mechanism is installed on the sampling pipe 1, and the variable volume sealing mechanism enhances the sealing sampling effect of shale gas by changing the storage space of the core sample.

[0046] The variable volume sealing mechanism includes:

[0047] An installation ring 2 is installed in the sampling pipe 1, and the installation ring 2 is coaxially arranged with the sampling pipe 1.

[0048] A variable volume pipe 3 is installed on the installation ring 2. The variable volume pipe 3 is a cylindrical structure made of elastic material, and the variable volume pipe 3 is used to store core samples.

[0049] A cutting member 4 is installed on the installation ring 2. The cutting member 4 has an open state and a closed state, and the cutting member 4 is used to cut off the conduction channel between the installation ring 2 and the outside.

[0050] When taking characteristic samples of the shale gas reservoir, in order to enhance the sealing effect of shale gas and reduce the degree of shale gas dispersion after mining, and at the same time to improve the convenience of taking out the core sample from the sampling pipe 1, a variable volume sealing mechanism is set in the present invention. Due to the variability of the storage space of the core sample, the pressure difference between the storage space of the core sample and the outside is reduced, and the cutting member 4 is used to cut off the communication channel between the storage space of the core sample and the outside, so as to achieve a better sealing effect with a relatively simple structure.

[0051] Specifically, during the sampling operation, the sampling pipe 1 needs to be installed in the drill pipe 11. By rotating the drill bit 12 and the drill pipe 11, the sampling pipe 1 is caused to move into the shale gas reservoir. At the same time, with the opening in the middle of the drill bit 12, the mined core moves into the sampling pipe 1. It should be noted that in the present invention, the mounting ring 2 is coaxially arranged with the drill bit 12, and the inner diameter of the mounting ring 2 is greater than or equal to the inner hole of the drill bit 12. Therefore, the core can directly move through the mounting ring 2 into the variable-volume tube 3. When the downward drilling distance of the drill bit 12, the drill pipe 11, and the sampling pipe 1 reaches a preset value, the drilling equipment is turned off, and the cutting member 4 cuts off the conduction channel between the mounting ring 2 and the outside. During the cutting process, not only can the core be fractured, but also the inner hole of the mounting ring 2 can be sealed. Subsequently, the drill pipe 11 and the drill bit 12 carry the sample tube and move out of the well again. During this process, as the drill pipe 11 continues to rise, the external pressure value gradually decreases. When the pressure decreases, the shale gas in the core sample has a tendency to expand in volume, and the shale gas gradually separates from the core sample. Therefore, under the action of the internal and external pressure difference, the variable-volume tube 3 expands in volume. Through the change in volume, the internal pressure of the variable-volume tube 3 gradually decreases, thereby reducing the internal and external pressure difference of the variable-volume tube 3. The reduction of the internal and external pressure difference, combined with the cutting and sealing effect of the cutting member 4, can effectively inhibit the rate of the shale gas inside the variable-volume tube 3 from escaping to the outside. When the sampling pipe 1 moves out of the well, due to the expansion of the variable-volume tube 3, the degree of fit between the core sample and the variable-volume tube 3 decreases. Subsequently, when the mounting ring 2 is opened and the shale gas is discharged, the variable-volume tube 3 will shrink again, but it can still reduce the difficulty of taking out the core sample, thereby facilitating the transfer of the core sample to the pyrolysis desorption equipment.

[0052] By setting the variable-volume sealing mechanism in the present invention, during the opening and transportation of the core sample, through the variability of the volume of the storage space of the core sample, during the process of the external pressure decreasing, the internal and external pressure difference of the storage space of the core sample is effectively reduced. Then, in cooperation with the cutting member 4, the sealed storage of the core sample is realized. At the same time, by using the expansion of the variable-volume tube 3, the variable-volume tube 3 is separated from the core sample, and in combination with the elastic characteristics of the variable-volume tube 3, the difficulty of taking out the core sample is effectively reduced.

[0053] As a preferred embodiment of the present invention, the cutting member 4 includes a driving ring 41 and a cutting piece 42. A closing groove 24 is formed on the mounting ring 2. The driving ring 41 is rotatably installed in the closing groove 24. A cutting piece 42 is hingedly installed on the side of the closing groove 24 close to the center of the mounting ring 2. The cutting piece 42 is hinged to the driving ring 41 through a connecting rod 43. The plurality of cutting pieces 42 are formed by cutting a circular plate.

[0054] A drive motor 44 is fixedly installed on the installation ring 2. The output end of the drive motor 44 extends into the closing groove 24, and a transmission wheel 45 is fixedly installed at the output end of the drive motor 44. The transmission wheel 45 is meshed and connected with the drive ring 41.

