Pressure-controlled suction type underground PVT sampler and underground PVT sampling method

Abstract

The invention relates to the technical field of underground tools, in particular to a pressure control suction type underground PVT sampler and an underground PVT sampling method.The pressure control suction type underground PVT sampler comprises an upper connector, a control cylinder, a control head, a connector, an outer sleeve, a liquid storage cylinder, a throttling short section, a sampling cylinder, an inflow short section, a sealing short section and a lower connector, and the control cylinder is fixedly installed on the inner side of the lower end of the upper connector; the method comprises the following steps: (1) before an instrument enters a well, firstly testing the flow pressure of underground fluid, and debugging an initial pressure value in a pressure control section according to a flow pressure value of an underground sampling point; the device is reasonable and compact in structure and ingenious in conception, the sampling action of the sampler is controlled through the principle that water vapor expands after being heated, precise mechanical mechanisms such as electronic components and a clock are not arranged, the starting shear value is set according to the underground temperature, so that the starting action of the sampler is controlled, the higher the temperature is, the easier the sampling is, and due to the fact that under a certain volume, the sampling effect is good. The higher the temperature is, the larger the gas expansion is, the higher the pressure is, the larger the shearing force is, and the device has the characteristics of rapidness, stability and high efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of downhole tools, in particular to a pressure-controlled suction downhole PVT sampler and a downhole PVT sampling method. Background Art

[0002] High-pressure physical properties (PVT) of reservoir fluids have extensive application value in oilfield development. They serve as a crucial basis for studying oilfield drive types, determining oilfield development methods, calculating oilfield reserves, and selecting well operating systems. They are of irreplaceable importance for the correct understanding and evaluation of oil and gas fields. With the continuous advancement of oilfield development, the number of high-temperature, high-pressure, and ultra-deep wells (referred to as "three-super wells") is increasing. These wells have downhole pressures exceeding 120 MPa, downhole temperatures reaching 180°C, and depths generally exceeding 6,000 meters. Some wells also contain corrosive media such as carbon dioxide and hydrogen sulfide, posing unprecedented challenges to downhole sampling.

[0003] Currently, overseas countries primarily use suction-type downhole PVT samplers that are lowered via a cable. These have a nominal pressure rating of 20,000 psi and a temperature rating of 180°C, and employ clock-controlled sampling. However, in practice, these often fail to meet the nominal operating pressure and temperature specifications, particularly at temperatures above 150°C, significantly reducing the sampling success rate. While China has made some progress in high-temperature, high-pressure sampling technology, developing a flow-type, high-temperature, high-pressure sampler with a pressure rating of 140 MPa and a temperature rating of 175°C, the field of suction-type, high-temperature, high-pressure samplers with a pressure rating of 140 MPa and a temperature rating of 175°C remains unseen. Summary of the Invention

[0004] The present invention provides a pressure-controlled suction-type downhole PVT sampler and a downhole PVT sampling method, which overcome the deficiencies of the above-mentioned prior art and can effectively solve the problem that the existing suction-type sampler is difficult to sample under high temperature and high pressure conditions.

[0005] One of the technical solutions of the present invention is achieved through the following measures: a pressure-controlled suction downhole PVT sampler, including an upper joint, a control cylinder, a control head, a connector, an outer sleeve, a liquid storage cylinder, a throttling short section, a sampling cylinder, an inflow short section, a sealing short section and a lower joint, a control cylinder is fixedly installed on the inner side of the lower end of the upper joint, and a valve hole section, a pressure control section, a piston section and a connecting section are provided in the control cylinder, which are connected in sequence from top to bottom and have increasing inner diameters, a main needle valve is provided in the valve control section, a control piston is provided on the inner side of the upper end of the piston section, a push rod socket is provided in the center of the lower side of the control piston, and a valve hole is provided in the push rod socket. The starting shear nail is fixedly installed with an upper push rod, and a control head is provided on the lower side of the upper push rod. A mounting blind hole is provided in the center of the upper side of the control head, and a control valve stem is provided in the mounting blind hole. A valve stem assembly that can make the control valve stem move upward is provided on the outer side of the control valve stem. A liquid inlet blind hole that can be connected with the lower end of the mounting blind hole is provided on the lower side of the control head, and a liquid outlet blind hole that can be connected with the outer side of the lower part of the mounting blind hole is provided on the lower side of the control head. The outer side of the upper end of the control head is fixedly installed with the inner side of the lower end of the control tube, and a hanging outer ring platform is provided on the outer side of the middle of the control head. A connecting head is provided on the outer side of the lower side of the control head corresponding to the position below the hanging outer ring platform. An outer sleeve is fixedly installed on the outer side of the end, and a suspension inner ring platform is provided on the inner side of the upper end of the outer sleeve, which is located on the upper side of the suspension outer ring platform and abuts against the lower side of the control cylinder. A liquid storage cylinder is fixedly installed on the outer side of the lower end of the connector, and a throttling nipple is fixedly installed on the inner side of the lower end of the liquid storage cylinder. A throttling channel that runs through the upper and lower ends is provided on the throttling nipple, and a buffer pipeline is fixedly connected between the liquid inlet blind hole and the throttling channel. A sampling cylinder is fixedly installed on the outer side of the lower end of the throttling nipple, and an inflow nipple is fixedly installed on the inner side of the lower end of the sampling cylinder. A sealing nipple is fixedly installed on the inner side of the lower end of the inflow nipple, and a lower joint is fixedly installed on the inner side of the lower end of the sealing nipple. A closing top pipe with its upper end located above it is fixedly installed on the inner side of the upper end of the joint by closing shear nails, a receiving ring is provided on the inner side of the lower end of the lower joint, a sealing locking rod with its upper end located above it is provided in the sealing nipple, a suction hole with its lower end connected to the closing top pipe is provided on the outer side of the upper part of the sealing locking rod, and a sealing locking assembly is provided on the sealing nipple that can seal the upper end of the suction hole after the sealing locking rod is lowered; a check valve assembly is provided on the inner side of the lower part of the inflow nipple corresponding to the upper position of the sealing locking rod, a suction piston with its lower end located on the upper side of the inflow nipple is provided in the sampling cylinder, and a pressure-maintaining spring assembly is provided on the upper side of the suction piston.

[0006] The following is a further optimization and / or improvement of one of the above-mentioned technical solutions: The above-mentioned may also include a first plug, a first needle valve, a second plug, a second needle valve, a third plug, a third needle valve and a pressure relief plug. The outer side of the upper part of the control cylinder corresponding to the lower position of the main needle valve is provided with a first mounting hole and a second mounting hole that can be communicated with the valve hole section, and the first mounting hole and the second mounting hole are respectively provided with a first plug and a first needle valve. The outer side of the middle part of the throttling short section is provided with a third mounting hole and a fourth mounting hole that can be communicated with the throttling channel, and the third mounting hole and the fourth mounting hole are respectively provided with a second plug and a second needle valve. The outer side of the upper part of the inflow short section corresponding to the position above the one-flow valve assembly is provided with a fifth mounting hole and a sixth mounting hole that can be communicated with the inflow short section, and the fifth mounting hole and the sixth mounting hole are respectively provided with a third plug and a third needle valve. The outer side of the lower part of the connecting head is provided with a seventh mounting hole that can be communicated with the inside of the connecting head, and the seventh mounting hole is provided with a pressure relief plug.

