Hydraulic controlled balanced downhole safety valve and its use method

Abstract

The present invention relates to the field of oil production technology, and in particular to a hydraulically controlled balanced downhole safety valve and a method for using the same. The technical solution is as follows: a first hydraulic oil channel and a second hydraulic control pipeline are provided on the outer wall of a cylinder sleeve, the upper end surface height of the first hydraulic oil channel is higher than the upper end surface height of the second hydraulic oil channel, and the first hydraulic control pipeline is installed on the upper end surface of the first hydraulic oil channel, and the second hydraulic oil channel is installed on the upper end surface of the second hydraulic oil channel, and the hydraulic control pipeline for controlling the opening and closing of the downhole safety valve is changed from a single one to two hydraulic control pipelines in U-shaped linkage, and the hydraulic balance of the liquid column pressure of the two hydraulic control pipelines acting on the center pipe is equal; the force balance of the oil layer pressure acting on the center pipe is equal, and the two balance systems overcome the adverse effects of the liquid column pressure and the oil layer pressure on the switch of the hydraulically controlled balanced downhole safety valve in the prior art, and ensure that the present invention can be lowered deeper to achieve downhole safety control of deep wells, ultra-deep wells, high-pressure wells, medium-deep sea and other oil and gas wells.

Description

Technical Field

[0001] The invention relates to the technical field of oil extraction, and in particular to a hydraulically controlled balanced downhole safety valve and a use method thereof. Background Art

[0002] Since most offshore oil fields are located in storm surge prone areas, the working environment is harsh, and the development faces three major global problems: high temperature, high pressure, and water depth. The mining risk is high, and any small mistake in the development may lead to major accidents of oil and gas wells and personnel, causing huge economic losses, and may cause serious pollution to the marine environment, with immeasurable consequences. In order to ensure the safe and efficient development of offshore oil and gas wells, relevant laws and regulations at home and abroad stipulate that downhole safety valves should be installed below 30m of the seabed. With the continuous advancement to medium and deep waters, downhole safety valves are also required to go deeper and deeper.

[0003] At present, the commonly used downhole safety valve uses a hydraulic control line to control the opening or closing of the downhole safety valve from the ground. Its working principle is: high-pressure liquid is transmitted from the hydraulic control line to the piston part of the downhole safety valve. When the piston force is greater than the elastic force of the spring, the hydraulic pressure pushes the piston to overcome the elastic force of the spring and move downward, driving the center pipe to push open the valve plate of the downhole safety valve, and establish a normally open liquid channel inside the center pipe; when the safety valve needs to be closed, the hydraulic pressure in the hydraulic control line is released, the spring force is greater than the piston force, and the piston moves upward under the action of the spring, driving the center pipe upward. At this time, the valve plate is quickly closed under the elastic force of the torsion spring, cutting off the upper and lower liquid channels. In this way, the piston force generated by the hydraulic pressure in the hydraulic control line forms a pair of interacting forces with the spring, thereby controlling the opening or closing of the downhole safety valve.

[0004] However, with the need to develop deep-water areas or safe development of deep wells on land, ultra-deep high-temperature and high-pressure wells, downhole safety valves are getting deeper and deeper, resulting in longer and longer hydraulic control pipelines for controlling downhole safety valves, and higher and higher liquid column pressure in the hydraulic control pipelines. However, the borehole size of oil and gas wells is limited, and the size and elasticity of the spring inside the downhole safety valve are limited. The spring force is difficult to balance the piston force caused by the high liquid column pressure in the long hydraulic control pipeline, and it is impossible to control the conventional downhole safety valve to achieve production opening or emergency closing required for downhole safety control. To this end, two technologies, reducing the piston area and N2 balance chamber, have been adopted at home and abroad to achieve a downhole safety valve down to a depth of 3000m, but there are still the following shortcomings:

[0005] Technology 1: Change the piston cylinder into a piston rod, reduce the piston area, and reduce the piston force. This technical idea can meet the requirements of a certain downhole safety valve depth of about 1000m, but for deeper downhole requirements, the smaller piston rod is prone to instability when pushing and pulling the center pipe up and down.

