Pressure test device and test method for seabed drilling rig pressure-maintaining coring drill

Abstract

The present invention discloses a pressure test device and an experimental method suitable for a seabed drilling rig pressure coring drill, the device includes a hydraulic pump, a reversing valve, a pressure test chamber, a pressure cap screwing and unscrewing device, a pressure cap, a support frame and a temperature control device; flange cover I and flange cover II are respectively installed at both ends of the pressure test chamber, and a water inlet and a drain are respectively provided at both ends of the side wall of the pressure test chamber; the pressure cap screwing and unscrewing device includes a hydraulic motor, a screwing and unscrewing shaft and a pressure cap screwing and unscrewing head; the pressure cap is installed at one end of the inner tube of the drilling tool facing the hydraulic motor, and the pressure cap screwing and unscrewing device can achieve the sealing of the pressure cap and the inner tube of the drilling tool; the temperature control device includes a thermometer, a heating rod and a disc, the thermometer is installed on the support frame, and the temperature control device is electrically connected to the temperature controller. The present invention has a simple structure and is easy to operate. It can truly simulate the temperature and pressure changes of seawater during the salvage process of the drilling tool at any water depth, and can also truly simulate the changes in the internal pressure of the drilling tool during the lifting process.

Description

Technical Field

[0001] The invention relates to a pressure testing device and an experimental method suitable for a pressure-maintaining coring drill tool of a seabed drilling rig. Background Art

[0002] Natural gas hydrates exist in solid form under low temperature and high pressure. At present, the main method of natural gas hydrate exploration at home and abroad is pressure-maintaining sampling. When using a seabed drilling rig for exploration operations, the pressure-maintaining inner tubes that have completed the coring must be temporarily stored in the drill tool warehouse of the seabed drilling rig, and then recovered to the deck of the mother ship together with the seabed drilling rig after the entire drilling is completed. As a heavy underwater operation equipment, the seabed drilling rig has strict regulatory requirements for the recovery operation process. Compared with the traditional drilling ship sampling method of quickly lifting a single pressure-maintaining inner tube from the bottom of the hole to the deck of the mother ship through a salvage device, the pressure-maintaining inner tube stored in the seabed drilling rig's drill tool warehouse takes significantly longer time to pass through different seawater temperature ranges than the traditional drilling ship sampling method. Therefore, higher requirements are placed on the pressure-maintaining performance of the small-diameter, thin-walled pressure-maintaining drill tools matched with the seabed drilling rig.

[0003] The existing process flow of pressure-maintaining coring drilling for seabed drilling rigs is to place an empty pressure-maintaining rope coring inner tube without a pressure-maintaining sealing cover into the pressure-maintaining coring outer tube drilling tool, and pre-store a pressure-maintaining sealing cover in the pressure-maintaining sealing cover screwing and unscrewing mechanism on the seabed drilling rig. After the drilling is completed, the salvage winch is used to lower the salvage device, and the pressure-maintaining coring inner tube with the core is salvaged to the seabed drilling rig. The pressure-maintaining rope coring inner tube with the core is moved to the top of the pressure-maintaining sealing cover unscrewing mechanism by a manipulator, and the pressure-maintaining sealing cover is tightened together with the pressure-maintaining coring inner tube to complete the sealing of the lower end of the pressure-maintaining coring inner tube. A blind hole is provided at one end of the pressure-maintaining cap, and a hooked fork is provided at the other end of the pressure-maintaining cap. An annular sealing groove is provided in the middle of the blind hole for installing a Y-type sealing ring; the blind hole is provided with an internal thread for connecting with the inner tube of the drilling tool. The sealing of the upper end of the pressure-maintaining drilling tool is achieved by a one-way valve inside the drilling tool. Although the existing indoor pressure test equipment can simulate the environmental pressure at different seawater depths, it is impossible to complete the unscrewing and unscrewing of the pressure cap of the drill bit in the pressure chamber. And it is impossible to effectively simulate the temperature changes in different seawater intervals during the experiment. In addition, due to the large size of the existing pressure test equipment, its experimental efficiency is obviously low, and it cannot meet the pressure performance test requirements of small-diameter thin-walled pressure-maintaining drill bits. Summary of the invention

[0004] In order to solve the above-mentioned problems, the present invention provides a pressure test device and an experimental method which are simple in structure, easy to operate, can realistically simulate the changes in seawater temperature and pressure during the recovery of drilling tools at any water depth, and can also realistically simulate the changes in internal pressure of the drill pipe during the lifting process.

