A downhole positive pressure self-sand-retrieving hydraulic plug removal system and method

Abstract

This invention relates to the field of petroleum development technology, and provides a downhole positive pressure self-retrieving hydraulic deblocking system comprising: a high-pressure pump; tubing connected to the high-pressure pump; a drill plug nozzle; and a self-retrieving sand string disposed between the tubing and the drill plug nozzle. The self-retrieving sand string comprises: a central tube, the inner wall of which defines a string cavity, the string cavity being in fluid communication with the tubing and the drill plug nozzle to form at least a portion of a high-pressure fluid flow channel; and an outer wall tube coaxial with and circumferentially surrounding the central tube. This deblocking system removes and cleans the wellbore inner wall using water jet technology, while simultaneously recovering and returning deblocking debris and sand particles through a self-retrieving sand device design, achieving integrated deblocking and sand retrieval operations in horizontal wells. This invention also provides a downhole positive pressure self-retrieving hydraulic deblocking method using this deblocking system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil development, more particularly to a downhole positive pressure self-sand-retrieving hydraulic plug-removing system and a method for removing plug using the system. BACKGROUND

[0002] In the process of oilfield exploitation, sand and gravel accumulated in the wellbore and plugged into the casing can form a gray plug. The cause of the gray plug section may be that the loose sandstone bottom layer has low glue structure strength, causing sand and gravel to enter the wellbore with the formation fluid; or it may be that the oil and water wells have serious water production, uneven water injection or steam injection, etc., and artificial chemical or cement plugging agents are used to plug water, leak and channel in the target layer. In order to ensure the success rate and effectiveness of plugging, the entire well section often needs to be plugged, and the length of plugging can reach hundreds of meters. After plugging is completed, the generated gray plug section needs to be drilled out to restore production of the production well.

[0003] At present, the conventional plug-removing device uses two ways of screw rod plug-removing and top drive plug-removing to remove the plug, both of which have problems such as incomplete plug-removing, residual gray plug in the inner wall of the casing, poor flowback capacity, inability to apply to casing deformation wells, and difficulty in quickly restoring production after plug-removing. At the same time, for long-distance plug-removing operation, the existing plug-removing device has slow speed and high cost. For screw rod drilling, the output torque is small, and it cannot drill out the gray plug with high hardness and strength; for top drive drilling, the output torque is large, but the transmission capacity is poor in deep wells and the casing is easily damaged. At present, there is no effective measure to solve the problem of removing the gray plug section of straight wells, highly deviated wells and horizontal wells, especially the gray plug of horizontal wells, which is extremely difficult.

[0004] Therefore, it is a technical problem to be solved in the technical field of oil development to develop a plug-removing system and method which can quickly and cleanly drill out the gray plug section without damaging the casing, solve the flowback of horizontal wells to avoid sand burying of the pipe string, and quickly restore production after operation. SUMMARY

[0005] The present application aims to provide a downhole positive pressure self-sand-retrieving hydraulic plug-removing system, which removes the gray plug section by using water jet technology, cleans the inner wall of the wellbore, and realizes the recovery and flowback of gray plug debris and sand particles through the design of the self-sand-retrieving device, thereby realizing the integrated operation of plug-removing and sand-retrieving in horizontal wells. The present application also provides a downhole positive pressure self-sand-retrieving hydraulic plug-removing method using the plug-removing system.

[0006] According to the present application, a downhole positive pressure self-sand-retrieving hydraulic plug-removing system is provided, which comprises:

[0007] a high-pressure pump;

[0008] a tubing, the high-pressure pump being connected to the tubing and being configured to pump high-pressure liquid into the tubing;

[0009] a plug-removing gun; and

[0010] The self-sweeping string is disposed between the tubing and the plug gun and includes:

[0011] a center pipe having an inner wall defining a string inner lumen in fluid communication with the tubing and the plug gun to form at least a portion of the high pressure liquid flow path; and

[0012] an outer wall pipe coaxial with and circumferentially surrounding an exterior of the center pipe, wherein an inner wall of the outer wall pipe and an outer wall of the center pipe define an annular string outer lumen having a flow-through end proximate the tubing and a sand-in end proximate the plug gun, wherein the flow-through end allows passage of particles having a size less than a first threshold value and the sand-in end allows one-way passage of particles having a size less than a second threshold value into the string outer lumen, the first threshold value being less than the second threshold value.

[0013] According to one embodiment of the present invention, the plug removal system includes a backflow assist gun coupled between the tubing and the self-sweeping string, the backflow assist gun being configured to eject high pressure liquid within the high pressure liquid flow path to an exterior of the plug removal system.

[0014] According to one embodiment of the present invention, the backflow assist gun includes:

[0015] a backflow assist gun body being tubular and in fluid communication with the tubing and the center pipe of the self-sweeping string;

[0016] a backflow assist gun ejector including:

[0017] a backflow assist gun nose extending radially outward from the backflow assist gun body;

[0018] a backflow assist gun ejection channel extending radially through the backflow assist gun nose to communicate the high pressure liquid flow path and the exterior of the plug removal system;

[0019] a backflow assist gun filter element disposed within the backflow assist gun ejection channel;

[0020] a backflow assist gun packing element mounted to an end of the backflow assist gun ejection channel proximate the exterior of the plug removal system to secure the backflow assist gun filter element and seal the backflow assist gun ejection channel; and

[0021] a backflow assist gun ejection orifice extending through a sidewall of the backflow assist gun nose to communicate the backflow assist gun ejection channel and the exterior of the plug removal system;

[0022] wherein the high pressure liquid within the backflow assist gun ejection channel is filtered by the backflow assist gun filter element and ejected through the backflow assist gun ejection orifice toward the tubing.

[0023] According to an embodiment of the present application, the centerline of the assist-return spray hole forms an angle of 15-45° with the axis of the assist-return spray gun body.

[0024] According to an embodiment of the present application, the assist-return spray gun spray portion is disposed adjacent to the flow-through end of the sand recovery string.

[0025] According to an embodiment of the present application, the assist-return spray gun comprises a plurality of assist-return spray portions disposed at equal intervals circumferentially around the assist-return spray gun body.

[0026] According to an embodiment of the present application, the sand recovery string comprises a flow-through assembly, the flow-through assembly comprising:

[0027] a flow-through ring, the flow-through ring being annular and mounted to the flow-through end of the outer cavity of the string;

[0028] a flow-through hole, the flow-through hole extending axially through the flow-through ring to communicate the outer cavity of the string with the exterior of the plug removal system;

[0029] a flow-through ring filter element, the flow-through ring filter element being mounted within the flow-through hole and configured to allow particles having a size less than a first threshold to pass; and

[0030] a breathing hole pin, the breathing hole pin being mounted to an end face of the flow-through hole adjacent to the exterior of the plug removal system to secure the flow-through ring filter element and allow filtered up-return fluid to pass.

[0031] According to an embodiment of the present application, the flow-through assembly comprises a flow-through ring inner tube, the flow-through ring inner tube being tubular and in fluid communication with the tubing and the central tube of the sand recovery string, wherein the flow-through ring is circumferentially mounted to the outer wall of the flow-through ring inner tube.

[0032] According to an embodiment of the present application, the sand recovery string comprises a first sand recovery centralizing element connecting the outer wall tube and the flow-through assembly, the first sand recovery centralizing element comprising a first outer centralizing protrusion, the first outer centralizing protrusion extending radially from the outer wall of the first sand recovery centralizing element and being provided with a helical recess.

