A closed coring device suitable for inclined well sections and a drilling coring process

Abstract

The present invention provides a closed coring device and a drilling coring process suitable for inclined well sections. The closed coring device includes an upper joint, a differential short joint, an outer cylinder, a hanging mechanism, a rotary joint assembly, an inner cylinder, a core grabbing mechanism, an upper sealing piston, a lower sealing piston, and a coring drill bit. The upper joint, the differential short joint, the outer cylinder, and the coring drill bit are connected to form an outer cylinder string. The rotary joint assembly, the inner cylinder, and the core grabbing mechanism are arranged inside the outer cylinder string and connected to form an inner cylinder string. The inner cylinder string is suspended on the differential short joint by a hanging mechanism. The hanging mechanism can realize double-cylinder single-action. The upper sealing piston can realize drilling circulation and inner cylinder pressure relief. The lower sealing piston is fixed to the coring drill bit by an elastic locating pin and a plug. The drilling coring process can be realized by the above-mentioned closed coring device. The closed coring device provided by the present invention can reduce the risk of core blockage in closed coring in inclined well sections and improve the sealing rate. The drilling coring process provided by the present invention can improve construction efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of drilling coring technology, and in particular to a closed coring device and a drilling coring technology suitable for inclined well sections. Background Art

[0002] In oil and gas exploration and development, as well as reserve assessment, closed coring technology plays an important role. It can obtain cores that are not contaminated by drilling fluids and obtain a series of geological data such as oil and water saturation with relatively accurate accuracy. With the continuous development of domestic shale gas exploration and development technology, the demand for directional well drilling technology is increasing year by year. Correspondingly, the requirements for the supporting inclined well section coring technology are also getting higher and higher. At present, well-known drilling companies and petroleum universities at home and abroad have developed various types of closed coring tools. The application effect in vertical well sections is relatively good. However, when used in inclined well sections, problems such as easy plugging and low sealing rate are common. Only a few reports on the application or theoretical research of closed coring in inclined wells have been published. For example, the ZY-B type closed coring tool for highly deviated wells developed by the A Drilling Engineering Technology Research Institute reduces mechanical damage to the core by adding a suspension assembly and an inner barrel centralizer. This keeps the inner barrel centered, reduces mechanical damage to the core, and minimizes the risk of core plugging. While it has been effective in coring in deviated well sections, it still has some drawbacks, such as difficulty filling the sealing fluid and an inability to replace the sealing fluid at the lower end, which impacts construction efficiency and sealing rates. Therefore, it is of great significance to provide a closed coring device and drilling coring process suitable for deviated well sections.

[0003] A Chinese patent application numbered "CN202021245478.8" and titled "Diverter Suspension Device for Closed Coring in Horizontal Wells" discloses a diverter suspension device suitable for closed coring in horizontal wells. The device comprises an upper suspension tube, a connecting tube, a pressure cap, an axial bearing, a bearing seat, a radial bearing, a diverter joint, a piston, a piston rod, a return spring, and a spring seat. The upper portion of the diverter joint is fitted with a bearing seat, a pressure cap and an axial bearing are mounted on the outer side of the upper end of the diverter joint, a connecting tube is mounted on the inner side of the upper end of the bearing seat, an upper suspension tube is mounted on the inner side of the upper end of the connecting tube, an inner tube joint is mounted on the inner side of the lower end of the diverter joint, a pressure relief hole is provided on the side wall of the inner tube joint, and a radial bearing is fitted on the outer side of the lower portion of the bearing seat. The device has a reasonable structure and is simple to operate. It can prevent the mud and sealing fluid from being replaced during closed coring operations in horizontal wells, and prevent pressure buildup in the inner tube. However, this device differs from the structure of the present application and does not have the function of improving the sealing performance of inclined well coring.

[0004] Chinese patent application number CN201521003715.9, entitled "A Coring Tool for Coring Inclined Wells," discloses a coring tool suitable for coring in inclined wells. The tool comprises a suspension mechanism, a coring inner barrel, a flexible tube, a floating inner barrel with the same outer diameter as the coring inner barrel, a steel ball, a ball seat, and a tapered retaining groove. The floating inner barrel comprises an upper flow-restricting section and a lower air chamber section. The lower air chamber section comprises an axially symmetrical cylindrical annular cavity. The outer annular cavity serves as a closed air chamber, while the inner cylindrical cavity passes through the central axis of the floating inner barrel and serves as a cleaning channel. A ball seat is located at the center of the upper flow-restricting section, and a tapered retaining groove is provided on the ball seat. The steel ball is seated unidirectionally in the ball seat through the tapered retaining groove, sealing the cleaning channel. The suspension mechanism, flexible tube, and upper flow-restricting section of the floating inner barrel are sequentially connected, while the lower air chamber section of the floating inner barrel and the coring inner barrel are concentrically connected. The coring tool can effectively center the inner and outer core barrels without affecting the cleaning of rock debris, thus achieving efficient coring of inclined wells. However, the structure of the tool is different from that of the present application, and the structure for improving the concentricity of the barrel is also different. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the present invention aims to address one or more of the aforementioned problems. For example, one object of the present invention is to provide a closed coring device suitable for use in deviated well sections, which has a high sealing rate, is less susceptible to core blockage and tube extraction, and has low core entry resistance. Another object of the present invention is to provide a drilling and coring process suitable for use in deviated well sections that improves the core sealing rate and operation efficiency.

[0006] In order to achieve the above-mentioned objectives, the present invention provides, on the one hand, a closed coring device suitable for inclined well sections, said closed coring device comprising an upper joint, a differential short joint, an outer cylinder, a hanging mechanism, a rotary joint assembly, an inner cylinder, a core grabbing mechanism, an upper sealing piston, a lower sealing piston and a coring drill bit, wherein the upper joint, the differential short joint, the outer cylinder and the coring drill bit are fixedly connected to form an outer cylinder string of the closed coring device; the rotary joint assembly, the inner cylinder and the core grabbing mechanism are all arranged inside the outer cylinder string and fixedly connected from top to bottom to form an inner cylinder string of the closed coring device; a circulation channel is formed between the outer wall of the inner cylinder string and the inner wall of the outer cylinder string; the upper end of the upper joint is connected to the drill collar; the inner cylinder string is suspended on the differential short joint by a hanging mechanism; the hanging mechanism can realize double-cylinder single-action of the inner and outer cylinders; the upper sealing piston is arranged inside the upper joint and is connected to the inner cylinder, so as to realize drilling circulation and inner cylinder pressure relief; the lower sealing piston passes through the core grabbing mechanism and is fixed to the coring drill bit by an elastic locating pin and a plug.

[0007] According to an exemplary embodiment of one aspect of the present invention, the suspension mechanism may include a pressure relief plug, a half ring, a bearing, a water diversion joint and a sealing ring, wherein the pressure relief plug is connected to the upper sealing piston; the bearing suspends the inner cylinder string on the differential nipple; the half ring is arranged at the upper end of the bearing to axially lock the bearing; the upper end of the water diversion joint and the lower end of the upper joint form a tolerance fit so that the inner cylinder string is concentric with the outer cylinder and the inner diameter of the drill bit; the sealing ring is arranged at the lower end of the upper sealing piston and is installed in the water diversion joint together with the upper sealing piston.