[0005] The technical solution adopted by the present invention is: a pressure test device suitable for seabed drilling rig pressure-maintaining coring drilling tools, including a hydraulic pump, a reversing valve, a pressure testing chamber, a pressure-maintaining cap unscrewing device, a pressure-maintaining cap, a support frame and a temperature control device; the pressure testing chamber is a tubular structure, and flange cover I and flange cover II are respectively installed at its two ends, and a water inlet and a water outlet are respectively arranged at the two ends of the side wall of the pressure testing chamber; the pressure-maintaining cap unscrewing device includes a hydraulic motor, an unscrewing shaft and a pressure-maintaining cap unscrewing head, the hydraulic motor is installed in the pressure testing chamber through a disc bracket, and the two oil ports of the hydraulic motor are respectively connected to the oil outlet hole of the reversing valve through pipelines; the oil inlet of the hydraulic pump and the oil return hole of the reversing valve are respectively connected through pipelines The oil tank and the oil outlet of the hydraulic pump are connected to the oil inlet hole of the reversing valve through a pipeline; the output shaft of the hydraulic motor is connected to one end of the unscrewing shaft, and the pressure-maintaining cap unscrewing head is installed at the other end of the unscrewing shaft; the pressure-maintaining cap is installed at the end of the drill tool inner tube facing the hydraulic motor, and the unscrewing head can achieve the sealing of the pressure-maintaining cap and the drill tool inner tube; the drill tool inner tube is supported on a support frame through multiple fixing devices, and the support frame is arranged in the pressure test chamber and is coaxial with the pressure test chamber; the temperature control device includes a thermometer, a heating rod and a disc, the thermometer is installed on the support frame, the heating rod is fixed on the disc, the disc is fixed in the pressure test chamber, and the temperature control device is electrically connected to the temperature controller; the pressure test chamber is provided with a pressurizing device and a pressure relief device.

[0006] In the above-mentioned pressure test device suitable for seabed drilling rig pressure-maintaining coring drill tools, the disc bracket is connected to the flange cover I through a threaded connecting rod; the flange cover I is provided with three through holes, and two ends of two through holes are respectively provided with a hydraulic straight joint; the two oil ports of the hydraulic motor are respectively connected to the hydraulic straight joints at the inner ends of the two through holes through pipelines, and the hydraulic straight joints at the outer ends of the two through holes are respectively connected to the two oil outlet holes of the reversing valve through pipelines; the flange cover II is provided with a through hole, and a watertight connector is provided in the through hole, the inner end of the watertight connector is electrically connected to the temperature control device, and the outer end of the watertight connector is electrically connected to the temperature controller; the inner end of the other through hole is provided with a hydraulic straight joint, and the hydraulic straight joint is connected to the oil drain port of the hydraulic motor through a pipeline, and the other through hole is connected to the oil tank through the oil drain pipeline.

[0007] In the above-mentioned pressure testing device suitable for seabed drilling rig pressure-maintaining coring drill tools, a spline is provided at the end of the unscrewing shaft facing away from the hydraulic motor, a blind hole is provided at one end of the pressure-maintaining cap unscrewing head facing the unscrewing shaft, a spline groove is provided on the inner side of the blind hole, and the end of the unscrewing shaft facing away from the hydraulic motor is installed in the blind hole of the pressure-maintaining cap unscrewing head and connected by a spline; the bottom of the blind hole is connected to the end of the unscrewing shaft by a spring; a plurality of shift forks are provided on the end face of the pressure-maintaining cap unscrewing head; a blind hole is provided on the end face of the pressure-maintaining cap facing away from the hydraulic motor, an annular sealing groove is provided in the middle of the side wall of the blind hole, and a Y-shaped sealing ring is installed in the sealing groove; a hooked shift fork is provided on the end face of the pressure-maintaining cap facing the hydraulic motor, and the hooked shift fork cooperates with the shift fork on the end face of the pressure-maintaining cap unscrewing head; the blind hole is provided with an internal thread for threaded connection with the inner tube of the drilling tool.

