Floating guide shoe, central string and completion structure capable of completely closing fluid channels

Abstract

A floating guide shoe, a central string, and a completion structure capable of completely closing a fluid passage. The floating guide shoe includes a housing, a guide shoe, and a check valve unit; it also includes a reverse closing unit, which closes when the reverse pressure difference between the inner cavity of the housing and the external space of the floating guide shoe reaches or exceeds a second threshold. Firstly, by setting the reverse closing unit, the fluid passage of the floating guide shoe can be completely closed, avoiding the automatic pressure relief of the check valve unit when the pressure in the inner cavity of the floating guide shoe is too high in the prior art, and it can be used in cooperation with a flow control screen pipe with a staged and stepwise adjustable diversion ability to realize the stepwise adjustment of the diversion ability of the downhole flow control screen pipe; secondly, by setting the elasticity of the claw and the inclination of the back surface of the claw, the pressure for closing the fluid passage of the floating guide shoe can be accurately set; thirdly, by setting the angle of the claw chamfer and the inclined groove on the surface, the pressure resistance of the reverse closing unit after the fluid passage is completely closed can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil extraction, and relates to a floating guide shoe capable of completely closing a fluid passage, a central string using the floating guide shoe, and a completion structure. Background Art

[0002] A guide shoe is a conical or spherical structure provided at the front end of a central string in an oil and gas well, which is used to prevent the central string from scraping or inserting into the wellbore when lowering into the well, and guide the central string to smoothly reach the bottom of the well.

[0003] A floating guide shoe is a device provided with a check valve unit in its inner cavity and a guide shoe at its front end. In addition to the function of guiding the central string to lower into the well, the floating guide shoe also has the function of one-way flow guiding in the forward direction (i.e., from the inner cavity of the floating guide shoe to the outside). The floating guide shoe has the following functions. One is to use its front conical or spherical shape to guide the central string to smoothly reach the bottom of the well; the other is to establish a normal flushing channel. Specifically, by pressurizing and injecting flushing fluid into the inner cavity of the central string, when the pressure difference between the fluid pressure in the inner cavity of the central string and the fluid pressure in the wellbore annulus reaches or exceeds the opening pressure of the check valve unit, the check valve unit opens, and the flushing fluid passes through the inner cavity of the outer shell of the floating guide shoe, the check valve unit, the inner cavity of the guide shoe, and the diversion channel in sequence from the inner cavity of the central string, and finally enters the wellbore annulus, carrying the substances in the wellbore annulus out of the wellhead, so as to realize normal flushing; the third is to prevent the debris in the wellbore annulus from flowing back into the central string through the floating guide shoe. Specifically, because a check valve unit is provided in the inner cavity of the floating guide shoe, when the fluid pressure in the wellbore annulus is greater than the fluid pressure in the central string, the check valve unit closes, so as to prevent the fluid in the wellbore annulus from entering the inner cavity of the central string through the floating guide shoe.

[0004] In the prior art, the opening or closing of the check valve unit of the floating guide shoe is only controlled by the bottom hole pressure difference and cannot be completely closed. Once the positive bottom hole pressure difference is higher than the opening pressure of the check valve unit, the check valve unit will open, and the fluid in the inner cavity of the central string will flow out and relieve pressure through the diversion channel of the floating guide shoe, so that a higher fluid pressure cannot be generated inside the central string. Summary of the Invention

[0005] The purpose of the present invention is to overcome some or all of the defects in the prior art, and provide a floating guide shoe capable of completely closing a flow channel, a central string using the floating guide shoe, and a completion structure, which can generate a higher fluid pressure inside the central string.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides a floating guide shoe capable of completely closing a fluid passage, comprising an outer housing 1, a guide shoe 2, and a check valve unit 3; wherein, the outer housing 1 is a columnar hollow structure; the guide shoe 2 is arranged at the front end of the outer housing 1 and has a hollow structure inside; the rear end of the guide shoe 2 is fixedly connected to the front end of the outer housing 1, so as to realize the communication between the inner cavity of the guide shoe 2 and the inner cavity of the outer housing 1; a diversion channel 21 for realizing the communication between the inner cavity of the guide shoe and the external space of the floating guide shoe is arranged at the front end and / or side wall of the guide shoe 2; the check valve unit 3 is arranged in the inner cavity of the outer housing 1 and is in a closed state initially to block the communication between the inner cavity of the outer housing 1 and the external space of the floating guide shoe through the diversion channel 21 of the guide shoe 2; when the positive pressure difference between the inner cavity of the outer housing 1 and the external space of the floating guide shoe 2 reaches or exceeds a first threshold, the check valve unit 3 opens, so that the inner cavity of the outer housing 1 is communicated with the external space of the floating guide shoe through the diversion channel 21; when the positive pressure difference between the inner cavity of the outer housing 1 and the external space of the floating guide shoe is less than the first threshold, the check valve unit 3 returns to the closed state; the floating guide shoe further comprises a reverse closing unit 4; wherein, the reverse closing unit 4 is arranged in the inner cavity of the outer housing 1 and is arranged in series with the check valve unit 3 in the inner cavity of the outer housing 1; the reverse closing unit 4 is in an open state initially; when the reverse pressure difference between the inner cavity of the outer housing 1 and the external space of the floating guide shoe reaches or exceeds a second threshold, the reverse closing unit 4 closes, so as to block the communication between the inner cavity of the outer housing 1 and the external space of the floating guide shoe through the diversion channel 21 of the guide shoe 2; after the reverse closing unit 4 is closed, it is no longer controlled by positive or reverse pressure and returns to the open state.