[0033] According to an embodiment of the present application, the sand recovery string comprises a sand entry assembly, the sand entry assembly comprising:

[0034] a sand entry ring, the sand entry ring being annular and mounted to the sand entry end of the outer cavity of the string;

[0035] a sand entry channel, the sand entry channel extending axially through the sand entry ring to communicate the outer cavity of the string with the exterior of the plug removal system; and

[0036] a one-way sand entry structure, the one-way sand entry structure being mounted within the sand entry channel and configured to allow particles having a size less than a second threshold to enter the outer cavity of the string unidirectionally.

[0037] According to an embodiment of the present application, the one-way sand entry structure comprises:

[0038] a one-way filter joint secured in the sand entry passage adjacent to the outer cavity of the pipe string and having a first sand entry aperture;

[0039] a sand entry ball seat secured in the sand entry passage adjacent to the exterior of the de- plug system and having a second sand entry aperture, wherein a portion of the sand entry passage defined between the one-way filter joint and the sand entry ball seat forms a sand entry cavity;

[0040] a sand entry ball disposed in the sand entry cavity;

[0041] a sand entry spring having one end connected to the one-way filter joint and an opposite end connected to the sand entry ball, wherein the sand entry spring is in a pre-tensioned state to cause the sand entry ball to abut against the sand entry ball seat and seal the second sand entry aperture; and

[0042] a sand entry ball sleeve circumferentially disposed in the sand entry cavity to define a radial displacement of the sand entry ball.

[0043] According to one embodiment of the present application, the self-sand recovery string comprises a second sand recovery centralizer element connecting the outer wall pipe and the sand entry assembly, the second sand recovery centralizer element comprising a second outer centralizer projection extending radially from an outer wall of the second sand recovery centralizer element and provided with helical recesses.

[0044] According to one embodiment of the present application, the self-sand recovery string comprises a negative pressure sand flushing assembly, the negative pressure sand flushing assembly comprising:

[0045] a negative pressure sand flushing body in a tubular shape and in fluid communication with the central pipe of the self-sand recovery string; and

[0046] a negative pressure sand flushing jetting portion configured to jet the high-pressure liquid in the high-pressure liquid flow passage into the outer cavity of the pipe string in a direction in which the oil pipe is located.

[0047] According to one embodiment of the present application, the outer wall pipe comprises a plurality of segments spaced from each other, and the self-sand recovery string comprises a sand recovery support centralizer element mounted between adjacent segments of the outer wall pipe, the sand recovery support centralizer element comprising:

[0048] a support outer centralizer projection extending radially from an outer wall of the support centralizer element and provided with helical recesses;

[0049] a support inner centralizer projection extending radially from an inner wall of the support centralizer element until abutting against an outer wall of the central pipe, wherein the support inner centralizer projection is provided with an inner flow passage extending axially therethrough; and

[0050] a filter aperture extending through a wall portion of the sand recovery support centralizer element to communicate the outer cavity of the pipe string and the exterior of the de-plug system and allow particles having a particle size less than a second threshold value to pass through.

[0051] According to an embodiment of the present application, the drill plug gun comprises:

[0052] a drill plug gun body;

[0053] a central channel extending axially through the drill plug gun body;

[0054] a front-end channel in fluid communication with the central channel and configured to face away from the open end of the sand wash pipe string; and

[0055] a rear-end channel in fluid communication with the central channel and configured to face toward the open end of the sand wash pipe string.

[0056] According to an embodiment of the present application, the plug removal system comprises:

[0057] a centralizer comprising a first centralizer and a second centralizer respectively arranged at two ends of the sand wash pipe string, the first centralizer and the second centralizer being provided with an outer flow passage extending axially therethrough;

[0058] an adjusting nipple arranged between the sand wash pipe string and the drill plug gun.

[0059] According to an embodiment of the present application, the plug removal system comprises a plurality of sand wash pipe strings arranged in the same direction and connected in sequence.

[0060] According to an embodiment of the present application, the plug removal system comprises a backflow assisting gun connected between adjacent sand wash pipe strings.

[0061] According to the present application, a downhole positive pressure type sand wash hydraulic plug removal method is provided, comprising the following steps:

[0062] Step one, lower the plug removal system into the casing until the end face of the drill plug gun is adjacent to the ash plug section;

[0063] Step two, start the high-pressure pump to pump high-pressure liquid into the oil pipe to break the ash plug section and promote the sand-containing liquid to flow upward through the pipe string outer cavity of the sand wash pipe string and the oil jacket annulus;

[0064] Step three, the sand wash pipe string collects sand in the sand-containing liquid through the pipe string outer cavity;

[0065] Step four, turn off the high-pressure pump, remove the plug removal system from the casing, and clean the sand in the pipe string outer cavity.

[0066] According to an embodiment of the present application, step two comprises:

[0067] the high-pressure liquid is sprayed through at least one of the central channel and the front-end channel of the drill plug gun to break the ash plug section;

[0068] High-pressure liquid is sprayed out through the rear-end hole of the plug-drilling gun to provide upward power for the sand-containing liquid and clean the inner wall of the casing;

[0069] High-pressure liquid is sprayed out through the rear-end hole of the plug-drilling gun to provide upward power for the sand-containing liquid and clean the inner wall of the casing;

[0070] High-pressure liquid is sprayed out through the rear-end hole of the plug-drilling gun to provide upward power for the sand-containing liquid and clean the inner wall of the casing;

[0071] Due to the adoption of the technical solutions, the present application has at least the following beneficial effects:

[0072] 1. The plug-removing system according to the present application adopts water jet technology to remove the ash plug section, clean the inner wall of the casing without damaging the casing, and realizes the recycling and flowback of ash plug debris and sand particles through the self-sand-retrieving device design, so that the production well can be quickly put into production after the operation is completed, and the plug-removing and sand-retrieving integrated operation of the horizontal well can be realized.

[0073] 2. The plug-removing system according to the present application has simple process, novel structure design, and high working reliability, and meets the requirements of tests and field construction.

[0074] 3. The plug-removing system according to the present application is detachably sealed and connected through the tubing buckle, the required components can be adjusted according to the actual working conditions, and the plug-removing system can also be applied to the ash plug section of the straight well or high-deviation well.

[0075] 4. The plug-removing system according to the present application comprises a multi-stage self-sand-retrieving pipe string, so that the length of the entire plug-removing system is adjustable and has high flexibility.

[0076] 5. The plug-removing system according to the present application is provided with multiple return-assisting guns to prevent the pipe string from being buried by sand during the pipe string operation, and the negative-pressure sand-washing assembly in the sand-retrieving pipe string is used to generate negative pressure at the sand-feeding assembly end and accelerate the upward flow of the mixed liquid into the sand-retrieving pipe string. BRIEF DESCRIPTION OF DRAWINGS

[0077] The accompanying drawings are included to provide a further understanding of the present disclosure and constitute a part of the specification, and together with the following detailed description, serve to explain the present disclosure but do not constitute a limitation thereof. In the drawings:

[0078] Figure 1 is a schematic view of a downhole positive-pressure self-sand-retrieving hydraulic plug-removing system according to an embodiment of the present application;

[0079] Figure 2 is a sectional view of a downhole positive-pressure self-sand-retrieving hydraulic plug-removing system according to an embodiment of the present application;

[0080] Figure 3is a cross-sectional view of a self-sand-retrieving string according to an embodiment of the present application;

[0081] Figure 4 is a cross-sectional view of a backflow-assisting gun according to an embodiment of the present application;

[0082] Figure 5 is a cross-sectional view of a flow-through assembly according to an embodiment of the present application;

[0083] Figure 6 is a cross-sectional view of a sand-feeding assembly according to an embodiment of the present application;

[0084] Figure 7a and Figure 7b are a cross-sectional view and a side view, respectively, of a negative-pressure sand-flushing assembly according to an embodiment of the present application;

[0085] Figure 8a and Figure 8b are a cross-sectional view and a sectional view, respectively, of a drill-pipe-cleaning gun according to an embodiment of the present application;

[0086] Figure 9 is a schematic diagram of a downhole positive-pressure self-sand-retrieving hydraulic cleanout system according to another embodiment of the present application;

[0087] Figure 10 shows a flowchart of a downhole positive-pressure self-sand-retrieving hydraulic cleanout method according to an embodiment of the present application.