[0008] In the above-mentioned pressure testing device suitable for seabed drilling rig pressure-maintaining coring drill tools, the support frame includes multiple support discs and multiple connecting rods, the multiple support discs are coaxially arranged, a through hole is provided at the center of the support disc, a sliding bearing is installed in the through hole, and a plurality of arc-shaped through holes and a plurality of threaded holes are provided on the support disc. The plurality of arc-shaped through holes are evenly arranged along the circumferential direction, and the plurality of threaded holes are also evenly arranged along the circumferential direction; the two ends of the connecting rod are respectively connected to the two coaxial threaded holes of two adjacent support discs; the plurality of connecting rods are evenly arranged along the circumferential direction; the inner tube of the drill tool is supported by the sliding bearings at the centers of the plurality of support discs.

[0009] In the above-mentioned pressure testing device suitable for seabed drilling rig pressure-maintaining coring drill tools, the fixing device includes a circular ring bracket, an arc-shaped chuck and a threaded push rod. The circular ring bracket is installed on a supporting disc. The concave arc surface of the arc-shaped chuck contacts the outer side surface of the inner tube of the drill tool, and the inner end of the threaded push rod contacts the back side of the arc-shaped chuck. The threaded push rod is installed on the circular ring bracket.

[0010] The above-mentioned pressure test device suitable for seabed drilling rig pressure-maintaining coring drill tools also includes a pressure gauge, and the pressurizing device includes a pressure pump and a liquid inlet pipe; the pressure relief device includes a pressure relief pipe and a pressure relief valve; three pipe joint through holes are provided on the flange cover II, the outer end of one pipe joint through hole is connected to the pressure relief pipe through a hydraulic straight joint, and the pressure relief pipe is provided with a pressure relief valve, the outer end of another pipe joint through hole is connected to one end of the liquid inlet pipe through a hydraulic straight joint, and the other end of the liquid inlet pipe is connected to the outlet of the pressure pump, and the inlet of the pressure pump is connected to the water tank through a pipe; a hydraulic straight joint is provided at each end of the third pipe joint through hole, and the two hydraulic straight joints are respectively connected to the inner pipe of the drilling tool and the pressure gauge through a pipe.

[0011] A pressure testing method for a seabed drilling rig pressure-maintaining coring drill tool using the pressure testing device for seabed drilling rig pressure-maintaining coring drill tool comprises the following steps:

[0012] Step 1: Assemble the support frame, place the drill tool inner tube and the pressure-maintaining cap in the support frame, and pre-assemble the pressure-maintaining cap and the drill tool inner tube; after the pre-assembly is completed, fix the drill tool inner tube with the help of a fixing device; put the fixed drill tool inner tube and the support frame into the pressure test chamber together; connect the disc with the heating device to the flange cover II, and install the flange cover II at one end of the pressure test chamber by bolts; install the hydraulic motor on the disc bracket, connect the two oil pipes to the two oil ports of the hydraulic motor, install the unscrewing shaft and unscrewing head, and connect the flange cover I to the other end of the pressure test chamber by bolts;

[0013] Step 2: Inject cold water into the pressure test chamber through the water inlet. The water temperature is selected with reference to the seawater temperature at the depth of the seabed natural gas hydrate reservoir. After the water injection is completed, exhaust gas is discharged and the water inlet is blocked;

[0014] Step 3: According to the experimental requirements, uniformly pressurize the pressure test chamber, with a pressurization range of 5 - 40Mpa and a pressurization rate of 0.2-0.6 Mpa / min;

[0015] Step 4: Use a thermometer to check whether the actual water temperature in the pressure test chamber is consistent with the ambient water temperature required by the experiment. If it is lower than the ambient water temperature required by the experiment, start the heating device to heat the water temperature in the pressure test chamber to the water temperature required by the experiment; if the water temperature in the pressure test chamber is consistent with the experimental requirements, proceed directly to step 5;

[0016] Step 5: Start the hydraulic motor to drive the screwing head to rotate to complete the sealing action between the pressure retaining cover and the inner tube of the drilling tool;

[0017] Step 6: Release the pressure in the pressure test chamber to simulate the process of continuous reduction of external environmental pressure during the recovery of the drilling tool; the rate of decrease of the pressure in the test chamber should be consistent with the recovery speed of the drilling tool in actual construction operations;

[0018] Step 7: Start the heating device to heat the seawater in the pressure test chamber during the depressurization process to simulate the change in water temperature when the drill tool passes through seawater layers of different depths during the recovery process. The heating rate is determined according to the residence time of the drill tool in seawater layers of different temperature ranges during the recovery process. The maximum water temperature does not exceed 40°C.