[0007] The above may also include an inlet throttling nozzle, an outlet throttling nozzle, an upper throttling nozzle and a lower throttling nozzle. The inlet throttling nozzle is fixedly installed on the lower side of the control head corresponding to the liquid inlet blind hole position, the outlet throttling nozzle is fixedly installed on the lower side of the control head corresponding to the liquid outlet blind hole position, the upper throttling nozzle is fixedly installed at the upper end of the throttling channel, and the lower throttling nozzle is fixedly installed at the lower end of the throttling channel; a buffer pipeline is fixedly connected between the inlet throttling nozzle and the upper throttling nozzle, and the buffer pipeline includes an upper pipe section, a spiral coil section and a lower pipe section that are fixedly connected together from top to bottom, and the spiral coil section is located in the liquid storage cylinder.

[0008] The above-mentioned sealing locking assembly may include a pressure cap, a sealing gasket, a locking pin, a locking block and a locking spring. A locking ring groove is provided on the outer side of the lower part of the sealing locking rod. A sealing gasket is provided between the sealing short section and the sealing locking rod at a position corresponding to the upper end of the suction hole and the locking ring groove. A pressure cap, the lower end of which is against the sealing gasket, is fixedly installed on the inner side of the upper end of the sealing short section; at least two locking holes are provided along the circumferential interval on the outer side of the upper part of the sealing short section corresponding to the position below the locking ring groove, a locking pin is fixedly installed on the outer end of the locking hole, a locking block is provided at the inner end of the locking hole, the inner end of the locking hole is against the outer side of the sealing locking rod, and a locking spring is provided in the locking hole corresponding to the position between the locking pin and the locking block.

[0009] The above may also include an O-ring, an O-ring is provided between the outer side of the lower part of the main needle valve and the control cylinder, an O-ring is provided between the control piston and the control cylinder, an O-ring is provided between the lower part of the control cylinder and the control head, an O-ring is provided between the control valve stem corresponding to the position between the upper end of the liquid inlet blind hole and the upper end of the liquid outlet blind hole and the control head, an O-ring is provided between the lower part of the control head and the connecting head, an O-ring is provided between the lower part of the connecting head and the liquid storage cylinder, an O-ring is provided between the upper part of the throttling short section and the liquid storage cylinder, an O-ring is provided between the lower part of the throttling short section and the sampling cylinder, an O-ring is provided between the upper part of the inflow short section and the sampling cylinder, an O-ring is provided between the upper part of the sealing short section and the inflow short section, and an O-ring is provided between the upper part of the lower joint and the sealing short section.

[0010] The above can also include a filter assembly, which includes a pressure pipe and a filter screen. A mounting ring groove is provided on the lower side of the lower joint, a filter screen is provided on the upper end of the mounting ring groove, and a pressure pipe is fixedly installed on the lower end of the mounting ring groove.

[0011] The above-mentioned pressure-maintaining spring assembly may include a spring rod and a pressure-maintaining spring. The spring rod is fixedly mounted on the upper end of the suction piston, and a pressure-maintaining spring with its upper end located above the spring rod is provided on the outer side of the spring rod.

[0012] The above-mentioned one-flow valve assembly may include a one-flow valve body and a reset spring. A reset ring is provided on the outer side of the lower end of the one-flow valve body, and a reset spring is provided on the upper side of the reset ring and is located outside the one-flow valve body.

[0013] The above can also include a needle plug and a nut. A fixed ring groove is provided on the upper side of the inflow nipple, a nut is fixedly installed in the fixed ring groove, and a needle plug is provided on the lower side of the suction piston and inserted into the nut.

[0014] The above-mentioned valve stem assembly may include a limit nut, an upper spring and a lower spring. The limit nut is fixedly installed on the inner side of the upper end of the control head. The control valve stem is arranged in the limit nut. A blocking ring is arranged on the outer side of the middle part of the control valve stem. An upper spring is arranged on the outer side of the control valve stem corresponding to the position between the limit nut and the blocking ring, and a lower spring is arranged on the outer side of the control valve stem corresponding to the position below the blocking ring.

[0015] The second technical solution of the present invention is achieved by the following measures: a downhole PVT sampling method using the above-mentioned pressure-controlled suction downhole PVT sampler comprises the following steps: (1) Before the instrument is put into the well, the downhole fluid flow pressure is tested first. According to the flow pressure value of the downhole sampling point, the initial pressure value in the pressure control section is adjusted. The sampling tube is injected with the preset liquid and pressurized. The sampler is in the closed state. The installed and debugged sampler is placed in the blowout preventer. (2) After the instrument is put into the well and the sampler is lowered to the sampling position, the gas in the control cylinder expands due to heat and the water vaporizes at high temperature. The pressure on the control piston in the control cylinder gradually increases. When the pressure exceeds the shear value of the starting shear pin, the starting shear pin is cut off and the control piston moves downward. (3) The control valve stem in the control head moves upward under the action of the valve stem assembly, and the liquid inlet blind hole is connected with the liquid outlet blind hole, so that the preset liquid in the sampling cylinder flows into the liquid storage cylinder through the throttling channel, the buffer pipeline, the liquid inlet blind hole and the liquid outlet blind hole in sequence, thereby reducing the pressure in the sampling cylinder; (4) The suction piston moves upward under the action of the downhole high-pressure fluid, sucking the downhole fluid from bottom to top through the lower joint, the sealing nipple and the check valve assembly in the inflow nipple into the sampling tube; (5) After the suction piston moves up to the top of the sampling tube, the pressure-maintaining spring assembly is compressed to form a reaction force, which pushes the check valve assembly and the sealing locking rod in the inflow short section downward, shearing off the shear pin; (6) The sealing locking rod moves downward to the locking block and enters the locking ring groove, locking the sealing locking rod so that it cannot move. Under the action of the pressure cap and the sealing gasket, the suction hole is blocked, the fluid channel is closed, and the locking pin in the sealing short section enters the slot of the sealing locking rod, sealing the sample in the sampling tube and completing the sampling.

[0016] The present invention has a reasonable and compact structure and an ingenious design. It controls the sampling action of the sampler through the principle of water vapor expansion due to heat. It does not have electronic components, clocks or other precise mechanical mechanisms. The starting shear value is set according to the downhole temperature, thereby controlling the opening action of the sampler. The higher the temperature, the easier it is to sample, because under a certain volume, the higher the temperature, the greater the gas expansion, the higher the pressure, and the greater the shear force. It has the characteristics of being fast, stable and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Attachment Figure 1 This is a schematic diagram of the main cross-sectional structure of Section I in Examples 1 to 13.

[0018] Attachment Figure 2 This is a schematic diagram of the main cross-sectional structure of Section II in Examples 1 to 13.

[0019] Attachment Figure 3 This is a schematic diagram of the main cross-sectional structure of Section III in Examples 1 to 13.

[0020] Attachment Figure 4 This is a schematic diagram of the main cross-sectional structure of Section I in the use state of Examples 1 to 13.

