A sand flushing and well washing string suitable for secondary sand control horizontal wells

Abstract

The invention discloses a sand flushing and well washing pipe string suitable for secondary sand prevention horizontal wells, which belongs to the field of downhole operation tools for oil and water wells and can take into account the advantages of positive circulation and reverse circulation sand flushing. During the sand flushing process, liquid enters from the annulus of the oil casing. When the pipe string is close to the deposited formation sand, the liquid enters the oil pipe from the annulus of the oil casing after conversion, and the deposited formation sand is impacted and flushed from the oil pipe. The flow rate is relatively large, and the compacted formation deposited sand in the screen pipe can be easily impacted and loosened. During the upward return process, the liquid carries the formation sand and converts it from the annulus of the oil casing to the oil pipe to flow upward. The speed is relatively large, the formation sand is not easy to settle, and the sand flushing effect is good.

Description

Technical Field

[0001] The invention belongs to the field of downhole operation tools for oil and water wells, and particularly relates to a sand flushing and well washing tubing string suitable for secondary sand control horizontal wells. Background Art

[0002] The Liaohe Oilfield's reservoirs are mostly unconsolidated sandstone, resulting in severe sand production problems. Sand control measures must be implemented during production. Screen sand control technology, a simple and effective method, is widely used, with screen sand control accounting for the majority of applications in horizontal wells.

[0003] There are two main forms of horizontal well screen sand control completion: one is to connect a 7-inch screen under the 7-inch casing and complete the well with cementing on the top; the other is to complete the well by hanging a 7-inch screen in a 9-5 / 8-inch casing with a hanger. The screen size of the oil layer section of both sand control completion methods is 7 inches. During the production process, moderate sand control is generally adopted, that is, the coarser formation sand is blocked outside the screen, and the finer formation sand can enter the screen and be discharged to the surface with the crude oil. As the production time increases, if the fine formation sand that enters the screen cannot be completely discharged to the surface with the crude oil, it will settle and accumulate inside the screen. When problems occur in the screen and secondary sand control operations are required, the formation sand deposited in the horizontal well screen needs to be flushed out first. Therefore, the sand flushing operation is an important operation step in the secondary sand control construction process of horizontal wells, which directly affects whether the subsequent secondary sand control string can be smoothly lowered.

[0004] During the sand flushing process of secondary sand control horizontal well construction, there are two difficulties that need to be solved. The first is to flush away the sedimentary sand in the downhole screen. However, due to the long horizontal well section and the high sand production, the sedimentary sand in the screen is generally severely compacted and difficult to flush out. The second is that the formation sand will not be deposited again during the process of returning with the liquid. The horizontal well sand flushing methods can be divided into two types according to the liquid flow path: one is positive circulation sand flushing, that is, the ground pump truck pumps liquid into the oil pipe, sprays it out from the pen tip, flushes the sedimentary sand section in the well, and then discharges it upwards from the oil casing annulus to the ground; the other is reverse circulation sand flushing, that is, the ground pump truck pumps liquid into the oil casing annulus, flushes the sedimentary sand in the well, and then discharges it upwards along the space in the oil pipe to the ground, such as Figure 1 shown.

[0005] Because the space inside the tubing is much smaller than the annulus between the tubing and casing, that is, the space between the tubing and the casing, the liquid flow rate in the tubing is much greater than that in the casing annulus. Taking the example of running a 3.5-inch tubing into a 7-inch well for sand flushing, the area of ​​the casing annulus is 3.06 times the cross-sectional area of ​​the tubing. Therefore, under the premise of a certain pump displacement, during the reverse circulation sand flushing process: during the sand flushing process, the liquid is pumped into the casing annulus, and due to the low flow rate, it is difficult to push out the compacted sedimentary sand. However, during the process of liquid carrying the formation sand back up, the formation sand is not easily settled due to the high flow rate in the tubing. During the positive circulation sand flushing process, the liquid is pumped into the tubing at a high flow rate, and the compacted sedimentary sand is easily pushed out during the sand flushing process. However, during the process of liquid carrying the formation sand back up, the casing annulus is larger, the liquid flow rate is slower, and the formation sand is easily settled again.

