Tight sandstone gas reservoir starting pressure gradient testing device

Abstract

The utility model discloses a tight sandstone gas reservoir starting pressure gradient testing device, which comprises an upper box body, a lower end cover and a middle box body, the upper box body and the lower end cover are respectively sleeved at the upper end and the lower end of the middle box body, and an annular cavity of the upper box body is communicated with an annular cavity of the middle box body; clamping mechanisms are arranged on the inner sides of the upper box body, the lower end cover and the middle box body in a communicating manner, are uniformly distributed in the circumferential direction of the annular cavity and can be used for clamping a rock core; an adjusting device is arranged on the upper box body in a communicating mode and can adjust the pressure intensity in the annular cavity. According to the utility model, the clamping mechanism and the adjusting device are arranged, so that the clamping acting force on the rock core can be adjusted as required, and the pressure gradient test data error caused by the clamping pressure change is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of pressure testing, in particular to a starting pressure gradient testing device for a tight sandstone gas reservoir. Background Technique

[0002] As a typical unconventional gas reservoir, during the water flooding development process of a tight sandstone gas reservoir, with the gradual intrusion of edge and bottom water, the range of the gas-water two-phase flow region generated inside the gas reservoir continues to expand. Compared with several or low water saturation rock samples, the gas permeability of rock samples under high water content conditions is much smaller, and the gap can reach 10 to 1000 times. The level of water saturation has an obvious impact on the seepage characteristics of the gas reservoir. The reservoirs of tight sandstone gas reservoirs are generally highly water-bearing, and the interaction between gas and water will cause the starting pressure gradient effect. The gas-phase starting pressure gradient is the critical pressure gradient for gas-phase flow when gas and water coexist. Accurately describing it is an important prerequisite for effectively understanding the gas-water two-phase seepage law of tight gas reservoirs.

[0003] The literature "Experimental Study on the Starting Pressure Gradient of Tight Sandstone Gas Reservoirs in the Ordos Basin" (Bai Huifang, Unconventional Oil & Gas, 2020, 7(03): 60-64) uses a KS-VI type pore-permeability combined tester to conduct a sensitivity analysis on the two influencing factors of the starting pressure gradient, namely permeability and water saturation. Among them, the high-pressure core holder uses a rigid clamping method; the invention patent "Method and Device for Determining the Starting Pressure Gradient of Unconventional Gas Reservoirs" (Zhu Weiyao, University of Science and Technology Beijing, CN113898338B) predicts the starting pressure gradient by constructing a fitting function between the starting pressure gradient, movable water saturation, and permeability. Through pressure gradient testing, providing data support for the critical pressure gradient of gas-phase flow when gas and water coexist can effectively improve the gas reservoir development efficiency. When conducting pressure gradient testing, the core needs to be fixedly clamped. Currently, the general clamping method is to use rigid clamping, that is, a clamping device is set up and then fixedly sleeved on the outer periphery of the core. On the one hand, the contact area is too large, which has a greater impact on the core. On the other hand, during the pressure gradient testing process, the core undergoes slight deformation under pressure, resulting in an increase in the clamping force of the clamping device on the core. In the actual gas reservoir exploitation process, due to the small change in the external environment, the change in the pressure borne by the rock and ore within a short period can be ignored. Therefore, the change in pressure during the testing process will make the test data inaccurate.

[0004] In view of the deficiencies of the existing technology, it is necessary to further improve the existing technology. Content of the Utility Model

[0005] The purpose of the utility model is to provide a starting pressure gradient testing device for a tight sandstone gas reservoir, aiming to improve the problem that the change in clamping pressure during the core testing process makes the test data inaccurate, resulting in errors in the measured pressure gradient data.

[0006] The present utility model is realized as follows: A starting pressure gradient testing device for a tight sandstone gas reservoir, comprising an upper box body, a lower end cover and a middle box body. The upper box body and the lower end cover are respectively sleeved on the upper and lower ends of the middle box body, and the annular cavities of the upper box body and the middle box body are communicated; clamping mechanisms are communicated and arranged on the inner sides of the upper box body and the middle box body. The clamping mechanisms are evenly distributed along the circumferential direction of the annular cavity and can clamp the core; an adjusting device is communicated on the upper box body, and the adjusting device can adjust the pressure in the annular cavity.

