A pressure control device for pressure-maintaining coring

Abstract

The present invention belongs to the technical field of oil and gas field exploration and exploitation, and discloses a pressure control device for pressure-maintaining coring, comprising a pressure-controlling upper joint, a pressure-controlling lower joint, a sleeve joint and an inner cylinder connected in sequence, the interior of the pressure-controlling upper joint is a nitrogen chamber, a piston chamber and a first hydraulic chamber, an injection hole and an exhaust hole are provided at the top, a first needle valve is provided in the injection hole, a piston is slidably connected in the piston chamber, the interior of the pressure-controlling lower joint is a second hydraulic chamber and a third hydraulic chamber, the second hydraulic chamber is connected to the first hydraulic chamber; the top of the pressure-controlling lower joint is provided with an axial leakage hole and a radial leakage hole, a second needle valve is provided in the radial leakage hole; the sleeve joint and the pressure-controlling lower joint are clearance-matched, and the second hydraulic chamber and the third hydraulic chamber can be connected; the third hydraulic chamber is connected to the inner cylinder. The present invention adjusts the inner cylinder pressure by nitrogen, realizes safe and controllable inner cylinder pressure in pressure-maintaining coring operation, and solves the technical problem that pressure-maintaining coring operation cannot be performed in ultra-high pressure formations.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field exploration and exploitation, and in particular to a pressure control device for pressure-maintaining coring. Background Art

[0002] With the development of the global oil and gas industry, oil and gas exploration areas have rapidly expanded from land to deep water, target layers from medium and shallow layers to deep and ultra-deep layers, and resource types from conventional to unconventional. Major exploration breakthroughs have been made in the eastern region at depths of 4,500m and above, and in the western region at depths of 6,000m and above. The overall depth of oil and gas exploration has been extended by 1,500m. Deep, high-temperature and high-pressure formations and unconventional natural gas have become major replacement areas for onshore oil and gas exploration in China. In the process of in-depth research on the reservoir conditions of deep oil and gas reservoirs and formulating technical routes for oil and gas reservoir development, it is extremely important to obtain complete and accurate underground core data through drilling coring for deep oil and gas exploration and development. So far, the drilling coring tools used for deep oil and gas mainly include conventional coring tools and closed coring tools. The cores obtained by the above coring tools have no pressure protection and sealing measures, resulting in a large loss of oil and gas components during the drilling process, making it impossible to accurately obtain test data such as oil layer porosity, permeability, and saturation. The existing pressure-maintaining coring technology can no longer meet the needs of pressure-maintaining coring operations in ultra-high pressure formations.

[0003] The pressure-maintaining coring tool in the prior art can withstand a maximum pressure of 40MPa in the inner tube. Although the pressure bearing capacity is enhanced, the bottom hole pressure still greatly exceeds the pressure bearing limit of the pressure-maintaining coring tool for ultra-high pressure formation pressure-maintaining coring operations. When performing pressure-maintaining coring operations in ultra-deep wells, blindly pursuing the pressure-maintaining effect not only greatly increases the tool development cost, but also brings great safety risks to on-site operators, and is not conducive to the development of subsequent tests and experiments. At present, there is no relevant pressure control technology for pressure-maintaining coring in ultra-high pressure formations. In the field of coring in drilling wells deeper than 4,000 meters, there is no application example of pressure-maintaining coring. Only conventional coring technology can be used for coring operations, which seriously affects the in-depth development of deep geological evaluation work. Therefore, on the basis of the pressure-maintaining coring tool, a control device that can adjust the inner tube pressure is developed to reduce the inner tube pressure to a safe and controllable range, while realizing the "oil and gas preservation" function. This is a key technology for realizing deep oil and gas pressure-maintaining coring, and will play an important role in promoting the development of deep and ultra-deep oil and gas geological evaluation work in my country. Summary of the invention

[0004] The object of the present invention is to provide a pressure control device for pressure-maintaining coring to solve the problem of pressure-maintaining coring in deep ultra-high pressure formations.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] A pressure control device for pressure-maintaining coring, comprising:

[0007] A pressure-controlled upper joint, wherein the interior of the pressure-controlled upper joint is a nitrogen chamber, a piston chamber and a first hydraulic chamber from top to bottom, an air injection hole and an air exhaust hole are provided at the top of the pressure-controlled upper joint, a first needle valve is provided in the air injection hole, and the first needle valve can open and close the air injection hole, and connect or isolate the air exhaust hole and the nitrogen chamber; a piston is slidably connected in the piston chamber, the top of the piston chamber is communicated with the first nitrogen chamber, and the bottom of the piston is communicated with the first hydraulic chamber;

[0008] A pressure-controlled lower joint, the top of which is connected to the bottom of the pressure-controlled upper joint, the interior of which is a second hydraulic chamber and a third hydraulic chamber from top to bottom, the second hydraulic chamber being communicated with the first hydraulic chamber; an axial leakage hole and a radial leakage hole are provided at the top of the pressure-controlled lower joint, a second needle valve is provided in the radial leakage hole, the second needle valve can conduct or isolate the axial leakage hole and the radial leakage hole, the axial leakage hole is communicated with the first hydraulic chamber;

[0009] A sleeve joint, wherein the sleeve joint is sleeved on the pressure-controlling lower joint and has a clearance fit with the pressure-controlling lower joint, and the sleeve joint can connect the second hydraulic chamber and the third hydraulic chamber;

[0010] The inner cylinder has a top end connected to the bottom end of the pressure-controlled lower joint, and the third hydraulic chamber is in communication with the inner cylinder.

[0011] Optionally, the piston chamber includes a plurality of sub-piston chambers, and the plurality of sub-piston chambers are symmetrically distributed around the axial direction of the pressure-control upper joint, and a sub-piston is slidably connected in each of the sub-piston chambers.

[0012] Optionally, a first sealing ring is sleeved on the sub-piston.

[0013] Optionally, at least two of the first sealing rings are sleeved on each of the sub-pistons, and at least two of the first sealing rings are arranged at intervals.

[0014] Optionally, the pressure-controlled down joint and the sliding sleeve joint are connected and positioned by a shear pin.

[0015] Optionally, the sub-piston chamber is connected to the nitrogen chamber via a plurality of air guide holes, and the aperture of the air guide holes is smaller than the aperture of the sub-piston chamber.

[0016] Optionally, the pressure-controlling upper joint and the pressure-controlling lower joint are threadedly connected, and the pressure-controlling lower joint and the inner tube are threadedly connected.

[0017] Optionally, a first flow guide hole is provided at the top of the pressure-controlled lower joint, two ends of the first flow guide hole are respectively connected to the first hydraulic chamber and the second hydraulic chamber, and the aperture of the first flow guide hole is smaller than the inner diameter of the first hydraulic chamber and the second hydraulic chamber.

[0018] Optionally, an annular cavity is provided between the pressure-controlled lower joint and the sliding sleeve joint, the second hydraulic cavity is communicated with the annular cavity through a second guide hole, and the third hydraulic cavity is communicated with the annular cavity through a third guide hole.

[0019] Optionally, the third hydraulic chamber is communicated with the inner cylinder through a fourth guide hole.

[0020] Beneficial effects of the present invention:

[0021] The pressure control device for pressure-maintaining coring of the present invention adjusts the inner barrel pressure through nitrogen, so that the high-pressure pressure of the inner barrel is reduced to the range that the coring tool can withstand, and the pressure of the inner barrel in the pressure-maintaining coring operation is safe and controllable. During the pressure control process, the nitrogen in the pressure-controlled upper joint will not enter the inner barrel, preventing foreign gas from mixing into the inner barrel and causing distortion of the gas content test. The core and fluid obtained are the most authentic formation data at the bottom of the well. It can reduce the pressure of the inner barrel without causing oil and gas loss in the inner barrel, and achieve pressure control of "maintaining oil and gas", solving the technical problem that ultra-high pressure formations cannot perform pressure-maintaining coring operations, providing technical means and solutions for implementing pressure-maintaining coring operations in ultra-deep oil and gas reservoirs, and providing strong technical guarantees for the efficient exploration and development of deep oil and gas reservoirs in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall structure of a pressure control device for pressure-maintaining coring of the present invention;

[0023] Figure 2 It is a perspective view of the piston structure in a pressure control device for pressure-maintaining coring of the present invention;

[0024] Figure 3 It is a structural schematic diagram of a neutron piston of a pressure control device for pressure-maintaining coring of the present invention;

[0025] Figure 4 It is a structural schematic diagram of a pressure-controlled down-contact joint in a pressure control device for pressure-maintaining coring of the present invention;

[0026] Figure 5 It is a structural schematic diagram of a first needle valve in a pressure control device for pressure-maintaining coring of the present invention.