[0006] In addition, the upper end of the piston of the downhole safety valve is connected to the hydraulic pressure in the control pipeline, and the lower end is connected to the oil layer pressure in the connecting oil pipe. When the downhole safety valve is opened, the hydraulic pressure that controls the downhole safety valve needs to overcome or balance the oil layer pressure before it can generate a piston force under a certain hydraulic pressure to balance the spring force of the downhole safety valve. For example: For deep wells, if the oil layer pressure is 90MPa, the pressure of the hydraulic control pipeline needs to overcome the 90MPa oil layer pressure first, and then increase the hydraulic pressure to balance the spring force and control the switch of the downhole safety valve. This results in extremely high hydraulic sealing pressure of the hydraulic control pipeline, and the piston of the downhole safety valve needs to move + long-term high-pressure sealing, which is extremely difficult and prone to failure. In addition, the movement of the slender piston under high pressure is more prone to instability.

[0007] (3) Technology 2: Adding an N2 balance tank to balance the liquid column pressure of the hydraulic control pipeline through the pressure of nitrogen. However, there are problems: long-term high-pressure gas sealing is difficult; nitrogen N2 is a gas. According to the Bernoulli equation, under ideal gas conditions, the pressure of the N2 balance tank is affected by the temperature and pressure of the oil and gas wells. It is necessary to combine the specific well conditions of each well to design the appropriate N2 amount and matching pressure, which is difficult to operate; and if any of these factors is wrong, it may cause the N2 balance tank to fail, causing safety risks.

[0008] In view of this problem, a hydraulically controlled balanced downhole safety valve and a use method thereof are proposed. Summary of the invention

[0009] The purpose of the present invention is to address the deficiencies in the prior art and propose a hydraulically controlled balanced downhole safety valve and a method of use. The hydraulic pressure of the liquid column pressures of the two hydraulically controlled pipelines acting on the central pipe is equally balanced; the force acting on the central pipe by the oil layer pressure is equally balanced. The two balance systems overcome the adverse effects of the liquid column pressure and the oil layer pressure in the prior art on the switching of the hydraulically controlled balanced downhole safety valve, ensuring that the present invention can be lowered deeper to achieve downhole safety control of deep wells, ultra-deep wells, high-pressure wells, medium and deep sea oil and gas wells, and also avoid the safety hazards and risks caused by the inability to open or close normally.

[0010] The present invention mentions a hydraulically controlled balanced downhole safety valve, and its technical solution is: it includes a center tube and a cylinder sleeve, the center tube is installed in the cylinder sleeve, and also includes an upper joint, a spring, a first hydraulic control pipeline, a valve seat, a valve plate, a torsion spring, a pin, a lower joint, and a second hydraulic control pipeline. The upper end of the cylinder sleeve is movably connected to the upper joint, and the lower end is movably connected to the lower joint. A first hydraulic oil channel is provided on one side of the outer wall of the cylinder sleeve, and a second hydraulic oil channel is installed on the other side. The upper end surface height of the first hydraulic oil channel is higher than the upper end surface height of the second hydraulic oil channel. The first hydraulic control pipeline is installed on the upper end surface of the first hydraulic oil channel, and the second hydraulic control pipeline is installed on the upper end surface of the second hydraulic oil channel. ; A valve seat is installed on the inner wall of the lower end of the cylinder sleeve, and the lower end of the valve seat is movably connected to the valve plate, and a torsion spring is installed on one side of the valve plate through a pin; a spring is installed on the outer wall of the center tube, and the spring is located between the upper limit protrusion of the center tube and the upper end surface of the cylinder sleeve; the first hydraulic control pipeline and the second hydraulic control pipeline for controlling opening and closing form a U-shaped structure from the connection point downhole to the wellhead, and the liquid column pressure of the first hydraulic control pipeline and the second hydraulic control pipeline acts on the hydraulic balance of the center tube, and the control pressures in the first hydraulic control pipeline and the second hydraulic control pipeline are independently sealed; the diameters of the upper and lower ends of the center tube are equal, and the force acting on the center tube by the oil layer pressure is balanced and equal.

[0011] Preferably, an annular sealing protrusion is provided on the middle and lower outer wall of the above-mentioned center tube, a mechanical seal is formed between the annular sealing protrusion and the inner wall of the cylinder liner, and the lower outlet of the first hydraulic oil channel is located above the annular sealing protrusion, and the lower outlet of the second hydraulic oil channel is located below the annular sealing protrusion.

[0012] Preferably, a lower limit sealing protrusion is provided on the inner wall of the lower end of the cylinder sleeve, and a mechanical seal is formed between the outer wall of the lower end of the center tube and the lower limit sealing protrusion.

[0013] Preferably, a central tube docking channel is provided at the lower portion of the inner cavity of the lower joint, and a conical guide groove is provided at the upper portion of the central tube docking channel.