[0006] At present, the main methods of sand flushing in horizontal wells are as follows, and the sand flushing process is positive sand flushing:

[0007] ①Connect the oil pipe to the pen tip and lower it into the screen to flush the sand;

[0008] ② Conventional closed continuous sand washing or continuous tube sand washing, the tools are the same as above, that is, the oil pipe is connected to the pen tip;

[0009] ③Rotary jet pen tip sand washing;

[0010] ④Hydraulic jet pump negative pressure sand flushing.

[0011] Among them, the continuous sand flushing process effectively solves the problem of sedimentation of formation sand during the discharge process caused by the need to stop the pump when lowering the oil pipe during the sand flushing process, resulting in discontinuous liquid flow. The rotary jet, hydraulic jet negative pressure sand flushing and other processes are mainly used to solve the problem of compacted formation sediment sand not being able to be flushed. The research direction of the above topics is mainly focused on the development of new sand flushing tools, the main purpose of which is to solve the problem of formation sand not being able to be flushed or not being flushed cleanly. The sand flushing method is still positive circulation sand flushing, and the sedimentation problem of formation sand during the return process caused by the large cross-sectional area of ​​the oil casing annulus and the low liquid flow rate is not considered. Summary of the Invention

[0012] In order to overcome the defects of the existing sand flushing method that cannot take into account both the impulsive compaction of deposited sand and the avoidance of sedimentation during the return of formation sand, the present invention provides a sand flushing and well washing tubing string suitable for secondary sand control horizontal wells, which can take into account the advantages of positive circulation and reverse circulation sand flushing. During the sand flushing process, liquid enters from the oil casing annulus. When the tubing string approaches the deposited formation sand, the liquid is converted from the oil casing annulus into the oil pipe, and the deposited formation sand is impacted and flushed from the oil pipe. The flow rate is relatively high, and the compacted formation sedimentary sand in the screen pipe can be easily impacted and loosened. During the return process, the liquid carries the formation sand and is converted from the oil casing annulus to the oil pipe to flow upward. The speed is relatively high, the formation sand is not easy to settle, and the sand flushing effect is good.

[0013] The technical solution adopted by the present invention to solve its technical problems is: a sand flushing and well washing string suitable for secondary sand control horizontal wells, including an oil pipe lowered into the casing, an oil-casing annulus is formed between the casing and the oil pipe, and a positive and negative circulation sand flushing conversion device is connected to the oil pipe, so that the liquid entering the well from the oil-casing annulus and the liquid carrying formation sand and moving upward along the oil-casing annulus after sand flushing can complete the flow channel conversion from the oil-casing annulus to the oil pipe after passing through the positive and negative circulation sand flushing conversion device; an expansion seal is sleeved on the lower part of the outer wall of the positive and negative circulation sand flushing conversion device to seal the oil-casing annulus at this position.

[0014] As a further embodiment of the present invention, the forward and reverse circulation sand flushing conversion device includes a fixed pipe and an internal driving pipe in a sliding connection. When the internal driving pipe is in a first position relative to the fixed pipe, the upper and lower parts of the inner cavity of the forward and reverse circulation sand flushing conversion device are connected, and the inner cavity of the forward and reverse circulation sand flushing conversion device is separated from the external oil casing annulus; when the internal driving pipe slides to a second position relative to the fixed pipe, the fixed pipe and the internal driving pipe are connected, the inner cavity of the forward and reverse circulation sand flushing conversion device is connected to the external oil casing annulus, and the upper and lower parts of the inner cavity of the forward and reverse circulation sand flushing conversion device are separated.