[0088] in the drawings,

[0089] 10 tubing;

[0090] 20 backflow-assisting gun, 20a primary backflow-assisting gun, 20b secondary backflow-assisting gun, 20c tertiary backflow-assisting gun, 21 backflow-assisting gun body, 22 backflow-assisting gun jet, 211 backflow-assisting gun protrusion, 212 backflow-assisting gun jet channel, 213 backflow-assisting gun filter element, 214 backflow-assisting gun blocking element, 215 backflow-assisting gun jet hole;

[0091] 30 sand-retrieving string, 30a first-stage sand-retrieving string, 30b second-stage sand-retrieving string, 30c third-stage sand-retrieving string, 31 central tube, 32 outer wall tube, 33 flow passage assembly, 331 flow passage ring, 332 flow passage hole, 333 flow passage ring filter element, 334 breathing hole pin, 335 flow passage ring inner tube, 34 first sand-retrieving centralizer element, 341 first outer centralizer protrusion, 35 sand-feeding assembly, 351 sand-feeding ring, 352 sand-feeding channel, 353 sand-feeding one-way filter joint, 354 sand-feeding ball seat, 355 sand-feeding cavity, 356 sand-feeding ball, 357 sand-feeding spring, 358 sand-feeding ball sleeve, 359 sand-feeding ring inner tube, 36 second sand-retrieving centralizer element, 361 second outer centralizer protrusion, 37 negative pressure sand flushing assembly, 371 negative pressure sand flushing body, 372 negative pressure sand flushing spray part, 3721 negative pressure sand flushing convex part, 3722 negative pressure sand flushing spray hole channel, 3723 negative pressure sand flushing filter element, 3724 negative pressure sand flushing blocking element, 3725 negative pressure sand flushing spray hole, 38 sand-retrieving support centralizer element, 381 support outer centralizer protrusion, 382 support inner centralizer protrusion, 383 filter hole, 39 back cap, C1 string inner cavity, C2 string outer cavity, E1 flow passage end, E2 sand-feeding end;

[0092] 40 drill plug jetting gun, 41 high-pressure jet, 42 drill plug jetting gun body, 43 central hole, 44 front end hole, 45 rear end hole, 46 drainage groove;

[0093] 51 first centralizer, 52 second centralizer;

[0094] 60 adjustment sub;

[0095] 70 variable thread;

[0096] 80 casing, 81 oil-casing annulus;

[0097] 90 plug section, 91 plug-removing section, 92 plug-remaining section. DETAILED DESCRIPTION

[0098] The specific embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustration and explanation of the present disclosure, and are not intended to limit the present disclosure.

[0099] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application, for example, the terms "length", "width", "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like specify relative positions according to the orientations or positions shown in the drawings, which are for the convenience of description only, and cannot be understood as a limitation of the technical solutions.

[0100] The terms "comprising" and "having," and any variations thereof, used in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion; the terms "first," "second," etc., used in the specification, claims, and accompanying drawings are used to distinguish different objects, not to describe a particular order. "A plurality of" means two or more, unless otherwise explicitly specified.

[0101] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0102] Figure 1 and Figure 2 Schematic diagrams and cross-sectional views of a downhole positive pressure self-retrieving hydraulic deblocking system according to an embodiment of the present invention are shown. The deblocking system generally includes a high-pressure pump (not shown), tubing 10 connected to the high-pressure pump, a drill plug nozzle 40, and a self-retrieving sand string 30 disposed between the tubing 10 and the drill plug nozzle 40. The high-pressure pump is configured to pump high-pressure fluid into the tubing 10. Specifically, the self-retrieving sand string 30 includes a central tube 31 and an outer wall tube 32 coaxial with and circumferentially surrounding the outside of the central tube 31. The inner wall of the central tube 31 may define a string cavity C1, which is in fluid communication with the tubing 10 and the drill plug nozzle 40 to form at least a portion of a high-pressure fluid flow channel. The inner wall of the outer wall tube 32 and the outer wall of the central tube 31 define an annular string cavity C2. The string cavity C2 has a flow end E1 adjacent to the tubing 10 and a sand inlet end E2 adjacent to the drill plug nozzle 40. The flow end E1 allows particles smaller than the first threshold to pass through, while the sand inlet end E2 allows particles smaller than the second threshold to enter the outer cavity C2 of the tubing in one direction. The first threshold is smaller than the second threshold. Therefore, when the deblocking system is lowered into the casing 80 containing the ash plug section 90, the high-pressure liquid containing abrasive is transmitted through the high-pressure liquid flow channel to the drill plug spray gun 40 and sprayed onto the end face of the ash plug section 90 to form a high-pressure jet 41. The sprayed high-pressure liquid mixes with the sand and gravel crushed by the high-pressure jet 41 to form a sand-laden liquid. This sand-laden liquid enters the outer cavity C2 of the tubing from the sand inlet end E2 and continuously flows upwards. The gas, liquid, and a small amount of smaller particles (smaller than the first threshold) flow out of the outer cavity C2 of the tubing through the flow end E1 and enter the annulus 81 between the self-removing sand tubing 30 and the casing 80. Larger particles (larger than the first threshold and smaller than the second threshold) remain in the outer cavity C2 of the tubing, achieving the sand removal effect.

[0103] Preferably, the plug removal system according to the present application can further comprise a backflow assisting gun 20 connected between the tubing 10 and the sand washing string 30. The backflow assisting gun 20 is arranged to inject high pressure liquid in the high pressure liquid flow passage to the outside of the plug removal system, so as to disperse the upflowing sand laden fluid in the tubing annulus 81 and further provide upward force to the upflowing sand laden fluid in the tubing annulus 81.

[0104] As shown in Figure 3 Fig. 1, the sand washing string 30 can comprise, in addition to the central pipe 31 and the outer wall pipe 32, a flow through assembly 33 arranged at the flow through end E1, a sand inlet assembly 35 arranged at the sand inlet end E2, a negative pressure sand flushing assembly 37 for providing negative pressure to the string outer cavity C2, and a plurality of centralizing elements.

[0105] The following will be described in detail with reference to the accompanying Figures 3-8b Specific examples of the above components will be described in detail.

[0106] Assisted return spray gun

[0107] Figure 4 Fig. 2 shows a sectional view of an embodiment of the backflow assisting gun 20. As shown in the figure, the backflow assisting gun 20 can comprise a backflow assisting gun body 21 and a backflow assisting gun injection part 22 arranged on the backflow assisting gun body 21.

[0108] The backflow assisting gun body 21 is generally tubular and in fluid communication with the tubing 10 and the central pipe 31 of the sand washing string 30, and the cavity defined by the inner wall of the tubular body can jointly form part of the high pressure liquid flow passage with the string inner cavity C1. In the embodiment of the present application, the backflow assisting gun body 21 can be connected to the tubing 10 and the central pipe 31 of the sand washing string 30 by, for example, a tubing buckle.