[0008] According to an exemplary embodiment of one aspect of the present invention, the upper sealing piston can seal the sealing liquid in the inner cylinder through the sealing ring and the pressure relief plug. The upper sealing piston can be provided with a flow channel hole and a pressure relief hole. The flow channel hole realizes drilling circulation through the drilling fluid. When the pressure relief plug is unscrewed to a certain opening, the pressure relief hole is exposed to realize pressure relief of the inner cylinder; the lower sealing piston may include an O-ring and a rubber plug to effectively seal the sealing liquid and ensure the unidirectional flow of the sealing liquid.

[0009] According to an exemplary embodiment of one aspect of the present invention, the end surface of the elastic locating pin may be provided with drilled holes and cut grooves to make the locating pin elastic, and the elastic locating pin and the lower sealing piston may form an interference fit and will not fall off after shearing.

[0010] According to an exemplary embodiment of one aspect of the present invention, a fitting gap may exist between the lower end of the inner cylinder and the step surface of the core drill bit, and a width of the fitting gap is 0.1 to 0.2 mm.

[0011] According to an exemplary embodiment of one aspect of the present invention, the closed coring device may further include an inner cylinder straightening short section, which is arranged at the lower end of the inner cylinder and located at the upper end of the core grabbing mechanism. The inner cylinder straightening short section can straighten the inner cylinder and, together with the water diversion joint, make the inner cylinder string concentric with the outer cylinder and the inner diameter of the drill bit.

[0012] According to an exemplary embodiment of one aspect of the present invention, the inner cylinder straightening short section may include a main body and a plurality of steel balls, wherein the main body is processed as a whole, has a plurality of rectangular protrusions in the middle, and a straight groove is arranged in the middle of the protrusion along the axial direction; the steel balls are arranged in the straight grooves, and the maximum exposed diameter of the steel balls is smaller than the inner diameter of the outer cylinder. The steel balls form rolling friction with the inner wall of the outer cylinder, and during the rotation of the outer cylinder, the steel balls can support the inner cylinder without eccentricity; an annular flow channel groove is arranged on the main body, which can reduce the erosion of the drilling fluid vortex on the main body.

[0013] According to an exemplary embodiment of one aspect of the present invention, the core gripping mechanism may include a core claw assembly and a flip-type core gripping assembly, the core claw assembly being arranged at the upper end of the flip-type core gripping assembly, wherein the core claw assembly includes a clamp seat and a core claw, the inner wall of the clamp seat is provided with a conical surface, the outer surface of the core claw is provided with a conical surface which matches the inner conical surface of the clamp seat, and the conical surface of the clamp seat is provided with a plurality of through chip removal grooves for facilitating the removal of cuttings on the conical surface; the flip-type core gripping assembly includes a support card, a clamping sleeve, a sliding sleeve, a pin and a torsion spring, wherein one end of the support card is fixed to the clamping sleeve by a pin, and the other end can be freely rotated out of the clamping sleeve, the free end of the support card faces the core claw assembly, the front end of the support card is a knife tip type, which can be inserted into the core to prevent it from falling; the torsion spring passes through the pin, one end is inserted into the support card, and the other end is inserted into the clamping sleeve, and the torsion spring can turn the support card into the sliding sleeve.

[0014] According to an exemplary embodiment of one aspect of the present invention, the upper end of the upper joint can be connected to the drill collar through a drill pipe thread, and the upper sealing piston is arranged inside the upper joint and can be limited by the threaded end face of the drill pipe. The stroke of the upper sealing piston and the threaded end face of the drill pipe can be greater than the sealing surface length of the lower sealing piston after shearing, ensuring that the sealing fluid can be effectively released after shearing.

[0015] Another aspect of the present invention provides a drilling coring process suitable for inclined well sections. The coring process can be achieved by the closed coring device suitable for inclined well sections as described above, and the coring process includes the following steps: after the coring tool is assembled, it is connected to the drill bit, the coring tool is lowered to a position 2 to 3 meters from the bottom of the well, and the pump is turned on to circulate the drilling fluid; after the circulation is completed, the turntable or top drive is started, and the drill bit is slowly lowered to explore the bottom. After reaching the bottom, 30 to 50 kN of drilling pressure is applied to shear the pins; after the shearing is completed, the drilling pressure, speed and displacement are adjusted to start tree core drilling. After the tree core is drilled 0.3 to 0.5 meters, the drilling pressure, speed and displacement are adjusted again to start coring drilling; after the coring is completed, the core is cut and the drill is pulled out to relieve pressure and remove the core.

[0016] According to an exemplary embodiment of another aspect of the present invention, the coring process may further include: when the drilling pressure increases and then suddenly drops and the drilling pressure remains unchanged after pressurization, the static pressure is 60kN, and the changes in the drilling pressure are observed. If the shearing is normal, the coring is started; otherwise, the drill is pulled out for inspection.

[0017] According to an exemplary embodiment of another aspect of the present invention, the coring process may further include: when pulling out the drill, if the suspended weight is increased to stabilize and does not drop, stop lifting the drill bit, keep the core in a tensile state, increase the drilling fluid displacement circulation until the core is pulled out; if the suspended weight does not change, continue drilling for 0.3 to 0.5 meters and then repeat the core cutting operation.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The closed coring device for inclined well sections proposed by the present invention can improve the sealing rate and effectively reduce the probability of core blockage;

[0020] (2) The closed coring device for inclined well sections proposed by the present invention can better ensure that the centers of the inner and outer barrels coincide with each other, thereby reducing the resistance to coring;

[0021] (3) The closed coring device for inclined well sections proposed by the present invention has a reasonable structure, convenient operation, and easy function realization;

[0022] (4) The drilling and coring process for inclined well sections proposed in the present invention can effectively improve the work efficiency of assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other objects and features of the present invention will become more apparent from the following description in conjunction with the accompanying drawings, in which:

[0024] Figure 1 A schematic structural diagram of the enclosed coring device of the present invention is shown;

[0025] Figure 2 A schematic structural diagram of the suspension mechanism of the present invention is shown;

[0026] Figure 3a Shows a schematic structural diagram of the lower sealing piston of the present invention;

[0027] Figure 3b Shows a schematic structural diagram of a conventional lower sealing piston;

[0028] Figure 4a A schematic structural diagram of the elastic positioning pin of the present invention is shown;

[0029] Figure 4b Shows a schematic structural diagram of a cylindrical positioning pin;

[0030] Figure 5 A schematic diagram showing the drop position of a conventional positioning pin is shown;

[0031] Figure 6 A schematic diagram showing the fitting clearance of the present invention is shown;

[0032] Figure 7a A schematic structural diagram of the inner barrel centralizing sub of the present invention is shown;

[0033] Figure 7b Shows a schematic structural diagram of a roller-type righting sub;

[0034] Figure 8a The drilling fluid Figure 7aFlow state in the righting nipple;

[0035] Figure 8b The drilling fluid Figure 7b Flow state in the righting nipple;

[0036] Figure 9 Shows a schematic structural diagram of the chip removal groove of the present invention;

[0037] Figure 10 A schematic structural diagram of the flip-type center grip assembly of the present invention is shown;

[0038] Figure 11 Shown Figure 10 Schematic diagram of the structure of part A;

[0039] Figure 12 A schematic diagram of the sliding sleeve inverted tooth structure of the present invention is shown;

[0040] Figure 13 A schematic diagram of the structure of the toca according to the present invention when it is compressed outwards is shown;

[0041] Figure 14 The figure shows the structure of the toca of the present invention when inserted into the core.