[0008] Optionally, the reverse closing unit 4 comprises a first sealing valve seat 41 and a first sealing sliding sleeve 42, wherein, the first sealing valve seat 41 is a circular ring-shaped structure as a whole, and the outer side is fixedly connected and sealed with the inner side of the outer housing 1; the first sealing sliding sleeve 42 is a shaft-shaped structure as a whole and comprises a claw end 421 and a closing end 422; wherein, the claw end 421 comprises claws 424 with a plurality of claw tips 423 arranged along the circumferential direction facing away from the axis direction; the closing end 422 is a closed structure; when the reverse closing unit 4 is in the open state, the claw end 421 is located in the inner cavity of the first sealing valve seat 41, and the closing end 422 of the first sealing sliding sleeve 42 is located outside the front end of the first sealing valve seat 41; the inner cavity of the first sealing valve seat 41 and the space between the plurality of claws 423 form the fluid passage inside the floating guide shoe; when the reverse closing unit 4 is in the closed state, the closing end 422 of the first sealing sliding sleeve 42 is located in the cavity of the first sealing valve seat 41 and is in sealing cooperation with the first sealing valve seat 41 to block the fluid passage inside the floating guide shoe.

[0009] Optionally, a first groove 411 is provided at a position inside the first sealing valve seat 41 that matches the tips 423 of the plurality of pawls 421 for accommodating the tips 423 of the pawls 421.

[0010] Optionally, the back 425 of the tip 423 is a bevel structure; the side wall 412 of the first groove 411 corresponding to the back 425 of the tip 423 is a bevel structure with the same inclination angle as the back 425 of the tip 423.

[0011] Optionally, a sliding passage 30 is provided inside the one-way valve unit 3 along the axial direction of the floating guide shoe. A piston 5 and a push rod 6 are arranged in the sliding passage 30; one end of the piston 5 faces the direction of the floating guide shoe, and a push rod 6 is provided at the other end; one end of the push rod 6 is connected to or adjacent to the piston 5, and the other end is connected to or adjacent to the first sealing sleeve 42; when the reverse pressure difference between the inner cavity of the outer housing 1 and the outer space of the floating guide shoe reaches or exceeds a second threshold value, the piston 5 moves towards the push rod 6 under the action of the fluid pressure difference, pushing the push rod 6 and the first sealing sleeve 42 to move until the tips 423 of the pawls 421 disengage from the first groove 411 and are snap-fitted and fixed to the upper end of the first sealing valve seat 41.

[0012] Optionally, the inner side of the tip 423 of the pawl 421 is a chamfer structure; the upper end of the first sealing valve seat 41 is provided with a bevel groove 413 that matches the snap-fitting and fixing position of the tip 423 of the pawl 421, and the inclination angle of the bevel of the bevel groove 413 is the same as the chamfer angle of the inner side of the tip 423 of the pawl 421.

[0013] Optionally, a positioning block 426 is provided at the closed end 422 of the first sealing sleeve 42; a positioning groove 414 that matches the positioning block 426 is provided on the lower end surface of the first sealing valve seat 41.

[0014] Optionally, one or more sealing rings are provided on the outer side of the closed end 422 of the first sealing sleeve 42 along the circumferential direction.

[0015] Optionally, the one-way valve unit 3 includes a second sealing valve seat 33 and a second sealing valve sleeve 35, and a spring 36 in a compressed state is provided between the second sealing valve seat 33 and the second sealing valve sleeve 35; in the initial state, the elastic force of the spring causes the second sealing valve seat 33 and the second sealing valve sleeve 35 to be combined to be in a sealed state; when the positive pressure difference between the inner cavity of the outer housing 1 and the external space of the floating guide shoe is greater than the first threshold, the second sealing valve sleeve 35 is separated from the second sealing valve seat 33 under the action of pressure, so that the one-way valve unit 3 is opened; when the positive pressure difference between the inner cavity of the outer housing 1 and the external space of the floating guide shoe is less than the first threshold, the second sealing valve sleeve 35 is combined with the second sealing valve seat 33 under the elastic force of the spring 36, and the one-way valve unit 3 returns to the closed state.

[0016] Optionally, the second sealing valve sleeve 35 is an overall shaft-like structure, and a through sliding channel 30 is provided at the axis.

[0017] Optionally, a first support sleeve 8 is provided between the one-way valve unit 3 and the reverse closing unit 4. The first support sleeve 8 is a cylindrical structure, and the outer side of the first support sleeve 8 is attached to the inner side of the outer housing 1.