[0055] During the process of core sample sampling, in the initial state, the cutting piece 42 is stored in the closing groove 24. At this time, the inner hole of the installation ring 2 is open. As the drill bit 12 and the drill pipe 11 continue to drill, the core sample extends into the variable volume tube 3. When the drilling depth reaches a preset value, under the control of a preset program at this time, the drive motor 44 is caused to start. When the drive motor 44 rotates, since the outer side of the drive ring 41 is designed in a gear shape, through the meshing of the transmission wheel 45 and the drive ring 41, the drive ring 41 is driven to rotate. The drive ring 41 and the cutting piece 42 are hinged and connected through a connecting rod 43. In the present invention, the cutting piece 42 is cut from a complete circular plate. In addition to being hinged to the connecting rod 43, the cutting piece 42 is also directly hinged to the closing groove 24. When the drive ring 41 and the connecting rod 43 push the cutting piece 42 to move, multiple cutting pieces 42 gradually recombine into a circular plate. During this process, the core sample is first cut, and then the inner hole of the installation ring 2 is cut and sealed, thereby cooperating with the volume change of the variable volume tube 3 to achieve the sealed storage of the core sample. It should be noted that in order to enhance the tight fit degree between multiple cutting plates, in other embodiments of the present invention, an elastic sheet is fixedly installed on the side of the cutting piece 42 away from the variable volume tube 3, and the area of the elastic sheet is larger than the area of the cutting piece 42. When multiple cutting plates are combined, the elastic sheets are mutually extruded, thereby enhancing its sealing effect.

[0056] As a preferred embodiment of the present invention, the variable volume sealing mechanism further includes a plastic sealing bag 5. The plastic sealing bag 5 is installed inside the variable volume tube 3. The plastic sealing bag 5 is a cylindrical structure with one end open. The diameter and length of the plastic sealing bag 5 are both larger than those of the variable volume tube 3. The open end of the plastic sealing bag 5 is detachably and fixedly connected to the installation ring 2.

[0057] In order to further enhance the sealing effect on shale gas, a plastic sealing bag 5 is provided in the present invention. The plastic sealing bag 5 is made of a wear-resistant plastic film. The plastic sealing bag 5 is installed inside the variable volume tube 3, and the open end of the plastic sealing bag 5 is fixedly installed on the installation ring 2. During sampling, the core enters the plastic sealing bag 5 through the inner hole of the installation ring 2. The plastic sealing bag 5 is used to cover the core and shale gas, thereby cooperating with the variable volume tube 3 to achieve double wrapping of the core sample. On the one hand, when the pressure difference inside and outside the storage space of the core sample changes, the plastic sealing bag 5 cooperates with the variable volume tube 3 to double cover the shale gas and the shale core, reducing the probability of shale gas escaping. On the other hand, when the sample is taken out, the plastic sealing bag 5 and the core sample are taken out together. The smooth surface characteristic of the plastic sealing bag 5 can be used to reduce the difficulty of taking out the core sample.

[0058] The installation ring 2 is composed of a threaded ring 21 and a clamping ring 22. The threaded ring 21 is threadedly connected to the sampling tube 1. The threaded ring 21 and the clamping ring 22 are coaxially arranged, and the threaded ring 21 and the clamping ring 22 are fixedly connected by bolts. In the initial state, the opening of the plastic-sealed bag 5 is clamped and installed between the threaded ring 21 and the clamping ring 22.

[0059] Sealing gaskets 23 are fixedly installed on the sides of the threaded ring 21 and the assembly ring that are close to each other, and the plastic-sealed bag 5 extends into the gap of the sealing gasket 23.

[0060] When taking out the core sample, first, with the cooperation of tools, relative rotation is caused between the sampling tube 1 and the threaded ring 21, and then the sampling tube 1 is taken out. Subsequently, the staff removes the variable-volume tube 3 from the installation ring 2. At this time, the plastic-sealed bag 5 wrapped around the core sample is directly exposed. Since the length and size of the plastic-sealed bag 5 are both larger than those of the variable-volume tube 3, while the length of the core sample is smaller than that of the variable-volume tube 3, the plastic-sealed bag 5 is inverted, so that the core sample can be far away from the installation ring 2. At this time, the staff uses cable ties, straps, etc. to tie the junction of the plastic-sealed bag 5 and the installation ring 2. After tying, the threaded ring 21 and the clamping ring 22 are disassembled, and the shale gas and core sample wrapped in the plastic-sealed bag 5 can be obtained. It is directly placed in a pyrolysis desorption device, and during the pyrolysis desorption process, the plastic-sealed bag 5 is damaged by high temperature or mechanical force, and then the total content of shale gas in the core sample can be measured.