[0014] Preferably, the upper outer wall of the above-mentioned center tube forms a mechanical sealing structure with the inner wall of the upper joint, and forms an upper piston chamber for opening the valve between the annular sealing protrusion and the inner wall of the cylinder sleeve to form a mechanical seal. The high-pressure hydraulic oil from the first hydraulic oil channel pushes the center tube to move downward, and the downward-moving center tube pushes open the valve plate and is connected with the center tube docking channel of the lower joint.

[0015] Preferably, a lower piston chamber for closing the valve is formed between the annular sealing protrusion of the above-mentioned center tube and the lower limit sealing protrusion of the cylinder sleeve. The center tube is pushed upward by the high-pressure hydraulic oil from the second hydraulic oil channel and the spring. After the center tube moves up a certain distance, the valve plate is reset by the torsion spring.

[0016] Preferably, the upper outlet of the first hydraulic oil channel is connected to the first hydraulic control pipeline via a first pressure cap, and the upper outlet of the second hydraulic oil channel is connected to the second hydraulic control pipeline via a second pressure cap.

[0017] Preferably, the upper end of the above-mentioned cylinder liner is provided with a cylinder liner upper joint, the lower end is provided with a cylinder liner lower joint, a first hydraulic control mounting protrusion is provided on one side of the cylinder liner, and a second hydraulic control mounting protrusion is provided on the other side, wherein the first hydraulic oil channel is located in the inner cavity of the first hydraulic control mounting protrusion, the second hydraulic oil channel is located in the inner cavity of the second hydraulic control mounting protrusion, and the height of the first hydraulic control mounting protrusion is higher than the height of the second hydraulic control mounting protrusion, the upper end surface of the first hydraulic control mounting protrusion is provided with a first pressure cap mounting hole, and the upper end surface of the second hydraulic control mounting protrusion is provided with a second pressure cap mounting hole.

[0018] The method for using the hydraulically controlled balanced downhole safety valve mentioned in the present invention comprises the following process:

[0019] (i) When controlled to open: by controlling the pressure on the first hydraulic control pipeline at the wellhead, the high-pressure liquid flows downward along the first hydraulic control pipeline into the first hydraulic oil channel. Since the upper joint, the cylinder sleeve and the center tube form an upper piston chamber, the center tube, under the action of the high-pressure liquid, overcomes the spring force and moves downward, so that the center tube pushes the valve plate open and continues to move downward, so that the lower end of the center tube is limited at the lower joint, and the valve plate rotates downward around the pin and rotates into the annulus between the center tube and the lower joint. At this time, a normally open liquid channel is established in the center tube, and the hydraulically controlled balanced downhole safety valve is in an open state;

[0020] (ii) When closed by control: the first hydraulic control pipeline is controlled to release pressure at the wellhead, and the center pipe is pushed upward and reset under the action of the spring. At this time, the valve plate loses the support of the center pipe and resets and closes under the push of the torsion spring, blocking the liquid channel formed by the center pipe, thus realizing the closure of the hydraulically controlled balanced downhole safety valve;

[0021] In addition, when the spring fails, by pressurizing the second hydraulic control pipeline at the wellhead, high-pressure liquid flows downward along the second hydraulic control pipeline into the second hydraulic oil channel, and enters the lower piston chamber formed between the lower limit sealing protrusion of the cylinder sleeve and the lower part of the center pipe, thereby pressurizing the center pipe upward. The valve plate, without the support of the center pipe, resets and closes under the push of the torsion spring, thereby forcing the hydraulically controlled balanced downhole safety valve to be closed.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The present invention can be lowered into a well on the seabed or a deep well on the ground. The upper end surface height of the first hydraulic oil channel is slightly higher than the upper end surface height of the second hydraulic oil channel. Therefore, the first hydraulic control pipeline and the second hydraulic control pipeline lowered into the deep well are nearly equal. Therefore, the hydraulic pressure acting on the upper and lower parts of the central pipe and the force of the spring acting on the central pipe are in a balanced state. In addition, the diameters of the upper and lower ends of the central pipe are equal, and the force of the oil layer pressure acting on the central pipe is balanced and equal; therefore, no matter how deep the hydraulically controlled balanced downhole safety valve is lowered into the deep well, the liquid column pressures in the first hydraulic control pipeline and the second hydraulic control pipeline are balanced. Therefore, the switching action of the hydraulically controlled balanced downhole safety valve is only affected by the ground control hydraulic pressure, and it is easy to control the opening or closing of the hydraulically controlled balanced downhole safety valve, thereby avoiding safety hazards and risks caused by failure to open or close normally. The two balancing systems of the present invention overcome the adverse effects of the liquid column pressure and oil layer pressure of the hydraulic control system of the conventional downhole safety valve on the downhole safety valve switch, ensuring that the hydraulically controlled balanced downhole safety valve of the present invention can be lowered deeper, thereby realizing downhole safety control of deep wells, ultra-deep wells, high-pressure wells, medium-deep sea and other oil and gas wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure when the central tube of the present invention is closed;