[0109] The backflow assisting gun injection part 22 can comprise a backflow assisting gun protrusion 211 extending radially outward from the backflow assisting gun body 21, a backflow assisting gun injection channel 212 extending radially through the backflow assisting gun protrusion 211, a backflow assisting gun filter element 213 arranged in the backflow assisting gun injection channel 212, a backflow assisting gun blocking element 214 mounted to the end of the backflow assisting gun injection channel 212 adjacent to the outside of the plug removal system, and a backflow assisting gun injection hole 215 extending through the side wall of the backflow assisting gun protrusion 211. The backflow assisting gun injection channel 212 can be in communication with the high pressure liquid flow passage and the outside of the plug removal system, so as to facilitate installation or replacement of the backflow assisting gun filter element 213 inside. The backflow assisting gun filter element 213 can be a screen or other form of filter element, and the mesh size of the screen is preferably not greater than the particle size of the abrasive contained in the high pressure liquid, so as to avoid the abrasive being ejected from the backflow assisting gun injection hole 215. The backflow assisting gun filter element 213 can be limited in displacement in a first direction along the channel axis by a boss extending radially from the inner wall of the backflow assisting gun injection channel 212, for example, by a distance of 1-10 mm.Figure 4 The displacement of the cleanup gun filter element 213 downward is prohibited. The cleanup gun blocking element 214 can be a dead plug screwed to the inner wall of the cleanup gun jet channel 212, which is used to limit the displacement of the cleanup gun filter element 213 in the other direction along the channel axis, to fix and seal the cleanup gun jet channel 212. Alternatively, the dead plug can be welded to the end of the cleanup gun jet channel 212. The cleanup gun jet 215 is used to communicate the cleanup gun jet channel 212 and the outside of the plug removal system, so that the high-pressure liquid in the cleanup gun jet channel 212 is jetted through the cleanup gun filter element 213 and then through the cleanup gun jet 215 towards the direction of the oil pipe 10.

[0110] Preferably, the cleanup gun jet 215 can be designed to jet the high-pressure liquid obliquely towards the direction of the oil pipe 10, deviating from the axis of the cleanup gun body 21, to facilitate the dispersion of the sand in the oil jacket annulus 81 and the upward flow of the sand-containing liquid. For example, the center line of the cleanup gun jet 215 can form an angle of 15-45°, preferably 15-30°, with the axis of the cleanup gun body 21. The cleanup gun jetting part 22 can be disposed adjacent to the flow-through end E1 of the sand washing string 30, i.e. the cleanup gun jetting part 22 can be located at one end of the cleanup gun body 21 and connected to the end of the base pipe 31 adjacent to the flow-through end E1. Due to the boss-like structure of the flow-through end E1 of the sand washing string 30 and the sand-containing liquid filtered from the flow-through end E1 containing a small amount of sand, a small amount of sand is likely to accumulate here. The placement of the cleanup gun jetting part 22 of the cleanup gun 20 adjacent to the flow-through end E1 can effectively prevent the accumulation of sand here and at the same time provide power for the upward flow of the sand-containing liquid in the oil jacket annulus 81. The cleanup gun 20 can include a plurality of cleanup gun jetting parts 22, e.g. 3-5, disposed equidistantly and circumferentially around the cleanup gun body 21, so as to uniformly accelerate the sand-containing liquid in the circumferential direction.

[0111] Flow through assembly

[0112] The flow-through assembly 33 is disposed at the flow-through end E1 of the string outer cavity C2, for filtering out gas, liquid and a small amount of particles with small particle size from the sand-containing liquid, and retaining particles with slightly larger particle size in the string outer cavity C2. Figure 5 A cross-sectional view of one embodiment of the flow-through assembly 33 is shown. As shown, the flow-through assembly 33 can include a flow-through ring 331 mounted to the flow-through end E1 of the string outer cavity C2, a flow-through hole 332 extending axially through the flow-through ring 331, and a flow-through ring filter element 333 mounted in the flow-through hole 332.

[0113] The flow-through ring 331 is generally annular and is mounted to the flow-through end El of the outer cavity C2 of the tubular string by connecting to the central pipe 31 and the outer wall pipe 32 respectively. The inner wall and the outer wall of the flow-through ring 331 can be provided with threads, and the outer wall can be threadedly connected to the inner wall of the outer wall pipe 32 or the inner wall of the first sand-fishing centralizing element which will be described in detail below. In an embodiment of the present application, the inner wall of the flow-through ring 331 can be directly threadedly connected to the outer wall of the central pipe 31. In another embodiment of the present application, the flow-through assembly 33 further comprises a flow-through ring inner pipe 335 which is tubular, and the flow-through ring 331 can be threadedly connected to the outer wall of the flow-through ring inner pipe 335 in a circumferential ring shape. One end of the flow-through ring inner pipe 335 is sealingly connected to the central pipe 31 by a tubing collar, and the other end is sealingly connected to the tubing 10 or the body 21 of the assisted return jet gun, thereby forming part of the high-pressure liquid flow passage.

[0114] The flow-through hole 332 communicates the outer cavity C2 of the tubular string with the outside of the debris-removal system. The flow-through ring filter element 333 can be a filter screen or other forms of filter element, and the mesh size of the filter screen is set to allow particles with a particle size less than a first threshold value to pass through, wherein the first threshold value can be set according to the actual working conditions, referring to the material of the sand screen 90, the proportion of liquid in the sand-laden fluid, the sand grain size distribution, the sand production rate, and other parameters. In an embodiment of the present application, the first threshold value can be as small as to allow only gas and liquid to pass through, so as to achieve its flow-through gas venting function. The flow-through ring filter element 333 can be limited in displacement in a first direction along the axis of the flow-through hole 332 by a boss extending radially from the inner wall of the flow-through hole 332, for example, the displacement of the flow-through ring filter element 333 to the right is prohibited in the Figure 5 The breathing hole peg 334 has a hole opening in the inner diameter and is mounted to the end face of the flow-through hole 332 adjacent to the outside of the debris-removal system, for limiting the displacement of the flow-through ring filter element 333 in another direction along the axis of the flow-through hole 332, so as to fix the flow-through ring filter element 333 and allow the filtered upflowing fluid to pass through.

[0115] The flow-through assembly 33 can comprise a plurality of flow-through holes 332 which are axially circumferentially arranged at equal intervals, for example, 6-12, so as to uniformly vent gas in a circumferential direction and also provide upflowing power for the sand-laden fluid in the tubing annulus 81.

[0116] Sand inlet assembly 35

[0117] The sand inlet assembly 35 is arranged at the sand inlet end E2 of the outer cavity C2 of the tubular string, so as to allow the sand-laden fluid to enter the outer cavity C2 of the tubular string in one direction, i.e., to allow the sand-laden fluid to enter the outer cavity C2 of the tubular string and prevent the sand-laden fluid from leaving the outer cavity C2 of the tubular string. Figure 6A cross-sectional view of one embodiment of the sand entry assembly 35 is shown. As shown, the sand entry assembly 35 can include a sand entry ring 351 mounted to the sand entry end E2 of the outer cavity C2 of the tubular string, a sand entry passage 352 extending axially through the sand entry ring 351, and a one-way sand entry structure mounted within the sand entry passage 352.

[0118] The sand entry ring 351 is generally annular and is mounted to the sand entry end E2 of the outer cavity C2 of the tubular string by way of connection to the central pipe 31 and the outer wall pipe 32, respectively. The inner wall and the outer wall of the sand entry ring 351 can be threaded, and the outer wall can be threadably connected to the inner wall of the outer wall pipe 32 or to the inner wall of a second sand plug centralizing element, which will be described in detail below. In one embodiment of the present application, the inner wall of the sand entry ring 351 can be directly threadably connected to the outer wall of the central pipe 31. In another embodiment of the present application, the sand entry ring 351 further includes a sand entry ring inner pipe 359 (see Figure 3 ) that is tubular, and the sand entry ring 351 can be threadably connected to the outer wall of the sand entry ring inner pipe 359 circumferentially around the inner wall. One end of the sand entry ring inner pipe 359 is sealingly connected to the central pipe 31 by way of a tubing nipple, and the other end is connected to the drill plug gun 40, thereby forming part of the high pressure fluid flow passage.