[0061] As a preferred embodiment of the present invention, it further includes a forced variable-volume mechanism for adjusting the volume of the variable-volume tube 3. The forced variable-volume mechanism includes:

[0062] Installation rods 6, the installation ring 2 is detachably and fixedly installed on the installation ring 2 by bolts, and a plurality of the installation rods 6 are evenly arranged along the circumferential direction of the installation ring 2;

[0063] Electric telescopic rods 61, the installation rods 6 are fixedly installed with electric telescopic rods 61. One end of the electric telescopic rod 61 away from the installation rod 6 is fixedly installed with a connecting plate 62, and the connecting plate 62 is fixedly installed on the outer wall of the variable-volume tube 3.

[0064] The installation rods 6 are all designed in an inverted L shape. The electric telescopic rods 61 are divided into two groups, and the two groups of electric telescopic rods 61 are respectively perpendicular to the side wall and the top end of the variable-volume tube 3.

[0065] In the initial state, the length of the electric telescopic rod 61 is the smallest, after sampling, the length of the electric telescopic rod 61 is the largest, and in the sealed transportation state, the length of the electric telescopic rod 61 gradually decreases.

[0066] In order to further enhance the sampling effect, a forced variable volume mechanism is provided in the present invention. When sampling, the length of the electric telescopic rod 61 is the smallest in the initial state, so the electric telescopic rod 61 pulls the connecting plate 62 and moves closer to the mounting rod 6. At this time, the diameter and length of the variable volume tube 3 are the largest. In this state, the drill bit 12 drills in, causing the columnar core sample to enter the plastic bag 5. Since the accommodation space is maximized, the friction effect between the core sample and the plastic bag 5 is effectively reduced, and the probability of damage to the plastic bag 5 is reduced. After drilling to a preset depth, the drill bit 12 stops drilling. Under the control of a preset program, the drill bit 12 is drilled in sequence. The electric telescopic rod 61 is extended, the driving motor 44 is started, and the electric telescopic rod 61 is retracted. When the electric telescopic rod 61 is extended, the connecting plate 62 is pushed close to the core sample, and the elastic deformation of the varactor 3 is cooperated, so that the plastic bag 5 is attached to the core sample, and the material in the gap between the plastic bag 5 and the core sample is discharged. When the driving motor 44 is started, the cutting piece 4 cuts off the conductive channel between the core sample and the mounting ring 2 and the outside world. Then the electric telescopic rod 61 is retracted again, so that the inner cavity diameter and length of the varactor 3 are forced to increase slowly. When the sampling tube 1 is lifted to the outside of the wellbore, the pressure difference between the inside and outside of the varactor 3 is reduced.

[0067] like Figure 9 As shown, a method for using a shale gas reservoir characteristic sampling device comprises the following steps:

[0068] S1: Before sampling, the drill bit 12 is separated from the drill pipe 11, and the sampling device is installed in the drill pipe 11, and penetrates into the well and moves toward the shale gas reservoir;

[0069] S2: The drill bit 12 is driven by the drill rod 11 to rotate and drill the shale. The core enters the variable volume sealing mechanism from the middle cavity of the drill bit 12. When the drilling depth reaches a preset value, sampling is stopped;

[0070] S3: The forced variable capacitance mechanism first shrinks the volume of the variable capacitance tube 3, and then the cutting piece 4 cuts off the conducting channel between the mounting ring 2 and the outside world, and then the forced variable capacitance mechanism drives the volume of the variable capacitance tube 3 to gradually expand;

[0071] S4: Pull up the drill pipe 11, separate the drill bit 12 from the drill pipe 11 outside the well, take out the sampling device, and rotate the threaded ring 21 to separate the sampling tube 1 from the variable volume sealing mechanism;

[0072] S5: manually tie the open end of the plastic bag 5, disassemble the mounting ring 2, obtain the core sealed and wrapped by the plastic bag 5, and then directly open the plastic bag 5 in the thermal desorption device to carry out the thermal desorption operation.

[0073] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and all these changes and improvements fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A shale gas reservoir characteristic sampling device, including a sampling pipe (1). The sampling pipe (1) is a tubular structure with openings at both ends. The sampling pipe (1) is installed in the inner cavities of a drill pipe (11) and a drill bit (12). The sampling pipe (1) is used to store core samples. It is characterized in that: It further includes a variable - volume sealing mechanism. The variable - volume sealing mechanism is installed on the sampling pipe (1). The variable - volume sealing mechanism enhances the sealing sampling effect of shale gas by changing the storage space of core samples. The variable - volume sealing mechanism includes: An installation ring (2). The installation ring (2) is installed inside the sampling pipe (1). The installation ring (2) is coaxially arranged with the sampling pipe (1). A variable - volume pipe (3). The variable - volume pipe (3) is installed on the installation ring (2). The variable - volume pipe (3) is a cylindrical structure made of elastic material. The variable - volume pipe (3) is used to store core samples. A cutting member (4). The cutting member (4) is installed on the installation ring (2). The cutting member (4) has an open state and a closed state. The cutting member (4) is used to cut off the conduction channel between the installation ring (2) and the outside.