[0021] Attachment Figure 5 This is a schematic diagram of the main cross-sectional structure of Section II in the use state of Examples 1 to 13.

[0022] Attachment Figure 6 This is a schematic diagram of the main cross-sectional structure of Section III in the use state of Examples 1 to 13.

[0023] The codes in the accompanying drawings are: 1 for the upper joint, 2 for the control cylinder, 3 for the control head, 4 for the connecting head, 5 for the outer sleeve, 6 for the liquid storage cylinder, 7 for the throttling nipple, 8 for the sampling cylinder, 9 for the inflow nipple, 10 for the sealing nipple, 11 for the lower joint, 12 for the pressure control section, 13 for the main needle valve, 14 for the control piston, 15 for the push rod jack, 16 for the start shear nail, 17 for the upper push rod, 18 for the control valve stem, 19 for the liquid inlet blind hole, 20 for the liquid outlet blind hole, 21 for the buffer pipeline, 22 for closing the push pipe, 23 for closing the shear nail, 24 for the receiving ring platform, 25 for the suction hole, 26 for the check valve assembly, 27 for the pressure holding spring assembly, 28 for the suction piston, 29 for the suction hole, 30 for the suction hole, 31 for the suction hole, 32 for the suction hole, 33 for the suction hole, 34 for the suction hole, 35 for the suction hole, 36 for the check valve assembly, 37 for the pressure holding spring assembly, 38 for the suction piston, 39 for the suction hole, 40 for the suction hole, 41 for the suction hole, 42 for the suction hole, 43 for the suction hole, 44 for the suction hole, 45 for the suction hole, 46 for the suction hole, 47 for the suction hole, 48 for the suction hole, 49 for the suction hole, 50 for the suction hole, 51 for the suction hole, 52 for the suction hole, 53 for the suction hole, 54 for the suction hole, 55 for the suction hole, 56 for the suction hole, 57 for the suction hole, 58 for the suction hole, 59 for the suction hole, 60 for the 9 is the first plug, 30 is the first needle valve, 31 is the second plug, 32 is the second needle valve, 33 is the third plug, 34 is the third needle valve, 35 is the pressure relief plug, 36 is the inlet throttling nozzle, 37 is the outlet throttling nozzle, 38 is the upper throttling nozzle, 39 is the lower throttling nozzle, 40 is the pressure cap, 41 is the sealing gasket, 42 is the locking pin, 43 is the locking block, 44 is the locking spring, 45 is the O-ring, 46 is the needle plug, 47 is the nut, 48 is the limit nut, 49 is the upper spring, 50 is the lower spring, 51 is the pressure tube, 52 is the filter screen, 53 is the prefabricated liquid, 54 is the sample liquid, 55 is the locking ring groove, and 56 is the locking sealing rod. DETAILED DESCRIPTION

[0024] The present invention is not limited to the following embodiments, and specific implementation methods can be determined based on the technical solutions of the present invention and actual conditions.

[0025] In the present invention, for the convenience of description, the relative position relationship of each component is described based on the Figure 1 The positional relationships of front, back, top, bottom, left, and right are described in the layout of the manual. Figure 1 The layout direction is determined by the

[0026] The present invention will be further described below in conjunction with the embodiments and accompanying drawings: Example 1: As shown in the attached Figure 1 、 2As shown in Figures 3, 4, 5 and 6, the pressure-controlled suction downhole PVT sampler includes an upper joint 1, a control cylinder 2, a control head 3, a connecting head 4, an outer sleeve 5, a liquid storage cylinder 6, a throttling short section 7, a sampling cylinder 8, an inflow short section 9, a sealing short section 10 and a lower joint 11. The control cylinder 2 is fixedly installed on the inner side of the lower end of the upper joint 1. The control cylinder 2 is provided with a valve hole section, a pressure control section 12, a piston section and a connecting section which are sequentially connected from top to bottom and have increasing inner diameters. A main needle valve 13 is provided in the valve control section. A control piston 14 is provided on the inner side of the upper end of the piston section. A push rod socket 15 is provided at the center of the lower side of the control piston 14. A push rod socket 15 is fixedly installed with a pressure control section 12 through a starting shear nail 16. An upper push rod 17 is provided, and a control head 3 is provided on the lower side of the upper push rod 17. A mounting blind hole is provided in the center of the upper side of the control head 3, and a control valve stem 18 is provided in the mounting blind hole. A valve stem assembly that can make the control valve stem 18 move upward is provided on the outside of the control valve stem 18. A liquid inlet blind hole 19 that can be communicated with the lower end of the mounting blind hole is provided on the lower side of the control head 3, and a liquid outlet blind hole 20 that can be communicated with the outer side of the lower part of the mounting blind hole is provided on the lower side of the control head 3. The outer side of the upper end of the control head 3 is fixedly installed with the inner side of the lower end of the control tube 2. A hanging outer ring platform is provided on the outer side of the middle of the control head 3, and a connecting head 4 is provided on the outer side of the lower side of the control head 3 corresponding to the position below the hanging outer ring platform. An outer sleeve is fixedly installed on the outer side of the upper end of the connecting head 4 5. The inner side of the upper end of the outer sleeve 5 is provided with a suspension inner ring platform located on the upper side of the suspension outer ring platform and abutting against the lower side of the control cylinder 2. The outer side of the lower end of the connector 4 is fixedly installed with a liquid storage cylinder 6. The inner side of the lower end of the liquid storage cylinder 6 is fixedly installed with a throttling short section 7. The throttling short section 7 is provided with a throttling channel that passes through from top to bottom. A buffer pipeline 21 is fixedly connected between the liquid inlet blind hole 19 and the throttling channel. The outer side of the lower end of the throttling short section 7 is fixedly installed with a sampling cylinder 8. The inner side of the lower end of the sampling cylinder 8 is fixedly installed with an inflow short section 9. The inner side of the lower end of the inflow short section 9 is fixedly installed with a sealing short section 10. The inner side of the lower end of the sealing short section 10 is fixedly installed with a lower joint 11; the inner side of the upper end of the lower joint 11 is closed by a shear nail 23 is fixedly installed with a closing top pipe 22 whose upper end is located above it, and a receiving ring platform 24 is provided on the inner side of the lower end of the lower joint 11. A sealing locking rod 56 with its upper end located above it is provided in the sealing short section 10, and a suction hole 25 with a lower end that can be connected with the closing top pipe 22 is provided on the outer side of the upper part of the sealing locking rod 56. The sealing short section 10 is provided with a sealing locking assembly that can block the upper end of the suction hole 25 after the sealing locking rod 56 is lowered; a check valve assembly 26 is provided on the inner side of the lower part of the inflow short section 9 corresponding to the upper side position of the sealing locking rod 56, and a suction piston 28 with its lower end located on the upper side of the inflow short section 9 is provided in the sampling cylinder 8, and a pressure maintaining spring assembly 27 is provided on the upper side of the suction piston 28. During use, the present invention controls the sampling action of the sampler through the principle of thermal expansion of water vapor. It does not have electronic components, clocks and other precise mechanical mechanisms. The starting shear value is set according to the downhole temperature, thereby controlling the opening action of the sampler. The higher the temperature, the easier it is to sample, because under a certain volume, the higher the temperature, the greater the gas expansion, the higher the pressure, and the greater the shear force.As required, 15 ml of water and nitrogen at a certain pressure (2 MPa to 3 MPa, determined according to the downhole temperature) are injected into the pressure control section 12. Prefabricated liquid 53 is provided in the sampling tube 8 between the throttle nipple 7 and the suction piston 28. A hand pump is used to pump 2 MPa of pre-filled liquid or nitrogen into the sampling tube 8.