[0025] Figure 2 It is a schematic diagram of the structure when the central tube of the present invention is closed;

[0026] Figure 3 It is a schematic diagram of the structure of the central tube;

[0027] Figure 4 It is a schematic diagram of the structure of the cylinder liner;

[0028] Figure 5 is a schematic diagram of the structure of the lower joint;

[0029] In the above figure: upper joint 1, center tube 2, spring 3, first hydraulic control pipeline 4, first pressure cap 5, cylinder sleeve 6, valve seat 7, valve plate 8, torsion spring 9, pin 10, lower joint 11, second hydraulic control pipeline 12, second pressure cap 13, annular sealing protrusion 2.1, upper limit protrusion 2.2, first hydraulic oil channel 6.1, second hydraulic oil channel 6.2, lower limit sealing protrusion 6.3, first hydraulic control installation protrusion 6.4, second hydraulic control installation protrusion 6.5, cylinder sleeve upper joint 6.6, cylinder sleeve lower joint 6.7, center tube docking channel 11.1, tapered guide groove 11.2, internal thread 11.3, external thread 11.4, first center tube diameter d1, second center tube diameter d2, third center tube diameter d3. DETAILED DESCRIPTION

[0030] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0031] Example 1, reference Figure 1-Figure 5 The present invention mentions a hydraulically controlled balanced downhole safety valve, comprising a center pipe 2 and a cylinder sleeve 6, wherein the center pipe 2 is installed in the cylinder sleeve 6, and further comprising an upper joint 1, a spring 3, a first hydraulic control pipeline 4, a valve seat 7, a valve plate 8, a torsion spring 9, a pin 10, a lower joint 11, and a second hydraulic control pipeline 12. The upper end of the cylinder sleeve 6 is movably connected to the upper joint 1, and the lower end is movably connected to the lower joint 11. A first hydraulic oil channel 6.1 is provided on one side of the outer wall of the cylinder sleeve 6, and a second hydraulic oil channel 6.2 is installed on the other side. The upper end surface height of the first hydraulic oil channel 6.1 is higher than the upper end surface height of the second hydraulic oil channel 6.2. The first hydraulic control pipeline 4 is installed on the upper end surface of the first hydraulic oil channel 6.1, and the second hydraulic control pipeline 4 is installed on the upper end surface of the second hydraulic oil channel 6.2. pipeline 12; a valve seat 7 is installed on the inner wall of the lower end of the cylinder sleeve 6, and the lower end of the valve seat 7 is movably connected to the valve plate 8, and a torsion spring 9 is installed on one side of the valve plate 8 through a pin 10; a spring 3 is installed on the outer wall of the center pipe 2, and the spring 3 is located between the upper limit protrusion 2.2 of the center pipe 2 and the upper end surface of the cylinder sleeve 6; the first hydraulic control pipeline 4 and the second hydraulic control pipeline 12 for controlling opening and closing form a U-shaped structure from the connection point downhole to the wellhead, and the liquid column pressure of the first hydraulic control pipeline 4 and the second hydraulic control pipeline 12 acts on the hydraulic balance of the center pipe 2, and the control pressure in the first hydraulic control pipeline 4 and the second hydraulic control pipeline 12 is independently sealed; the diameters of the upper and lower ends of the center pipe 2 are equal, and the force acting on the center pipe 2 by the oil layer pressure is balanced and equal.

[0032] Reference Figure 3 An annular sealing protrusion 2.1 is provided on the middle and lower outer wall of the center tube 2 mentioned in the present invention, and a mechanical seal is formed between the annular sealing protrusion 2.1 and the inner wall of the cylinder sleeve 6, and the lower outlet of the first hydraulic oil channel 6.1 is located above the annular sealing protrusion 2.1, and the lower outlet of the second hydraulic oil channel 6.2 is located below the annular sealing protrusion 2.1.