[0018] In a second aspect, an embodiment of the present invention further provides a central string, and a floating guide shoe capable of completely closing the fluid passage as described in the first aspect is provided at the bottom end of the central string.

[0019] In a third aspect, an embodiment of the present invention further provides a completion structure, including a wellbore and a central string disposed in the wellbore; a floating guide shoe capable of completely closing the fluid passage as described in the first aspect is provided at the bottom end of the central string.

[0020] For the floating guide shoe capable of completely closing the fluid passage provided by the present invention, first, by providing a reverse closing unit, the fluid passage of the floating guide shoe can be completely closed, avoiding the pressure relief caused by the opening of the one-way valve unit when the pressure in the inner cavity of the floating guide shoe is too high in the prior art, and it can be used in cooperation with a flow control screen pipe having a staged and stepwise adjustable diversion ability to realize the stepwise adjustment of the diversion ability of the downhole flow control screen pipe; second, by reasonably setting the elastic strength of the claw and the inclination of the inclined surface on the back of the claw, the fluid pressure for closing the fluid passage of the floating guide shoe can be accurately set; third, by providing a chamfer of the claw and a bevel groove used in cooperation with the chamfer, the compressive resistance of the reverse closing unit after the fluid passage is completely closed can be improved, and the device will not fail due to a positive high pressure difference. Description of the Drawings

[0021] Figure 1 is an overall structural schematic diagram of a floating guide shoe in the prior art;

[0022] Figure 2It is a semi-sectional structural schematic diagram of a floating guide shoe in an embodiment of the present invention that can completely close a fluid channel;

[0023] Figure 3 It is Figure 2 a partial enlarged view of part A in

[0024] Figure 4 It is Figure 2 a partial enlarged view of part B in

[0025] Figure 5 It is a three-dimensional structural sectional view of a floating guide shoe in an embodiment of the present invention that can completely close a fluid channel;

[0026] Figure 6 It is a semi-sectional structural schematic diagram of a floating guide shoe in an embodiment of the present invention in the closed state of the reverse closing unit. Specific embodiments

[0027] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0029] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0030] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0031] In order to facilitate understanding of the embodiments of the present invention, the prior art and application scenarios of the embodiments of the present invention are first introduced.

[0032] like Figure 1 The figure shows a specific structural diagram of an existing floating guide shoe, which includes an outer shell 1-1, a check valve unit and a guide shoe 1-9. Among them, the outer shell 1-1 is a columnar hollow structure, or a cylindrical structure; the rear end of the outer shell 1-1 (that is, the end used to connect the center pipe column when in use, the end facing the wellhead) is used to fix the center pipe column by means of threads, snaps, locating pins, etc.; the front end of the outer shell 1-1 (that is, the end facing the deep bottom of the well when in use, the end away from the wellhead) is provided with a guide shoe 1-9, and the guide shoe 1-9 is a hollow structure with an open rear end. The rear end of the guide shoe 1-9 is fixedly connected to the front end of the outer shell 1-1 by a stop pin 1-10 (of course, other fixed connection methods can also be used), so that the inner cavity of the guide shoe 1-9 is connected to the inner cavity of the outer shell 1-1; the front end and / or side wall of the guide shoe 1-9 is provided with a guide channel 1-7 for connecting the inner cavity of the guide shoe 1-9 with the external space of the floating guide shoe (such as the wellbore annulus). The second supporting sleeve 1-11 is arranged between the one-way valve unit and the guide shoe 1-9, and is used to realize the positioning of the one-way valve unit in the inner cavity of the outer shell 1-1.

[0033] The shown check valve unit is arranged in the inner cavity of the outer housing 1-1. The check valve unit includes a third sealing valve seat 1-3 and a valve body 1-5. Among them, the third sealing valve seat 1-3 is of an annular structure. The outer side wall of the third sealing valve seat 1-3 is in sealing fit with the inner side wall of the outer housing 1-1, and the two are fixedly connected. A sealing ring 1-8 is also provided between the third sealing valve seat 1-3 and the outer housing 1-1 to improve the sealing effect between the two. One end of the valve body 1-5 is in fit with the third sealing valve seat 1-3, thereby closing the internal flow channel of the floating guide shoe. The other end of the valve body 1-5 is fixedly connected with a spring sleeve 1-4 through a positioning pin 1-2. A spring 1-6 in a compressed state is provided between the spring sleeve 1-4 and the third sealing valve seat 1-3. The spring is in a compressed state, thereby forming internal stress and acting on the valve body 1-5 and the third sealing valve seat 1-3, so that the two are in a fitting state when not under external pressure or force, thereby making the check valve unit in a closed state.