[0119] The sand entry passage 352 communicates the outer cavity C2 of the tubular string with the exterior of the plug removal system. The one-way sand entry structure is configured to allow particles having a size less than a second threshold value to pass into the outer cavity C2 of the tubular string in one direction. The second threshold value is intended to indicate that the sand entry passage 352 allows particles having a larger size to pass than the flow-through passage, which allows particles having a size less than a first threshold value to pass, thereby collecting sand within the outer cavity C2 of the tubular string. The second threshold value can be set in accordance with actual operating conditions, taking into account the material of the screen-out section 90, the distribution of sizes of the sand that is broken, and other parameters. In an embodiment of the present application, the second threshold value can be close to the inner diameter of the sand entry passage 352, so as to collect as much sand as possible.

[0120] In an embodiment of the present application, the one-way sand entry structure includes a one-way filter sub fixed within the sand entry passage 352 adjacent the outer cavity C2 and having a first sand entry aperture, a sand entry ball seat 354 fixed within the sand entry passage 352 adjacent the exterior of the plug removal system and having a second sand entry aperture, a sand entry ball 356 and a sand entry spring 357 disposed between the one-way filter sub and the sand entry ball seat 354. Specifically, the one-way filter sub can be threadably connected to the inner wall of the sand entry passage 352, and the sand entry ball seat 354 can be defined by a boss extending radially from the inner wall of the sand entry passage 352 to limit displacement in a first direction along the axis of the sand entry passage 352, for example in Figure 6The sand ball seat 354 is prohibited from moving to the right. Alternatively, the sand ball seat 354 can be fixed in one direction or in both directions in the sand inlet channel 352 in other ways. The part of the sand inlet channel 352 defined between the one-way filter joint and the sand ball seat 354 forms a sand inlet cavity 355. The sand spring 357 is connected at one end to the one-way filter joint and at the opposite end to the sand ball 356. Normally, the sand spring 357 is in a pre-tightened state, so that the sand ball 356 is pressed against the sand ball seat 354 under a certain pressure and seals the second sand inlet hole. When the upward flow of the sand-containing liquid is greater than the pressure exerted by the sand spring 357 on the sand ball 356, the sand ball 356 moves away from the sand ball seat 354, opening the second sand inlet hole, and the sand-containing liquid enters the sand inlet cavity 355 and then enters the outer cavity C2 of the pipe string through the first sand inlet hole. When the sand-containing liquid from the outer cavity C2 of the pipe string rushes into the sand inlet cavity 355, it exerts pressure on the sand ball 356, making it more stably pressed against the sand ball seat 354 and sealing the second sand inlet hole, thereby preventing the sand-containing liquid from flowing out of the outer cavity C2 of the pipe string, achieving the effect of one-way sand inlet. In specific working conditions, the pre-tightening force of the sand spring 357 needs to be set to be less than the flow pressure of the upward sand-containing liquid, so as to ensure that the one-way sand inlet structure does not cut off the upward sand-containing liquid and does not block the sand. The one-way sand inlet structure can also include a sand ball sleeve 358 that is circumferentially arranged in the sand inlet cavity 355 to limit the radial displacement of the sand ball 356.

[0121] The sand inlet assembly 35 can include a plurality of sand inlet channels 352, for example 6-12, which are axially and equidistantly arranged, so as to uniformly collect the sand-containing liquid in the circumferential direction. At the end of the sand inlet ring 351 away from the outer cavity C2 of the pipe string, the back cap 39 can be used to threadedly connect with the outer wall of the sand inlet ring inner tube 359, preventing the sand inlet assembly 35 from being loosened.

[0122] Negative pressure sand flush assembly 37

[0123] Figure 7a and Figure 7b respectively show a partial cross-sectional view and a side view of one embodiment of the negative pressure sand washing assembly 37. As shown, the negative pressure sand washing assembly 37 can include a negative pressure sand washing body 371 and a negative pressure sand washing jet 372 arranged on the negative pressure sand washing body 371.

[0124] The negative pressure sand washing body 371 is generally tubular and in fluid communication with the central pipe 31 of the self-sand-retrieving pipe string 30, and the cavity defined by the tubular inner wall thereof can jointly form part of the high-pressure liquid flow channel with the inner cavity C1 of the pipe string. In the embodiment of the present application, one end of the negative pressure sand washing body 371 can be sealingly connected to the central pipe 31 through a tubing buckle, and the other end can be sealingly connected to the sand inlet ring inner tube 359 through a tubing buckle.

[0125] The negative pressure sand washing jetting part 372 is arranged to jet the high pressure liquid in the high pressure liquid flow channel into the tubular string outer cavity C2 in the direction of the oil pipe 10. As shown in Figure 3 and Figure 7a As shown, similar to the structure of the auxiliary backflow jetting gun jetting part 22, the negative pressure sand washing jetting part 372 can include a negative pressure sand washing protrusion 3721 extending radially outward from the negative pressure sand washing body 371, a negative pressure sand washing jetting hole 3725 channel 3722 extending radially through the negative pressure sand washing protrusion 3721, a negative pressure sand washing filter element 3723 arranged in the negative pressure sand washing jetting hole 3725 channel 3722, a negative pressure sand washing plugging element 3724 mounted to one end of the negative pressure sand washing jetting hole 3725 channel 3722 adjacent to the tubular string outer cavity C2, and a negative pressure sand washing jetting hole 3725 extending through the side wall of the negative pressure sand washing protrusion 3721. Among them, the negative pressure sand washing jetting hole 3725 channel 3722 can be connected with the high pressure liquid flow channel and the tubular string outer cavity C2, so as to facilitate the installation or replacement of the negative pressure sand washing filter element 3723 inside. The negative pressure sand washing filter element 3723 can be a screen or other form of filter element, and the mesh number of the screen is preferably not greater than the particle size of the abrasive contained in the high pressure liquid, so as to avoid the abrasive being sprayed from the negative pressure sand washing jetting hole 3725 to the tubular string outer cavity C2. The negative pressure sand washing filter element 3723 can be limited to displacement in a first direction along the axis of the hole channel by a boss extending radially from the inner wall of the negative pressure sand washing jetting hole 3725 channel 3722, for example, in Figure 7a the negative pressure sand washing filter element 3723 is prohibited from downward displacement. The negative pressure sand washing plugging element 3724 can be a dead plug threadedly connected with the inner wall of the negative pressure sand washing jetting hole 3725 channel 3722, for limiting the displacement of the negative pressure sand washing filter element 3723 in another direction along the axis of the hole channel, so as to fix and seal the negative pressure sand washing jetting hole 3725 channel 3722. Alternatively, the dead plug can be welded and sealed to the end of the negative pressure sand washing jetting hole 3725 channel 3722. The negative pressure sand washing jetting hole 3725 is used to connect the negative pressure sand washing jetting hole 3725 channel 3722 and the tubular string outer cavity C2, and to assist the upward flow of the sand-containing liquid in the tubular string outer cavity C2.

[0126] Preferably, the negative pressure sand washing jetting hole 3725 can be designed to jet the high pressure liquid obliquely toward the direction of the oil pipe 10 deviating from the axis of the negative pressure sand washing body 371, so as to facilitate the washing and dispersion of the sand and rock in the oil casing annulus 81 and the upward flow of the sand-containing liquid. For example, the center line of the negative pressure sand washing jetting hole 3725 can form an angle of 15-45°, preferably 15-30°, with the axis of the negative pressure sand washing body 371. The negative pressure sand washing jetting part 372 can be arranged adjacent to the sand feeding assembly 35, so as to form a local negative pressure between the negative pressure sand washing assembly 37 and the sand feeding assembly 35, and to help the compression of the sand feeding spring 357, facilitating the entry of the sand-containing liquid outside the plug removal system into the tubular string outer cavity C2.