[0027] In the figure:

[0028] 1. Pressure control upper joint; 11. Nitrogen chamber; 111. Air guide hole; 12. Piston chamber; 121. Sub-piston chamber; 122. Fifth guide hole; 13. First hydraulic chamber; 14. Air injection hole; 141. Sixth guide hole; 15. Exhaust hole; 16. First needle valve; 161. External thread; 162. Internal hole; 163. Second sealing ring; 17. Piston; 171. Sub-piston; 172. First sealing ring;

[0029] 2. Control pressure lower joint; 21. Second hydraulic chamber; 211. Second flow guide hole; 22. Third hydraulic chamber; 221. Third flow guide hole; 222. Fourth flow guide hole; 23. Axial leakage hole; 24. Radial leakage hole; 25. Second needle valve; 26. First flow guide hole; 27. Annular chamber; 28. Upper step surface; 29. ​​Lower step surface;

[0030] 3. Slip-on joint; 31. Mounting hole; 4. Inner tube; 5. Shear pin. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0032] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0034] In the description of this embodiment, the terms "upper", "lower", "right", etc., directions or positional relationships are based on the directions or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0035] The present invention provides a pressure control device for pressure-maintaining coring, such as Figure 1 As shown, it includes a pressure-controlled upper joint 1, a pressure-controlled lower joint 2, a sliding joint 3 and an inner tube 4. The interior of the pressure-controlled upper joint 1 is composed of a nitrogen chamber 11, a piston chamber 12 and a first hydraulic chamber 13 from top to bottom. An injection hole 14 and an exhaust hole 15 are provided at the top of the pressure-controlled upper joint 1. A first needle valve 16 is provided in the injection hole 14. The first needle valve 16 can open and close the injection hole 14, and connect or isolate the exhaust hole 15 and the nitrogen chamber 11; a piston 17 is slidably connected in the piston chamber 12, the top of the piston chamber 12 is connected to the nitrogen chamber 11, and the bottom of the piston 17 is connected to the first hydraulic chamber 13. The top end of the pressure-controlled lower joint 2 is connected to the bottom end of the pressure-controlled upper joint 1, and the interior of the pressure-controlled lower joint 2 is the second hydraulic chamber 21 and the third hydraulic chamber 22 from top to bottom, and the second hydraulic chamber 21 is connected to the first hydraulic chamber 13; the top end of the pressure-controlled lower joint 2 is provided with an axial leakage hole 23 and a radial leakage hole 24, and the radial leakage hole 24 is provided with a second needle valve 25, and the second needle valve 25 can conduct or isolate the axial leakage hole 23 and the radial leakage hole 24, and the axial leakage hole 23 is connected to the first hydraulic chamber 13; the sliding sleeve joint 3 is sleeved on the pressure-controlled lower joint 2 and has a clearance fit with the pressure-controlled lower joint 2, and the sliding sleeve joint 3 can connect the second hydraulic chamber 21 and the third hydraulic chamber 22 respectively; the top end of the inner tube 4 is connected to the bottom end of the pressure-controlled lower joint 2, and the third hydraulic chamber 22 is connected to the inner tube 4.