[0034] When the check valve unit is in the initial state (closed state), it can block the communication between the inner cavity of the outer housing 1-1 and the external space (such as the wellbore annulus) of the floating guide shoe through the diversion channel 1-7 of the guide shoe 1-9. When the positive pressure difference (the "positive pressure" here is only an artificial definition given for easy understanding and does not limit the present technical solution) between the inner cavity of the outer housing 1-1 and the external space of the floating guide shoe reaches or exceeds the first threshold value, the valve body 1-5 moves downward under the action of fluid pressure, overcoming the spring force, so that its lower end is separated from the third sealing valve seat 1-3, and the check valve unit opens, thereby enabling the inner cavity of the outer housing to communicate with the external space of the floating guide shoe through the diversion channel, and the fluid in the central string can flow through the check valve from top to bottom and finally enter the external space (such as the wellbore annulus) through the diversion channel 1-7 of the guide shoe 1-9. When the positive pressure difference between the inner cavity of the outer housing 1-1 and the external space of the floating guide shoe is less than the first threshold value (including being negative), the check valve unit returns to the closed state. The first threshold value can be set to 0.1 to 1 Mpa, and most practical applications do not exceed 0.5 Mpa. By changing parameters such as the spring force and the throttling surface of the valve body 1-5, the first threshold value of the check valve unit can be set.

[0035] In a practical application scenario, a floating guide shoe with a check valve unit must be used during the completion operation of a new open-hole well. This is because mud needs to be retained in the open-hole section to prevent the open hole from collapsing. After the central string is lowered into the wellbore, these muds need to be washed out, and the completion fluid is used to displace the mud out of the wellbore in a positive direction.

[0036] On the other hand, the inventors of this patent have also developed a flow control screen pipe for oil and gas wells that can gradually adjust the diversion capacity in stages. The flow control screen pipe includes one or more fluid valves, and each of the one or more fluid valves has a first side facing the inner cavity of the flow control screen pipe and a second side facing the wellbore annulus outside the flow control screen pipe. Among them, the one or more fluid valves are closed in the initial state to block the corresponding fluid channels. And, each of the one or more fluid valves has its own predetermined opening threshold and is configured to open when the fluid pressure difference between the fluid pressure applied to the first side of the fluid valve from the inner cavity of the base pipe and the fluid pressure applied to the second side of the fluid valve from the annulus is greater than or equal to its own predetermined opening threshold, so as to open the corresponding fluid channel, enabling the fluid in the annulus to flow into the inner cavity of the base pipe through the corresponding fluid channel. After the continuous packer operation is completed and put into production, the flow control device can use the ground pressure equipment to apply liquid pressure to the completion string installed with this screen pipe, and open the specified-stage fluid valve of the screen pipe according to production needs to increase the production liquid volume. This flow control screen pipe can easily and conveniently achieve the staged and gradual adjustment of the diversion capacity of the flow control screen pipe, thereby ensuring the daily oil production of the oil well and extending the effective production time of the oil well throughout the exploitation period.

[0037] However, since a floating guide shoe is installed at the bottom of the water control completion string equipped with the adjustable water control screen pipe, when the ground equipment applies liquid pressure to the water control string, the floating guide shoe will open at a relatively low positive pressure difference (for example, below 0.5 Mpa). And the flow rate of the diversion channel of the floating guide shoe is very large. Under the drainage effect of the diversion channel, it is difficult to form a relatively high liquid pressure (or pressure difference) inside the water control screen pipe. On the other hand, the minimum liquid pressure difference required for the fluid valve of the flow control screen pipe to open is much larger than the opening pressure of the floating guide shoe (generally between 3 - 15 Mpa). Therefore, for the water control string installed with the above floating guide shoe, it is difficult to achieve the liquid pressure required for the water control screen pipe to open the next-stage fluid valve in terms of structure and function. For the completion string installed with the above flow control screen pipe that can gradually adjust the diversion capacity in stages, if you want to achieve the staged and gradual adjustment function of the diversion capacity of the flow control screen pipe, you must completely close the flow channel of the floating guide shoe so that the ground perfusion equipment can apply a sufficiently high pressure to the inner cavity of the completion string to form a sufficiently high pressure difference for opening the various-stage fluid valves on the flow control screen pipe. [[ID=?]]

[0038] The technical solutions provided by the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0039] As Figures 2 to 5As shown in the figure, a floating guide shoe capable of completely closing a fluid passage includes a housing 1, a guide shoe 2, and a check valve unit 3. Among them, the housing 1 is a columnar hollow structure, and its diameter should be consistent with that of other pipe joints of the central pipe string. The guide shoe 2 is arranged at the front end of the housing 1 (i.e., the end close to the bottom of the well), and the inside of the guide shoe 2 is a hollow structure. The rear end of the guide shoe 2 is fixedly connected to the front end of the housing 1, so as to realize the communication between the inner cavity of the guide shoe 2 and the inner cavity of the housing 1. Various connection methods such as threaded connection and clamping can be adopted for connection. The front end and / or side wall of the guide shoe 2 are provided with a diversion channel 21 for realizing the communication between the inner cavity of the guide shoe and the external space of the floating guide shoe, which serves as a channel for the fluid to flow through during well flushing.