[0033] Reference Figure 4 The inner wall of the lower end of the cylinder sleeve 6 mentioned in the present invention is provided with a lower limit sealing protrusion 6.3, and the outer wall of the lower end of the center tube 2 forms a mechanical seal with the lower limit sealing protrusion 6.3.

[0034] In addition, the upper end of the above-mentioned cylinder sleeve 6 is provided with a cylinder sleeve upper joint 6.6, and the lower end is provided with a cylinder sleeve lower joint 6.7. A first hydraulic control mounting protrusion 6.4 is provided on one side of the cylinder sleeve 6, and a second hydraulic control mounting protrusion 6.5 is provided on the other side, wherein the first hydraulic oil channel 6.1 is located in the inner cavity of the first hydraulic control mounting protrusion 6.4, the second hydraulic oil channel 6.2 is located in the inner cavity of the second hydraulic control mounting protrusion 6.5, and the height of the first hydraulic control mounting protrusion 6.4 is higher than the height of the second hydraulic control mounting protrusion 6.5, and the upper end surface of the first hydraulic control mounting protrusion 6.4 is provided with a first pressure cap mounting hole, and the upper end surface of the second hydraulic control mounting protrusion 6.5 is provided with a second pressure cap mounting hole.

[0035] Reference Figure 5 The lower part of the inner cavity of the lower joint 11 mentioned in the present invention is provided with a center tube docking channel 11.1, and a conical guide groove 11.2 is provided at the upper part of the center tube docking channel 11.1, which is used to guide the downward moving center tube 2 to accurately dock with the center tube docking channel 11.1. In addition, the upper end of the lower joint 11 is provided with an internal thread 11.3 for connecting with the lower end of the cylinder sleeve 6; the lower end of the lower joint 11 is provided with an external thread 11.4.

[0036] The upper outer wall of the above-mentioned center tube 2 forms a mechanical sealing structure with the inner wall of the upper joint 1, and forms an upper piston chamber for opening the valve between the annular sealing protrusion 2.1 and the inner wall of the cylinder sleeve 6. The high-pressure hydraulic oil from the first hydraulic oil channel 6.1 pushes the center tube 2 to move downward, and the downward moving center tube 2 pushes open the valve plate 8 and communicates with the center tube docking channel 11.1 of the lower joint 11.

[0037] A lower piston chamber for closing the valve is formed between the annular sealing protrusion 2.1 of the above-mentioned center tube 2 and the lower limit sealing protrusion 6.3 of the cylinder sleeve 6. The high-pressure hydraulic oil from the second hydraulic oil channel 6.2 and the spring 3 push the center tube 2 upward. After the center tube 2 moves up a certain distance, the valve plate 8 is reset by the torsion spring 9.

[0038] The upper outlet of the first hydraulic oil channel 6.1 is connected to the first hydraulic control pipeline 4 through the first pressure cap 5, and the upper outlet of the second hydraulic oil channel 6.2 is connected to the second hydraulic control pipeline 12 through the second pressure cap 13.

[0039] The method for using the hydraulically controlled balanced downhole safety valve mentioned in the present invention comprises the following process:

[0040] (i) When controlled to open: by controlling the pressure on the first hydraulic control pipeline 4 at the wellhead, the high-pressure liquid flows downward along the first hydraulic control pipeline 4 into the first hydraulic oil channel 6.1. Since the upper joint 1, the cylinder sleeve 6 and the center pipe 2 form an upper piston chamber, the center pipe 2, under the action of the high-pressure liquid, overcomes the action of the spring 3 and moves downward, so that the center pipe 2 pushes the valve plate 8 open and continues to move downward, so that the lower end of the center pipe 2 is limited at the lower joint 11, and the valve plate 8 rotates downward around the pin 10 and rotates into the annulus between the center pipe 2 and the lower joint 11. At this time, a normally open liquid channel is established in the center pipe 2, and the hydraulically controlled balanced downhole safety valve is in an open state;

[0041] (ii) When controlled to close: the first hydraulic control pipeline 4 is controlled to release pressure at the wellhead, and the center pipe 2 is pushed upward and reset under the action of the spring 3. At this time, the valve plate 8, without the support of the center pipe 2, is reset and closed under the push of the torsion spring 9, thereby blocking the liquid channel formed by the center pipe 2 and closing the hydraulically controlled balanced downhole safety valve. In addition, when the spring 3 fails, the second hydraulic control pipeline 12 is pressurized at the wellhead, and the high-pressure liquid flows downward along the second hydraulic control pipeline 12 into the second hydraulic oil channel 6.2, and enters the lower piston chamber formed between the lower limit sealing protrusion 6.3 of the cylinder sleeve 6 and the lower part of the center pipe 2, so that the center pipe 2 is pressurized and moves upward. The valve plate 8, without the support of the center pipe 2, is reset and closed under the push of the torsion spring 9, thereby forcing the hydraulically controlled balanced downhole safety valve to be closed.