[0019] Step 8: By observing the pressure gauge connected to the inside of the drill pipe of the drill tool, record the pressure changes inside the drill pipe of the drill tool during the entire recovery process;

[0020] Step 9: After the pressure relief is completed, open the drain port of the pressure test chamber to drain the water in the pressure test chamber;

[0021] Step 10: Repeat Step 2 to Step 9 several times.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The invention has a simple structure and is easy to operate. It can truly simulate the temperature and pressure changes of seawater during the salvage process of the drilling tool at any water depth, and can also truly simulate the changes in the internal pressure of the drilling tool during the lifting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the present invention.

[0025] Figure 2It is a structural schematic diagram of the support assembly of the present invention.

[0026] Figure 3 It is a structural schematic diagram of the fixing device of the present invention.

[0027] Figure 4 It is a structural schematic diagram of the flange cover I of the present invention.

[0028] Figure 5 It is a structural schematic diagram of the flange cover II of the present invention.

[0029] Figure 6 It is a structural schematic diagram of the support disc of the present invention.

[0030] Figure 7 It is a structural schematic diagram of a disc of the present invention.

[0031] Figure 8 It is a structural schematic diagram of a pressure-maintaining cap unscrewing head of the present invention.

[0032] Fig. 9 It is a schematic structural diagram of the pressure-maintaining cap of the present invention.

[0033] Fig.10 It is a cross-sectional view of the pressure retaining cap of the present invention.

[0034] In the figure: 1-hydraulic pump, 2-reversing valve, 3-flange cover I, 4-pressure test chamber, 5-hydraulic straight joint, 6-hydraulic motor, 7-pressure retaining cap screwing and removing device, 8-pressure retaining cap screwing and removing head, 801-spline groove, 802-blind hole, 803-shift fork, 9-drain port, 10-pressure retaining cap, 1001-shift fork with hook, 1002-blind hole, 1003-sealing groove, 1004-internal thread, 11-thermometer, 12-support disc, 1201-arc-shaped through hole, 1202-sliding bearing, 1203-threaded hole, 1204-through hole, 13-drilling tool inner tube, 14-fixing device, 1401-arc-shaped chuck, 1402-threaded push rod, 15-connecting rod, 16-limiting pin, 17-heating rod, 18-disc, 19-water inlet, 20-flange cover II, 21-pressure gauge, 22-pressure relief valve, 23-pressure pump, 24-temperature controller. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings.

[0036] like Figure 1-10As shown, the present invention includes a hydraulic pump 1, a reversing valve 2, a hydraulic straight joint 5, a pressure test chamber 4, a pressure retaining cap unscrewing device 7, a support frame, a fixing device 14, a temperature control device, a disc 18, a pressure pump 23, a pressure gauge 21 and a pressure relief valve 22. The pressure test chamber 4 is a tubular structure, and flange cover I 3 and flange cover II 20 are respectively installed at both ends by bolts. A water inlet 19 and a drain port 9 are respectively provided at both ends of the side wall of the pressure test chamber 4.

[0037] The pressure-maintaining cap screwing and unscrewing device 7 includes a hydraulic motor 6, a screwing and unscrewing shaft and a pressure-maintaining cap screwing and unscrewing head 8. The hydraulic motor 6 is installed on a disc bracket, and the disc bracket is installed in the pressure testing chamber 4. The disc bracket includes a mounting plate and a plurality of connecting rods; the connecting rod adopts a double-headed stud, and a plurality of threaded holes are provided on the mounting plate for installing one end of the connecting rod, and the other end of the connecting rod is installed on the flange cover 1 3. The blind hole 301 on the inner end surface of the flange cover 1 3 is a threaded hole for screwing with the other end of the connecting rod. A rotating shaft hole is provided at the center of the mounting plate for the output shaft of the hydraulic motor 6 to pass through, and the hydraulic motor 6 is installed on the disc. The output shaft of the hydraulic motor 6 is connected to one end of the screwing and unscrewing shaft, and the pressure-maintaining cap screwing and unscrewing head 8 is installed on the other end of the screwing and unscrewing shaft. The other end of the unscrewing shaft 8 (the end facing away from the hydraulic motor) is provided with a spline, and the end of the pressure-maintaining cap unscrewing head 8 facing the unscrewing shaft is provided with a blind hole 802, and the inner side surface of the blind hole 802 is provided with a spline groove 801. The bottom of the blind hole 801 is connected to the end of the unscrewing shaft through a spring. The end of the unscrewing shaft facing away from the hydraulic motor is installed in the blind hole 802 of the pressure-maintaining cap unscrewing head and is connected by a spline. Three shift forks 803 are provided on the end face of the pressure-maintaining cap unscrewing head. The pressure-maintaining cap 10 is installed on the end of the drill tool inner tube 13 facing the hydraulic motor 6. It is not tightened initially, and the drill tool inner tube 13 is supported on the support frame by a fixing device. Fig.10 As shown, the end face of the pressure-maintaining cap 10 facing away from the hydraulic motor is provided with a blind hole 1002, and the middle part of the side wall of the blind hole 1002 is provided with an annular sealing groove 1003, and a Y-shaped sealing ring is installed in the sealing groove 1003, and the Y-shaped sealing ring can achieve the sealing between the sealing cap 10 and the inner tube 13 of the drilling tool. The end face of the pressure-maintaining cap 10 facing the hydraulic motor is provided with a hooked fork 1001, and the hooked fork 1001 cooperates with the fork 803 on the end face of the pressure-maintaining cap screwing and removing head 8, and the blind hole 1002 is provided with an internal thread for screwing with the inner tube of the drilling tool. When sealing, the hydraulic motor 6 is controlled to rotate, and the hydraulic motor 6 drives the pressure-maintaining cap 10 to rotate and tighten through the fork 803; the pressure-maintaining cap 10 moves along the axis of the inner tube 13 of the drilling tool, and the spring pushes the pressure-maintaining cap screwing and removing head 8 to move together with the pressure-maintaining cap 10, and the hooked fork 1001 is always kept in cooperation with the fork 803.