[0027] This invention uses a temperature- and pressure-controlled sampler switch, with seals made of PEEK and FFKM materials. The maximum operating temperature can reach over 220°C, meeting the sampling requirements of "three super wells" (super wells), making it a true suction-type high-temperature and high-pressure sampler. The development of this new sampler will effectively address the sampling challenges under high-temperature and high-pressure conditions, providing technical support for the accurate acquisition of high-pressure physical properties of oil and gas reservoir fluids, and is of great significance for advancing oilfield development technology.

[0028] The above-mentioned pressure-controlled suction downhole PVT sampler can be further optimized and / or improved according to actual needs: Example 2: As shown in the attached Figure 1 、 2 As shown in , 3, 4, 5, and 6, it also includes a first plug 29, a first needle valve 30, a second plug 31, a second needle valve 32, a third plug 33, a third needle valve 34 and a pressure relief plug 35. The control cylinder 2 corresponding to the lower position of the main needle valve 13 is provided with a first mounting hole and a second mounting hole on the upper outer side thereof, which can be communicated with the valve hole section. The first mounting hole and the second mounting hole are respectively provided with a first plug 29 and a first needle valve 30. The throttling short section 7 is provided with a third mounting hole and a fourth mounting hole on the middle outer side thereof, which can be communicated with the throttling channel. The third mounting hole and the fourth mounting hole are respectively provided with a second plug 31 and a second needle valve 32. The inflow short section 9 corresponding to the position above the check valve assembly 26 is provided with a fifth mounting hole and a sixth mounting hole on the upper outer side thereof, which can be communicated with the inflow short section 9. The fifth mounting hole and the sixth mounting hole are respectively provided with a third plug 33 and a third needle valve 34. The lower outer side of the connector 4 is provided with a seventh mounting hole which can be communicated with the connector 4. The seventh mounting hole is provided with a pressure relief plug 35. During use, such an arrangement facilitates the injection of gas into the pressure control section 12 and the injection of the prefabricated liquid 53 into the sampling tube 8 .

[0029] Example 3: As shown in the attached Figure 1 、 2, 3, 4, 5, and 6, it also includes an inlet throttling nozzle 36, an outlet throttling nozzle 37, an upper throttling nozzle 38, and a lower throttling nozzle 39. The inlet throttling nozzle 36 is fixedly installed on the lower side of the control head 3 corresponding to the position of the liquid inlet blind hole 19, and the outlet throttling nozzle 37 is fixedly installed on the lower side of the control head 3 corresponding to the position of the liquid outlet blind hole 20. The upper end of the throttling channel is fixedly installed with an upper throttling nozzle 38, and the lower end of the throttling channel is fixedly installed with a lower throttling nozzle 39; a buffer pipeline 21 is fixedly connected between the inlet throttling nozzle 36 and the upper throttling nozzle 38, and the buffer pipeline 21 includes an upper pipe section, a spiral coil section, and a lower pipe section that are fixedly connected together from top to bottom, and the spiral coil section is located in the liquid storage cylinder 6. During use, the inner diameter of the lower throttling nozzle can be 0.8mm, the inner diameter of the upper throttling nozzle can be 0.5mm, and the inner diameter of the outlet throttling nozzle 37 can be 0.3mm. Three-stage throttling is used to control the flow of the preset liquid in the sampling tube 8. The upper throttling nozzle and the buffer line 21 are connected by metal-to-metal sealing, with a pressure resistance of more than 180MPa. The buffer line 21 and the inlet throttling nozzle 36 are connected by metal-to-metal sealing.

[0030] Example 4: As shown in the attached Figure 1 、 2 As shown in Figures 3, 4, 5 and 6, the sealing locking assembly includes a pressure cap 40, a sealing gasket 41, a locking pin 42, a locking block 43 and a locking spring 44. A locking ring groove 55 is provided on the outer side of the lower part of the sealing locking rod 56. A sealing gasket 41 is provided between the sealing short section 10 and the sealing locking rod 56 at a position corresponding to the upper end of the suction hole 25 and the locking ring groove 55. A pressure cap 40, whose lower end abuts against the sealing gasket 41, is fixedly installed on the inner side of the upper end of the sealing short section 10; at least two locking holes are provided at intervals along the circumference on the outer side of the upper part of the sealing short section 10 corresponding to the position below the locking ring groove 55, a locking pin 42 is fixedly installed on the outer end of the locking hole, a locking block 43 is provided on the inner end of the locking hole, whose inner end abuts against the outer side of the sealing locking rod 56, and a locking spring 44 is provided in the locking hole corresponding to the position between the locking pin 42 and the locking block 43. During use, the sealing locking rod 56 moves downward to the locking block 43 and enters the locking ring groove 55, locking the sealing locking rod 56 so that it cannot move. Under the action of the pressure cap 40 and the sealing gasket 41, the suction hole 25 is blocked, the fluid channel is closed, and the locking pin 42 in the sealing short section 10 enters the card groove of the sealing locking rod 56, sealing the sample in the sampling tube 8 and completing the sampling.

[0031] Example 5: As shown in the attached Figure 1 、 2, 3, 4, 5, 6, also includes an O-ring 45, an O-ring 45 is provided between the outer side of the lower part of the main needle valve 13 and the control cylinder 2, an O-ring 45 is provided between the control piston 14 and the control cylinder 2, an O-ring 45 is provided between the lower part of the control cylinder 2 and the control head 3, an O-ring 45 is provided between the control valve stem 18 and the control head 3 at a position corresponding to the position between the upper end of the liquid inlet blind hole 19 and the upper end of the liquid outlet blind hole 20, and an O-ring 45 is provided between the lower part of the control head 3 and the connecting head 4. There is an O-ring 45. An O-ring 45 is provided between the lower part of the connector 4 and the liquid storage cylinder 6, an O-ring 45 is provided between the upper part of the throttling nipple 7 and the liquid storage cylinder 6, an O-ring 45 is provided between the lower part of the throttling nipple 7 and the sampling cylinder 8, an O-ring 45 is provided between the upper part of the inflow nipple 9 and the sampling cylinder 8, an O-ring 45 is provided between the upper part of the sealing nipple 10 and the inflow nipple 9, and an O-ring 45 is provided between the upper part of the lower joint 11 and the sealing nipple 10. During use, the provision of O-rings 45 ensures the sealing between the various components.

[0032] Example 6: As shown in the attached Figure 1 、 2 As shown in Figures 3, 4, 5, and 6, the filter assembly further includes a pressure pipe 51 and a filter screen 52. A mounting ring groove is provided on the underside of the lower joint 11, the filter screen 52 is provided at the upper end of the mounting ring groove, and the pressure pipe 51 is fixedly mounted at the lower end of the mounting ring groove. During use, the filter screen 52 can have a pore size of 100 to 120 mesh. The filter screen 52 is compressed by the pressure pipe 51 to effectively prevent underground particulate matter from clogging the inflow channel.