[0036] The pressure control device for pressure-maintaining coring of the present invention uses a multi-chamber to dynamically adjust and reduce the pressure of the inner tube 4 during the drilling process after closing the sealing valve under the pressure-maintaining coring drilling condition, so that the pressure of the inner tube 4 is reduced to a range that the coring tool can withstand. The specific working process is as follows:

[0037] Before the coring tool is put into the well, nitrogen is filled into the nitrogen chamber 11 through the gas injection hole 14, and the piston 17 is pushed to the bottom of the piston chamber 12 to complete the pressurization. After the coring tool completes drilling the core, the pressure control device is differentially moved relative to the outer cylinder of the coring tool through the differential device. During the differential process, the impact force of the outer cylinder is used to push the sleeve joint 3 downward relative to the pressure-controlled lower joint 2 and sit on the step of the pressure-controlled lower joint 2 for positioning. At this time, the sleeve joint 3 is connected with the second hydraulic chamber 21 and the third hydraulic chamber 22, and the high-pressure fluid in the inner cylinder 4 enters the first hydraulic chamber 13 of the pressure-controlled upper joint 1 through the third hydraulic chamber 22 and the second hydraulic chamber 21 in turn, and generates an upward thrust on the piston 17. During the drilling process, because the nitrogen pressure in the nitrogen chamber 11 is lower than the bottom hole pressure, the piston 17 moves upward under the action of thrust and compresses the nitrogen in the nitrogen chamber 11. During this process, the pressure in the first hydraulic chamber 13 gradually decreases, and the nitrogen pressure in the nitrogen chamber 11 is compressed and gradually increases. When the pressure of the nitrogen chamber 11 and the pressure of the first hydraulic chamber 13 reach equilibrium, the piston 17 stops moving, thereby completing the control conversion of the inner tube 4 from high pressure to low pressure, so that the pressure of the inner tube 4 is reduced to within the strength tolerance range of the inner tube 4.

[0038] After the coring tool reaches the ground, the first needle valve 16 is unscrewed to allow the nitrogen in the nitrogen chamber 11 to be discharged from the gas injection hole 14 to relieve the pressure; the second needle valve 25 is unscrewed to allow the fluid in the first hydraulic chamber 13 to be discharged from the axial leakage hole 23 and discharged through the radial leakage hole 24, thereby completing the pressure relief of the fluid in the inner tube 4.

[0039] The differential device is a supporting technical tool in the working application process of the present invention, specifically involving a hydraulic lifting device, which can lift the inner cylinder 4 relative to the outer cylinder by throwing a ball and holding pressure. The coring outer cylinder is a supporting technical tool in the working application process of the present invention, and its main function is to transmit drilling pressure and torque. The specific structure can adopt any achievable method in the prior art, which is a conventional technology in the field.

[0040] It can be understood that the present invention adjusts the pressure of the inner cylinder 4 by nitrogen, so that the high pressure of the inner cylinder 4 is reduced to the range that the coring tool can bear, and the pressure of the inner cylinder 4 in the pressure-maintaining coring operation is safe and controllable. During the pressure control process, the nitrogen in the pressure-controlled upper joint 1 will not enter the inner cylinder 4, preventing foreign gas from mixing into the inner cylinder 4 and causing distortion of the gas content test. The core and fluid obtained are the most authentic formation data at the bottom of the well. It can reduce the pressure of the inner cylinder 4 without causing oil and gas loss in the inner cylinder 4, and realize the pressure control of "maintaining oil and gas", solving the technical problem that ultra-high pressure formations cannot perform pressure-maintaining coring operations, providing technical means and solutions for implementing pressure-maintaining coring operations in ultra-deep oil and gas reservoirs, and providing strong technical guarantees for the efficient exploration and development of deep oil and gas reservoirs in my country.

[0041] Optionally, the piston chamber 12 includes a plurality of sub-piston chambers 121 , and the plurality of sub-piston chambers 121 are symmetrically distributed around the axial direction of the pressure-control upper joint 1 , and a sub-piston 171 is slidably connected in each sub-piston chamber 121 .

[0042] like Figure 2 In the embodiment shown, five groups of small sub-piston chambers 121 are used in the piston chamber 12 to dynamically adjust the spatial volume of the pressure-maintaining inner cylinder 4, which can ensure that the pressure of the inner cylinder 4 slowly reaches equilibrium and stability, and does not generate excessive excitation pressure on the inner cylinder 4 and the core. Among the five sub-piston chambers 121, the first sub-piston chamber 121 is set on the axis of the pressure-control upper joint 1, and the remaining four are axially symmetrically distributed around the first sub-piston chamber 121. Preferably, the sub-piston 171 adopts a floating piston, which is supported by high-pressure liquid during operation and does not contact the inner wall of the sub-piston chamber 121, which can reduce wear and improve efficiency.