[0127] As shown in Figure 7bAs shown, the negative pressure sand flushing can include multiple negative pressure sand flushing jets 372 that are circumferentially arranged at equal intervals around the negative pressure sand flushing body 371, for example, 3-5, so as to uniformly generate accelerated swirling flow of sand-containing liquid in the circumferential direction.

[0128] Centralising element

[0129] like Figure 3 As shown, the self-removing sand pipe string 30 may include multiple straightening elements, such as: a first sand-removing straightening element 34 connecting the outer wall pipe 32 and the flow assembly 33, and a second sand-removing straightening element 36 connecting the outer wall pipe 32 and the sand inlet assembly 35.

[0130] The first sand-removing and centralizing element 34 is generally tubular. Its outer wall at one end and its inner wall at the other end can be threadedly connected to the inner wall of the outer wall tube 32 and the outer wall of the flow ring 331, respectively, forming part of the outer cavity C2 of the tubular column with the annular cavity defined by the central tube 31 and / or the inner tube 335 of the flow ring. The first sand-removing and centralizing element 34 may include a first outer centralizing protrusion 341 extending radially outward from its outer wall. This first outer centralizing protrusion 341 is provided with a spiral recess to form a spiral flow channel within the annular space 81, thus scraping sand, centralizing, and accelerating the upward swirling flow of the sand-laden liquid without intercepting or blocking sand.

[0131] Similar to the first sand-removing and straightening element 34, the second sand-removing and straightening element 36 is generally tubular. Its outer wall at one end and its inner wall at the other end can be threadedly connected to the inner wall of the outer wall tube 32 and the outer wall of the sand inlet ring 351, respectively, forming part of the outer cavity C2 of the tubular column with the annular cavity defined by the central tube 31 and / or the inner tube 359 of the sand inlet ring. The second sand-removing element may also include a second outer straightening protrusion 361 extending radially from its outer wall and having a spirally recessed shape. This second outer straightening protrusion 361 has the same function as the first outer straightening protrusion 341.

[0132] In embodiments of the present application, the outer wall pipe 32 can be composed of multiple segments spaced apart from each other. The centralizing element can further comprise a sand-reaming support centralizing element 38 installed between adjacent segments of the outer wall pipe 32. The number of segments of the outer wall pipe 32 and the sand-reaming support centralizing element 38 can be adjusted adaptively under specific working conditions. The sand-reaming support centralizing element 38 is generally tubular in shape, and the outer wall / inner wall at both ends thereof can be threadedly connected to the inner wall / outer wall of adjacent segments, so that it forms part of the outer string cavity C2 together with the annular cavity defined by the central pipe 31. The sand-reaming support centralizing element 38 can also comprise a support outer centralizing protrusion 381 extending radially from the outer wall thereof and having a helical recess. The support outer centralizing protrusion 381 serves the same purpose as the first outer centralizing protrusion 341 and the second outer centralizing protrusion 361. Preferably, the sand-reaming support centralizing element 38 can further comprise a support inner centralizing protrusion 382 extending radially from the inner wall thereof until abutting against the outer wall of the central pipe 31, so as to ensure the central position of the central pipe 31. The support inner centralizing protrusion 382 is provided with an inner flow-through passage extending axially therethrough, so as to ensure no flow blockage and no sand blockage.

[0133] Preferably, the sand-reaming support centralizing element 38 can further comprise a filter hole 383 extending through the wall thereof at the helical recess, so as to communicate the outer string cavity C2 with the outside of the plug-removal system and allow particles having a particle size smaller than a second threshold value to pass through. The filter hole 383 of the sand-reaming support centralizing element 38 serves the same purpose as the flow-through hole 332 of the flow-through ring 331, i.e., flow-through venting. Therefore, the filter hole 383 can have a similar structure as the flow-through hole 332.

[0134] Drill plug spray gun 40

[0135] The plug-reaming gun 40 is arranged at the end of the plug-removal system closest to the ash plug segment 90. Figure 8a and Figure 8b Partially cutaway and side views of one embodiment of the plug-reaming gun 40 are shown respectively. As shown, the plug-reaming gun 40 can comprise a plug-reaming gun body 42, a central bore 43 extending axially through the plug-reaming gun body 42, a front-end bore 44 and a rear-end bore 45 in fluid communication with the central bore 43.

[0136] The plug-reaming gun body 42 can be designed in the shape of a bullet head, so as to facilitate its smooth entry into the casing 80. The central bore 43 is coaxial with and in fluid communication with the string inner cavity CI of the sand-reaming string 30, so as to jet high-pressure liquid forward of the plug-reaming gun 40 and break the ash plug segment 90.

[0137] The front-end hole 44 is arranged to face away from the opening of the sand control string 30, and preferably is arranged to be inclined to the axis of the central hole 43 to face the plug section 90 in front of the drill plug gun 40 to spray high-pressure liquid. The front-end hole 44 and the axis of the central hole 43 can form an angle of 15-45°, preferably 15-30°, to facilitate the functions of assisting the return, increasing the flow, cleaning the well wall and breaking the front-end plug. A plurality of front-end holes 44 are arranged to form at least one circular ring around the central hole 43, so that the high-pressure liquid sprayed from the front-end hole 44 and the central hole 43 forms a plug pushing surface. The number of front-end holes 44 constituting a single circular ring is preferably 3-6, and the specific number can be determined according to the inner diameter of the well casing 80 to be unblocked. In specific working conditions, drill plug guns 40 with different angles between the front-end hole 44 and the central hole 43 can be selected to complete the unblocking work of different plug sizes.

[0138] The rear-end hole 45 is arranged to face the opening of the sand control string 30, and preferably is arranged to be inclined to the axis of the central hole 43 to face the rear of the drill plug gun 40 to spray high-pressure liquid. The rear-end hole 45 and the axis of the central hole 43 can form an angle of 15-45°, preferably 15-30°. A plurality of rear-end holes 45 are arranged to form at least one circular ring around the central hole 43, so that the high-pressure liquid sprayed from the rear-end hole 45 plays a role in assisting the return of the sand-containing liquid and cleaning the inner wall of the casing 80. The number of rear-end holes 45 constituting a single circular ring is preferably 3-5.

[0139] The plug removal system can further comprise a centralizer. In the embodiment of the present application, the centralizer comprises a first centralizer 51 and a second centralizer 52 which are sealingly connected to both ends of the sand control string 30 through the tubing buckle. The double-stage centralization can ensure the centering of the sand control string 30. The first centralizer 51 away from one end of the sand control string 30 can be sealingly connected to the return-assisting gun body 21 or the tubing 10 through the tubing buckle, and the outer wall thereof is circumferentially provided with a plurality of centralizing bosses, preferably 6-8 centralizing bosses. Adjacent centralizing bosses are processed with an outer flow passage extending axially through, which helps to return without flow interception. The second centralizer 52 away from one end of the sand control string 30 can be sealingly connected to the drill plug gun 40 or the adjusting sub which will be described in detail below. The second centralizer 52 can have the same structure as the first centralizer 51.

[0140] At least one adjusting section 80 may be disposed between the self-retrieving sand string 30 and the drill plug nozzle 40. Specifically, the adjusting section 80 is generally tubular, with one end connected to the central tube 31 or the inner tube 359 of the self-retrieving sand string 30 via a tubing thread seal, and the other end directly connected to the drill plug nozzle body 42 via a tubing thread seal, or connected to the drill plug nozzle body 42 via a changer 70 after diameter conversion. Thus, the cavity defined by the adjusting section 80 and the changer 70 constitutes part of the high-pressure liquid flow channel. Under specific operating conditions, the length and flexibility of the plug removal system can be controlled by adjusting the number and length of the adjusting sections 80, and the backflow capability of the drill plug nozzle 40 can be affected.