[0007] Preferably, the upper box body is provided with a first annular cavity, the lower end of the first annular cavity is an opening, the middle box body is provided with a second annular cavity, both the upper and lower ends of the second annular cavity are openings, reinforcing plates are arranged on the inner sides of the first annular cavity and the second annular cavity, and holes are arranged on the reinforcing plates.

[0008] Preferably, two rings of annular plates are arranged inside and outside at the opening of the first annular cavity and the opening at the lower end of the second annular cavity. The outer side surface of the outer annular plate is provided with threads, and threaded annular grooves are arranged at the opening at the upper end of the second annular cavity and the upper end of the lower end cover. The annular plate can be threadedly inserted into the adjacent threaded annular groove.

[0009] Preferably, the clamping mechanism comprises a sealing cylinder, a piston and a pressing disc. The piston is arranged inside the sealing cylinder, the pressing disc is arranged outside the sealing cylinder, and is connected with the piston through a connecting rod.

[0010] Preferably, a plurality of external threaded pipes are communicated and arranged on the inner sides of the upper box body and the middle box body. The end of the sealing cylinder is communicated with an internal threaded pipe, and the internal threaded pipe is threadedly and sealingly sleeved on the external threaded pipe.

[0011] Preferably, a first end pipe and a second end pipe are respectively arranged at the top of the upper box body and the bottom of the lower end cover. A pressing pipe, a first spring and a limiting ring plate are arranged inside the end pipe. The first spring is in a compressed state and is connected with the limiting ring plate and the pressing pipe at both ends respectively. The pressing pipe can contact the end surface of the core.

[0012] Preferably, a limiting groove is arranged on the side wall of the end pipe, the limiting groove is arranged along the height direction of the end pipe, a bolt penetrates through the pressing pipe, the end of the bolt extends into the limiting groove, and the limiting ring plate is threadedly connected with the end pipe.

[0013] Preferably, the adjusting device comprises a support pipe, a first sealing column, a second sealing column, a second spring and an adjusting cylinder. The support pipe is communicated and connected with the annular cavity of the upper box body. The adjusting cylinder is threadedly sleeved at the end of the support pipe. An inlet and outlet pipe and a communicating pipe are communicated on the side of the support pipe. The communicating pipe is of a U-shaped structure. The inlet and outlet pipe is opposite to the end of the communicating pipe far away from the upper box body. The first sealing column and the second sealing column are arranged in the support pipe at intervals and connected. The second spring is located between the sealing column and the adjusting cylinder and is in a compressed state. The inlet and outlet pipe is located between the first sealing column and the second sealing column.

[0014] Preferably, a limiting rod and an adjusting screw rod are arranged on the second sealing column, a threaded hole and a limiting hole are arranged on the first sealing column, the end of the limiting rod is inserted into the limiting hole, and the end of the adjusting screw rod is threadedly inserted into the threaded hole.

[0015] Compared with the prior art, the beneficial effects of the utility model are as follows: by rotating the adjusting cylinder, the compression degree of the second spring is adjusted, and then the elastic force of the second spring is forced to be gradually equal to the pressure when the hydraulic oil in the upper box body is balanced. On the one hand, the hydraulic oil acts on the piston to push the pressing disc to clamp the core. On the other hand, the hydraulic oil exerts a force on the second sealing column of the adjusting device to push the sealing column to compress the second spring. When the clamping force for clamping the core is lower than the set value, the second spring of the adjusting device pushes the first sealing column to slide, so that the first sealing column and the second sealing column are distributed on both sides of the inlet and outlet pipe, facilitating the hydraulic oil to sequentially enter the upper box body through the gap of the sealing column and the connecting pipe, and increasing the pressure of the hydraulic oil in the upper box body. When the microchange of the core causes the clamping force for clamping the core to be higher than the set value, at this time, the hydraulic oil pushes the second sealing column to compress the second spring until the first sealing column and the second sealing column are distributed on both sides of the inlet and outlet pipe, facilitating the hydraulic oil to flow out of the upper box body sequentially through the connecting pipe and the gap of the inlet and outlet pipe, reducing the pressure of the hydraulic oil in the upper box body, keeping the acting force of the pressing disc on the core stable, and reducing the error of the pressure gradient test data caused by the change of the clamping pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a three-dimensional structural schematic diagram of an embodiment of the utility model;