[0042] Reference numerals:

[0043] 1-upper joint, 2-upper differential short section, 3-lower differential short section, 4-outer cylinder, 5-suspension mechanism, 51-pressure relief plug, 52-half ring, 53-bearing, 54-water diversion joint, 55-sealing ring, 6-inner cylinder, 61-spiral groove, 7-rotating joint assembly, 8-core grabbing mechanism, 81-core claw assembly, 811-clamp seat, 8111-chip groove, 82-flip core grabbing assembly, 821-support card, 822-card sleeve, 823-torsion spring, 824-pin, 825-sleeve, 8251-conical surface , 9-upper sealing piston, 10-lower sealing piston, 101-O-ring, 102-rubber plug, 11-coring drill bit, 12-elastic positioning pin, 121-drilling, 122-grooving, 13-plug, 14-connecting sleeve, 15-drop position, 16-inner tube straightening short section, 161-body, 162-steel ball, 163-annular flow channel groove, 164-gentle slope, 165-bump, 17-straight step, 18-I-shaped flow channel groove, 19-roller, 20-drilling tool, 21-fit clearance, 22-sealing piston stroke. DETAILED DESCRIPTION

[0044] Hereinafter, a closed coring device and a drilling coring process applicable to a deviated well section of the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0045] It should be noted that terms such as "first" and "second" are used solely for ease of description and distinction and should not be construed as indicating or implying relative importance. Terms such as "upper," "lower," "inner," "outer," "left," and "right" are used solely for ease of description and to establish relative orientations or positions, and should not be construed as indicating or implying that the components referred to must have a particular orientation or position.

[0046] Figure 1 A schematic structural diagram of the enclosed coring device of the present invention is shown; Figure 2 A schematic structural diagram of the suspension mechanism of the present invention is shown; Figure 3a Shows a schematic structural diagram of the lower sealing piston of the present invention;

[0047] Figure 3b Shows a schematic structural diagram of a conventional lower sealing piston; Figure 4a A schematic structural diagram of the elastic positioning pin of the present invention is shown; Figure 4b Shows a schematic structural diagram of a cylindrical positioning pin; Figure 5 A schematic diagram showing the drop position of a conventional positioning pin is shown; Figure 6 A schematic diagram showing the fitting clearance of the present invention is shown;

[0048] Figure 7a A schematic structural diagram of the inner barrel centralizing sub of the present invention is shown; Figure 7b Shows a schematic structural diagram of a roller-type righting sub; Figure 8a The drilling fluid Figure 7a Flow state in the righting nipple; Figure 8b The drilling fluid Figure 7b Flow state in the righting nipple; Figure 9 Shows a schematic structural diagram of the chip removal groove of the present invention; Figure 10 A schematic structural diagram of the flip-type center grip assembly of the present invention is shown; Figure 11 Shown Figure 10 Schematic diagram of the structure of part A; Figure 12 A schematic diagram of the sliding sleeve inverted tooth structure of the present invention is shown; Figure 13 A schematic diagram of the structure of the toca according to the present invention when it is compressed outwards is shown; Figure 14 The figure shows the structure of the toca of the present invention when inserted into the core.

[0049] It should be noted that the direction from top to bottom in the specification is Figure 1 、 Figure 2 、 Figure 5 、 Figure 10 、 Figure 13 and Figure 14 From left to right in the .

[0050] In a first exemplary embodiment of the present invention, as Figure 1As shown in the figure, the closed coring device suitable for inclined well sections mainly includes an upper joint 1, a differential short joint, an outer tube 4, a suspension mechanism, a rotary joint assembly 7, an inner tube 6, a core grabbing mechanism 8, an upper sealing piston 9, a lower sealing piston 10 and a coring drill bit 11.

[0051] The differential sub includes an upper differential sub 2 and a lower differential sub 3. The upper joint 1, the upper differential sub 2, the outer tube 4, the lower differential sub 3 and the core drill bit 11 are fixedly connected from top to bottom to form an outer tube string of a closed coring device. Here, the upper joint 1, the upper differential sub 2 and the outer tube 4 can be connected by a special thread of the coring tool, and the lower differential sub 3 and the core drill bit 11 can be connected by a thread of the coring tool. Figure 2 As shown in , the upper end of the upper joint 1 can be provided with a drill pipe thread connected to the drilling tool 20 (drill collar), and the drilling pressure and torque can be transmitted to the core drill bit through the upper joint. Figure 1 As shown in , the rotary joint assembly 7, the inner cylinder 6 and the core grabbing mechanism 8 are all arranged inside the outer cylinder string and can be fixedly connected by threads from top to bottom to form the inner cylinder string of the closed coring device. A drilling fluid circulation channel is formed between the outer wall of the inner cylinder string and the inner wall of the outer cylinder string. The inner cylinder string is suspended on the differential short section by a suspension mechanism. While ensuring the effective sealing of the sealing fluid, the suspension mechanism can realize the double-cylinder single-action of the inner and outer cylinders (that is, the outer cylinder rotates and the inner cylinder does not rotate), reducing the mechanical damage to the core caused by the rotation of the inner cylinder and reducing the risk of core blockage. As shown in Figure 1 As shown in the figure, the upper sealing piston 9 is located within the upper joint 1 and communicates with the inner barrel 6. It works in conjunction with the suspension mechanism and the lower sealing piston 10 to effectively seal the sealing fluid within the inner barrel. The upper sealing piston also has a hole, which opens and closes to achieve normal drilling circulation and inner barrel pressure relief. The lower sealing piston 10 passes through the core grabbing mechanism 8 and is secured to the coring drill bit 11 via an elastic locating pin 12 and a plug 13.