[0141] Figure 9 Another embodiment of the downhole positive pressure self-retrieving hydraulic deblocking system according to the present invention is shown. As shown, the deblocking system may include multiple self-retrieving sand strings 30 arranged in the same direction and connected sequentially, such as a primary self-retrieving sand string 30a, a secondary self-retrieving sand string 30b, and a tertiary self-retrieving sand string 30c. The number of self-retrieving sand strings 30 is not limited to this. Figure 9 The number and length of the three self-recovering sand tubing strings 30 shown can be adjusted by those skilled in the art according to specific working conditions. "Set in the same direction" means that the flow ends E1 of multiple self-recovering sand tubing strings 30 are all set in the same direction—that is, towards the tubing 10; while the sand inlet ends E2 of multiple self-recovering sand tubing strings 30 are all set in the opposite direction—that is, towards the drill plug nozzle 40. In this embodiment, a return nozzle 20 can be set between adjacent self-recovering sand tubing strings 30. As shown in the figure, a first-stage return nozzle 20a can be set between the first-stage self-recovering sand tubing string 30a and the tubing 10, a second-stage return nozzle 20b can be set between the second-stage self-recovering sand tubing string 30b and the first-stage self-recovering sand tubing string 30a, and a third-stage return nozzle 20c can be set between the third-stage self-recovering sand tubing string 30c and the second-stage self-recovering sand tubing string 30b. Those skilled in the art can install one or more return nozzles 20 between two adjacent self-retrieving sand tubing strings 30, or install one or more return nozzles 20 at intervals between multiple self-retrieving sand tubing strings 30, depending on the actual working conditions. On the one hand, installing multiple self-retrieving sand tubing strings 30 can increase the flexibility of the deblocking system, making it easier to enter horizontal wells to perform deblocking work; on the other hand, installing multiple return nozzles 20 can provide upward return power to the sand-bearing fluid at intervals of the first distance, increasing the return flow rate, and promptly removing sand and gravel that will accumulate, avoiding jamming of the deblocking system, and ensuring that the upward return channel is smooth and unblocked.

[0142] The outer wall of the drill plug spray gun body 42 is provided with multiple discharge grooves 46 at equal intervals around the periphery. Each discharge groove 46 is radially recessed and extends along the axial direction to provide a return channel for the sand-containing liquid.

[0143] Figure 10A downhole positive pressure self-sand-retrieving plug-removing hydraulic method according to the present application is shown, which generally comprises the following steps:

[0144] Step one, lower the plug-removing system into the casing 80 until the plug-removing gun 40 is adjacent to the end face of the ash plug section 90;

[0145] Step two, start the high-pressure pump to pump high-pressure liquid into the tubing 10 to crush the ash plug section 90 and promote the sand-containing liquid to flow upward through the outer cavity C2 of the self-sand-retrieving string 30 and the oil-casing annulus 81;

[0146] Step three, the self-sand-retrieving string 30 collects the sand in the sand-containing liquid through the outer cavity C2;

[0147] Step four, shut down the high-pressure pump, remove the plug-removing system from the casing 80, and clean the sand in the outer cavity C2.

[0148] In the embodiment of the present application, the high-pressure liquid can flow out through at least one of the central channel 43 and the front-end channel 44 of the plug-removing gun 40 to crush the ash plug section 90, through the rear-end channel 45 of the plug-removing gun 40 to provide upward flow power for the sand-containing liquid and clean the inner wall of the casing 80, through the auxiliary flow gun injection part 22 of the auxiliary flow gun 20 to avoid the accumulation of the sand-containing liquid in the casing 80 and provide upward flow power for the sand-containing liquid in the casing 80, and through the negative pressure sand flushing injection part 372 of the negative pressure sand flushing assembly 37 to generate negative pressure in the outer cavity C2 and provide upward flow power for the sand-containing liquid in the outer cavity C2.

[0149] The ash plug section 90 comprises a plug-removing section 91 to be drilled and a remaining plug section 92 to be kept. The sand-retrieving efficiency of the self-sand-retrieving string 30 can be converted according to the particle volume generated by the plug-removing section 91, Figure 1 The single-stage self-sand-retrieving string 30 shown can complete the collection of 72% of the volume of the plug-removing section 91, and the remaining sand is returned to the ground through the oil-casing annulus 81 for recovery. For the Figure 9 The plug-removing system shown comprising the multi-stage self-sand-retrieving string 30 has a reduced sand-retrieving efficiency of the multi-stage self-sand-retrieving string 30 due to the increased proportion of the oil-casing annulus 81, but can still complete the collection of 60% of the volume of the plug-removing section 91, and the remaining sand is returned to the ground through the oil-casing annulus 81 for recovery.

[0150] The parts of the plug-removing system according to the present application are detachably sealed and connected by tubing joints, and the required components can be adjusted according to the actual working conditions. For example, for the drilling of the plug-removing section 90 of the ash plug in a straight well or a highly deviated well, the required discharge capacity for the return flow in the straight well is small, so the self-sand-retrieving string 30 can be removed and directly transmitted by the tubing 10. The plug-removing system adopts double-stage centralizing, the plug-removing gun 40 is lowered to the upper end face of the ash plug, the high-pressure pump is started to pump high-pressure abrasive liquid, the ash plug section 90 is cleaned, and the sand-containing liquid is returned through the oil-casing annulus 81, thereby establishing a circulation system.

[0151] The preferred embodiments of the present disclosure are described in detail above with reference to the drawings, but the present disclosure is not limited to the specific details in the above-described embodiments. Various simple modifications can be made to the technical solutions of the present disclosure within the technical concept of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0152] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations are not described again in the present disclosure.

[0153] In addition, various different embodiments of the present disclosure can also be combined in any manner, as long as they do not deviate from the idea of the present disclosure, and they should also be considered as disclosed by the present disclosure.

Claims

1. A downhole positive pressure self-sand-retrieving hydraulic un-plugging system, characterized in that, Comprising: a high pressure pump; a tubing string, the high pressure pump being connected to the tubing string and configured to pump a high pressure fluid into the tubing string; a drill plug gun; and a sandface string, the sandface string being disposed between the tubing string and the drill plug gun, and the sandface string comprising: a center pipe, an inner wall of the center pipe defining a string inner cavity, the string inner cavity being in fluid communication with the tubing string and the drill plug gun to form at least a portion of a high pressure fluid flow passage; and an outer wall pipe, the outer wall pipe being coaxial with the center pipe and circumferentially surrounding an exterior of the center pipe, wherein an inner wall of the outer wall pipe and an outer wall of the center pipe define an annular string outer cavity, the string outer cavity having a flow-through end adjacent to the tubing string and a sand-in end adjacent to the drill plug gun, wherein the flow-through end allows passage of particles having a size less than a first threshold value, and the sand-in end allows one-way passage of particles having a size less than a second threshold value into the string outer cavity, the first threshold value being less than the second threshold value; a back-off assist gun connected between the tubing string and the sandface string, the back-off assist gun being configured to eject the high pressure fluid in the high pressure fluid flow passage to an exterior of the plug removal system.