[0017] Figure 2 is a planar structural schematic diagram of an embodiment of the utility model;

[0018] Figure 3 is the utility model Figure 1 a three-dimensional structural schematic diagram of the upper box body therein;

[0019] Figure 4 is the utility model Figure 1 a three-dimensional structural schematic diagram of the top of the upper box body therein;

[0020] Figure 5 is the utility model Figure 1 a three-dimensional structural schematic diagram of the adjusting device therein;

[0021] Figure 6 is the utility model Figure 5 a three-dimensional structural schematic diagram of the sealing column therein;

[0022] Figure 7 is the utility model Figure 1 a three-dimensional structural schematic diagram of the middle box body therein;

[0023] Figure 8 is a schematic three-dimensional structure diagram of the clamping mechanism in the present utility model Figure 2 .

[0024] In the figure: 1. upper box body; 11. external threaded pipe; 12. first annular cavity; 13. reinforcing plate; 14. first end pipe; 15. limiting groove; 16. pressing pipe; 17. first spring; 18. limiting ring plate; 2. middle box body; 21. second annular cavity; 3. lower end cover; 31. second end pipe; 4. adjusting device; 41. support pipe; 42. connecting pipe; 43. inlet and outlet pipe; 44. second spring; 45. first sealing column; 46. second sealing column; 47. adjusting cylinder; 48. limiting rod; 49. adjusting screw; 5. clamping mechanism; 51. sealing cylinder; 52. pressing disc; 53. piston; 54. internal threaded pipe Specific embodiments

[0025] In the present utility model, unless otherwise clearly defined and limited, the terms "installation", "connection", "connection", "fixation" and other terms shall be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific situations

[0026] The following will be further described in conjunction with the drawings and specific embodiments

[0027] Embodiment 1

[0028] As Figure 1 , Figure 2 , Figure 3 , Figure 7As shown in the figure, a startup pressure gradient test device for a tight sandstone gas reservoir includes an upper box body 1, a lower end cover 3, multiple middle box bodies 2, and multiple sets of clamping mechanisms 5. The upper box body 1 and the middle box bodies 2 are both arranged in a ring structure, the lower end cover 3 is arranged in a disc structure, and a first annular cavity 12 and a second annular cavity 21 are respectively arranged inside the side walls of the upper box body 1 and the middle box bodies 2. The lower end of the first annular cavity 12 is open, and both the upper and lower ends of the second annular cavity 21 are open. When using this device for mechanical testing, the corresponding number of middle box bodies 2 can be selected according to the length of the core, and multiple sets of middle box bodies 2 are stacked vertically. Adjacent middle box bodies 2 are sleeved and connected to each other. Then, the upper box body 1 and the lower end cover 3 are respectively sleeved on the upper and lower ends of multiple sets of middle box bodies 2, and at the same time, the first annular cavity 12 and the second annular cavity 21 are sealed and communicated. Multiple sets of clamping mechanisms 5 are evenly arranged inside the upper box body 1 and the middle box bodies 2 and are communicated with the first annular cavity 12 and the second annular cavity 21. The clamping mechanisms 5 are evenly distributed along the circumferential direction of the annular cavity. At least two sets of adjusting devices 4 are communicated with the upper box body 1. One set of adjusting devices 4 is connected to a hydraulic oil tank and a pump. Through the operation of the pump, hydraulic oil is transported into the space composed of the annular cavity and the clamping mechanisms 5 to change the state of the clamping mechanisms 5. The core is clamped by the clamping mechanisms 5 so that it is stably placed in the space composed of the upper box body 1, the lower end cover 3, and the middle box bodies 2, and the state of the adjusting devices 4 can be adjusted according to requirements to keep the pressure in the annular cavity balanced.