[0015] As a further embodiment of the present invention,

[0016] The fixed pipe includes an upper joint, a cylinder sleeve, an outer protective sleeve, an inner pipe, a flow pipe, and a lower joint; the internal drive pipe is a sliding inner pipe, wherein:

[0017] The outer wall of the upper joint is provided with a plurality of groove flow channels a, the top ends of the groove flow channels a are connected to the interior of the upper joint through the through holes a provided on the wall of the upper joint;

[0018] The cylinder sleeve is connected to the lower end of the upper joint. The outer wall of the cylinder sleeve is provided with a plurality of groove flow channels b. The top end of the groove flow channel b is aligned and connected with the groove flow channel a. The bottom end of the groove flow channel b is connected with the through hole b provided on the wall of the cylinder sleeve.

[0019] The outer protective sleeve is connected to the upper joint and the outer wall of the liquid cylinder sleeve, and the groove flow channel a and the groove flow channel b are encapsulated into a closed flow channel; the outer protective sleeve and the liquid cylinder sleeve are provided with a communication port a and a communication port b formed by correspondingly connecting the notches;

[0020] The inner tube is connected to the inner wall of the bottom of the cylinder sleeve, and a through hole c is opened on the inner tube to communicate with the through hole b;

[0021] The flow tube is connected to the inner wall of the inner tube, and a cavity is formed between the two. The through hole c is correspondingly connected to the cavity.

[0022] The sliding inner tube is slidably connected to the upper joint and the inner wall of the liquid cylinder sleeve, a compression chamber is formed between the sliding inner tube and the liquid cylinder sleeve, and a liquid chamber connected to the communication port b is formed between the sliding inner tube and the liquid cylinder sleeve; the bottom of the sliding inner tube slides vertically in the cavity between the flow tube and the inner tube, and a slider is connected to its bottom end, and the slider is slidably connected to the inner wall of the inner tube; a communicating cavity is also provided on the wall of the sliding inner tube, which is used to communicate with the communicating port a when the sliding inner tube moves to the second position, so that the inner cavity of the positive and negative circulation sand flushing conversion device is connected to the external oil casing annulus; a plug structure is provided on the top of the sliding inner tube, which is used to seal the inner cavity of the upper joint when the sliding inner tube moves to the second position, so that the upper and lower parts of the inner cavity of the positive and negative circulation sand flushing conversion device are separated;

[0023] The lower joint is connected to the outer wall of the inner tube. A liquid inlet is formed between the lower joint and the flow tube. The liquid inlet communicates with a plurality of groove flow channels c provided on the outer wall of the flow tube.

[0024] As a further embodiment of the present invention, when the sliding inner tube is in the first position, the slider blocks the through hole c, and when the sliding inner tube moves upward to the second position, the slider moves upward out of the through hole c.

[0025] As a further embodiment of the present invention, the expansion seal is threadedly connected to the outer wall of the lower joint.

[0026] As a further embodiment of the present invention, the expansion seal is a cup packer.

[0027] As a further embodiment of the present invention, a compression spring is provided in the compression chamber.

[0028] As a further embodiment of the present invention, the diameter of the notch on the outer protective sleeve is larger than the diameter of the notch on the cylinder sleeve.

[0029] As a further embodiment of the present invention, the outer protective sleeve and the liquid cylinder sleeve are respectively connected to the upper joint through positioning pins.

[0030] As a further embodiment of the present invention, a bottom sand flushing device connected to the bottom end of the oil pipe for increasing the liquid flow rate is also included.

[0031] As a further embodiment of the present invention, the outer diameter of the bottom sand flushing device is larger than the outer diameter of the oil pipe.

[0032] As a further embodiment of the present invention, the bottom sand flushing device includes a joint, a sand flushing device body, and a sand flushing nozzle. One end of the joint is connected to the oil pipe, and the other end is connected to the sand flushing device body. The inner wall of the sand flushing device body is connected to the sand flushing nozzle. A negative pressure chamber is formed between the outer wall of the sand flushing nozzle and the inner wall of the sand flushing device body, and the inner diameter of the sand flushing nozzle gradually decreases from top to bottom.

[0033] As a further embodiment of the present invention, a plurality of water holes communicating with the negative pressure chamber are provided on the side wall of the sand flushing device body.

[0034] As a further embodiment of the present invention, the inner diameter of the water hole gradually increases from the outside to the inside.