2. The shale gas reservoir characteristic sampling device according to claim 1, characterized in that: The cutting member (4) includes a driving ring (41) and cutting pieces (42). A closing groove (24) is formed on the installation ring (2). The driving ring (41) is rotatably installed in the closing groove (24). One side of the closing groove (24) close to the center of the installation ring (2) is hingedly installed with a cutting piece (42). The cutting piece (42) is hingedly connected to the driving ring (41) through a connecting rod (43). Multiple cutting pieces (42) are formed by cutting a circular plate.

3. The shale gas reservoir characteristic sampling device according to claim 2, wherein: A driving motor (44) is fixedly installed on the installation ring (2). The output end of the driving motor (44) extends into the closing groove (24), and a transmission wheel (45) is fixedly installed at the output end of the driving motor (44). The transmission wheel (45) is meshed with the driving ring (41).

4. The shale gas reservoir characteristic sampling device according to claim 3, wherein: The variable - volume sealing mechanism further includes a plastic - sealed bag (5). The plastic - sealed bag (5) is installed inside the variable - volume pipe (3). The plastic - sealed bag (5) is a cylindrical structure with one end open. The diameter and length of the plastic - sealed bag (5) are both larger than those of the variable - volume pipe (3). The open end of the plastic - sealed bag (5) is detachably and fixedly connected to the installation ring (2).

5. The shale gas reservoir characteristic sampling device according to claim 4, characterized in that: The installation ring (2) is composed of a threaded ring (21) and a clamping ring (22). The threaded ring (21) is thread - connected to the sampling pipe (1). The threaded ring (21) and the clamping ring (22) are coaxially arranged. The threaded ring (21) and the clamping ring (22) are bolt - fixed. In the initial state, the open end of the plastic - sealed bag (5) is clamped and installed between the threaded ring (21) and the clamping ring (22).

6. The shale gas reservoir characteristic sampling device according to claim 5, characterized in that: Sealing gaskets (23) are fixedly installed on the sides of the threaded ring (21) and the assembly ring close to each other. The plastic - sealed bag (5) extends into the gap of the sealing gaskets (23).

7. The shale gas reservoir characteristic sampling device according to claim 6, characterized in that: It further includes a forced variable - volume mechanism. The forced variable - volume mechanism is used to adjust the volume of the variable - volume pipe (3). The forced variable - volume mechanism includes: Installation rods (6). The installation ring (2) is detachably and fixedly installed on the installation ring (2) through bolts. Multiple installation rods (6) are evenly arranged along the circumferential direction of the installation ring (2). The electric telescopic rod (61), the mounting rod (6) is fixedly installed with the electric telescopic rod (61), and one end of the electric telescopic rod (61) far from the mounting rod (6) is fixedly installed with a connecting plate (62), and the connecting plate (62) is fixedly installed on the outer wall of the variable volume tube (3).

8. The shale gas reservoir characteristic sampling device according to claim 7, wherein: The mounting rods (6) are all designed in an inverted L shape, the electric telescopic rods (61) are divided into two groups, and the two groups of electric telescopic rods (61) are respectively perpendicular to the side wall of the variable volume tube (3) and the top of the variable volume tube (3).

9. The shale gas reservoir characteristic sampling device according to claim 8, wherein: In the initial state, the length of the electric telescopic rod (61) is the smallest, after sampling, the length of the electric telescopic rod (61) is the largest, and in the sealed transportation state, the length of the electric telescopic rod (61) gradually shrinks.

10. A method for using a sampling device for shale gas reservoir characteristics, characterized in that: This method is applicable to the shale gas reservoir characteristic sampling device described in claim 9, and this method includes the following steps: S1: Before sampling, disassemble the drill bit (12) from the drill pipe (11), install the sampling device in the drill pipe (11), and penetrate into the wellbore and advance towards the shale gas reservoir; S2: Drive the drill bit (12) to rotate by the drill pipe (11) to drill the shale, the core enters the variable volume sealing mechanism through the central cavity of the drill bit (12), and after the drilling depth reaches the preset value, stop sampling; S3: The forced variable volume mechanism first drives the volume of the variable volume tube (3) to contract, then the cutting member (4) cuts off the conduction channel between the mounting ring (2) and the outside, and then the forced variable volume mechanism drives the volume of the variable volume tube (3) to gradually expand; S4: Lift the drill pipe (11), disassemble the drill bit (12) from the drill pipe (11) outside the wellbore, take out the sampling device, and rotate the threaded ring (21) to separate the sampling tube (1) from the variable volume sealing mechanism; S5: Manually tie the open end of the plastic sealing bag (5), disassemble the mounting ring (2), obtain the core sealed and wrapped by the plastic sealing bag (5), and then directly open the plastic sealing bag (5) in the pyrolysis desorption device to perform pyrolysis desorption operation.

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