[0029] As Figure 3 , Figure 7 shown, in order to realize the sleeve connection between the upper box body 1 and the middle box bodies 2, and the sleeve connection between adjacent middle box bodies 2, two rings of annular plates are arranged inside and outside the opening of the first annular cavity 12 and the opening at the lower end of the second annular cavity 21. The outer side surface of the outer annular plate is provided with threads. Threaded annular grooves are provided at the opening at the upper end of the second annular cavity 21 and the upper end of the lower end cover 3, and a sealing gasket is provided at the bottom of the threaded annular groove. The annular plate can be screwed into the adjacent threaded annular groove, and the annular plate presses against the sealing gasket. Because the box bodies are connected by screwing, it provides support for the staff to adjust the number of middle box bodies 2 according to requirements and controls the stable connection between the box bodies. To ensure the strength of the box bodies, reinforcing plates 13 are arranged inside the first annular cavity 12 and the second annular cavity 21. Through the action of the reinforcing plates 13, the inner and outer side walls of the annular cavity can be controlled to remain relatively stable. The reinforcing plates 13 are provided with holes to provide a channel for the hydraulic oil to flow in the annular cavity.

[0030] As Figure 2 , Figure 8As shown in the figure, in order to clamp and fix the core through the clamping mechanism 5, the clamping mechanism 5 includes a sealing cylinder 51, a piston 53 and a pressing disc 52. The piston 53 is arranged inside the sealing cylinder 51, and the pressing disc 52 is arranged outside the sealing cylinder 51 and is connected to the piston 53 through a connecting rod. At the same time, a plurality of external thread pipes 11 are arranged in a communicating manner inside the upper box body 1 and the middle box body 2. The end of the sealing cylinder 51 is provided with an internal thread pipe 54 in a communicating manner, and the internal thread pipe 54 is threadedly and hermetically sleeved on the external thread pipe 11. When hydraulic oil is injected into the annular cavity, the hydraulic oil flows into the sealing cylinder 51 and pushes the piston 53 to drive the pressing disc 52 to move, thereby changing the position of the pressing disc 52 to press the core and realizing the stable clamping of the core. Since the sealing cylinder 51 is detachably connected to the box body by threads, the clamping mechanism 5 can be quickly disassembled and assembled according to needs, improving the practicability of the device and providing convenience for maintenance or replacement.

[0031] As Figure 2 , Figure 4 shown, in order to connect the device to the storage oil tank, a first end pipe 14 and a second end pipe 31 are respectively arranged at the top of the upper box body 1 and the bottom of the lower end cover 3. An abutting pipe 16, a first spring 17 and a limiting ring plate 18 are arranged inside the end pipe. The first spring 17 is in a compressed state and is connected to the limiting ring plate 18 and the abutting pipe 16 at both ends respectively. The abutting pipe 16 can contact the end face of the core. During the test, through the action of the first spring 17, the abutting pipe 16 is controlled to press the end face of the core, restricting the position of the core and at the same time providing the possibility for the core to move. After the core is clamped, the end in the middle of the upper box body 1 is communicated with the injection port of the storage oil tank through a precision micro-flow constant speed pump, facilitating the setting of a specific flow rate for gradient testing. At the same time, the end in the middle of the lower end cover 3 is communicated with the recovery port of the storage oil tank through a capillary tube, and a pressure sensor is arranged on the capillary tube to measure the pressure in the capillary tube when the flow rate of the constant speed pump is 0.5 mL / min, 0.3 mL / min, 0.2 mL / min, 0.1 mL / min, 0.05 mL / min, 0.02 mL / min. According to the pressure difference - flow rate method, the pressure gradients at 0.5 mL / min, 0.3 mL / min, 0.2 mL / min, 0.1 mL / min, 0.05 mL / min, 0.02 mL / min are measured, realizing the test of the starting pressure gradient of the tight sandstone gas reservoir.