[0038] The disc support is connected to the flange cover 13 through a threaded connecting rod; the flange cover 13 is provided with three through holes 302, and a hydraulic straight joint 5 is provided at both ends of two through holes. The two oil ports of the hydraulic motor 6 are connected to the hydraulic straight joints 5 at the inner ends of the two through holes through pipelines, and the hydraulic straight joints at the outer ends of the two through holes are connected to the two oil outlet holes of the reversing valve 2 through pipelines; the oil outlet of the hydraulic pump 1 is connected to the oil inlet of the reversing valve through a pipeline, and the oil inlet of the hydraulic pump 1 and the oil return hole of the reversing valve 2 are connected to the oil tank through pipelines. A hydraulic straight joint 5 is provided at the inner end of another through hole 302, and the hydraulic straight joint 5 is connected to the oil drain port of the hydraulic motor 6, and the other through hole is connected to the oil tank through a pipeline.

[0039] The support frame includes a plurality of support discs 12 and a plurality of connecting rods 15. The plurality of support discs 12 are coaxially arranged. A through hole 1204 is provided at the center of the support disc 12. A sliding bearing 1202 is installed in the through hole 1204. The support disc 12 is provided with a plurality of arc-shaped through holes 1201 and a plurality of threaded holes 1203. The plurality of arc-shaped through holes 1201 are evenly arranged along the circumferential direction, and the plurality of threaded holes 1203 are also evenly arranged along the circumferential direction. The two ends of the connecting rod 15 are respectively connected to the two coaxial threaded holes of two adjacent support discs 12; the plurality of connecting rods between the two support discs are evenly arranged along the circumferential direction. The inner tube 13 of the drilling tool is supported by the sliding bearings at the center of the plurality of support discs. The fixing device 14 includes a circular ring bracket, an arc-shaped chuck 1401 and a threaded push rod 1402. The circular ring bracket is installed on a supporting disc. The concave arc surface of the arc-shaped chuck 1401 contacts the outer side surface of the drilling tool inner tube 13, and the inner end of the threaded push rod 1402 contacts the back side of the arc-shaped chuck 1401. The threaded push rod 1402 is installed on the circular ring bracket.