[0043] Optionally, a first sealing ring 172 is sleeved on the sub-piston 171 .

[0044] like Figure 3 As shown, at least two first sealing rings 172 are sleeved on each sub-piston 171, and at least two first sealing rings 172 are arranged at intervals. Specifically, two annular grooves are arranged at intervals on the sub-piston 171, and the two first sealing rings 172 are sleeved in the two annular grooves respectively. When the sub-piston 171 slides up and down in the sub-piston cavity 121, the first sealing ring 172 can seal the gap between the sub-piston 171 and the sub-piston cavity 121, realize sliding sealing, and prevent the liquid in the first hydraulic cavity 13 from entering the upper nitrogen cavity 11.

[0045] Optionally, the pressure-controlled down joint 2 and the sleeve joint 3 are connected and positioned by a shear pin 5 .

[0046] like Figure 1 and Figure 4 As shown, the pipe walls of the pressure-controlled down-joint 2 and the sleeve joint 3 are correspondingly provided with through radial mounting holes 31, and the shear pins 5 are inserted into the mounting holes 31. When the outer tube and the inner tube 4 are differentially moved, the shear pins 5 can be sheared off by the impact of the outer tube, and then the fixed connection between the sleeve joint 3 and the pressure-controlled down-joint 2 is released, and the sleeve joint 3 moves downward under the differential action. Figure 4 The pressure-controlled lower joint 2 is a dumbbell-shaped structure. The sliding joint 3 is sleeved on the middle section of the pressure-controlled lower joint 2, and its two ends can respectively stop at the upper step surface 28 and the lower step surface 29 of the pressure-controlled lower joint 2. When the shear pin 5 is inserted into the sliding joint 3 and the pressure-controlled lower joint 2, the top of the sliding joint 3 abuts against the upper step surface 28 of the pressure-controlled lower joint 2. When the shear pin 5 is sheared off, the sliding joint 3 moves downward and stops at the lower step surface 29 of the pressure-controlled lower joint 2 to achieve re-positioning.

[0047] Optionally, the sub-piston chamber 121 is connected to the nitrogen chamber 11 via a plurality of air guide holes 111 , and the aperture of the air guide holes 111 is smaller than the aperture of the sub-piston chamber 121 .

[0048] like Figure 1 As shown, the air guide hole 111 is arranged at the bottom of the nitrogen chamber 11, and is connected to a plurality of sub-piston chambers 121 respectively. The aperture of the air guide hole 111 is smaller than the aperture of the sub-piston chamber 121. The nitrogen above the sub-piston 171 can enter the nitrogen chamber 11 upward under the action of the hydraulic pressure at the bottom of the sub-piston 171. The air guide hole 111 with a smaller aperture is arranged to facilitate the connection between the piston chamber 12 and the nitrogen chamber 11, and the plurality of air guide holes 111 are connected respectively, which is conducive to the slow switching from hydraulic pressure to air pressure and avoids the generation of excessive excitation pressure. Corresponding to the air guide hole 111, the bottom of each sub-piston chamber 121 is provided with a fifth guide hole 122. The aperture of the fifth guide hole 122 is smaller than the aperture of each sub-piston chamber 121 and larger than the aperture of the air guide hole 111. The high-pressure liquid in the first hydraulic chamber 13 can enter the sub-piston chamber 121 through the fifth guide hole 122 to push the sub-piston 171 to slide upward.

[0049] Optionally, the pressure-controlled upper joint 1 is threadedly connected to the pressure-controlled lower joint 2 , and the pressure-controlled lower joint 2 is threadedly connected to the inner tube 4 .

[0050] In this embodiment, the threaded connection is convenient for installation, has high axial connection strength, and is conducive to maintaining coaxiality. The threaded connection is a conventional internal and external thread matching connection method. The specific structure of the threaded connection omitted in the drawings is not used as a key structural improvement, but only as a preferred connection method.