[0040] The check valve unit 3 can adopt any structure in the prior art. In this embodiment, the check valve unit 3 is arranged in the inner cavity of the housing 1 and is in a closed state initially to block the communication between the inner cavity of the housing 1 and the external space of the floating guide shoe through the diversion channel 21 of the guide shoe 2. When the positive pressure difference between the inner cavity of the housing 1 and the external space of the floating guide shoe 2 reaches or exceeds the first threshold value, the check valve unit 3 opens, so that the inner cavity of the housing 1 is communicated with the external space of the floating guide shoe through the diversion channel 21. When the positive pressure difference between the inner cavity of the housing 1 and the external space of the floating guide shoe is less than the first threshold value, the check valve unit 3 returns to the closed state. Thus, the opening and closing of the check valve unit 3 can be controlled by the pressure difference between the central pipe string and the wellbore annulus. Preferably, the first threshold value is 0.1 - 0.5 Mpa.

[0041] The floating guide shoe further includes a reverse closing unit 4. Among them, the reverse closing unit 4 is arranged in the inner cavity of the housing 1 and is arranged in series with the check valve unit 3 in the inner cavity of the housing 1, that is, as long as one unit is in the closed state, the fluid passage of the floating guide shoe can be closed. In the series structure, the front and rear position sequences of the check valve unit 3 and the reverse closing unit 4 are not limited. The initial state of the reverse closing unit 4 is open; when the reverse pressure difference between the inner cavity of the housing 1 and the external space of the floating guide shoe (i.e., the fluid pressure in the wellbore annulus is greater than the fluid pressure in the inner cavity of the housing 1) reaches or exceeds the second threshold value, the reverse closing unit 4 closes, so as to block the communication between the inner cavity of the housing 1 and the external space of the floating guide shoe through the diversion channel 21 of the guide shoe 2; after the reverse closing unit 4 is closed, it is no longer controlled by the positive or reverse pressure and returns to the open state. Thus, when high-pressure fluid is injected into the central pipe string, the floating guide shoe will no longer have a pressure relief situation. Preferably, the second threshold value is 1 - 20 Mpa.

[0042] In an embodiment of the present application, the reverse closing unit 4 includes a first sealing valve seat 41 and a first sealing sliding sleeve 42. Among them, the first sealing valve seat 41 is integrally of an annular structure, and its outer side is fixedly connected and sealed to the inner side of the outer housing 1; preferably, a first anti-rotation pin 7 is provided between the first sealing valve seat 41 and the outer housing 1 to realize the connection and fixation between the first sealing valve seat 41 and the outer housing 1. The first sealing sliding sleeve 42 is integrally of a shaft-like structure and includes a claw end 421 and a closing end 422, and the claw end 421 and the closing end 422 can axially move in the inner cavity of the first sealing sliding sleeve 42. Among them, the claw end 421 includes a plurality of claws 424 with claw tips 423 arranged along the circumferential direction facing away from the axis, and the claws 424 are used to position the first sealing sliding sleeve 42 relative to the first sealing valve seat 41. The closing end 422 is a closed structure for closing the fluid passage. When the reverse closing unit 4 is in the open state, the claw end 421 is located in the inner cavity of the first sealing valve seat 41, and the closing end 422 of the first sealing sliding sleeve 42 is located outside the front end of the first sealing valve seat 41. The inner cavity of the first sealing valve seat 41 and the space between the plurality of claws 423 constitute the fluid passage inside the floating guide shoe, so as to ensure the smoothness of the fluid passage inside the floating guide shoe. When the reverse closing unit 4 is in the closed state, the closing end 422 of the first sealing sliding sleeve 42 is located in the cavity of the first sealing valve seat 41 and is in sealed cooperation with the first sealing valve seat 41 to block the fluid passage inside the floating guide shoe; moreover, this blocking is permanent. After the reverse closing unit 4 is closed, it is no longer controlled by positive or negative pressure and returns to the open state.

[0043] In an embodiment of the present application, a first groove 411 is provided at a position on the inner side of the first sealing valve seat 41 that matches the claw tips 423 of the plurality of claws 421 for accommodating the claw tips 423 of the claws 421. Preferably, the first groove 411 is an annular groove, so that no matter at any circumferential angle the claws 421 are located, they can be caught in the first groove 411. The claws 421 have a certain elasticity. When the claws 421 are caught in the first groove 411, the first groove 411 has a limiting effect on the claws 421, so as to realize the limiting of the first sealing valve seat 41 on the first sealing sliding sleeve 42.

[0044] In an embodiment of the present application, the back 425 of the claw tip 423 is a bevel structure; the side wall 412 of the first groove 411 corresponding to the back 425 of the claw tip 423 is a bevel structure with the same inclination angle as the back 425 of the claw tip 423. By reasonably setting parameters such as the inclination angle of the bevel of the back 425 of the claw tip 423, the length, width, elasticity, etc. of the clamping claw 421, the force required to push the first sealing sliding sleeve 42 upward to the closed position can be accurately obtained to meet the user's requirements for different trigger pressure or perfusion pressure settings. Preferably, the trigger pressure can be set to 1 - 20 Mpa. After the reverse closing unit 4 is closed, it can ensure that no matter a pressure difference of 40 Mpa is applied in the forward or reverse direction, the locked state will not be damaged.