[0035] As a further embodiment of the present invention, a plurality of water troughs are provided on the side wall of the sand flushing device body to serve as channels for liquid to flow upward.

[0036] The beneficial effects of the present invention include: 1. Liquid enters the well from the casing annulus from the ground, passes through the forward and reverse circulation sand flushing conversion device, and the flow path is converted, and the liquid enters the oil pipe from the casing annulus at a higher speed, and then passes through the bottom sand flushing device to impact the lower accumulated formation sand, which has a better impact effect on the lower accumulated formation sand; the lower accumulated formation sand becomes loose after being impacted by the fluid, and moves upward along the casing annulus under the fluid's carrying, and after passing through the forward and reverse circulation sand flushing conversion device again, the fluid enters the oil pipe from the casing annulus at a higher speed, thereby strengthening the fluid sand carrying effect, making it difficult for the formation sand to settle, and achieving a better sand carrying effect;

[0037] ② The bottom sand flushing device adopts a sand flushing nozzle and negative pressure chamber design. After the fluid passes through the bottom sand flushing device, the speed becomes faster and the impact force becomes greater, which has a cleaning effect on the formation sand around the device and a better sand flushing effect;

[0038] ③ The expansion seal is set on the lower joint at the bottom of the forward and reverse circulation sand flushing conversion device. When the fluid passes downward from the oil casing annulus, throttling occurs at this part, causing the oil casing annulus pressure above the expansion seal to rise, and then the expansion seal expands to seal the oil casing annulus where it is located. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 a is a schematic diagram of the prior art positive cycle sand flushing;

[0040] Figure 1 b is a schematic diagram of reverse circulation sand flushing in the prior art;

[0041] Figure 2 Schematic diagram of the flow of the sand flushing process of the sand flushing well washing pipe string of the present invention;

[0042] Figure 3 This is a schematic structural diagram of the forward and reverse circulation sand flushing conversion device of the present invention in a closed state;

[0043] Figure 4 This is a schematic structural diagram of the forward and reverse circulation sand flushing conversion device of the present invention in an open state;

[0044] Figure 5 This is a schematic diagram of the upper joint structure of the forward and reverse circulation sand flushing conversion device of the present invention;

[0045] Figure 6 yes Figure 5 AA cross-section of

[0046] Figure 7 yes Figure 5 BB cross-section diagram;

[0047] Figure 8 This is a schematic diagram of the flow pipe structure of the forward and reverse circulation sand flushing conversion device of the present invention;

[0048] Figure 9 yes Figure 8 CC cross-section diagram;

[0049] Figure 10 This is a schematic structural diagram of the bottom sand flushing device of the present invention;

[0050] Figure 11 yes Figure 10 sectional view of ;

[0051] Figure 12 yes Figure 10 AA cross-section of

[0052] Figure 13 yes Figure 10 A partial enlarged schematic diagram;

[0053] Figure 14 yes Figure 10 A partial enlarged schematic diagram.

[0054] Explanation of the reference numerals in the figure: 1. Forward and reverse circulation sand flushing conversion device, 2. Bottom sand flushing device, 3. Expansion seal, 4. Upper joint, 5. Outer protective sleeve, 6. Liquid cylinder sleeve, 7. Sliding inner tube, 8. Inner tube, 9. Slider, 10. Flow tube, 11. Lower joint, 12. Liquid inlet, 13. Compression chamber, 14. Liquid chamber, 15. Connecting port a, 16. Connecting chamber, 17. Connecting port b, 18. Groove flow channel a, 19. Through hole a, 20. Joint, 21. Sand flushing device body, 22. Negative pressure chamber, 23. Water eye, 24. Sand flushing nozzle, 25. Water tank. DETAILED DESCRIPTION

[0055] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0056] In the description of the present invention, it should be noted that the terms "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used solely to distinguish components and should not be construed as indicating or implying relative importance.