[0032] As Figure 4 shown, in order to be able to adjust the position of the abutting pipe 16 according to needs, a limiting groove 15 is arranged on the side wall of the end pipe. The limiting groove 15 is arranged along the height direction of the end pipe. A bolt is penetrated through the abutting pipe 16, and the end of the bolt extends into the limiting groove 15. The limiting ring plate 18 is threadedly connected to the end pipe.

[0033] As Figure 5As shown, the adjusting device 4 includes a support pipe 41, a first sealing column 45, a second sealing column 46, a second spring 44 and an adjusting cylinder 47. The support pipe 41 is connected to the annular cavity of the upper box body 1 in a communicating manner. The adjusting cylinder 47 is threadedly sleeved at the end of the support pipe 41. A feed pipe 43 and a communicating pipe 42 are provided in a communicating manner on the side of the support pipe 41. The communicating pipe 42 is arranged in a U-shaped structure. The feed pipe 43 faces the end of the communicating pipe 42 away from the upper box body 1. The first sealing column 45 and the second sealing column 46 are arranged in the support pipe 41 at intervals and connected. The second spring 44 is located between the sealing column and the adjusting cylinder 47 and is in a compressed state. The feed pipe 43 is located between the first sealing column 45 and the second sealing column 46. When hydraulic oil is injected into the annular cavity, by rotating the adjusting cylinder 47, the compression degree of the second spring 44 is changed, and the positions of the first sealing column 45 and the second sealing column 46 are adjusted so that the gap between the first sealing column 45 and the second sealing column 46 faces the feed pipe 43. At this time, the feed pipe 43, the communicating pipe 42 and the support pipe 41 form a hydraulic oil flow passage. Therefore, the hydraulic oil can flow into the annular cavity and the sealing cylinder 51 to push the piston 53 to move. After the pressing disc 52 presses the core to make it stably placed, the adjusting cylinder 47 is rotated again to change the compression degree of the second spring 44 so that the first sealing column 45 blocks the feed pipe 43 and the communicating pipe 42. At this time, the hydraulic oil exerts a reaction force on the second sealing column 46. With the cooperation of the second spring 44 and the adjusting cylinder 47, a stable pressure is formed in the annular cavity. When the pressure in the annular cavity changes, the operator can rotate the adjusting cylinder 47 to change the compression degree of the second spring 44 to force the pressure in the annular cavity to be balanced again.

[0034] Embodiment 2

[0035] As Figure 1 、 Figure 2 、 Figure 3 、 Figure 7As shown, a device for testing the start-up pressure gradient of a tight sandstone gas reservoir comprises an upper box body 1, a lower end cover 3, a plurality of sets of middle boxes 2 and a plurality of groups of clamping mechanisms 5. The upper box body 1 and the middle box body 2 are both arranged as annular structures, the lower end cover 3 is arranged as a disc structure, and a first annular cavity 12 and a second annular cavity 21 are respectively arranged in the side walls of the upper box body 1 and the middle box body 2, the lower end of the first annular cavity 12 is arranged as an opening, and the upper and lower ends of the second annular cavity 21 are both arranged as openings. When the device is used for mechanical testing, a corresponding number of middle boxes 2 can be selected according to the length of the core, and a plurality of sets of middle boxes 2 can be stacked up and down, and adjacent middle boxes 2 can be connected to each other by being sleeved, and then the upper box body 1 and the lower end cover 3 are respectively sleeved on the upper and lower ends of the plurality of sets of middle boxes 2, and at the same time, the first annular cavity 12 and the second annular cavity 21 are sealed and communicated. Multiple groups of clamping mechanisms 5 are evenly arranged on the inner side of the upper box body 1 and the middle box body 2, and are arranged in communication with the first annular cavity 12 and the second annular cavity 21. The clamping mechanisms 5 are evenly distributed along the circumferential direction of the annular cavity. At least two groups of adjusting devices 4 are arranged in communication on the upper box body 1, and one group of adjusting devices 4 is connected to the hydraulic oil tank and the pump. The hydraulic oil is delivered to the space composed of the annular cavity and the clamping mechanism 5 through the operation of the pump, and the state of the clamping mechanism 5 is changed. The core is clamped by the clamping mechanism 5 so that it is stably placed in the space composed of the upper box body 1, the lower end cover 3 and the middle box body 2, and the state of the device 4 can be adjusted according to the demand to keep the pressure in the annular cavity balanced.