[0051] Optionally, a first flow guide hole 26 is provided at the top of the pressure-controlled lower joint 2, and two ends of the first flow guide hole 26 are respectively connected to the first hydraulic chamber 13 and the second hydraulic chamber 21, and the aperture of the first flow guide hole 26 is smaller than the inner diameter of the first hydraulic chamber 13 and the second hydraulic chamber 21.

[0052] like Figure 1 and Figure 3 As shown, the top of the pressure-controlled lower joint 2 is provided with a first guide hole 26 for connecting the first hydraulic chamber 13 and the second hydraulic chamber 21, and the aperture of the first guide hole 26 is smaller than the inner diameter of the first hydraulic chamber 13, and the aperture of the first guide hole 26 is smaller than the inner diameter of the second hydraulic chamber 21. The high-pressure liquid in the second hydraulic chamber 21 can be limited by the first guide hole 26 to avoid excessive pressure caused by rapid hydraulic release. Figure 3 The aperture of the first flow guide hole 26 is larger than the aperture of the axial leakage hole 23 and larger than the aperture of the radial leakage hole 24. A plurality of radial leakage holes 24 are arranged around the axial direction of the pressure-controlled lower joint 2, and the plurality of radial leakage holes 24 are arranged radially, and a second needle valve 25 is arranged in each radial leakage hole 24.

[0053] The first needle valve 16 and the second needle valve 25 have the same structure. Figure 5 As shown, taking the first needle valve 16 as an example, one end is provided with an external thread 161 for threaded connection with the gas injection hole 14 or the radial leakage hole 24, and the axis corresponding to the external thread 161 is provided with an inner hole 162 for an external installation tool to tighten or loosen the first needle valve 16 or the second needle valve 25. A second sealing ring 163 is provided on the valve body at the other end of the first needle valve 16 and the second needle valve 25. The second sealing ring 163 is one or more. When multiple second sealing rings 163 are provided, multiple second sealing rings 163 are arranged at intervals on the valve body to seal the gas injection hole 14 or the radial leakage hole 24 to prevent leakage of gas or liquid.

[0054] Optionally, an annular cavity 27 is provided between the pressure-controlled lower joint 2 and the sleeve joint 3 , the second hydraulic cavity 21 is connected to the annular cavity 27 through the second flow guide hole 211 , and the third hydraulic cavity 22 is connected to the annular cavity 27 through the third flow guide hole 221 .

[0055] like Figure 1 As shown, the second flow guide hole 211 is a radial small hole, which is arranged near the bottom end of the second hydraulic chamber 21. Before the shear pin 5 is cut off, the second flow guide hole 211 connects the second hydraulic chamber 21 and the annular chamber 27, and the inner cylinder 4 is in a sealed state. After the shear pin 5 is cut off, under the action of hydraulic differential, the sleeve joint 3 moves downward, and the third hydraulic chamber 22 connects the annular chamber 27 through the third flow guide hole 221. The third flow guide hole 221 is a radial small hole, which is arranged near the top end of the third hydraulic chamber 22. At this time, the second hydraulic chamber 21 and the third hydraulic chamber 22 are connected to the annular chamber 27 at the same time, and the high-pressure liquid in the inner cylinder 4 moves upward in sequence, passing through the inner cylinder 4-third hydraulic chamber 22-third flow guide hole 221-annular chamber 27-second flow guide hole 211-second hydraulic chamber 21-first flow guide hole 26-first hydraulic chamber 13 one by one. Under the action of the high-pressure liquid, the piston 17 moves upward to compress the nitrogen in the nitrogen chamber 11 until the pressure in the first hydraulic chamber 13 and the nitrogen chamber 11 reaches equilibrium. When the liquid continuously passes through the third guide hole 221, the second guide hole 211 and the first guide hole 26 with smaller apertures, and under the action of multiple sub-pistons 171, the liquid pressure is gradually released to avoid the generation of exciting pressure.

[0056] Optionally, the third hydraulic chamber 22 is communicated with the inner cylinder 4 through a fourth guide hole 222 .

[0057] like Figure 1 The fourth guide hole 222 is an axial hole, which is coaxially arranged at the axis center with the third hydraulic chamber 22. The aperture of the fourth guide hole 222 is smaller than the inner aperture of the third hydraulic chamber 22 and smaller than the inner aperture of the inner cylinder 4, which is beneficial to control the speed and flow rate of the high-pressure liquid in the inner cylinder 4 entering the third hydraulic chamber 22 and avoid generating exciting pressure.