[0057] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0058] Example 1

[0059] A sand washing string suitable for secondary sand control horizontal wells, such as Figure 2 As shown, it includes an oil pipe inserted into the casing, an oil-casing annulus is formed between the casing and the oil pipe, a forward and reverse circulation sand flushing conversion device 1 is connected to the oil pipe, and an expansion seal 3 is sleeved on the lower part of the outer wall of the forward and reverse circulation sand flushing conversion device 1.

[0060] A forward and reverse circulation sand flushing conversion device 1 is set up, and its main function is to realize that when the fluid flows downward, it enters the interior of the device from the oil casing annulus, and then flows downward from the oil pipe to complete the sand flushing operation, and to realize that the liquid flowing upward after the sand flushing operation enters the interior of the device from the oil casing annulus and then enters the oil pipe upward, completing the two flow channel conversions of the fluid and realizing efficient sand flushing and sand carrying.

[0061] Figure 3 As shown, the forward and reverse circulation sand flushing conversion device 1 includes an upper joint 4, a liquid cylinder sleeve 6, an outer protective sleeve 5, an inner tube 8, a flow pipe 10, a lower joint 11, and a sliding inner tube 7.

[0062] Two groove flow channels a18 are opened on the outer wall of the upper joint 4. The top of the groove flow channel a18 is connected to the interior of the upper joint 4 through a through hole a19 opened on the wall of the upper joint 4.

[0063] The liquid cylinder sleeve 6 is connected to the lower end of the upper joint 4. Two groove flow channels b (not shown in the figure) are opened on the outer wall of the liquid cylinder sleeve 6. The top ends of the two groove flow channels b are aligned and connected with the two groove flow channels a respectively. The bottom ends of the groove flow channels b are connected with the through hole b (not shown in the figure) opened on the wall of the liquid cylinder sleeve 6.

[0064] The outer protective sleeve 5 is connected to the upper joint 4 and the outer wall of the liquid cylinder sleeve 6, encapsulating the groove flow channel a and the groove flow channel b into a closed flow channel; the outer protective sleeve 5 and the liquid cylinder sleeve 6 are provided with a communication port a15 and a communication port b17 formed by corresponding notches;

[0065] Preferably, the diameter of the notch on the outer protective sleeve 5 is larger than the diameter of the notch on the liquid cylinder sleeve 6. The outer protective sleeve 5 and the liquid cylinder sleeve 6 are respectively connected to the upper joint 4 through positioning pins to ensure that the two notches on the outer protective sleeve 5 and the liquid cylinder sleeve 6 are aligned.

[0066] The inner tube 8 is connected to the inner wall of the bottom of the cylinder sleeve 6, and a through hole c (not shown in the figure) is opened on the inner tube 8 and communicates with the through hole b;

[0067] The flow tube 10 is connected to the inner wall of the inner tube 8, and a cavity is formed between the two. The through hole c is connected to the cavity.

[0068] The lower joint 11 is connected to the outer wall of the inner tube 8. A liquid inlet 12 is formed between the lower joint 11 and the flow tube 10. The liquid inlet 12 communicates with three groove flow channels c (not shown in the figure) provided on the outer wall of the flow tube 10, so that liquid can enter the groove flow channels c through the liquid inlet 12.

[0069] The lower outer wall of the lower joint 11 is provided with a thread, and the expansion seal 3 is threadedly connected to the outer wall of the lower joint 11. Preferably, the expansion seal 3 is a leather cup packer;

[0070] The sliding inner tube 7 is slidably connected to the upper joint 4 and the inner wall of the liquid cylinder sleeve 6. A compression chamber 13 is formed between the sliding inner tube 7 and the liquid cylinder sleeve 6. A compression spring is provided in the compression chamber 13.