2. The system of claim 1, wherein, The back-off assist gun comprising: a back-off assist gun body, the back-off assist gun body being tubular and in fluid communication with the tubing string and the center pipe of the sandface string; a back-off assist gun ejection portion, the back-off assist gun ejection portion comprising: a back-off assist gun protrusion, the back-off assist gun protrusion extending radially outwardly from the back-off assist gun body; a back-off assist gun ejection bore, the back-off assist gun ejection bore extending radially through the back-off assist gun protrusion to communicate the high pressure fluid flow passage and the exterior of the plug removal system; a back-off assist gun filter element, the back-off assist gun filter element being disposed within the back-off assist gun ejection bore; a back-off assist gun blocking element, the back-off assist gun blocking element being mounted to an end of the back-off assist gun ejection bore adjacent to the exterior of the plug removal system to secure the back-off assist gun filter element and seal the back-off assist gun ejection bore; and a back-off assist gun ejection port, the back-off assist gun ejection port extending through a sidewall of the back-off assist gun protrusion to communicate the back-off assist gun ejection bore and the exterior of the plug removal system; wherein the high pressure fluid in the back-off assist gun ejection bore is filtered by the back-off assist gun filter element and ejected through the back-off assist gun ejection port toward a direction of the tubing string. A centerline of the back-off assist gun ejection port forms an angle of 15-45° with an axis of the back-off assist gun body.

3. The aspiration system of claim 2, wherein, The back-off assist gun ejection portion is disposed adjacent to the flow-through end of the sandface string.

4. The access system of claim 2, wherein, The back-off assist gun comprises a plurality of back-off assist gun ejection portions circumferentially spaced apart around the back-off assist gun body.

5. The system of any one of claims 2-4, wherein, The sandface string comprises a flow-through assembly, the flow-through assembly comprising:

6. The access system of claim 1, wherein, a flow-through ring, the flow-through ring being annular and mounted to the flow-through end of the string outer cavity; a flow-through bore, the flow-through bore extending axially through the flow-through ring to communicate the string outer cavity and the exterior of the plug removal system; ​ A flow-by ring filter element is mounted within the flow-by aperture and configured to allow particles having a size less than the first threshold to pass therethrough; and A breath hole pin is mounted to an end surface of the flow-by aperture adjacent to an exterior of the debris removal system to secure the flow-by ring filter element and allow filtered upflow to pass therethrough.

7. The aspiration system of claim 6, wherein, The flow-by assembly includes a flow-by ring inner tube that is tubular and in fluid communication with the tubing and the central pipe of the sand recovery string, wherein the flow-by ring is circumferentially mounted to an outer wall of the flow-by ring inner tube.

8. The access system of claim 6, wherein, The sand recovery string includes a first sand recovery centralizer element connecting the outer wall pipe and the flow-by assembly, the first sand recovery centralizer element including a first outer centralizer projection extending radially from an outer wall of the first sand recovery centralizer element and configured with helical recesses.

9. The access system of claim 1, wherein, The sand recovery string includes a sand inlet assembly, the sand inlet assembly including: a sand inlet ring that is annular and mounted to the sand inlet end of the string outer cavity; a sand inlet passage extending axially through the sand inlet ring to communicate the string outer cavity with an exterior of the debris removal system; and a one-way sand inlet structure mounted within the sand inlet passage and configured to allow particles having a size less than the second threshold to pass unidirectionally into the string outer cavity.

10. The aspiration system of claim 9, wherein, The one-way sand inlet structure includes: a one-way filter sub mounted within the sand inlet passage adjacent to the string outer cavity and having a first sand inlet aperture; a sand inlet ball seat mounted within the sand inlet passage adjacent to the exterior of the debris removal system and having a second sand inlet aperture, wherein a portion of the sand inlet passage defined between the one-way filter sub and the sand inlet ball seat forms a sand inlet cavity; a sand inlet ball disposed within the sand inlet cavity; a sand inlet spring having one end connected to the one-way filter sub and an opposite end connected to the sand inlet ball, wherein the sand inlet spring is in a pre-tensioned state to bias the sand inlet ball against the sand inlet ball seat and seal the second sand inlet aperture; and a sand inlet ball sleeve circumferentially disposed within the sand inlet cavity to limit radial displacement of the sand inlet ball.

11. The aspiration system of claim 9, wherein, The sand recovery string includes a second sand recovery centralizer element connecting the outer wall pipe and the sand inlet assembly, the second sand recovery centralizer element including a second outer centralizer projection extending radially from an outer wall of the second sand recovery centralizer element and configured with helical recesses.

12. The access system of claim 1, wherein, The sand recovery string includes a negative pressure sand washing assembly, the negative pressure sand washing assembly including: a negative pressure sand washing body that is tubular and in fluid communication with the central pipe of the sand recovery string; and a negative pressure sand washing jet configured to jet the high pressure liquid within the high pressure liquid flow passage into the string outer cavity in a direction toward the tubing.

13. The access system of claim 1, wherein, The outer wall pipe includes a plurality of segments spaced apart from one another, and the sand recovery string includes a sand recovery support centralizer element mounted between adjacent segments of the outer wall pipe, the sand recovery support centralizer element including: a support outer centralizing protrusion extending radially from an outer wall of the support centralizing element and provided with a helical recess; a support inner centralizing protrusion extending radially from an inner wall of the support centralizing element until abutting against an outer wall of the central pipe, wherein the support inner centralizing protrusion is provided with an inner flow-through channel extending axially therethrough; and a filter hole extending through a wall portion of the sand-retrieving support centralizing element to communicate the pipe string outer cavity with an outside of the plug removal system and allow particles with a particle size less than a second threshold to pass through.

14. The access system of claim 1, wherein, The plug drilling gun comprises: a plug drilling gun body; a central channel extending axially through the plug drilling gun body; a front end channel in fluid communication with the central channel and arranged to face away from the self-sand-retrieving pipe string opening; and a rear end channel in fluid communication with the central channel and arranged to face towards the self-sand-retrieving pipe string opening. The plug removal system comprises:

15. The access system of claim 1, wherein, centralizers comprising a first centralizer and a second centralizer arranged at two ends of the self-sand-retrieving pipe string respectively, the first centralizer and the second centralizer being provided with an outer flow-through channel extending axially therethrough; an adjustment nipple arranged between the self-sand-retrieving pipe string and the plug drilling gun. The plug removal system comprises a plurality of the self-sand-retrieving pipe strings arranged in the same direction and connected in sequence.

16. The access system of claim 1, wherein, The plug removal system comprises a backflow assisting gun connected between adjacent self-sand-retrieving pipe strings.

17. The aspiration system of claim 16, wherein, The method comprises the following steps:

18. A downhole positive pressure self-sand-retrieving hydraulic un-plugging method, characterized in that, Step one, lowering the plug removal system into the casing until the plug drilling gun is adjacent to an end face of the ash plug section; Step two, starting a high-pressure pump to pump high-pressure liquid into the oil pipe to break the ash plug section and promote the upward flow of the sand-containing liquid through the pipe string outer cavity of the self-sand-retrieving pipe string and the oil-casing annulus; Step three, the self-sand-retrieving pipe string collects sand in the sand-containing liquid through the pipe string outer cavity, comprising: the high-pressure liquid is sprayed out through at least one of the central channel and the front end channel of the plug drilling gun to break the ash plug section; the high-pressure liquid is sprayed out through the rear end channel of the plug drilling gun to provide upward flow power for the sand-containing liquid and clean the inner wall of the casing; the high-pressure liquid is sprayed out through the backflow assisting gun of the backflow assisting gun to avoid the accumulation of the sand-containing liquid in the casing and provide upward flow power for the sand-containing liquid in the casing; the high-pressure liquid is sprayed out through the negative pressure sand washing jetting part of the negative pressure sand washing assembly to generate negative pressure in the pipe string outer cavity and provide upward flow power for the sand-containing liquid in the pipe string outer cavity; Step four, closing the high-pressure pump, removing the plug removal system from the casing, and cleaning the sand in the pipe string outer cavity. ​

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