[0052] In this exemplary embodiment, the suspension mechanism is convenient in structure, and while ensuring the inner cylinder is rotating and sealed, the filling method of the sealing liquid does not need to be changed, and the assembly work efficiency is higher. Figure 2As shown in , the suspension mechanism 5 may include a pressure relief plug 51, a half ring 52, a bearing 53, a water diversion joint 54 and a sealing ring 55. The sealing ring 55 is assembled on the lower end of the upper sealing piston 9 and is installed in the water diversion joint 54 together with the upper sealing piston 9, and is limited by the inner step of the water diversion joint. Here, the sealing ring can be an O-ring. The water diversion joint suspends the inner cylinder string as a whole on the differential short section through the bearing. Under the action of the bearing, the friction force transmitted to the inner cylinder string by the differential short section during rotation is extremely weak, which can avoid driving the inner cylinder to rotate and causing mechanical crushing of the core, resulting in the accumulation of rock debris and blockage of the core. The half ring 52 is arranged on the upper end of the bearing 53 to lock the bearing 53 axially. Furthermore, the upper end of the water diverter joint 54 forms a tolerance fit with the lower end of the upper joint 1. Through dimensional control and the application of a wear-resistant lubricant on the mating surface, this allows for the alignment of the upper end of the inner barrel without affecting the bearing's performance. This, combined with the lower inner barrel alignment nipple, also helps to align the inner barrel, ensuring better alignment of the inner and outer barrel centers and concentricity of the entire inner barrel string with the outer barrel and the drill bit's inner diameter. This reduces core insertion resistance and avoids core insertion difficulties caused by inner barrel eccentricity. Furthermore, the threads at the lower end of the water diverter joint can extend slightly beyond the threaded end of the differential nipple, leaving ample space for a pipe wrench to facilitate threaded tightening and unthreading with the lower tool string.

[0053] The way / process of the suspension mechanism to achieve double-drum single-motion of the inner and outer cylinders is as follows: the outer cylinder rotates under the drive of the drill pipe, and the inner cylinder is suspended on the inner step of the upper differential short section through a bearing. When the outer cylinder rotates, the upper bearing ring rotates with the outer cylinder, and the lower bearing ring does not move. The force of the outer cylinder rotation cannot be transmitted to the inner cylinder, causing the inner cylinder to be in a relatively static state, achieving double-drum single-motion (that is, the coring tool consists of two layers, the inner cylinder and the outer cylinder, but in the actual coring process, the outer cylinder rotates and the inner cylinder does not rotate).

[0054] In this exemplary embodiment, the upper sealing piston communicates with the inner cylinder, effectively sealing the sealing fluid within the inner cylinder via a sealing ring and a pressure relief plug. The upper sealing piston is provided with a flow channel and a pressure relief hole. The flow channel allows for normal drilling fluid circulation. When the pressure relief plug is unscrewed to a certain degree, the pressure relief hole is exposed, allowing pressure to be released from the inner cylinder. This prevents pressure buildup in the inner cylinder due to a sealed inner cylinder and / or obstructed upper piston travel, which could lead to the upper piston ejecting after the drill pipe clip is removed.

[0055] In addition, by controlling the size of the upper sealing piston, a sealing stroke is provided for the O-ring of the lower sealing piston before entering the inner cylinder, which can effectively seal the sealing fluid while effectively releasing the sealing fluid. Specifically, the upper sealing piston and the pressure relief plug can be connected by threads and installed inside the upper joint, and the position is limited by the threaded end face of the drill pipe. There is a stroke between the upper sealing piston and the threaded end face of the drill pipe, such as Figure 2As shown in , this stroke is the sealing piston stroke 22. The sealing piston stroke is greater than the sealing surface length of the lower sealing piston after shearing, ensuring effective release of the sealing fluid after shearing. That is, the upper sealing piston stroke is greater than the stroke required for the lower sealing piston to move upward to expose the O-ring after shearing, ensuring smooth outflow of the sealing fluid.

[0056] In this exemplary embodiment, the lower sealing piston passes through the core claw assembly and is fixed to the core drill bit through an elastic positioning pin and a plug. Figure 3a As shown in the figure, the lower sealing piston adopts a sealing combination of an O-ring 101 and a rubber plug 102. Before the shear pin is sheared, the two have a dual role to ensure that the sealing fluid is effectively sealed. The O-ring needs to be sealed before entering the inner cylinder to prevent the loss of the sealing fluid. After entering the inner cylinder, the O-ring can no longer have a sealing effect. To ensure that the sealing fluid can flow out smoothly, the sealing of the sealing fluid can be achieved by the one-way sealing of the rubber plug. That is, the rubber plug can ensure the effective sealing of the sealing fluid while ensuring the one-way flow of the sealing fluid. The drilling fluid cannot enter the inner cylinder through the rubber plug, which prevents the drilling fluid from entering the inner cylinder and mixing with the sealing fluid to cause slurry mixing, thereby improving the sealing rate.

[0057] In a closed coring device, the upper and lower sealing pistons work together to ensure the effective sealing of the sealing fluid. In a horizontal well, the coring tool is in a horizontal position, and the sealing fluid sinks to the bottom of the inner barrel due to gravity, leaving a certain space above. Because the sealing fluid is in a closed state before the pin is sheared, there is a certain pressure differential between the inside and outside of the inner barrel (the pressure outside the inner barrel is greater than the pressure inside the inner barrel). When the pin is sheared, the drilling fluid outside the inner barrel is forced into the inner barrel due to the pressure differential, forming a slurry with the sealing fluid, affecting the sealing fluid's performance.

[0058] like Figure 3b As shown in the figure, the conventional lower sealing piston of existing closed coring tools usually adopts a sealing structure with double O-rings 101. Before the pin is sheared, the O-rings are fitted to a strict tolerance, ensuring effective sealing of the sealing fluid. After the pin is sheared, the sealing piston moves upward a certain distance into the inner barrel (the upper sealing piston is designed to have a certain upward movement space). To ensure that the sealing fluid can effectively flow out of the inner barrel, the fitting tolerance of the O-ring and the inner wall of the inner barrel will increase, and a small gap will be fitted to provide space for the sealing fluid to flow out. This causes the drilling fluid and the sealing fluid to mix. The lower sealing piston of the present invention solves this problem.

[0059] In this exemplary embodiment, the positioning pin is a part that fixes the lower sealing piston to the core drill bit. The existing structure generally adopts a cylindrical positioning pin. Figure 4bAs shown in . After the cylindrical locating pin is cut, the cut part will gradually move upwards as it enters the core. At the same time, under the action of gravity, the pin will tend to fall downwards. When the pin is first cut, the lower sealing piston cooperates with the step surface of the drill bit, which limits the pin to a certain extent and prevents it from falling. However, when it moves to the upper end of the core claw, the space outside the pin will increase, making it easy to fall into the core claw. The falling position of the conventional locating pin is shown in 15 Figure 5 As shown in FIG, the pin is stuck in the end face of the connecting sleeve 14, which will hinder the entry into the core and cause blockage. In view of this situation, the present invention provides an elastic positioning pin, such as Figure 4a As shown in the figure, the end surface of the elastic positioning pin is drilled with holes 121 and slotted with grooves 122, which give the pin a certain degree of elasticity and form a tolerance (interference fit) with the mating surface of the lower sealing piston. During assembly, the pin's diameter is reduced by tapping, but it still forms a tight fit with the lower sealing piston, ensuring that it will not fall out after shearing.