[0071] A liquid chamber 14 is formed between the sliding inner tube 7 and the cylinder sleeve 6 and is connected to the communication port b17;

[0072] The wall of the sliding inner tube 7 is also provided with a connecting cavity 16 for moving on the sliding inner tube 7. Figure 4 In the second position shown, the sliding inner tube 7 is connected to the communication port a15, so that the inner cavity of the forward and reverse circulation sand flushing conversion device 1 is connected to the external oil casing annulus; a plug structure is provided on the top of the sliding inner tube 7, which is used to engage with the inner wall boss of the upper joint 4 when the sliding inner tube 7 moves to the second position, thereby sealing the inner cavity of the upper joint 4 and isolating the upper and lower parts of the inner cavity of the forward and reverse circulation sand flushing conversion device 1;

[0073] The bottom of the sliding inner tube 7 slides vertically in the cavity between the flow tube 10 and the inner tube 8, and the bottom end thereof is threadedly connected with a slider 9, which is slidably connected to the inner wall of the inner tube 8;

[0074] When the sliding inner tube 7 is in Figure 3 In the first position shown, the slider 9 is blocked at the through hole c, so as to prevent the liquid from flowing from the liquid inlet 12 along the groove flow channel c through the cavity between the flow tube 10 and the inner tube 8 into the connected through hole c and through hole b, and then into the flow channel outside the upper joint 4 and the cylinder sleeve 6, so as to prevent the forward and reverse circulation sand washing conversion device 1 from being connected from top to bottom; when the sliding inner tube 7 is moved up to Figure 4In the second position shown, the slider 9 moves upward out of the through hole c;

[0075] The above-mentioned fluids and liquids all refer to sand flushing fluids.

[0076] According to the above implementation scheme, its working method:

[0077] The downward process of sand flushing fluid:

[0078] Assemble the sand flushing and well washing string on the ground and lower it into the well where sand flushing is required;

[0079] Use a pump truck to pump sand flushing fluid from the surface through the casing annulus into the well, and the sand flushing fluid moves downward to the outside of the forward and reverse circulation sand flushing conversion device 1. At this time, the forward and reverse circulation sand flushing conversion device 1 is in a closed state. Figure 3 As shown, no liquid is flowing into the liquid chamber 14, the compression spring in the compression chamber 13 is not compressed, the communication chamber 16 and the communication port a15 are not connected, and the forward and reverse circulation sand flushing conversion device 1 is isolated from the outside space, preventing fluid from entering the forward and reverse circulation sand flushing conversion device 1. At the same time, the flow passage outside the upper joint 4 and the liquid cylinder sleeve 6 is blocked at the lower end by the slider 9, preventing vertical flow.

[0080] The fluid then continues to flow downward along the casing annulus, causing throttling at the cup packer. The pressure in the casing annulus above the cup packer increases, and the cup packer expands under the action of pressure, and the casing annulus at this location is sealed.

[0081] Since the annulus of the oil casing is sealed at the cup packer, the pressure in the annulus of the oil casing continues to increase if fluid is continuously pumped into the annulus on the ground. The fluid enters the liquid chamber 14 from the connecting port b17, pushing the sliding inner tube 7 upward to compress the compression spring 10 in the compression chamber 13, causing the slider 9 to slide upward, and finally the forward and reverse cycle sand flushing conversion device 1 becomes open. Figure 4 shown.

[0082] At this time, the plug structure on the top of the sliding inner tube 7 blocks the upper joint 4, and the upper and lower parts of the forward and reverse circulation sand flushing conversion device 1 are no longer connected, while the connecting cavity 16 and the connecting port a15 are connected, and the interior of the forward and reverse circulation sand flushing conversion device 1 is connected to the external oil casing annulus.

[0083] The fluid in the outer annulus of the oil casing of the forward and reverse circulation sand flushing conversion device 1 enters the interior of the forward and reverse circulation sand flushing conversion device 1 through the connecting cavity 16 and the connecting port a15, flows downward out of the oil pipe, and impacts the formation sand accumulated at the bottom.

[0084] Return to the ground process:

[0085] The fluid carries the formation sand and flows upward from the casing annulus.

[0086] The fluid carries the formation sand and flows upward through the casing annulus to the leather cup packer. Due to the expansion of the leather cup packer, the casing annulus is sealed, and the fluid carries the formation sand and enters along the liquid inlet 12 between the lower joint 11 and the flow pipe 10, along the groove flow channel c on the outer wall of the flow pipe 10, through the cavity between the flow pipe 10 and the inner pipe 8, into the connected through-hole c and through-hole b, and then enters the flow channel outside the upper joint 4 and the liquid cylinder sleeve 6, and finally enters the forward and reverse circulation sand flushing conversion device 1 through the through-hole a19 in the upper joint 4, and then enters the oil pipe upward and returns to the wellhead along the oil pipe.