[0040] The support frame is arranged in the pressure test chamber and is coaxial with the pressure test chamber 4. The temperature control device includes a thermometer 11, a heating rod 17 and a disc 18. The thermometer 11 is installed on the support frame, the heating rod 17 is fixed on the disc 18, and the disc 18 is fixed in the pressure test chamber 4 by a limit pin. A through hole 1801 is arranged in the middle of the disc 18, 6 threaded holes 1803 are evenly distributed around the through hole, and 3 arc-shaped through holes 1802 are arranged in the edge area of ​​the disc. Three blind holes 2001 are arranged on the inner end surface of the flange cover II 20, and the blind holes 2001 are threaded holes. A limit pin is installed in each blind hole 2001, and the other end of the limit pin is connected to the corresponding threaded hole 1803 through a thread. A through hole is arranged on the flange cover II 20, and a watertight connector is arranged in the through hole. The inner end of the watertight connector is electrically connected to the temperature control device, and the outer end of the watertight connector is electrically connected to the temperature controller 24. The flange cover II is provided with three pipe joint through holes, the outer end of one pipe joint through hole is connected to the pressure relief pipe through a hydraulic straight joint, and the pressure relief pipe is provided with a pressure relief valve 22. The outer end of another pipe joint through hole is connected to one end of the liquid inlet pipe through a hydraulic straight joint, and the other end of the liquid inlet pipe is connected to the outlet of the pressure pump 23, and the inlet of the pressure pump 23 is connected to the water tank through a pipe. A hydraulic straight joint is respectively provided at both ends of the third pipe joint through hole, and the two hydraulic straight joints are respectively connected to the inner pipe 13 of the drilling tool and the pressure gauge 21 through pipes.

[0041] The specific method of using the pressure test device for the seabed drilling rig pressure-maintaining coring drill of the present invention is to simulate recovery from a water depth of 2000 meters as an example. The pressure of the seawater at a water depth of 2000 meters is 20 MPa, and the temperature of the seawater is 3-5°C. The method comprises the following steps:

[0042] Step 1: Assemble the support frame, place the drill tool inner tube 13 and the pressure maintaining cap in the support frame, pre-assemble the pressure maintaining cap 10 and the drill tool inner tube, and after the pre-assembly is completed, fix the drill tool inner tube 13 by adjusting the relative distance between the arc-shaped chuck 1401 and the threaded push rod 1402 with the help of the drill tool fixing device to prevent the drill tool inner tube 13 from axial displacement and rotation; put the fixed drill tool inner tube 13 and the support frame into the pressure test chamber 4 together; install the disc 18 on the flange cover II 20, and fasten the flange cover II 20 to one end of the pressure test chamber with bolts; install the hydraulic motor 6 on the disc bracket, connect the two oil pipes to the two oil ports of the hydraulic motor 6, install the unscrewing shaft and the pressure maintaining cap unscrewing head 8, and then fasten the flange cover I3 to the pressure test chamber 4 with bolts.

[0043] Step 2: Inject 2~3 °C cold water into the pressure test chamber through the water inlet 19; after the water injection is completed, perform the exhaust process and block the water injection hole with a plug.

[0044] Step 3: Start the pressure pump 23 to pressurize the pressure test chamber 4. Since the pressure retaining cap 10 has not completed the sealing operation with the drill bit inner tube 13, the pressure test chamber 4 is now connected to the inside of the drill bit inner tube 13. After pressurizing to 20 Mpa, stabilize the pressure for 5 minutes, and the pressurization rate is 0.2-0.6 Mpa / min.

[0045] Step 4: Check whether the actual water temperature in the pressure test chamber 4 reaches 3~5°C through the thermostat. If it is lower than this temperature, start the heating device.

[0046] Step 5: Start the hydraulic pump to drive the hydraulic motor 6. The output shaft of the hydraulic motor 6 is connected to the unscrewing shaft, driving the unscrewing shaft to rotate. The boss on the unscrewing shaft is connected to the spline groove 801 on the pressure-maintaining cap unscrewing head 8, driving the pressure-maintaining cap unscrewing head 8 to rotate. During the rotation process, the spring drives the pressure-maintaining cap unscrewing head to move axially, thereby forming a sealing action between the pressure-maintaining cover and the inner tube of the drill bit.

[0047] Step 6: Open the pressure relief valve 22. According to the recovery speed of the drilling tool in the actual construction operation, the rate of 2000-200 meters is 50m / min, which takes 36 minutes, and the pressure relief rate is 0.5 MPa / min. The rate of 200-0 meters is 20m / min, which takes 10 minutes, and the pressure relief rate is 0.2 MPa / min.

[0048] Step 7: Start the heating device to heat the seawater in the pressure test chamber during the pressure relief process. Adjust the water temperature heating rate in the pressure test chamber according to the temperature change during the recovery of the drilling tools in the actual construction operation. The temperature change of the seawater from 2000 to 200 meters is 3°C-20°C. The temperature change of this process is completed within 36 minutes through the thermostat. The temperature change of the seawater from 200 to 0 meters is 20°C-30°C. The temperature change is completed within 10 minutes through the thermostat.