[0045] In an embodiment of the present application, a sliding channel 30 is provided inside the one - way valve unit 3 along the axis direction of the floating guide shoe. A piston 5 and a push rod 6 are arranged in the sliding channel 30. The purpose of setting the piston 5 and the push rod 6 is that when the reverse fluid pressure reaches the second threshold, the reverse pressure difference of the fluid is converted into a force through the piston 5 and acts on the first sealing sliding sleeve 42 through the push rod 6, so that the first sealing sliding sleeve 42 enters the locked state. Specifically, one end of the piston 5 faces the direction of the floating guide shoe and contacts the fluid, for receiving the fluid pressure in the wellbore annulus; the other end is provided with a push rod 6. The lower end of the push rod 6 is connected to or adjacent to the piston 5, and the other end is connected to or adjacent to the first sealing sliding sleeve 42 (it can adopt a fixed connection method or maintain a certain distance at one end). When the reverse pressure difference between the inner cavity of the outer housing 1 and the outer space of the floating guide shoe reaches or exceeds the second threshold, the piston 5 moves in the direction of the push rod 6 under the action of the fluid pressure difference, pushing the push rod 6 and the first sealing sliding sleeve 42 to move until the claw tip 423 of the clamping claw 421 disengages from the first groove 411 and is clamped and fixed at the upper end of the first sealing valve seat 41, and then enters the locked state. Preferably, the second threshold is 1 - 20 Mpa.

[0046] In an embodiment of the present application, the inner side of the claw tip 423 of the clamping claw 421 is a chamfer structure; the upper end of the first sealing valve seat 41 is provided with a bevel groove 413 that matches the clamping and fixing position of the claw tip 423 of the clamping claw 421. The inclination angle of the bevel of the bevel groove 413 is the same as the chamfer angle of the inner side of the claw tip 423 of the clamping claw 421. Preferably, the bevel groove 413 is an annular groove, so that no matter from which angle the clamping claw 421 enters, it can be clamped into the bevel groove 413. By setting the chamfer and the bevel groove, it can be ensured that the claw tip 423 can be more effectively clamped into the bevel groove 413 and will not slip off due to external force, thereby ensuring that the reverse closing unit 4 can more effectively maintain the locked state.

[0047] In one embodiment of the present application, the closed end 422 of the first sealing sleeve 42 is provided with a positioning block 426; the lower end surface of the first sealing valve seat 41 is provided with a positioning groove 414 that matches the positioning block 426. The positioning groove 414 is a circular ring structure, and the positioning block 426 can be block-shaped or can be a circular ring with a matching shape. The purpose of providing the positioning block 426 and the positioning groove 414 is to position the first sealing valve seat 41 when the reverse sealing unit 4 is closed, so as to prevent the first sealing valve seat 41 from penetrating upward. On the other hand, the positioning block 426 and the positioning groove 414, when combined, also have a sealing effect.

[0048] In one embodiment of the present application, one or more sealing rings (not shown) are provided along the circumferential direction outside the closed end 422 of the first sealing sleeve 42. The purpose of providing the sealing rings is to further enhance the positioning effect between the first sealing sleeve 42 and the first sealing valve seat 41.

[0049] In one embodiment of the present application, the structure of the one-way valve unit 3 is similar to the prior art described herein, and includes a second sealing valve seat 33 and a second sealing valve sleeve 35, with a compressed spring 36 disposed between the second sealing valve seat 33 and the second sealing valve sleeve 35. For the specific structure of the one-way valve unit 3, please refer to the above description of the floating guide shoe of the prior art. A second stop pin 38 is disposed between the second sealing valve seat 33 and the outer shell 1 to enhance the fixing effect therebetween. The lower end of the second sealing valve sleeve 35 cooperates with the second sealing valve seat 33 to open or close the one-way valve unit 3, and the upper end is fixedly connected to a spring sleeve 34 via a positioning pin 32. The upper portion of the second sealing valve seat 33 is also provided with a plurality of parallel axial through holes 37 serving as fluid passages.

[0050] In the initial state, the spring's elastic force causes the second sealing valve seat 33 and the second sealing valve sleeve 35 to engage, creating a sealed state. When the positive pressure differential between the inner cavity of the outer shell 1 and the outer space of the floating guide shoe exceeds the first threshold, the second sealing valve sleeve 35, under the action of pressure, separates from the second sealing valve seat 33, thereby opening the check valve unit 3. Fluid flows through the through-hole 37 and the gap between the second sealing valve sleeve 35 and the second sealing valve seat 33, enters the cavity of the guide shoe 2, and flows into the wellbore annulus through the diversion channel 21. When the positive pressure differential between the inner cavity of the outer shell 1 and the outer space of the floating guide shoe falls below the first threshold, the second sealing valve sleeve 35, under the elastic force of the spring 36, reengages with the second sealing valve seat 33, and the check valve unit 3 returns to the closed state. Thus, during positive wellwashing operations, the check valve unit 3 achieves one-way fluid conduction.