[0042] The further working principle of the present invention is:

[0043] The first center tube diameter d1 matches with the inner wall of the upper joint 1, and the second center tube diameter d2 matches with the inner wall of the cylinder sleeve 6. By relying on the difference in circular area between the first center tube diameter d1 and the second center tube diameter d2, an upper piston cavity is formed. When the pressure is applied from the wellhead to the first hydraulic control pipeline 4, the high-pressure liquid can overcome the spring force, push the center tube 2 downward, and push open the valve plate 8. The center tube 2 continues to move downward under pressure, and the valve plate 8 moves to the annulus between the center tube 2 and the lower joint 11, reducing the erosion of the valve plate 8 by the fluid produced in the well, and establishing a normally open liquid channel in the center tube 2. The hydraulically controlled balanced downhole safety valve is in an open state. state; when the first hydraulic control pipeline 4 is depressurized, the center pipe 2 is pushed upward under the action of the spring 3, the valve plate 8 loses the support of the center pipe 2, and the fluid channel of the center pipe 2 is closed under the action of the torsion spring 9; in addition, in order to prevent the spring 3 from failing to close the hydraulically controlled balanced downhole safety valve, by pressing the second hydraulic control pipeline 12 at the wellhead, a lower piston chamber is formed under the cooperation of the second center pipe diameter d2, the third center pipe diameter d3 and the cylinder sleeve 6, and the high-pressure liquid forces the center pipe 2 to move upward under force, thereby realizing the forced closure of the hydraulically controlled balanced downhole safety valve to avoid safety hazards and risks.

[0044] The advantages of the present invention mainly include:

[0045] 1. The pressure of the liquid columns in the first hydraulic control pipeline 4 and the second hydraulic control pipeline 12 is balanced. The control pipeline is changed from one hydraulic control pipeline to two hydraulic control pipelines. The first hydraulic control pipeline 4 connected to the center pipe 2 is pressurized to control the opening of the hydraulically controlled balanced downhole safety valve; the spring 3 or the second hydraulic control pipeline 12 connected to the center pipe 2 is pressurized to control the closing of the hydraulically controlled balanced downhole safety valve. Since the hydraulic pressure of the two hydraulic control lines of the hydraulically controlled downhole safety valve acts on the middle and upper part and the middle and lower part of the central pipe 2 respectively, the height difference can be ignored compared with the length of the hydraulic control line that is several thousand meters in the deep well. In this way, the two deep and long hydraulic control lines form a U-shaped connection, and the pressure of the liquid columns in the two hydraulic control lines acts on the central pipe 2 almost equally, so that the pressure balance of the liquid columns is achieved. At this time, the opening of the hydraulically controlled downhole safety valve is only affected by the elastic force of the spring 3 and the pressure of the high-pressure liquid provided to the first hydraulic control line 4 at the wellhead, and has nothing to do with the insertion depth of the hydraulically controlled downhole safety valve.

[0046] Second, the oil layer pressure on the center pipe 2 is independent of the control pressure in the hydraulic control line. Since the diameter d1 of the first center pipe is equal to the diameter d3 of the third center pipe, the oil layer pressure acts on the upper and lower pressures of the center pipe 2 in an equal balance. Therefore, the opening and closing of the hydraulically controlled balanced downhole safety valve are independent of the formation pressure of the hydraulically controlled balanced downhole safety valve. In addition, the wall thickness of the large-diameter center pipe 2 is large, which can ensure the high-pressure bearing capacity of the hydraulically controlled balanced downhole safety valve and avoid the instability of the slender piston rod in the prior art.