[0036] like Figure 3 , Figure 7 As shown, in order to realize the sleeve connection between the upper box body 1 and the middle box body 2, and the sleeve connection between the adjacent middle boxes 2, two circles of annular plates are arranged inside and outside the opening of the first annular cavity 12 and the opening of the lower end of the second annular cavity 21, and the outer side of the outer annular plate is provided with a thread, and the opening of the upper end of the second annular cavity 21 and the upper end of the lower end cover 3 are provided with a threaded ring groove, and a sealing gasket is provided at the bottom of the threaded ring groove, and the annular plate can be threadedly inserted into the adjacent threaded ring groove, and the annular plate presses the sealing gasket. Because the boxes are threadedly sleeved, support is provided for the staff to adjust the number of middle boxes 2 according to needs, and the control boxes are stably connected. In order to ensure the strength of the box, a reinforcing plate 13 is provided on the inner side of the first annular cavity 12 and the second annular cavity 21. The inner and outer side walls of the annular cavity can be controlled to remain relatively stable through the action of the reinforcing plate 13, and holes are provided on the reinforcing plate 13 to provide a channel for the hydraulic oil to circulate in the annular cavity.

[0037] like Figure 2 , Figure 8As shown in the figure, in order to clamp and fix the core through the clamping mechanism 5, the clamping mechanism 5 includes a sealing cylinder 51, a piston 53 and a pressing disc 52. The piston 53 is arranged inside the sealing cylinder 51, and the pressing disc 52 is arranged outside the sealing cylinder 51 and is connected to the piston 53 through a connecting rod. At the same time, a plurality of external threaded pipes 11 are arranged in the upper box body 1 and the middle box body 2 in a communicating manner. An internal threaded pipe 54 is arranged at the end of the sealing cylinder 51 in a communicating manner, and the internal threaded pipe 54 is threadedly and hermetically sleeved on the external threaded pipe 11. When hydraulic oil is filled into the annular cavity, the hydraulic oil flows into the sealing cylinder 51 and pushes the piston 53 to drive the pressing disc 52 to move, thereby changing the position of the pressing disc 52 to press the core and realizing the stable clamping of the core. Since the sealing cylinder 51 is detachably connected to the box body by threads, the clamping mechanism 5 can be quickly disassembled and assembled according to requirements, improving the practicability of the device and facilitating maintenance or replacement.

[0038] As Figure 2 shown, in order to connect the device to the oil storage tank, a first end pipe 14 and a second end pipe 31 are respectively arranged at the top of the upper box body 1 and the bottom of the lower end cover 3. A pressing pipe 16, a first spring 17 and a limiting ring plate 18 are arranged inside the end pipe. The first spring 17 is in a compressed state and is connected to the limiting ring plate 18 and the pressing pipe 16 at both ends respectively. The pressing pipe 16 can contact the end face of the core. During the test, through the action of the first spring 17, the pressing pipe 16 is controlled to press the end face of the core, restricting the position of the core and at the same time providing the possibility for the core to move. After the core is clamped, the end in the middle of the upper box body 1 is connected to the injection port of the oil storage tank through a precision micro-flow constant speed pump, facilitating setting a specific flow rate for gradient testing. At the same time, the end in the middle of the lower end cover 3 is connected to the recovery port of the oil storage tank through a capillary tube, and a pressure sensor is arranged on the capillary tube to measure the pressure in the capillary tube when the flow rate of the constant speed pump is 0.5 mL / min, 0.3 mL / min, 0.2 mL / min, 0.1 mL / min, 0.05 mL / min, 0.02 mL / min. According to the pressure difference-flow method, the pressure gradients at 0.5 mL / min, 0.3 mL / min, 0.2 mL / min, 0.1 mL / min, 0.05 mL / min, 0.02 mL / min are measured, realizing the test of the starting pressure gradient of the tight sandstone gas reservoir. Figure 4 As