[0058] Supplementary explanation, such as Figure 1 and Figure 2 A sixth flow guide hole 141 connected to the gas injection hole 14 is provided at the bottom thereof. The aperture of the sixth flow guide hole 141 is smaller than that of the gas injection hole 14. When the high-pressure nitrogen in the nitrogen chamber 11 is deflated, the first needle valve 16 is first unscrewed to connect the nitrogen chamber 11 with the exhaust hole 15. The high-pressure nitrogen is discharged to the exhaust hole 15 through the sixth flow guide hole 141. The small aperture is conducive to controlling the flow rate and flow velocity of the high-pressure gas.

[0059] The pressure control device for pressure-maintaining coring of the present invention is a supporting device for the pressure-maintaining coring tool. Before the tool is put into the well, nitrogen is filled into the nitrogen chamber 11 through the gas injection hole 14, and the piston 17 is pushed to the bottom of the piston chamber 12 to complete the pressure filling. The working process is as follows:

[0060] After the coring tool has completed drilling the core, the pressure control device is differentially moved relative to the outer cylinder of the coring tool through the differential device. During the differential process, the impact force of the outer cylinder is used to shear off the shear pin 5, and the sliding sleeve joint 3 is pushed to sit on the lower step surface 29 of the pressure-controlled lower joint 2. At this time, the second guide hole 211, the annular cavity 27 and the third guide hole 221 on the pressure-controlled lower joint 2 are kept in communication, and the high-pressure fluid in the inner cylinder 4 enters the first hydraulic chamber 13 through the fourth guide hole 222, the third hydraulic chamber 22, the third guide hole 221, the annular cavity 27, the second guide hole 211, the second hydraulic chamber 21 and the first guide hole 26 in sequence, and generates an upward thrust on the piston 17.

[0061] During the drilling process, because the nitrogen pressure in the nitrogen chamber 11 is lower than the bottom hole pressure, the piston 17 moves upward under the action of thrust and compresses the nitrogen in the nitrogen chamber 11. During this process, the pressure in the first hydraulic chamber 13 gradually decreases, and the nitrogen pressure in the nitrogen chamber 11 is compressed and gradually increases. When the pressure in the nitrogen chamber 11 and the pressure in the first hydraulic chamber 13 reach equilibrium, the piston 17 stops moving, thereby completing the control conversion from high pressure to low pressure of the inner cylinder 4, so that the pressure of the inner cylinder 4 is reduced to within the tolerable range of the strength of the inner cylinder 4.

[0062] After the coring tool reaches the ground, the first needle valve 16 is unscrewed to allow the nitrogen in the nitrogen chamber 11 to be discharged through the sixth guide hole 141 and the exhaust hole 15 to relieve the pressure; the second needle valve 25 is unscrewed to allow the fluid in the first hydraulic chamber 13 to be discharged from the axial leakage hole 23 and discharged through the radial leakage hole 24, thereby completing the pressure relief of the fluid in the inner tube 4.

[0063] The present invention adjusts the pressure of the inner cylinder 4 by nitrogen, so that the high pressure of the inner cylinder 4 is reduced to the range that the coring tool can bear, and the pressure of the inner cylinder 4 in the pressure-maintaining coring operation is safe and controllable. The use of multiple groups of sub-piston chambers 121 to dynamically adjust the spatial volume of the pressure-maintaining inner cylinder 4 can ensure that the pressure of the inner cylinder 4 slowly reaches equilibrium and stability, and does not generate excessive exciting pressure on the inner cylinder 4 and the core. During the pressure control process, the nitrogen in the pressure control device will not enter the inner cylinder 4, preventing foreign gas from mixing into the inner cylinder 4 and causing distortion of the gas content test, and the core and fluid obtained are the most authentic formation data at the bottom of the well.