[0047] Embodiment 2, a hydraulically controlled balanced downhole safety valve mentioned in the present invention comprises a center pipe 2 and a cylinder sleeve 6, wherein the center pipe 2 is installed in the cylinder sleeve 6, wherein the center pipe 2 also comprises an upper joint 1, a spring 3, a first hydraulic control pipeline 4, a valve seat 7, a valve plate 8, a torsion spring 9, a pin 10, a lower joint 11, and a second hydraulic control pipeline 12, wherein the upper end of the cylinder sleeve 6 is movably connected to the upper joint 1, and the lower end is movably connected to the lower joint 11, a first hydraulic oil channel 6.1 is provided on one side of the outer wall of the cylinder sleeve 6, and a second hydraulic control pipeline 12 is installed on the other side, and the first hydraulic oil channel 6 .1 has a higher height than the upper end surface height of the second hydraulic oil channel 6.2, and the first hydraulic control pipeline 4 is installed on the upper end surface of the first hydraulic oil channel 6.1, and the second hydraulic oil channel 6.2 is installed on the upper end surface of the second hydraulic oil channel 6.2; a valve seat 7 is installed on the inner wall of the lower end of the cylinder sleeve 6, and the lower end of the valve seat 7 is movably connected to the valve plate 8, and a torsion spring 9 is installed on one side of the valve plate 8 through a pin 10; a spring 3 is installed on the outer wall of the center tube 2, and the spring 3 is located between the upper limit protrusion 2.2 of the center tube 2 and the upper end surface of the cylinder sleeve 6.

[0048] The difference from Example 1 is:

[0049] Reference Figure 3 Specific examples are as follows: the outer diameters of the first center tube diameter d1 and the third center tube diameter d3 mentioned in the present invention are 70 mm, and the outer diameter of the second center tube diameter d2 is 73 mm. The upper piston cavity is formed by the difference in circular area between the first center tube diameter d1 and the second center tube diameter d2. The second center tube diameter d2, the third center tube diameter d3 and the cylinder sleeve 6 cooperate to form the lower piston cavity. When the upper piston cavity is pressurized, it can push the center tube 2 downward, and when the lower piston cavity is pressurized, it can push the center tube 2 upward; and the upper and lower pressures of the center tube 2 acted on by the oil layer pressure are balanced and equal.

[0050] The above are only some preferred embodiments of the present invention. Any person skilled in the art may modify the above technical solutions or modify them into equivalent technical solutions. Therefore, the corresponding simple modifications or equivalent transformations made according to the technical solutions of the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A hydraulically controlled balanced downhole safety valve, comprising a center pipe (2) and a cylinder sleeve (6), wherein the center pipe (2) is installed in the cylinder sleeve (6), and wherein: It also comprises an upper joint (1), a spring (3), a first hydraulic control pipeline (4), a valve seat (7), a valve plate (8), a torsion spring (9), a pin (10), a lower joint (11), and a second hydraulic control pipeline (12); the upper end of the cylinder sleeve (6) is movably connected to the upper joint (1), and the lower end is movably connected to the lower joint (11); a first hydraulic oil channel (6.1) is provided on one side of the outer wall of the cylinder sleeve (6), and a second hydraulic oil channel (6.2) is installed on the other side; the upper end surface height of the first hydraulic oil channel (6.1) is higher than the upper end surface height of the second hydraulic oil channel (6.2); the upper end surface of the first hydraulic oil channel (6.1) is installed with the first hydraulic control pipeline (4), and the upper end surface of the second hydraulic oil channel (6.2) is installed with the second hydraulic control pipeline (12); the valve seat ( 7), the lower end of the valve seat (7) is movably connected to the valve plate (8), and a torsion spring (9) is installed on one side of the valve plate (8) through a pin (10); a spring (3) is installed on the outer wall of the center tube (2), and the spring (3) is located between the upper limit protrusion (2.2) of the center tube (2) and the upper end surface of the cylinder sleeve (6); the first hydraulic control pipeline (4) and the second hydraulic control pipeline (12) for controlling opening and closing form a U-shaped structure from the connection point downhole to the wellhead, and the liquid column pressure of the first hydraulic control pipeline (4) and the second hydraulic control pipeline (12) acts on the hydraulic balance of the center tube (2), and the control pressure in the first hydraulic control pipeline (4) and the second hydraulic control pipeline (12) is independently sealed; the diameters of the upper and lower ends of the center tube (2) are equal, and the force acting on the center tube (2) by the oil layer pressure is balanced and equal; An annular sealing protrusion (2.1) is provided on the middle and lower outer wall of the central tube (2), a mechanical seal is formed between the annular sealing protrusion (2.1) and the inner wall of the cylinder sleeve (6), and the lower outlet of the first hydraulic oil channel (6.1) is located above the annular sealing protrusion (2.1), and the lower outlet of the second hydraulic oil channel (6.2) is located below the annular sealing protrusion (2.1); The inner wall at the lower end of the cylinder sleeve (6) is provided with a lower limit sealing protrusion (6.3), and the outer wall at the lower end of the center tube (2) and the lower limit sealing protrusion (6.3) form a mechanical seal; A central tube docking channel (11.1) is provided at the lower portion of the inner cavity of the lower joint (11), and a conical guide groove (11.2) is provided at the upper portion of the central tube docking channel (11.1); The upper outer wall of the center tube (2) forms a mechanical seal structure with the inner wall of the upper joint (1), and forms a mechanical seal between the annular sealing protrusion (2.1) and the inner wall of the cylinder sleeve (6), forming an upper piston chamber for opening the valve. The high-pressure hydraulic oil from the first hydraulic oil channel (6.1) pushes the center tube (2) to move downward, and the downwardly moving center tube (2) pushes open the valve plate (8) and communicates with the center tube docking channel (11.1) of the lower joint (11); A lower piston chamber for closing the valve is formed between the annular sealing protrusion (2.1) of the center tube (2) and the lower limit sealing protrusion (6.3) of the cylinder sleeve (6). The center tube (2) is pushed upward by the high-pressure hydraulic oil from the second hydraulic oil channel (6.2) and the spring (3). After the center tube (2) moves upward for a certain distance, the valve plate (8) is reset by the torsion spring (9).