[0051] In an embodiment of the present application, the second sealing valve sleeve 35 is integrally in a shaft-like structure, and a through sliding channel 30 is provided at the axis. The sliding channel 30 is used to arrange a piston 5 and a push rod 6.

[0052] In an embodiment of the present application, a first support sleeve 8 is provided between the check valve unit 3 and the reverse closing unit 4. The first support sleeve 8 is in a cylindrical structure, and the outer side of the first support sleeve 8 is attached to the inner side of the outer housing 1. The function of the first support sleeve 8 is to position and fix the positions of the check valve unit 3 and the reverse closing unit 4 in the inner cavity of the outer housing 1.

[0053] The assembling process of the present device is as follows: First, the reverse closing unit 4, the first support sleeve 8, and the check valve unit 3 are assembled in sequence from bottom to top in the inner cavity of the outer housing 1, and finally the guide shoe is installed. The upward force of the guide shoe acts on the check valve unit 3, the first support sleeve 8, and the reverse closing unit 4 in sequence, thereby fixing the above components.

[0054] This embodiment also provides a central string. A floating guide shoe capable of completely closing the fluid passage as described above is provided at the bottom end of the central string; the central string adopts the flow control screen pipe for oil and gas wells that can be adjusted step by step in stages to control the diversion capacity, so that the diversion capacity of the downhole flow control screen pipe can be adjusted step by step.

[0055] This embodiment also provides a completion structure, including a wellbore and a central string arranged in the wellbore; a floating guide shoe capable of completely closing the fluid passage as described above is provided at the bottom end of the central string; the central string adopts the flow control screen pipe for oil and gas wells that can be adjusted step by step in stages to control the diversion capacity, so that the diversion capacity of the downhole flow control screen pipe can be adjusted step by step.

[0056] Obviously, since the central string and the completion structure adopt the floating guide shoe capable of completely closing the fluid passage as described above, they also have the technical effects described above.

[0057] The operation steps of the floating guide shoe, central string and completion structure that can completely close the fluid channel given in the above embodiments are as follows: During the stage of lowering the central string, the reverse closing unit 4 is opened and the check valve unit 3 is closed to prevent the mud and other substances in the wellbore from entering the central string; after the central string is lowered into the well, the surface equipment injects the well flushing fluid into the well through the central string. The reverse closing unit 4 remains in the open state, and the check valve unit 3 is automatically opened under the action of the injection pressure to realize forward well flushing, and the mud and other substances in the wellbore annulus are discharged through the wellhead; during the production stage, oil and gas production is realized under the action of a relatively small reverse bottomhole pressure difference; when it is necessary to increase the flow guiding capacity of the flow control screen pipe, first, inject fluid into the wellbore annulus through the surface equipment to generate a relatively large reverse pressure difference at the bottomhole. The reverse closing unit 4 is completely closed under the action of the reverse pressure difference, and then, inject fluid into the central string through the surface equipment to generate a relatively large forward pressure difference at the bottomhole. According to the need, the flow guiding devices of the flow control screen pipe are gradually opened through the forward pressure difference, so as to realize the gradual increase of the flow guiding capacity of the flow control screen pipe.

[0058] The above content is a further detailed description of the present invention in combination with specific preferred implementation manners, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A floating guide shoe capable of completely closing a fluid passage, comprising a housing body, a guide shoe, and a check valve unit; wherein, The housing body is a columnar hollow structure; The guide shoe is arranged at the front end of the housing body and is hollow inside; the rear end of the guide shoe is fixedly connected to the front end of the housing body, so as to realize the communication between the inner cavity of the guide shoe and the inner cavity of the housing body; the front end and / or side wall of the guide shoe are provided with a diversion channel for realizing the communication between the inner cavity of the guide shoe and the external space of the floating guide shoe; The check valve unit is arranged in the inner cavity of the housing body and is in a closed state initially to block the communication between the inner cavity of the housing body and the external space of the floating guide shoe through the diversion channel of the guide shoe; when the positive pressure difference between the inner cavity of the housing body and the external space of the floating guide shoe reaches or exceeds the first threshold value, the check valve unit opens, so that the inner cavity of the housing body is communicated with the external space of the floating guide shoe through the diversion channel; when the positive pressure difference between the inner cavity of the housing body and the external space of the floating guide shoe is less than the first threshold value, the check valve unit returns to the closed state; It is characterized in that: the floating guide shoe further comprises a reverse closing unit; wherein, The reverse closing unit is arranged in the inner cavity of the housing body and is arranged in series with the check valve unit in the inner cavity of the housing body; the initial state of the reverse closing unit is an open state; when the reverse pressure difference between the inner cavity of the housing body and the external space of the floating guide shoe reaches or exceeds the second threshold value, the reverse closing unit closes, so as to block the communication between the inner cavity of the housing body and the external space of the floating guide shoe through the diversion channel of the guide shoe; after the reverse closing unit closes, it is no longer controlled by positive or reverse pressure and returns to the open state.