[0064] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A pressure control device for pressure-maintaining coring, characterized in that: include: A pressure-controlled upper joint (1), wherein the interior of the pressure-controlled upper joint (1) is composed of a nitrogen chamber (11), a piston chamber (12) and a first hydraulic chamber (13) from top to bottom, and an injection hole (14) and an exhaust hole (15) are provided at the top of the pressure-controlled upper joint (1). A first needle valve (16) is provided in the injection hole (14), and the first needle valve (16) can open and close the injection hole (14), and connect or isolate the exhaust hole (15) and the nitrogen chamber (11); a piston (17) is slidably connected in the piston chamber (12), the top of the piston chamber (12) is connected to the nitrogen chamber (11), and the bottom of the piston (17) is connected to the first hydraulic chamber (13); A pressure-controlled lower joint (2), the top end of the pressure-controlled lower joint (2) is connected to the bottom end of the pressure-controlled upper joint (1), the interior of the pressure-controlled lower joint (2) is a second hydraulic chamber (21) and a third hydraulic chamber (22) from top to bottom, the second hydraulic chamber (21) is connected to the first hydraulic chamber (13); the top end of the pressure-controlled lower joint (2) is provided with an axial leakage hole (23) and a radial leakage hole (24), the radial leakage hole (24) is provided with a second needle valve (25), the second needle valve (25) can conduct or isolate the axial leakage hole (23) and the radial leakage hole (24), the axial leakage hole (23) is connected to the first hydraulic chamber (13); a sleeve joint (3), wherein the sleeve joint (3) is sleeved on the pressure-controlled lower joint (2) and has a clearance fit with the pressure-controlled lower joint (2); the sleeve joint (3) is capable of connecting the second hydraulic chamber (21) and the third hydraulic chamber (22); An inner cylinder (4), the top end of the inner cylinder (4) is connected to the bottom end of the pressure-controlled lower joint (2), and the third hydraulic chamber (22) is in communication with the inner cylinder (4); The piston chamber (12) comprises a plurality of sub-piston chambers (121), the plurality of sub-piston chambers (121) being symmetrically distributed around the axial direction of the pressure-control upper joint (1), and a sub-piston (171) being slidably connected in each of the sub-piston chambers (121).

2. The pressure control device for pressure-maintaining coring according to claim 1, characterized in that: The sub-piston (171) is sleeved with a first sealing ring (172).

3. The pressure control device for pressure-maintaining coring according to claim 2, characterized in that: At least two of the first sealing rings (172) are sleeved on each of the sub-pistons (171), and at least two of the first sealing rings (172) are arranged at intervals.

4. The pressure control device for pressure-maintaining coring according to claim 1, characterized in that: The pressure-controlled lower joint (2) and the sliding sleeve joint (3) are connected and positioned via a shear pin (5).

5. The pressure control device for pressure-maintaining coring according to claim 1, characterized in that: The sub-piston chamber (121) is connected to the nitrogen chamber (11) via a plurality of air guide holes (111), and the aperture of the air guide holes (111) is smaller than the aperture of the sub-piston chamber (121).

6. The pressure control device for pressure-maintaining coring according to claim 1, characterized in that: The pressure-controlling upper joint (1) and the pressure-controlling lower joint (2) are threadedly connected, and the pressure-controlling lower joint (2) and the inner tube (4) are threadedly connected.

7. The pressure control device for pressure-maintaining coring according to claim 1, characterized in that: A first flow guide hole (26) is provided at the top end of the pressure-controlled lower joint (2), and two ends of the first flow guide hole (26) are respectively connected to the first hydraulic chamber (13) and the second hydraulic chamber (21), and the aperture of the first flow guide hole (26) is smaller than the inner diameters of the first hydraulic chamber (13) and the second hydraulic chamber (21).

8. The pressure control device for pressure-maintaining coring according to claim 1, characterized in that: An annular cavity (27) is provided between the pressure-controlled lower joint (2) and the sleeve joint (3); the second hydraulic cavity (21) is communicated with the annular cavity (27) via a second flow guide hole (211); and the third hydraulic cavity (22) is communicated with the annular cavity (27) via a third flow guide hole (221).

9. The pressure control device for pressure-maintaining coring according to claim 1, characterized in that: The third hydraulic chamber (22) is in communication with the inner cylinder (4) via a fourth flow guide hole (222).

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