[0060] In this exemplary embodiment, the double-barrel single-action structure (inner-barrel rotating structure) of the sealed coring tool reduces the damage to the core caused by the rotation of the inner barrel, but there is still a problem, that is, the lower end of the inner barrel cannot form a seal with the step surface of the drill bit. Otherwise, the friction of the sealing surface will drive the inner barrel to rotate, and at this time, a drilling fluid channel will inevitably be formed, causing the drilling fluid to directly flush the core and the sealing fluid, affecting the sealing rate. To address this problem, Figure 6 As shown in the figure, there is a fitting gap 21 between the lower end of the inner barrel 6 of the present invention and the step surface of the core drill bit 11. The fitting gap can be controlled to 0.1 to 0.2 mm, for example, 0.1 mm, 0.15 mm or 0.2 mm, forming a small gap anti-scour flow limiting structure, thereby increasing the resistance to the flow of drilling fluid. Furthermore, a spiral groove 61 (shallow spiral groove) can be processed at the lower end of the inner barrel 6. The spiral groove on the surface of the inner barrel and the gap between the drill bit and the inner barrel work together to prevent the inner barrel from rotating when the drill bit rotates, thereby damaging the core. On the other hand, by adding the spiral groove, when the drilling fluid flows through the fitting gap and the spiral groove, a vortex is formed, which slows down or even blocks the drilling fluid from passing through the flow channel, reduces the erosion of the sealing fluid by the drilling fluid, and improves the sealing rate. In addition, the fitting surface between the lower end of the inner barrel and the step surface of the core drill bit can be sprayed with a wear-resistant material to increase the service life of the tool.

[0061] In this exemplary embodiment, when coring in the inclined well section, under the action of gravity, the inner cylinder will lean against the inner wall of the outer cylinder, and be eccentric with the outer cylinder and the inner hole of the drill bit, resulting in increased core feeding resistance. Figure 1As shown in FIG, the enclosed coring device of the present invention may also include an inner barrel centering sub 16. This sub is mounted at the lower end of the inner barrel 6 and the upper end of the core grabbing mechanism 8 to stabilize the inner barrel. This sub also works in conjunction with the water diversion joint to center the inner barrel, ensuring that the entire inner barrel string is concentric with the outer barrel and the inner diameter of the coring drill bit, thus preventing problems such as core feeding difficulties caused by inner barrel eccentricity.

[0062] like Figure 7a As shown in the figure, the inner tube straightening sub includes a body 161, steel balls 162, an annular flow channel groove 163, a gentle slope 164 and a protrusion 165. There are multiple rectangular protrusions 165 in the middle of the body 161, and a straight groove is milled axially in the middle of the protrusion 165. Several steel balls 162 are installed in the straight groove and welded at both ends. After assembly, the maximum diameter of the exposed steel balls is 2mm smaller than the inner diameter of the outer tube. Here, because the gap between the protrusions and the inner wall of the outer tube is very small, the number of protrusions cannot be too many and the width cannot be too large, otherwise the drilling fluid flow channel area will be insufficient. In addition, the wall thickness of the inner tube straightening sub is also small. The provision of a single straight groove can ensure the selection of steel balls with larger diameters, making the steel balls roll more smoothly. The steel balls are arranged in a straight line as a whole. The number of steel balls is not specifically limited. It can ensure that the gap between each two steel balls is 30% to 50% of the steel ball diameter and matches the length of the rectangular boss. Here, the number of rectangular bumps is preferably set to 4 per segment, which provides better stability. Too many bumps will affect the drilling fluid flow path, while too few bumps will result in poor stability.

[0063] The inner barrel straightening sub of the present invention adopts a steel ball straightening sub (spherical straightening unit), which does not require a pin and processes the main body as a whole, greatly improving the overall mechanical strength of the straightening sub and extending the service life under tensile and torsional loads at the bottom of the well. The integrally processed structure can also avoid the inner barrel straightening sub from breaking and failing when subjected to torque during core plugging and tension during core cutting, thereby affecting the quality of coring. Using the inner barrel straightening sub of the present invention to replace the existing roller straightening unit can solve or avoid the problem that the roller straightening unit needs to be fixed with a pin shaft inserted therethrough. When the roller is under pressure, the pin shaft is easily deformed by force, resulting in the roller being unable to rotate freely or the roller being sunken, etc., increasing friction, causing the protrusion to directly contact the inner wall of the outer barrel, causing the inner barrel to rotate with the outer barrel, affecting the function of the rotating mechanism, causing core damage and affecting core feeding, etc.

[0064] like Figure 7b As shown in the figure, the existing roller type straightening sub includes rollers 19, which adopt the structure of straight steps 17, and a straight flow channel 18 is provided on the surface of the roller. Figure 7aThe gentle slope 164 structure shown in the figure, and the surface of the righting nipple is also provided with an annular flow channel groove 163. Compared with the existing straight step structure, the gentle slope of the present invention allows the drilling fluid to flow more smoothly and has less erosion effect on the inner tube righting nipple. Compared with the existing straight flow channel groove, the annular flow channel groove of the present invention can reduce the eddy current generated during the flow of drilling fluid, reduce the erosion of the drilling fluid eddy current on the body, and thus reduce the erosion of the drilling fluid on the inner tube righting nipple. Figure 8a and Figure 8b From the flow state of the drilling fluid in the centralizing sub, it can be seen that the flow state of the drilling fluid in the inner tube centralizing sub of the present invention is smoother, and the drilling fluid generates more vortices in the conventional roller centralizing sub.

[0065] The specific method of using the inner cylinder righting sub of the present invention to right the inner cylinder is as follows: during the rotation of the outer cylinder, the steel balls support the inner cylinder to prevent it from being eccentric. At the same time, rolling friction is formed between the inner wall of the outer cylinder and the steel balls, thereby reducing the friction generated by the direct contact between the inner cylinder and the outer cylinder, and avoiding excessive friction, which drives the inner cylinder to rotate, causes core damage, and affects core feeding.

[0066] In this exemplary embodiment, Figure 1 As shown in FIG, the core gripping mechanism 8 may include a core claw assembly 81 and a flip core gripping assembly 82. The core claw assembly 81 is disposed on the upper end of the flip core gripping assembly 82.

[0067] Among them, the core claw assembly includes a clamp seat and a core claw. Here, the core claw can be a conventional clamp-type core claw. The inner wall of the clamp seat is provided with a conical surface, and the outside of the core claw is provided with a conical surface that matches the inner conical surface of the clamp seat. The clamp seat and the core claw can match through the conical surface. When cutting the core, the core claw moves down along the conical surface and gradually shrinks to grab the core. However, if there is rock debris accumulated on the conical surface, it will affect the contraction of the core claw, resulting in a loose grip of the core, causing the core to be lost or pulled out. In response to this problem, the clamp seat provided by the present invention is an inner groove type anti-pulling clamp seat, which is convenient for removing rock debris on the conical surface, improving the reliability of the core claw contraction, and reducing the probability of core pulling out. Figure 9 As shown in FIG, the clamp seat 811 of the present invention is provided with a plurality of through-going chip removal grooves 8111 on the mating conical surface. The chip removal grooves are evenly distributed on the conical surface, which facilitates the removal of core debris that falls onto the mating conical surface due to vibration of the drill tool during drilling, thereby preventing the accumulation of debris that would affect the normal contraction of the core claw, resulting in a loose core grip and causing core pull.