2. The floating guide shoe capable of completely closing the fluid passage according to claim 1, characterized in that: The reverse closing unit comprises a first sealing valve seat and a first sealing sliding sleeve, wherein, The first sealing valve seat is a circular ring structure as a whole, and the outer side is fixedly connected and sealed with the inner side of the housing body; The first sealing sliding sleeve is a shaft structure as a whole, including a claw end and a closing end; wherein, the claw end includes a plurality of claws with the claw tips facing away from the axis direction arranged along the circumferential direction; the closing end is a closed structure; When the reverse closing unit is in the open state, the claw end is located in the inner cavity of the first sealing valve seat, and the closing end of the first sealing sliding sleeve is located outside the front end of the first sealing valve seat; the inner cavity of the first sealing valve seat and the space between the plurality of claws form the fluid passage inside the floating guide shoe; When the reverse closing unit is in the closed state, the closing end of the first sealing sliding sleeve is located in the cavity of the first sealing valve seat and is in sealing cooperation with the first sealing valve seat, blocking the fluid passage inside the floating guide shoe.

3. The floating guide shoe capable of completely closing the fluid passage according to claim 2, wherein: A first groove is arranged at a position on the inner side of the first sealing valve seat matching the claw tips of the plurality of claws for accommodating the claw tips of the claws.

4. The floating guide shoe capable of completely closing a fluid passage according to claim 3, characterized in that: The back of the claw tip is a bevel structure; The side wall of the first groove corresponding to the back of the claw tip is a bevel structure with the same inclination angle as the back of the claw tip.

5. The floating guide shoe capable of completely closing the fluid passage according to claim 3, characterized in that: A sliding passage is provided inside the check valve unit along the axial direction of the floating guide shoe, and a piston and a push rod are arranged in the sliding passage; one end of the piston faces the direction of the floating guide shoe, and a push rod is arranged at the other end; one end of the push rod is connected to or adjacent to the piston, and the other end is connected to or adjacent to the first sealing sliding sleeve; When the reverse pressure difference between the inner cavity of the housing body and the external space of the floating guide shoe reaches or exceeds the second threshold, the piston moves in the direction of the push rod under the action of the fluid pressure difference, pushing the push rod and the first sealing sliding sleeve to move until the tip of the claw of the claw disengages from the first groove and is clamped and fixed at the upper end of the first sealing valve seat.

6. The floating guide shoe capable of completely closing the fluid passage according to claim 3, characterized in that: The inner side of the tip of the claw is a chamfered structure; The upper end of the first sealing valve seat is provided with an inclined groove matching the clamping and fixing position of the tip of the claw, and the inclination angle of the inclined surface of the inclined groove is the same as the chamfer angle of the inner side of the tip of the claw.

7. The floating guide shoe capable of completely closing the fluid passage according to claim 2, characterized in that: The closed end of the first sealing sliding sleeve is provided with a positioning block; The lower end surface of the first sealing valve seat is provided with a positioning groove matching the positioning block.

8. The floating guide shoe capable of completely closing the fluid passage according to claim 2, characterized in that: One or more sealing rings are arranged on the outer side of the closed end of the first sealing sliding sleeve along the circumferential direction.

9. The floating guide shoe capable of completely closing the fluid passage according to claim 1, characterized in that: The check valve unit includes a second sealing valve seat and a second sealing valve sleeve, and a compressed spring is arranged between the second sealing valve seat and the second sealing valve sleeve; in the initial state, the elastic force of the spring causes the second sealing valve seat and the second sealing valve sleeve to be combined in a sealed state; When the positive pressure difference between the inner cavity of the housing body and the external space of the floating guide shoe is greater than the first threshold, the second sealing valve sleeve is separated from the second sealing valve seat under the action of the pressure, so that the check valve unit is opened; When the positive pressure difference between the inner cavity of the housing body and the external space of the floating guide shoe is less than the first threshold, the second sealing valve sleeve is combined with the second sealing valve seat under the action of the elastic force of the spring, and the check valve unit returns to the closed state.

10. The floating guide shoe capable of completely closing the fluid passage according to claim 9, characterized in that: The second sealing valve sleeve is an overall shaft structure, and a through sliding passage is provided at the axis.

11. The floating guide shoe capable of completely closing the fluid passage according to claim 1, wherein: A first support sleeve is arranged between the check valve unit and the reverse closing unit, the first support sleeve is a cylindrical structure, and the outer side of the first support sleeve is attached to the inner side of the housing body.

12. A central string, characterized in that: The bottom end of the central pipe string is provided with a floating guide shoe capable of completely closing the fluid passage according to any one of claims 1 to 11.

13. A completion structure includes a wellbore and a central string disposed in the wellbore, characterized in that: The bottom end of the central pipe string is provided with a floating guide shoe capable of completely closing the fluid passage according to any one of claims 1 to 11.

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