[0049] Step 8: By observing the pressure gauge 21 connected to the inside of the drill tool inner tube, record the pressure change inside the drill tool inner tube 13 during the entire recovery process.

[0050] Step 9: After the pressure relief is completed, open the drain port of the pressure test chamber 4 to drain the water in the pressure test chamber.

[0051] Step 10: Repeat steps 2-9 several times.

Claims

1. A pressure test device suitable for seabed drilling rig pressure-maintaining coring drill tools, characterized in that: It includes a hydraulic pump, a reversing valve, a pressure testing chamber, a pressure-maintaining cap unscrewing device, a pressure-maintaining cap, a support frame and a temperature control device; the pressure testing chamber is a tubular structure, with flange cover I and flange cover II installed at both ends, and a water inlet and a water outlet are provided at both ends of the side wall of the pressure testing chamber; the pressure-maintaining cap unscrewing device includes a hydraulic motor, an unscrewing shaft and a pressure-maintaining cap unscrewing head, the hydraulic motor is installed in the pressure testing chamber through a disc bracket, and the two oil ports of the hydraulic motor are connected to the oil outlet hole of the reversing valve through pipelines; the oil inlet of the hydraulic pump and the oil return hole of the reversing valve are connected to the oil tank through pipelines, and the oil outlet of the hydraulic pump is connected to the oil outlet of the reversing valve through a pipeline. The oil inlet hole is connected; the output shaft of the hydraulic motor is connected to one end of the unscrewing shaft, and the pressure-maintaining cap unscrewing head is installed at the other end of the unscrewing shaft; the pressure-maintaining cap is installed on the end of the drill tool inner tube facing the hydraulic motor, and the pressure-maintaining cap unscrewing head can achieve the sealing of the pressure-maintaining cap and the drill tool inner tube; the drill tool inner tube is supported on a support frame by multiple fixing devices, and the support frame is arranged in the pressure test chamber and is coaxial with the pressure test chamber; the temperature control device includes a thermometer, a heating rod and a disc, the thermometer is installed on the support frame, the heating rod is fixed on the disc, the disc is fixed in the pressure test chamber, and the temperature control device is electrically connected to the temperature controller; the pressure test chamber is provided with a pressurizing device and a pressure relief device.

2. The pressure test device for seabed drilling rig pressure-maintaining coring drill according to claim 1 is characterized in that: The disc bracket is connected to the flange cover I through a threaded connecting rod; the flange cover I is provided with three through holes, and a hydraulic straight joint is respectively provided at both ends of two through holes; the two oil ports of the hydraulic motor are respectively connected to the hydraulic straight joints at the inner ends of the two through holes through pipelines, and the hydraulic straight joints at the outer ends of the two through holes are respectively connected to the two oil outlet holes of the reversing valve through pipelines; the flange cover II is provided with a through hole, and a watertight connector is provided in the through hole, the inner end of the watertight connector is electrically connected to the temperature control device, and the outer end of the watertight connector is electrically connected to the temperature controller; the inner end of the other through hole of the flange cover I is provided with a hydraulic straight joint, and the hydraulic straight joint is connected to the oil drain port of the hydraulic motor through a pipeline, and the other through hole is connected to the oil tank through the oil drain pipeline.

3. The pressure test device for seabed drilling rig pressure-maintaining coring drilling tools according to claim 1 is characterized in that: The unscrewing shaft is provided with a spline at the end facing away from the hydraulic motor, a blind hole is provided at one end of the pressure-maintaining cap unscrewing head facing the unscrewing shaft, a spline groove is provided on the inner side of the blind hole, the unscrewing shaft is installed in the blind hole of the pressure-maintaining cap unscrewing head at the end facing away from the hydraulic motor, and is connected by a spline; the bottom of the blind hole is connected to the end of the unscrewing shaft by a spring; a plurality of shift forks are provided on the end surface of the pressure-maintaining cap unscrewing head.

4. The pressure test device for seabed drilling rig pressure-maintaining coring drill according to claim 1 is characterized in that: The support frame includes multiple support discs and multiple connecting rods. The multiple support discs are coaxially arranged. A through hole is provided at the center of the support disc. A sliding bearing is installed in the through hole. The support disc is provided with multiple arc-shaped through holes and multiple threaded holes. The multiple arc-shaped through holes are evenly arranged along the circumferential direction, and the multiple threaded holes are also evenly arranged along the circumferential direction; the two ends of the connecting rod are respectively connected to the two coaxial threaded holes of two adjacent support discs; the multiple connecting rods are evenly arranged along the circumferential direction; the inner tube of the drilling tool is supported by the sliding bearings at the center of the multiple support discs.