[0033] Example 7: As shown in the attached Figure 1 、 2 As shown in Figures 3, 4, 5, and 6, the pressure-retaining spring assembly 27 includes a spring rod and a pressure-retaining spring. The spring rod is fixedly mounted on the upper end of the suction piston 28, and a pressure-retaining spring is disposed on the outer side of the spring rod, with its upper end positioned above it. During use, when the suction piston 28 ascends to the top of the sampling cylinder 8, the pressure-retaining spring compresses, creating a reaction force that pushes the check valve assembly 26 and the sealing locking rod 56 in the inflow nipple 9 downward, shearing and closing the shear pin 23.

[0034] Example 8: As shown in the attached Figure 1 、 2 As shown in Figures 3, 4, 5, and 6, the check valve assembly 26 includes a check valve body and a return spring. A return ring is provided on the outer side of the lower end of the check valve body, and a return spring is provided on the upper side of the return ring, located outside the check valve body. During use, the return spring pushes the sealing locking rod 56 downward, shearing and closing the shear pin 23.

[0035] Example 9: As shown in the attached Figure 1 、 2As shown in Figures 3, 4, 5, and 6, a needle plug 46 and a nut 47 are also included. A fixed ring groove is provided on the upper side of the inflow nipple 9, and a nut 47 is fixedly installed in the fixed ring groove. A needle plug 46 is provided on the lower side of the suction piston 28 and inserted into the nut 47. During use, the diameter of the needle plug 46 can be 3 mm and the length can be 15 mm. The diameter of the suction piston 28 can be 27 mm, and the area ratio is 1:81. A seal is formed between the suction piston 28 and the inflow nipple 9. If the pressure in the sampling tube 8 is 1 MPa, then 81 MPa is required outside to push the piston to move. Before sampling, a pressure of 1 to 2 MPa can be preset in the sampling tube 8 according to the downhole pressure. According to needs, a magnet is provided inside the suction piston 28. After sampling, the position of the piston can be judged by the magnet to determine whether the sampling is successful.

[0036] Example 10: As shown in the attached Figure 1 、 2 As shown in Figures 3, 4, 5, and 6, the valve stem assembly includes a limit nut 48, an upper spring 49, and a lower spring 50. The limit nut 48 is fixedly installed on the inner side of the upper end of the control head 3. The control valve stem 18 is arranged in the limit nut 48. A blocking ring is arranged on the outer side of the middle part of the control valve stem 18. An upper spring 49 is arranged on the outer side of the control valve stem 18 corresponding to the position between the limit nut 48 and the blocking ring, and a lower spring 50 is arranged on the outer side of the control valve stem 18 corresponding to the position below the blocking ring. During use, the control valve stem 18 in the control head 3 moves upward under the action of the upper spring 49 and the lower spring 50, and the liquid inlet blind hole 19 is connected with the liquid outlet blind hole 20, so that the preset liquid in the sampling cylinder 8 flows into the liquid storage cylinder 6 through the throttling channel, the buffer pipeline 21, the liquid inlet blind hole 19, and the liquid outlet blind hole 20 in sequence, thereby reducing the pressure in the sampling cylinder 8.

[0037] Example 11: As shown in the attached Figure 1 、 2 As shown in Figures 3, 4, 5, and 6, a downhole PVT sampling method using the above-mentioned pressure-controlled suction downhole PVT sampler includes the following steps: (1) Before the instrument is put into the well, the downhole fluid flow pressure is tested first. According to the flow pressure value of the downhole sampling point, the initial pressure value in the pressure control section 12 is adjusted. The sampling tube 8 is filled with the preset liquid and pressurized to close the sampler. The installed and debugged sampler is placed in the blowout preventer. (2) After the instrument is put into the well and the sampler is lowered to the sampling position, the gas in the control tube 2 expands due to heat and the water vaporizes at high temperature. The control piston 14 in the control tube 2 is subjected to gradually increasing pressure. When the pressure exceeds the shear value of the starting shear pin 16, the starting shear pin 16 is sheared and the control piston 14 moves downward. (3) The control valve stem 18 in the control head 3 moves upward under the action of the valve stem assembly, and the liquid inlet blind hole 19 is connected with the liquid outlet blind hole 20, so that the preset liquid in the sampling cylinder 8 flows into the liquid storage cylinder 6 through the throttling channel, the buffer line 21, the liquid inlet blind hole 19 and the liquid outlet blind hole 20 in sequence, thereby reducing the pressure in the sampling cylinder 8; (4) The suction piston 28 moves upward under the action of the downhole high-pressure fluid, sucking the downhole fluid from bottom to top through the lower joint 11, the sealing short section 10 and the check valve assembly 26 in the inflow short section 9 into the sampling tube 8; (5) After the suction piston 28 moves upward to the top of the sampling tube 8, the pressure-maintaining spring assembly 27 is compressed to form a reaction force, which pushes the check valve assembly 26 and the sealing locking rod 56 in the inflow short section 9 downward, shearing and closing the shear pin 23; (6) The sealing locking rod 56 moves downward to the locking block 43 and enters the locking ring groove 55, locking the sealing locking rod 56 so that it cannot move. Under the action of the pressure cap 40 and the sealing gasket 41, the suction hole 25 is blocked, the fluid channel is closed, and the locking pin 42 in the sealing short section 10 enters the card groove of the sealing locking rod 56, sealing the sample in the sampling tube 8, and completing the sampling.

[0038] During use, the initial pressure value in the sampler pressure control section 12 and the size of the starting pin in step (1) can be determined based on ground test data. The ground test sampler opening test: ① Using a 2.0mm pin, the initial pressure value is from 2.5MPa to 3.5MPa, increasing by 0.5MPa each time, heating from 100℃ to 180℃, increasing by 5℃ each time, and heating for more than 30 minutes for each 5℃ increase (for example, if it is not opened after heating at 100℃ for 30 minutes, heat it to 105℃ and continue heating for 30 minutes, and heat it sequentially); ② Using a 1.5mm pin, the initial pressure value is from 2.0MPa to 3.0MPa, increasing by 0.5MPa each time, heating from 100℃ to 180℃, increasing by 5℃ each time, and heating for more than 30 minutes for each 5℃ increase; record each test value and draw it into a table. After ground tests, the following design requirements can be adopted: the initial pressure in the control tube 2 is 1.7MPa, and a 1.5mm copper pin is used. When heated to 150℃, the pin is sheared within 15 minutes and the sampler is opened; the initial pressure in the control tube 2 is 2.7MPa, and a 1.5mm copper pin is used. When heated to 110℃, the pin is sheared within 15 minutes and the sampler is opened; the initial pressure in the control tube 2 is 3.0MPa, and a 2.0mm copper pin is used. When heated to 180℃, the pin is sheared within 15 minutes and the sampler is opened.