[0068] The flip core grip assembly of the present invention is a composite core gripping mechanism that prevents core pulling, which can avoid the situation where the clamp-type core claws may not firmly grip the core during core cutting due to the lubrication of the sealing fluid, thereby preventing the core from falling or pulling out. Figure 10 The support card 821, the card sleeve 822 and the sliding sleeve 825 shown in FIG, and Figure 11The torsion spring 823 and the pin 824 are shown in FIG.

[0069] like Figure 11 As shown in FIG, the support card 821 is a pivot-type support card, with one end being a rotating end fixed to the sleeve 822 via a pin 824. The support card 821 can be completely retracted into the sleeve 822 by rotation. The other end of the support card is a free end (front end), which can be rotated out of the sleeve into the sliding sleeve or out of the sliding sleeve into the core. The free end of the support card is configured to face the core claw assembly. Furthermore, the front end of the support card can be a knife-tip type. A torsion spring 823 passes through the pin 824, with one end inserted into the support card 821 and the other end inserted into the sleeve 822. Once assembled, the torsion spring will apply inward pressure to the support card, forcing it to rotate into the sliding sleeve.

[0070] like Figure 13 As shown in , when the core drill enters the core, the torsion bar will be in the outward compression stage. In this stage, the core enters the sliding sleeve 825 and contacts the torsion bar 821, which will exert outward pressure on the torsion bar. This pressure can offset the pressure of the torsion spring, forcing the torsion bar 821 to retract, which will not affect the core entering the inner barrel, but the torsion bar 821 will still remain in the sliding sleeve 825.

[0071] like Figure 14 As shown in , when the core is cut or dropped, the toggle clamp will be in the core insertion stage. In this stage, the core extraction tool is raised, and the core moves downward relative to the sliding sleeve 825. At this time, the core drives the sliding sleeve 825 to move downward, and the sliding sleeve 825 drives the free end of the toggle clamp 821 to rotate out and insert the core. Here, the sliding sleeve is not fixed and is in a free floating state, and as shown in Figure 12 As shown in , the inner surface of the sleeve is an inverted tooth structure, which does not affect the core feeding, but when the core falls, it will produce a large resistance, which makes the function of the sleeve moving down easier to achieve. Figure 14 As shown in , the sliding sleeve may be provided with a tapered surface 8251 that cooperates with the support card 821. When the sliding sleeve 825 moves downward, it actively drives the support card 821 to rotate inward, so that the tip (front end) of the support card can be inserted into the core, preventing the core from falling and playing a role in preventing the core from falling.

[0072] Here, it should be noted that, unless otherwise specified, the fixed connections involved in the above content can all be achieved through threading.

[0073] The working principle of the present invention is as follows: before coring, after filling the inner barrel with sealing fluid at the wellhead, the coring tool is connected to the drill pipe and lowered to the bottom of the well. The pump and top drive are turned on, and the drilling pressure is gradually increased until the drilling pressure can shear the elastic positioning pin. Then, drilling continues. The core entering the inner barrel will push the lower sealing piston and the inner barrel string upward. When the inner barrel string reaches the highest position, the lower sealing piston will squeeze out the sealing fluid, which will flow out from the inner hole of the coring drill bit, wrapping the core and achieving the function of sealed coring. After coring is completed, the drill tool is lifted, and the core is cut using the core claw assembly and the flip-type core grip assembly. The drill tool is lifted up and the coring operation is carried out after it is out of the well.

[0074] Confined coring in inclined wells differs from that in vertical wells in that, in inclined wells, the coring tool is tilted to a certain extent. This causes gravity to cause the inner and outer barrels to become misaligned with the drill bit, increasing the core feed resistance. In horizontal wells, the inner barrel is horizontal, and the confining fluid sinks. Air bubbles form at the top, creating a low-pressure zone. This can cause drilling fluid to mix with the inner barrel and the confining fluid, affecting sealing efficiency. In inclined wells, after shearing the locating pin, gravity can cause it to fall into the core claw assembly or even the wellbore, causing core blockage and downhole complications.

[0075] A second exemplary embodiment of the present invention provides a drilling coring process applicable to a deviated well section. The coring process can be implemented using the closed coring device applicable to the deviated well section described in the first exemplary embodiment, and the coring process includes the following steps:

[0076] After the coring tool is assembled, it is connected to the drill bit and lowered to a position 2 to 3 meters from the bottom of the well. The pump is turned on to circulate the drilling fluid. The operation is stable during the drilling process. Do not brake, release or stop suddenly to prevent premature shearing. If a keyway, dog leg or well diameter reduction section is encountered, it should be lowered slowly. If there is serious obstruction and the sedimentation exceeds 3 meters, it is prohibited to use the coring drill bit to ream the hole.

[0077] After the cycle is completed, start the turntable or top drive, slowly lower the drill bit to explore the bottom, and after reaching the bottom, increase the drilling pressure by 30 to 50 kN to shear the pin. Observe whether the drilling pressure changes normally. If the drilling pressure rises and then drops suddenly, it means that the pin (i.e., the elastic positioning pin) has been sheared off and the shear pin is normal.

[0078] After the shearing is completed, adjust the drilling pressure to 2030kN, the rotation speed to 30-40r / min, the displacement to 14-16L / s, and start core drilling. After drilling 0.3-0.5m, adjust the drilling pressure to 50-90kN, the rotation speed to 50-70r / min, the displacement to 18-22L / s, and start core drilling.

[0079] After the core drilling is completed, the core is cut and the drill is pulled out. The connecting threads between the upper joint and the drill bit are removed at the wellhead. A bulletproof wire guard is put on the upper end of the upper joint. The upper sealing piston and the pressure relief plug are loosened. After the pressure relief plug is unscrewed to a certain degree, the pressure relief hole is exposed for pressure relief.

[0080] Remove the threads connecting the upper sub and the upper differential nipple, attach the lifting nipple to the upper end of the upper sub, pull the inner barrel string out of the outer barrel as a whole, remove the core claw assembly, and hoist the inner barrel to 0.3-0.5m from the drill floor to extract the core. Here, a tracer can be used to check the core sealing rate.

[0081] In this exemplary embodiment, the coring process may further include: a preparatory process before coring, mainly including various inspections of the coring tool itself and the bottom hole conditions before the coring tool is lowered into the well, as well as issues that require attention during tool assembly.

[0082] (1) Inspection before assembly.

[0083] ① Check the wellbore quality to ensure that there is no fallen objects at the bottom of the well and the wellbore is unobstructed.

[0084] ② Check the inner and outer cylinders to ensure there are no defects such as flattening or cracks that affect strength, and the threads should be intact.

[0085] ③ Check the clamp. The tungsten carbide particles welded on the surface should be uniform and angular, and the overall elasticity should be moderate.

[0086] ④ Check the bearings and ensure they rotate smoothly.

[0087] ⑤ Check the inner tube straightening nipple. The outer diameter should be 1-2mm smaller than the inner diameter of the outer tube, and the roller should roll flexibly.