[0039] shown, in order to be able to adjust the position of the pressing pipe 16 according to requirements, a limiting groove 15 is arranged on the side wall of the end pipe. The limiting groove 15 is arranged along the height direction of the end pipe. A bolt is arranged through the pressing pipe 16, and the end of the bolt extends into the limiting groove 15. The limiting ring plate 18 is threadedly connected to the end pipe. Figure 4

[0040] As Figure 5 ​As shown in the figure, the adjusting device 4 includes a support pipe 41, a first sealing column 45, a second sealing column 46, a second spring 44 and an adjusting cylinder 47. The support pipe 41 is connected to the annular cavity of the upper box body 1 in a communicating manner. The adjusting cylinder 47 is threadedly sleeved at the end of the support pipe 41. A liquid inlet and outlet pipe 43 and a communicating pipe 42 are arranged on the side of the support pipe 41 in a communicating manner. The communicating pipe 42 is arranged in a U-shaped structure. The liquid inlet and outlet pipe 43 is opposite to the end of the communicating pipe 42 away from the upper box body 1. The first sealing column 45 and the second sealing column 46 are arranged in the support pipe 41 at intervals and connected to each other. The second spring 44 is located between the sealing column and the adjusting cylinder 47 and is in a compressed state. The liquid inlet and outlet pipe 43 is located between the first sealing column 45 and the second sealing column 46. When hydraulic oil is injected into the annular cavity, by rotating the adjusting cylinder 47, the compression degree of the second spring 44 is changed, and the positions of the first sealing column 45 and the second sealing column 46 are adjusted so that the gap between the first sealing column 45 and the second sealing column 46 faces the liquid inlet and outlet pipe 43. At this time, the liquid inlet and outlet pipe 43, the communicating pipe 42 and the support pipe 41 form a hydraulic oil flow channel. Therefore, the hydraulic oil can flow into the annular cavity and the sealing cylinder 51 to push the piston 53 to move. After the pressing disc 52 presses against the core, rotate the adjusting cylinder 47 again to change the compression degree of the second spring 44 so that the first sealing column 45 blocks the liquid inlet and outlet pipe 43 and the communicating pipe 42. At this time, the hydraulic oil exerts a reaction force on the second sealing column 46, and with the cooperation of the second spring 44 and the adjusting cylinder 47, a stable pressure is formed in the annular cavity. When the pressure in the annular cavity changes, the staff can rotate the adjusting cylinder 47 to change the compression degree of the second spring 44 to force the pressure in the annular cavity to be balanced again.

[0041] As Figure 6 shown in the figure, in order to be able to adjust the distance between the first sealing column 45 and the second sealing column 46 according to requirements, a limiting rod 48 and an adjusting screw 49 are arranged on the second sealing column 46. A threaded hole and a limiting hole are arranged on the first sealing column 45. The end of the limiting rod 48 is inserted into the limiting hole, and the end of the adjusting screw 49 is threadedly inserted into the threaded hole. By rotating the adjusting screw 49, the relative movement of the first sealing column 45 and the second sealing column 46 can be controlled, and the adjusted first sealing column 45 and second sealing column 46 can be kept relatively stationary.

[0042] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A start-up pressure gradient test device for tight sandstone gas reservoirs, characterized in that: The invention comprises an upper box body (1), a lower end cover (3) and a middle box body (2), wherein the upper box body (1) and the lower end cover (3) are respectively sleeved on the upper and lower ends of the middle box body (2), and the annular cavities of the upper box body (1) and the middle box body (2) are arranged in communication with each other; a clamping mechanism (5) is arranged in communication with each other on the inner sides of the upper box body (1) and the middle box body (2), and the clamping mechanism (5) is evenly distributed along the circumferential direction of the annular cavity and can clamp a rock core; an adjusting device (4) is arranged in communication with the upper box body (1), and the adjusting device (4) can adjust the pressure in the annular cavity.