[0039] Example 12: As shown in the attached Figure 1 、 2 , 3, 4, 5, 6, the best embodiment of the present invention can be designed as follows: (1) The lower end of the lower joint 11 is conical, and a threaded buckle and a pressure tube 51 connected to the nut 47 are provided at the bottom. A filter screen 52 is installed on the upper side of the pressure tube 51. The pressure tube 51 has a hole in the middle, and a through hole is formed upward from the top of the threaded buckle. There is a through hole from the bottom of the through hole to the top of the lower joint 11. A pin hole is provided at the lower end of the top of the lower joint 11, and is connected to the closing top tube 22 through a closing shear pin 23. A sealing O-ring groove is provided below the pin hole to install the O-ring 45. (2) The sealing locking rod 56 is a round T-shaped structure, and the locking ring groove is designed with an annular groove. There is a suction hole 25 at the bottom of the sealing locking rod 56. The suction hole 25 is inserted into the body of the sealing short section 10, and the bottom sits on the pressure tube 51. The sealing gasket 41 (O-ring 45) is used to seal it with the sealing short section 10. A gasket is installed on the top and is pressed with a pressure cap 40 to prevent the sealing gasket 41 from withdrawing. A seal can also be formed between the sealing locking rod 56 and the gasket; (3) A fixed ring groove is provided on the upper end of the inflow nipple 9 to install a nut 47 to form a sealed cavity, which is sealed with a needle plug 46 inserted into the nut 47 on the lower side of the sampling tube 8 suction piston 28, and an O-ring 45 is provided. The one-flow valve assembly 26 is divided into a one-flow valve body, a one-flow valve core, a one-flow pressure cap, and a one-flow spring. The one-flow valve body is larger at the bottom and smaller at the top (inverted T shape). A sealing ring groove is provided on the lower side of the one-flow valve body, and an O-ring 45 is used to seal the inflow nipple 9. Sealing, the through hole at the bottom of the one-flow valve body is a cone surface upwards, with through holes on both sides and an axial through hole upwards. The top is designed with a threaded connection to the one-flow pressure cap. The one-flow valve core is a cone with a sealing ring groove in the middle. The upper part of the cone is a thin rod that can be inserted into the one-flow spring. The side of the one-flow pressure cap is threaded, with a through hole in the middle and a thin rod at the bottom that can be inserted into the one-flow spring. The one-flow valve core, the one-flow spring and the one-flow pressure cap form a whole with the one-flow valve body to form a well-sealed one-flow valve; (4) The suction piston 28 is designed with two O-rings 45 and a back ring at intervals above and below, which fits tightly with the sampling tube 8. The ratio of the cross-sectional area of ​​the needle plug 46 to the cross-sectional area of ​​the suction piston 28 is 1:81. The needle plug 46 is inserted into the nut 47 and sealed with the O-ring 45. When a pressure of 1MPa is applied inside the sampling tube 8, 81MPa is required outside to push the suction piston 28, so that it can withstand higher pressure. A circular hole is designed inside the suction piston 28, and a magnet can be placed in the circular hole. A threaded buckle is designed at the front end of the circular hole to connect with the spring rod. After the sampler takes a sample, the magnet can be used to judge the position of the suction piston 28 outside the sampling tube 8 to judge whether the sampling is successful or not. (5) The throttling nipple 7 is connected to the upper throttling nozzle 38 and the lower throttling nozzle 39 by threads. The upper throttling nozzle 38 and the lower throttling nozzle 39 are sealed with an O-ring 45. The step-by-step throttling method is adopted. The valve stem of the second needle valve 32 is sealed with an O-ring 45 and a back ring. (6) Both ends of the buffer pipeline 21 are sealed with a high temperature and high pressure resistant metal-to-metal sealing method, and two O-rings 45 are provided at the bottom of the connector 4; (7) The liquid inlet blind hole 19 and the buffer pipeline 21 are connected by metal sealing. The liquid outlet blind hole 20 is installed with a throttle nozzle. The bottom of the installation blind hole is a lower round hole. The bottom of the lower round hole is connected to the liquid inlet blind hole 19. The bottom of the lower round hole is upwardly connected to the liquid outlet blind hole 20. The bottom of the lower round hole is upwardly connected to the middle round hole. The transition section between the middle round hole and the lower round hole is chamfered to facilitate the installation of the control valve stem 18 with the O-ring 45. The upper round hole above the middle round hole is a nut thread. A sealing ring groove is set at the lower part of the control valve stem 18, and a sealing ring groove is designed in the middle. The diameters of the other parts are the same; (8) The control cylinder 2 and the valve stem of the main needle valve 13 are sealed with an O-ring 45. Pin holes are designed on the front and rear sides of the lower end of the control piston 14. Slots are cut on the opposite sides from the top of the pin holes on both sides to the piston root to prevent the ejector rod from shearing off the pin and getting stuck in the piston. (9) The inflow nipple 9, sampling tube 8 and liquid storage tube 6 are connected by a buckle type.

[0040] Example 13: As shown in the attached Figure 1 、 2 As shown in Figures 3, 4, 5, and 6, the installation method of the best embodiment of the present invention can be: (1) Assemble the lower joint 11: Install the filter screen 52 in the mounting ring groove of the lower joint 11, and tighten the pressing tube 51. Flatten one end of the closing shear pin 23 and insert it into the pin hole of the lower joint 11. Insert the closing top pipe 22 into the lower joint 11. Pass the closing shear pin 23 through the pin hole of the closing top pipe 22. Fix the closing top pipe 22 on the lower joint 11. Install the O-ring 45 in the lower joint 11. (2) Assemble the sealing nipple 10: Screw the lower joint 11 to the inner side of the lower part of the sealing nipple 10 and tighten it. Install the sealing gasket 41 on the upper end of the sealing nipple 10 and press it with the pressure cap 40. Insert the sealing locking rod 56 into the sealing nipple 10 and push it onto the lower closing top pipe 22. Install the locking pin 42, locking block 43 and locking spring 44 on both sides of the sealing nipple 10. (3) Assemble the inflow subsection 9: Install the third plug 33 and the third needle valve 34 in the fifth mounting hole and the sixth mounting hole respectively and tighten them, assemble the check valve assembly 26, install the check valve assembly 26 into the inflow subsection 9, install the O-ring 45, gasket and nut 47 between the upper end of the inflow subsection 9 and the suction piston 28 in sequence, and install the upper part of the sealing subsection 10 into the inflow subsection 9; (4) Assemble the sampling tube 8: Install the O-ring 45 and the back ring on the suction piston 28, install the spring rod on the top of the suction piston 28, put the pressure-holding spring on the spring rod, install the check valve assembly 26 and the pressure-holding spring into the inflow short section 9, and then insert the front end of the piston into the front end of the inflow short section 9. Push the suction piston 28 into the sampling tube 8, insert the needle plug 46 set at the bottom of the suction piston 28 into the nut 47 set at the top of the inflow short section 9, and install the upper part of the inflow short section 9 into the sampling tube 8; (5) Assemble the throttle nipple 7: Put the O-ring 45 on the lower throttle nozzle, which is installed at the lower end of the throttle nipple 7. Put the O-ring 45 on the upper throttle nozzle, which is installed at the upper end of the throttle nipple 7 and connected to the upper end of the buffer line 21. Install the second plug 31 and the second needle valve 32 in the third mounting hole and the fourth mounting hole respectively and tighten them. Install the sampling tube 8 on the outer side of the lower end of the throttle nipple 7. (6) Assemble the control head 3: Connect the control head interface (inlet throttle nozzle 36) at the lower end of the control head 3 to the upper end of the buffer line 21, screw and tighten the throttle nozzle on the port (outlet throttle nozzle 37) at the lower end of the control head 3, install and tighten the throttle nozzle, insert the spring into the control valve stem 18 from the bottom, install the two O-rings 45 on the control valve stem 18, push the control valve stem 18 into the control head 3, install the limit nut 48, and install the outer sleeve 5; (7) Assemble the control cylinder 2: Install the O-ring 45 on the outside of the control piston 14, select the appropriate starting shear pin 16 according to the downhole temperature, install the control piston 14 and the upper push rod 17 together, push the control piston 14 and the upper push rod 17 into the control cylinder 2, connect the control cylinder 2 to the control head 3 and tighten it, install the first plug 29 and the first needle valve 30 in the first mounting hole and the second mounting hole respectively and tighten them.