[0088] ⑥ Check the O-ring plug and sealing plug to see if there are any cracks or hardening.

[0089] ⑦ Check the positioning pin, which should be an interference fit with the lower sealing piston.

[0090] ⑧The torsion spring force is moderate.

[0091] ⑨ The sealing liquid has moderate fluidity and cannot be solidified or diluted.

[0092] (2) Tool assembly.

[0093] Tool assembly is divided into two steps: site assembly and drill floor assembly:

[0094] a. Site assembly.

[0095] ① Assemble the upper sealing piston and the pressure relief plug thread to ensure that the pressure relief hole is blocked, and then install two O-rings on the lower end of the upper sealing piston.

[0096] ② After assembling the core claw assembly and the flip core grip assembly respectively, tighten the connecting threads of the two.

[0097] ③ Assemble the lower sealing piston, insert the lower sealing piston from the upper end of the core claw assembly, and hang it on the step inside the connecting sleeve.

[0098] ④ Connect the core claw assembly to the inner tube straightening nipple and the inner tube through threads.

[0099] ⑤The outer cylinder is connected to the lower differential short section by threads.

[0100] b. Drilling platform assembly.

[0101] ① Lift the outer cylinder onto the drilling platform and place it on the wellhead with slips and safety slips.

[0102] ② Assemble the rotary joint assembly, insert it from the upper end of the upper differential short section, and hang it on the differential short section.

[0103] ③ Lift the inner tube onto the drilling platform and seat the inner tube chuck on the upper end of the outer tube.

[0104] ④ Use the outer tube wire guard to lift the upper difference short section and tighten the connecting thread between the rotary joint assembly and the inner tube.

[0105] ⑤ Remove the inner cylinder chuck, lower it, and tighten the connecting thread between the upper differential short section and the outer cylinder.

[0106] ⑥ Connect the upper joint and the upper differential nipple.

[0107] ⑦ Lift the tool as a whole to expose the core claw assembly, and tighten the drill bit and outer cylinder through threads.

[0108] ⑧The positioning pin passes through the core drill bit, cooperates with the lower sealing piston, and installs the plug.

[0109] ⑨Fill the inner cylinder with sealing liquid through the upper joint.

[0110] ⑩Install the upper piston assembly into the upper joint to achieve a liquid-tight seal and complete the tool assembly.

[0111] In this exemplary embodiment, the coring process may further include: starting the pump to circulate the drilling fluid, activating the rotary table or top drive, slowly lowering the drill string to the bottom, and applying 30-50 kN of WOB to perform shearing. If the WOB remains unchanged after the increase in pressure, a static pressure of 60 kN is applied and the WOB changes are observed. If the WOB changes normally (an increase followed by a sudden drop), this indicates normal shearing, and coring is initiated. Otherwise, the drill is pulled out for inspection.

[0112] In this exemplary embodiment, the coring process may also include: when drilling to the designed size or encountering special circumstances such as core blockage, slowly lifting the drill string to cut the core, and carefully observing the weight indicator display. Generally, the core is broken by increasing the hanging weight by 50 to 400 kN and then immediately removing it. If the hanging weight is increased by 400 kN and remains stable, it may be a core blockage. At this time, the drilling tool should be stopped, the core should be kept in tension, and the drilling fluid flow rate should be increased and circulated until the core is broken. If the hanging weight of the coring tool does not change after being raised, the bottom core may be broken, which may easily lead to coring accidents such as core drop and barrel extraction. If the tool size allows, it is possible to continue drilling for 0.3 to 0.5 meters and then repeat the core cutting operation to ensure the recovery rate.

[0113] In this exemplary embodiment, the coring process may also include: during coring drilling, unless there are special circumstances, the pumping and rotation will not be stopped, and the drill bit will not be lifted off the bottom of the well. It is strictly forbidden to increase the drilling pressure to start the turntable. During coring drilling, it is necessary to pay attention to the changes in the mechanical drilling speed and pump pressure. If any abnormality is found, it must be dealt with decisively.

[0114] During core drilling, handling of abnormal situations includes:

[0115] Ⅰ. The pump pressure gradually increases and the mechanical drilling speed decreases accordingly. Lift the drill bit and the pump pressure will recover. This is usually due to drill bit wear and the drill should be cut to start drilling.

[0116] Ⅱ. The pump pressure suddenly increases and the mechanical drilling speed drops significantly. This is usually caused by entering soft formations and mud packing on the drill bit.

[0117] Ⅲ. When the pump pressure increases but the drilling speed remains basically unchanged and the pump pressure does not drop when the drill bit is lifted, it is usually because the water hole of the drill bit is clogged. If the problem cannot be eliminated, the core should be cut and the drill should be started.

[0118] IV. Large fluctuations in pump pressure and fluctuating drilling speed usually occur when drilling into soft and hard interlaced formations. The drilling pressure should be adjusted appropriately.

[0119] Ⅴ. The pump pressure decreases, the mechanical drilling speed drops significantly, or even there is no footage. This is usually due to core blockage, and the core should be cut to start drilling.

[0120] Ⅵ. If the pump pressure drops significantly, it may be caused by leakage in the drill bit, and the drill should be cut and the core should be pulled out.

[0121] In summary, the advantages proposed by the present invention include at least one of the following:

[0122] (1) The inner barrel straightening sub of the closed coring device for inclined well sections proposed by the present invention adopts an integral structure, which has higher mechanical strength and longer service life under tensile and torsion loads at the bottom of the well. Steel balls are used to replace the existing roller straightening devices, which reduces the friction between the inner barrel and the outer barrel.

[0123] (2) The suspension mechanism of the closed coring device for inclined well sections proposed by the present invention can prevent the loss of closed fluid and realize the double-drum single-action function of the inner and outer cylinders, thereby preventing the rotation of the inner cylinder from causing mechanical damage to the core and reducing the probability of core blockage;

[0124] (3) The lower sealing piston of the closed coring device for inclined well sections proposed by the present invention can prevent the mixing of the sealing fluid and the drilling fluid, thereby improving the sealing rate;

[0125] (4) The clamp seat of the closed coring device for inclined well sections proposed by the present invention is conducive to the discharge of core debris, avoiding the accumulation of debris and causing the core to be pulled out;

[0126] (5) The elastic positioning pin of the closed coring device for inclined well sections proposed by the present invention can solve the problem of obstructed coring. During assembly, the force-bearing diameter becomes smaller, but it is still in a tight fit with the lower sealing piston and will not fall off after the pin is sheared;

[0127] (6) The clearance between the lower end of the inner tube of the closed coring device for inclined well sections and the stepped surface of the coring drill bit proposed by the present invention is a small clearance anti-scouring and flow-limiting structure, which can increase the resistance to the flow of drilling fluid;

[0128] (7) The drilling and coring process for inclined well sections proposed by the present invention is easy to operate and can improve construction efficiency;

[0129] (8) The drilling and coring process for inclined well sections proposed by the present invention does not require a change in the sealing fluid filling method, and the assembly work efficiency is higher;

[0130] (9) The drilling coring process for inclined well sections proposed in the present invention can ensure that the coring operation is carried out efficiently and safely.