2. A tight sandstone gas reservoir startup pressure gradient test device according to claim 1, characterized in that: The upper box body (1) is provided with a first annular cavity (12), the lower end of which is arranged to be an opening; the middle box body (2) is provided with a second annular cavity (21), the upper and lower ends of which are arranged to be openings; the inner sides of the first annular cavity (12) and the second annular cavity (21) are both provided with reinforcing plates (13), and the reinforcing plates (13) are provided with holes.

3. A tight sandstone gas reservoir startup pressure gradient test device according to claim 2, characterized in that: Two circles of annular plates are arranged inside and outside the opening of the first annular cavity (12) and the opening of the lower end of the second annular cavity (21), and the outer side surface of the outer annular plate is provided with a thread. The opening of the upper end of the second annular cavity (21) and the upper end of the lower end cover (3) are provided with a threaded annular groove, and the annular plates can be threadedly inserted into adjacent threaded annular grooves.

4. The device for testing the start-up pressure gradient of a tight sandstone gas reservoir according to claim 1, characterized in that: The clamping mechanism (5) comprises a sealing cylinder (51), a piston (53) and a pressure plate (52); the piston (53) is arranged on the inner side of the sealing cylinder (51); the pressure plate (52) is arranged on the outer side of the sealing cylinder (51) and is connected to the piston (53) via a connecting rod.

5. A tight sandstone gas reservoir startup pressure gradient test device according to claim 4, characterized in that: A plurality of externally threaded tubes (11) are provided on the inner sides of the upper box body (1) and the middle box body (2), and an internally threaded tube (54) is provided on the end of the sealing tube (51), wherein the threaded sealing sleeve of the internally threaded tube (54) is provided on the externally threaded tube (11).

6. The device for testing the start-up pressure gradient of a tight sandstone gas reservoir according to claim 1, characterized in that: The top of the upper box body (1) and the bottom of the lower end cover (3) are respectively provided with a first end tube (14) and a second end tube (31); the inner side of the end tube is provided with a pressure tube (16), a first spring (17) and a limiting ring plate (18); the first spring (17) is in a compressed state, and its two ends are respectively connected to the limiting ring plate (18) and the pressure tube (16); the pressure tube (16) can contact the end surface of the core.

7. A tight sandstone gas reservoir startup pressure gradient test device according to claim 6, characterized in that: A limiting groove (15) is provided on the side wall of the end pipe, and the limiting groove (15) is provided along the height direction of the end pipe. A bolt is provided through the pressure pipe (16), and the end of the bolt extends into the limiting groove (15). The limiting ring plate (18) is connected to the end pipe thread.

8. The device for testing the start-up pressure gradient of a tight sandstone gas reservoir according to claim 1, characterized in that: The adjusting device (4) includes a support pipe (41), a first sealing column (45), a second sealing column (46), a second spring (44) and an adjusting cylinder (47). The support pipe (41) is connected to the annular cavity of the upper box body (1) in a communicating manner. The adjusting cylinder (47) is threadedly sleeved at the end of the support pipe (41). A feed-through pipe (43) and a communicating pipe (42) are arranged on the side of the support pipe (41) in a communicating manner. The communicating pipe (42) is arranged in a U-shaped structure. The feed-through pipe (43) faces the end of the communicating pipe (42) away from the upper box body (1). The first sealing column (45) and the second sealing column (46) are arranged in the support pipe (41) in an interval-connected manner. The second spring (44) is located between the sealing column and the adjusting cylinder (47) and is in a compressed state. The feed-through pipe (43) can be located between the first sealing column (45) and the second sealing column (46).

9. A tight sandstone gas reservoir startup pressure gradient test device according to claim 8, characterized in that: A limiting rod (48) and an adjusting screw rod (49) are arranged on the second sealing column (46). A threaded hole and a limiting hole are arranged on the first sealing column (45). The end of the limiting rod (48) is inserted into the limiting hole. The end of the adjusting screw rod (49) is threadedly inserted into the threaded hole.

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