[0041] The above technical features constitute the best embodiment of the present invention, which has strong adaptability and best implementation effect. Non-essential technical features can be added or removed according to actual needs to meet the requirements of different situations.

Claims

1. A pressure-controlled suction downhole PVT sampler, characterized in that It includes an upper joint, a control cylinder, a control head, a connecting head, an outer sleeve, a liquid storage cylinder, a throttling short section, a sampling cylinder, an inflow short section, a sealing short section and a lower joint. The control cylinder is fixedly installed on the inner side of the lower end of the upper joint. The control cylinder is provided with a valve hole section, a pressure control section, a piston section and a connecting section which are connected in sequence from top to bottom and have increasing inner diameters. The valve control section is provided with a main needle valve. The inner side of the upper end of the piston section is provided with a control piston. The center of the lower side of the control piston is provided with a push rod socket. An upper push rod is fixedly installed in the push rod socket by starting shear nails. A control head is provided on the lower side of the upper push rod. A mounting blind hole is provided in the center of the side, a control valve stem is provided in the mounting blind hole, a valve stem assembly that can make the control valve stem move upward is provided on the outside of the control valve stem, a liquid inlet blind hole that can be communicated with the lower end of the mounting blind hole is provided on the lower side of the control head, a liquid outlet blind hole that can be communicated with the outer side of the lower part of the mounting blind hole is provided on the lower side of the control head, the outer side of the upper end of the control head is fixedly installed with the inner side of the lower end of the control tube, a hanging outer ring platform is provided on the outer side of the lower side of the control head corresponding to the position below the hanging outer ring platform, an outer sleeve is fixedly installed on the outer side of the upper end of the connecting head, and the inner side of the upper end of the outer sleeve A suspension inner ring platform is provided which is located on the upper side of the suspension outer ring platform and abuts against the lower side of the control cylinder. A liquid storage cylinder is fixedly installed on the outer side of the lower end of the connector, a throttling nipple is fixedly installed on the inner side of the lower end of the liquid storage cylinder, a throttling passage which runs through the upper and lower ends is provided on the throttling nipple, a buffer pipeline is fixedly connected between the liquid inlet blind hole and the throttling passage, a sampling cylinder is fixedly installed on the outer side of the lower end of the throttling nipple, an inflow nipple is fixedly installed on the inner side of the lower end of the sampling cylinder, a sealing nipple is fixedly installed on the inner side of the lower end of the inflow nipple, and a lower joint is fixedly installed on the inner side of the lower end of the sealing nipple; the inner side of the upper end of the lower joint is closed by a valve. The shear nails are fixedly installed with a closing top pipe whose upper end is located above it, and a receiving ring is provided on the inner side of the lower end of the lower joint. A sealing locking rod is provided in the sealing nipple, and a suction hole is provided at the lower end of the sealing locking rod. The sealing nipple is provided with a sealing locking assembly that can block the upper end of the suction hole after the sealing locking rod is lowered; a check valve assembly is provided on the inner side of the lower part of the inflow nipple corresponding to the upper side of the sealing locking rod, and a suction piston is provided in the sampling cylinder, and a pressure-maintaining spring assembly is provided on the upper side of the suction piston.

2. The pressure-controlled suction downhole PVT sampler according to claim 1, characterized in that It also includes a first plug, a first needle valve, a second plug, a second needle valve, a third plug, a third needle valve and a pressure relief plug. The outer side of the upper part of the control cylinder corresponding to the lower position of the main needle valve is provided with a first mounting hole and a second mounting hole that can be communicated with the valve hole section, and the first mounting hole and the second mounting hole are respectively provided with a first plug and a first needle valve. The outer side of the middle part of the throttling short section is provided with a third mounting hole and a fourth mounting hole that can be communicated with the throttling channel, and the third mounting hole and the fourth mounting hole are respectively provided with a second plug and a second needle valve. The outer side of the upper part of the inflow short section corresponding to the position above the one-flow valve assembly is provided with a fifth mounting hole and a sixth mounting hole that can be communicated with the inflow short section, and the fifth mounting hole and the sixth mounting hole are respectively provided with a third plug and a third needle valve. The outer side of the lower part of the connecting head is provided with a seventh mounting hole that can be communicated with the inside of the connecting head, and the seventh mounting hole is provided with a pressure relief plug.

3. The pressure-controlled suction downhole PVT sampler according to claim 1 or 2, characterized in that It also includes an inlet throttling nozzle, an outlet throttling nozzle, an upper throttling nozzle and a lower throttling nozzle. The inlet throttling nozzle is fixedly installed on the lower side of the control head corresponding to the liquid inlet blind hole position, the outlet throttling nozzle is fixedly installed on the lower side of the control head corresponding to the liquid outlet blind hole position, the upper throttling nozzle is fixedly installed at the upper end of the throttling channel, and the lower throttling nozzle is fixedly installed at the lower end of the throttling channel; a buffer pipeline is fixedly connected between the inlet throttling nozzle and the upper throttling nozzle, and the buffer pipeline includes an upper pipe section, a spiral coil section and a lower pipe section that are fixedly connected together from top to bottom, and the spiral coil section is located in the liquid storage cylinder.

4. The pressure-controlled suction downhole PVT sampler according to claim 1 or 2, characterized in that The sealing locking assembly includes a pressure cap, a sealing gasket, a locking pin, a locking block and a locking spring. A locking ring groove is provided on the outer side of the lower part of the sealing locking rod. A sealing gasket is provided between the sealing short section and the sealing locking rod at a position corresponding to the upper end of the suction hole and the locking ring groove. A pressure cap, the lower end of which is against the sealing gasket, is fixedly installed on the inner side of the upper end of the sealing short section; at least two locking holes are provided along the circumferential interval on the outer side of the upper part of the sealing short section corresponding to the position below the locking ring groove, a locking pin is fixedly installed on the outer end of the locking hole, a locking block is provided at the inner end of the locking hole, the inner end of the locking hole is against the outer side of the sealing locking rod, and a locking spring is provided in the locking hole corresponding to the position between the locking pin and the locking block.