2. The hydraulically controlled balanced downhole safety valve according to claim 1 is characterized in that: The upper outlet of the first hydraulic oil channel (6.1) is connected to the first hydraulic control pipeline (4) via a first pressure cap (5), and the upper outlet of the second hydraulic oil channel (6.2) is connected to the second hydraulic control pipeline (12) via a second pressure cap (13).

3. The hydraulically controlled balanced downhole safety valve according to claim 2 is characterized in that: The cylinder sleeve (6) is provided with a cylinder sleeve upper joint (6.6) at the upper end and a cylinder sleeve lower joint (6.7) at the lower end; a first hydraulic control mounting protrusion (6.4) is provided on one side of the cylinder sleeve (6) and a second hydraulic control mounting protrusion (6.5) is provided on the other side; wherein the first hydraulic oil passage (6.1) is located in the inner cavity of the first hydraulic control mounting protrusion (6.4); the second hydraulic oil passage (6.2) is located in the inner cavity of the second hydraulic control mounting protrusion (6.5); the height of the first hydraulic control mounting protrusion (6.4) is higher than the height of the second hydraulic control mounting protrusion (6.5); the upper end surface of the first hydraulic control mounting protrusion (6.4) is provided with a first pressure cap mounting hole; and the upper end surface of the second hydraulic control mounting protrusion (6.5) is provided with a second pressure cap mounting hole.

4. The method for using the hydraulically controlled balanced downhole safety valve according to claim 3 is characterized in that The process includes: (i) When controlled to open: by controlling the first hydraulic control pipeline (4) to pressurize at the wellhead, high-pressure liquid flows downward along the first hydraulic control pipeline (4) into the first hydraulic oil passage (6.1). Since the upper joint (1), the cylinder sleeve (6) and the center pipe (2) form an upper piston chamber, the center pipe (2) moves downward under the action of the high-pressure liquid, overcoming the action of the spring (3), so that the center pipe (2) pushes open the valve plate (8) and continues to move downward, so that the lower end of the center pipe (2) is limited at the lower joint (11), and the valve plate (8) rotates downward around the pin (10) and rotates into the annulus between the center pipe (2) and the lower joint (11). At this time, a normally open liquid passage is established in the center pipe (2), and the hydraulically controlled balanced downhole safety valve is in an open state; (ii) When closed under control: the first hydraulic control pipeline (4) is controlled to release pressure at the wellhead, and the center pipe (2) is pushed upward to reset under the action of the spring (3). At this time, the valve plate (8) loses the support of the center pipe (2) and is reset to close under the push of the torsion spring (9), thereby blocking the liquid channel formed by the center pipe (2) and realizing the closure of the hydraulically controlled balanced downhole safety valve; In addition, when the spring (3) fails, the second hydraulic control pipeline (12) is pressurized at the wellhead, so that high-pressure liquid flows downward along the second hydraulic control pipeline (12) into the second hydraulic oil channel (6.2), and then into the lower piston chamber formed between the lower limit sealing protrusion (6.3) of the cylinder sleeve (6) and the lower part of the center pipe (2), thereby pressurizing the center pipe (2) to move upward. The valve plate (8) loses the support of the center pipe (2) and is reset and closed under the push of the torsion spring (9), thereby achieving forced closure of the hydraulically controlled balanced downhole safety valve.

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