5. The pressure test device for seabed drilling rig pressure-maintaining coring drilling tools according to claim 4 is characterized in that: The fixing device comprises a circular ring bracket, an arc-shaped chuck and a threaded push rod. The circular ring bracket is installed on a supporting disc. The concave arc surface of the arc-shaped chuck contacts the outer side surface of the inner tube of the drilling tool. The inner end of the threaded push rod contacts the back side of the arc-shaped chuck. The threaded push rod is installed on the circular ring bracket.

6. The pressure test device for seabed drilling rig pressure-maintaining coring drilling tools according to claim 1 is characterized in that: It also includes a pressure gauge, the pressurizing device includes a pressure pump and a liquid inlet pipe; the pressure relief device includes a pressure relief pipe and a pressure relief valve; three pipe joint through holes are provided on the flange cover II, the outer end of one pipe joint through hole is connected to the pressure relief pipe through a hydraulic straight joint, the pressure relief pipe is provided with a pressure relief valve, the outer end of another pipe joint through hole is connected to one end of the liquid inlet pipe through a hydraulic straight joint, the other end of the liquid inlet pipe is connected to the outlet of the pressure pump, and the inlet of the pressure pump is connected to the water tank through a pipe; a hydraulic straight joint is provided at each end of the third pipe joint through hole, and the two hydraulic straight joints are connected to the inner pipe of the drilling tool and the pressure gauge through a pipe.

7. A pressure testing method for a seabed drilling rig pressure-maintaining coring drill tool using the pressure testing device for a seabed drilling rig pressure-maintaining coring drill tool according to any one of claims 1 to 6, comprising the following steps: Step 1: Assemble the support frame, place the drill tool inner tube and the pressure-maintaining cap in the support frame, and pre-assemble the pressure-maintaining cap and the drill tool inner tube; after the pre-assembly is completed, fix the drill tool inner tube with the help of a fixing device; put the fixed drill tool inner tube and the support frame into the pressure test chamber together; connect the disc with the heating rod fixed to the flange cover II, and install the flange cover II at one end of the pressure test chamber with bolts; install the hydraulic motor on the disc bracket, connect the two oil pipes to the two oil ports of the hydraulic motor, install the unscrewing shaft and the pressure-maintaining cap unscrewing head, and connect the flange cover I to the other end of the pressure test chamber with bolts; Step 2: Inject ice-water mixture into the pressure test chamber through the water inlet. The water temperature is selected with reference to the seawater temperature at the depth of the seabed natural gas hydrate reservoir. After the water injection is completed, exhaust gas is discharged and the water inlet is blocked; Step 3: According to the experimental requirements, uniformly pressurize the pressure test chamber, with a pressurization range of 5 - 40Mpa and a pressurization rate of 0.2-0.6 Mpa / min; Step 4: Use a thermometer to check whether the actual water temperature in the pressure test chamber is consistent with the ambient water temperature required by the experiment. If it is lower than the ambient water temperature required by the experiment, start the heating rod to heat the water temperature in the pressure test chamber to the water temperature required by the experiment; if the water temperature in the pressure test chamber is consistent with the experimental requirements, proceed directly to step 5; Step 5: Start the hydraulic motor to drive the pressure retaining cap screwing and unscrewing head to rotate to complete the sealing action between the pressure retaining cap and the inner tube of the drilling tool; Step 6: Release the pressure in the pressure test chamber to simulate the process in which the external environmental pressure is continuously reduced during the recovery of the drilling tool; The rate of pressure drop in the pressure test chamber should be consistent with the recovery speed of the drilling tool in actual construction operations; Step 7: Start the heating rod to heat the seawater in the pressure test chamber during the pressure relief process, simulating the change in water temperature when the drill tool passes through seawater layers of different depths during the recovery process. The heating rate is determined according to the residence time of the drill tool in seawater layers of different temperature ranges during the recovery process. The maximum water temperature does not exceed 40°C. Step 8: By observing the pressure gauge connected to the inner tube of the drill tool, record the pressure change inside the inner tube of the drill tool during the entire recovery process; Step 9: After the pressure relief is completed, open the drain port of the pressure test chamber to drain the water in the pressure test chamber; Step 10: Repeat Step 2 to Step 9 several times.

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