[0131] Although the above description of a closed coring device and a drilling coring process suitable for an inclined well section of the present invention has been made in combination with exemplary embodiments, it should be clear to those skilled in the art that various modifications and changes may be made to the exemplary embodiments of the present invention without departing from the spirit and scope defined by the claims.

Claims

1. A closed coring device suitable for inclined well sections, characterized in that: The sealed coring device includes an upper joint, a differential nipple, an outer cylinder, a suspension mechanism, a rotary joint assembly, an inner cylinder, a core grabbing mechanism, an upper sealing piston, a lower sealing piston and a coring drill bit, wherein: The upper joint, the differential short section, the outer cylinder and the core drill bit are fixedly connected to form an outer cylinder string of a closed coring device; the rotary joint assembly, the inner cylinder and the core grabbing mechanism are all arranged inside the outer cylinder string and fixedly connected from top to bottom to form an inner cylinder string of a closed coring device; a circulation channel is formed between the outer wall of the inner cylinder string and the inner wall of the outer cylinder string; the upper end of the upper joint is connected to the drill collar; the inner cylinder string is suspended on the differential short section by a hanging mechanism; the hanging mechanism can realize double-cylinder single-action of the inner and outer cylinders; the upper sealing piston is arranged inside the upper joint and is connected with the inner cylinder, so as to realize drilling circulation and inner cylinder pressure relief; the lower sealing piston passes through the core grabbing mechanism and is fixed to the core drill bit by an elastic locating pin and a plug; the hanging mechanism includes a pressure relief plug, a half ring, a bearing, a water diversion joint and a sealing ring, wherein the relief The pressure plug is connected to the upper sealing piston; the bearing suspends the inner cylinder string on the differential short section; the half ring is arranged at the upper end of the bearing to lock the bearing axially; the upper end of the water diversion joint and the lower end of the upper joint form a tolerance fit, so that the inner cylinder string is concentric with the outer cylinder and the inner diameter of the drill bit; the sealing ring is arranged at the lower end of the upper sealing piston and is installed in the water diversion joint together with the upper sealing piston; the upper sealing piston seals the sealing liquid in the inner cylinder through the sealing ring and the pressure relief plug, and the upper sealing piston is provided with a flow channel hole and a pressure relief hole, and the flow channel hole realizes drilling circulation through the drilling fluid. When the pressure relief plug is unscrewed to a certain opening, the pressure relief hole is exposed to realize pressure relief of the inner cylinder; the lower sealing piston includes an O-ring and a rubber plug to effectively seal the sealing liquid and ensure the unidirectional flow of the sealing liquid.

2. The closed coring device for inclined well sections according to claim 1, characterized in that: The end surface of the elastic positioning pin is provided with a drilling hole and a cutting groove. The elastic positioning pin is elastic, and the elastic positioning pin forms an interference fit with the lower sealing piston.

3. The closed coring device for inclined well sections according to claim 1, characterized in that: There is a fitting gap between the lower end of the inner cylinder and the step surface of the core drill bit, and the width of the fitting gap is 0.1-0.2 mm.

4. The closed coring device for inclined well sections according to claim 1, characterized in that: The closed coring device also includes an inner cylinder straightening short section, which is arranged at the lower end of the inner cylinder and located at the upper end of the core grabbing mechanism. The inner cylinder straightening short section can straighten the inner cylinder and, together with the water diversion joint, make the inner cylinder string concentric with the outer cylinder and the inner diameter of the drill bit.

5. The closed coring device for inclined well sections according to claim 4, characterized in that: The inner tube straightening nipple includes a body and multiple steel balls, wherein the body is processed as a whole and has multiple rectangular protrusions in the middle. A straight groove is provided in the middle of the protrusion along the axial direction; the steel balls are arranged in the straight grooves, and the maximum exposed diameter of the steel balls is smaller than the inner diameter of the outer tube. The steel balls form rolling friction with the inner wall of the outer tube. During the rotation of the outer tube, the steel balls can support the inner tube from being eccentric; an annular flow channel groove is provided on the body to reduce the erosion of the body by the eddy current of the drilling fluid.

6. The closed coring device for inclined well sections according to claim 1, characterized in that: The core grabbing mechanism includes a core claw assembly and a flip core grabbing assembly, wherein the core claw assembly is arranged on the upper end of the flip core grabbing assembly, The core claw assembly includes a clamp seat and a core claw. The inner wall of the clamp seat is provided with a conical surface. The outer surface of the core claw is provided with a conical surface that matches the inner conical surface of the clamp seat. The conical surface of the clamp seat is provided with a plurality of through-cutting grooves to facilitate the removal of cuttings on the conical surface. The flip-type core gripping assembly includes a support card, a sleeve, a sliding sleeve, a pin and a torsion spring, wherein one end of the support card is fixed to the sleeve by a pin, and the other end can be freely rotated out of the sleeve. The free end of the support card faces the core claw assembly, and the front end of the support card is a knife tip type, which can be inserted into the core to prevent the core from falling; the torsion spring passes through the pin, one end is inserted into the support card, and the other end is inserted into the sleeve. The torsion spring can turn the support card into the sliding sleeve.

7. The closed coring device for inclined well sections according to claim 1, characterized in that: The upper end of the upper joint is connected to the drill collar through a drill pipe thread. The upper sealing piston is arranged inside the upper joint and is limited by the threaded end face of the drill pipe. The stroke of the upper sealing piston and the threaded end face of the drill pipe is greater than the sealing surface length of the lower sealing piston after shearing, ensuring that the sealing fluid can be effectively released after shearing.

8. A drilling coring process suitable for inclined well sections, characterized in that: The coring process is implemented by a closed coring device suitable for inclined well sections according to any one of claims 1 to 7, and comprises the steps of: After the coring tool is assembled, connect it to the drill string, lower it to a position 2-3 m from the bottom of the well, and start the pump to circulate the drilling fluid; After the cycle is completed, start the rotary table or top drive, slowly lower the drill bit to the bottom, and after reaching the bottom, increase the drilling pressure to 30~50kN to shear the pins; After the pin is sheared, adjust the drilling pressure, speed and displacement to start the core drilling. After the core is drilled 0.3-0.5m, adjust the drilling pressure, speed and displacement again to start the core drilling. After coring is completed, the core is cut and the drill is pulled out to relieve pressure and remove the core.

9. The drilling coring process applicable to inclined well sections according to claim 8, characterized in that: The coring process also includes: When the drilling pressure increases and then drops suddenly and remains unchanged after pressurization, maintain the static pressure at 60kN and observe the changes in drilling pressure. If the shearing is normal, start drilling the core; otherwise, pull out the drill for inspection.

10. The drilling coring process applicable to a deviated well section according to claim 8, characterized in that: The coring process also includes: When pulling out the drill, if the hanging weight is increased and kept steady without lowering, stop lifting the drill bit, keep the core in tension, and increase the drilling fluid flow rate until the core breaks; If the suspended weight does not change, continue drilling for 0.3 to 0.5 m and repeat the core cutting operation.

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