5. The pressure-controlled suction downhole PVT sampler according to claim 3, characterized in that The sealing locking assembly includes a pressure cap, a sealing gasket, a locking pin, a locking block and a locking spring. A locking ring groove is provided on the outer side of the lower part of the sealing locking rod. A sealing gasket is provided between the sealing short section and the sealing locking rod at a position corresponding to the upper end of the suction hole and the locking ring groove. A pressure cap, the lower end of which is against the sealing gasket, is fixedly installed on the inner side of the upper end of the sealing short section; at least two locking holes are provided along the circumferential interval on the outer side of the upper part of the sealing short section corresponding to the position below the locking ring groove, a locking pin is fixedly installed on the outer end of the locking hole, a locking block is provided at the inner end of the locking hole, the inner end of the locking hole is against the outer side of the sealing locking rod, and a locking spring is provided in the locking hole corresponding to the position between the locking pin and the locking block.

6. The pressure-controlled suction downhole PVT sampler according to claim 1, 2 or 5, characterized in that It also includes an O-ring, an O-ring is provided between the outer side of the lower part of the main needle valve and the control cylinder, an O-ring is provided between the control piston and the control cylinder, an O-ring is provided between the lower part of the control cylinder and the control head, an O-ring is provided between the control valve stem corresponding to the position between the upper end of the liquid inlet blind hole and the upper end of the liquid outlet blind hole and the control head, an O-ring is provided between the lower part of the control head and the connecting head, an O-ring is provided between the lower part of the connecting head and the liquid storage cylinder, an O-ring is provided between the upper part of the throttling short section and the liquid storage cylinder, an O-ring is provided between the lower part of the throttling short section and the sampling cylinder, an O-ring is provided between the upper part of the inflow short section and the sampling cylinder, an O-ring is provided between the upper part of the sealing short section and the inflow short section, and an O-ring is provided between the upper part of the lower joint and the sealing short section.

7. The pressure-controlled suction downhole PVT sampler according to claim 3, characterized in that It also includes an O-ring, an O-ring is provided between the outer side of the lower part of the main needle valve and the control cylinder, an O-ring is provided between the control piston and the control cylinder, an O-ring is provided between the lower part of the control cylinder and the control head, an O-ring is provided between the control valve stem corresponding to the position between the upper end of the liquid inlet blind hole and the upper end of the liquid outlet blind hole and the control head, an O-ring is provided between the lower part of the control head and the connecting head, an O-ring is provided between the lower part of the connecting head and the liquid storage cylinder, an O-ring is provided between the upper part of the throttling short section and the liquid storage cylinder, an O-ring is provided between the lower part of the throttling short section and the sampling cylinder, an O-ring is provided between the upper part of the inflow short section and the sampling cylinder, an O-ring is provided between the upper part of the sealing short section and the inflow short section, and an O-ring is provided between the upper part of the lower joint and the sealing short section.

8. The pressure-controlled suction downhole PVT sampler according to claim 4, characterized in that It also includes an O-ring, an O-ring is provided between the outer side of the lower part of the main needle valve and the control cylinder, an O-ring is provided between the control piston and the control cylinder, an O-ring is provided between the lower part of the control cylinder and the control head, an O-ring is provided between the control valve stem corresponding to the position between the upper end of the liquid inlet blind hole and the upper end of the liquid outlet blind hole and the control head, an O-ring is provided between the lower part of the control head and the connecting head, an O-ring is provided between the lower part of the connecting head and the liquid storage cylinder, an O-ring is provided between the upper part of the throttling short section and the liquid storage cylinder, an O-ring is provided between the lower part of the throttling short section and the sampling cylinder, an O-ring is provided between the upper part of the inflow short section and the sampling cylinder, an O-ring is provided between the upper part of the sealing short section and the inflow short section, and an O-ring is provided between the upper part of the lower joint and the sealing short section.

9. The pressure-controlled suction downhole PVT sampler according to claim 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9, characterized in that It also includes a filter assembly, which includes a pressure pipe and a filter screen, a mounting ring groove is provided on the lower side of the lower joint, a filter screen is provided on the upper end of the mounting ring groove, and a pressure pipe is fixedly installed on the lower end of the mounting ring groove; or / and, a pressure-maintaining spring assembly includes a spring rod and a pressure-maintaining spring, a spring rod is fixedly installed on the upper end of the suction piston, and a pressure-maintaining spring is provided on the outer side of the spring rod with the upper end located above the spring rod; or / and, a check valve assembly includes a check valve body and a reset spring, a reset ring platform is provided on the outer side of the lower end of the check valve body, and a reset spring is provided on the upper side of the reset ring platform and is located on the outer side of the check valve body; or / and, also includes a needle plug and a nut, a fixed ring groove is provided on the upper side of the inflow short section, a nut is fixedly installed in the fixed ring groove, and a needle plug is provided on the lower side of the suction piston and inserted into the nut; or / and, the valve stem assembly includes a limit nut, an upper spring and a lower spring, a limit nut is fixedly installed on the inner side of the upper end of the control head, a control valve stem is provided in the limit nut, a blocking ring is provided on the outer side of the middle part of the control valve stem, an upper spring is provided on the outer side of the control valve stem corresponding to the position between the limit nut and the blocking ring, and a lower spring is provided on the outer side of the control valve stem corresponding to the position below the blocking ring.

10. A downhole PVT sampling method using a pressure-controlled suction downhole PVT sampler as claimed in claims 4 to 9, characterized in that The steps are as follows: (1) Before the instrument is put into the well, the downhole fluid flow pressure is tested first. According to the flow pressure value of the downhole sampling point, the initial pressure value in the pressure control section is adjusted. The sampling tube is injected with the preset liquid and pressurized. The sampler is in the closed state. The installed and debugged sampler is placed in the blowout preventer. (2) After the instrument is put into the well and the sampler is lowered to the sampling position, the gas in the control cylinder expands due to heat and the water vaporizes at high temperature. The pressure on the control piston in the control cylinder gradually increases. When the pressure exceeds the shear value of the starting shear pin, the starting shear pin is cut off and the control piston moves downward. (3) The control valve stem in the control head moves upward under the action of the valve stem assembly, and the liquid inlet blind hole is connected with the liquid outlet blind hole, so that the preset liquid in the sampling cylinder flows into the liquid storage cylinder through the throttling channel, the buffer pipeline, the liquid inlet blind hole and the liquid outlet blind hole in sequence, thereby reducing the pressure in the sampling cylinder; (4) The suction piston moves upward under the action of the downhole high-pressure fluid, sucking the downhole fluid from bottom to top through the lower joint, the sealing nipple and the check valve assembly in the inflow nipple into the sampling tube; (5) After the suction piston moves up to the top of the sampling tube, the pressure-maintaining spring assembly is compressed to form a reaction force, which pushes the check valve assembly and the sealing locking rod in the inflow short section downward, shearing off the shear pin; (6) The sealing locking rod moves downward to the locking block and enters the locking ring groove, locking the sealing locking rod so that it cannot move. Under the action of the pressure cap and the sealing gasket, the suction hole is blocked, the fluid channel is closed, and the locking pin in the sealing short section enters the slot of the sealing locking rod, sealing the sample in the sampling tube and completing the sampling.

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