[0087] Continue the above process until the formation sand is flushed clean and the return fluid is sand-free, and the construction is completed.

[0088] Preferably, the sand flushing and well washing tubing string of the present invention also includes a bottom sand flushing device 2 connected to the bottom end of the oil pipe for increasing the liquid flow rate. The outer diameter of the bottom sand flushing device 2 is larger than the outer diameter of the oil pipe. Its outer diameter can be determined according to the inner diameter of the oil well oil layer screen pipe, and the outer diameter of the bottom sand flushing device 2 can be made 10-15 mm smaller than the inner diameter of the oil layer screen pipe.

[0089] like Figure 10 As shown, the bottom sand flushing device 2 includes a joint 20, a sand flushing device body 21, and a sand flushing nozzle 24. One end of the joint 20 is connected to the oil pipe, and the other end is connected to the sand flushing device body 21. The inner wall of the sand flushing device body 21 is connected to the sand flushing nozzle 24. A negative pressure chamber 22 is formed between the outer wall of the sand flushing nozzle 24 and the inner wall of the sand flushing device body 21. The inner diameter of the sand flushing nozzle 24 gradually decreases from top to bottom.

[0090] Preferably, the inner diameter of the upper portion of the sand flushing nozzle 24 is uniform, and the inner diameter of the bottom port gradually decreases from top to bottom. When the fluid passes through the sand flushing nozzle 24 , the speed gradually increases, forming a negative pressure in the negative pressure chamber 22 .

[0091] Several water holes 23 are provided on the sidewalls of the sand flushing device body 21, communicating with the negative pressure chamber 22. The inner diameter of the water holes 23 gradually increases from the outside to the inside, making it less likely for the water holes 23 to become clogged when formation sand or debris enters from the outside. In a horizontal well, when the bottom sand flushing device 2 is in a horizontal state, the formation sand in areas below and on the sides where it is not impacted by the water flow deteriorates in fluidity and is prone to reaccumulation. When the negative pressure in the negative pressure chamber 22 is generated by the high-speed water flow, the formation sand and debris surrounding the water holes 23 are sucked into the negative pressure chamber 22 by the negative pressure within the water holes 23 and mixed with the high-speed water flow, thus preventing the formation sand from reaccumulating below and on the sides when the bottom sand flushing device 2 is in a horizontal state.

[0092] A plurality of water troughs 25 are provided on the side wall of the sand flushing device body 21 to serve as channels for fluid to flow upward after impacting the accumulated formation sand.

[0093] (2) Sand scouring process

[0094] This process is between the downward process of the sand flushing fluid and the process of returning to the ground.

[0095] The sand flushing fluid is pumped into the well from the surface through the casing annulus. After passing through the forward and reverse circulation sand flushing conversion device 1, the fluid enters the oil pipe from the casing annulus and flows downward into the bottom sand flushing device 2.

[0096] The sand flushing fluid enters the sand flushing nozzle 24, and the flow velocity increases, and impacts the accumulated formation sand from the lower end outlet.

[0097] When the sand flushing liquid enters the sand flushing nozzle 24, the flow rate increases, and negative pressure is formed in the negative pressure chamber 22. The formation sand and debris around the water eye 23 are sucked into the negative pressure chamber 22 by the negative pressure in the water eye 23 and mixed with the high-speed water flow, thereby preventing the formation sand from accumulating again at the bottom and sides when the bottom sand flushing device 2 is in a horizontal state.

[0098] The sand flushing fluid carries the formation sand and flows upward along the water tank 25 outside the sand flushing device body 21, and enters the process of returning to the ground.

[0099] The effect of the forward and reverse circulation sand flushing conversion device 1 is that it can take into account the advantages of both forward circulation and reverse circulation sand flushing. During the sand flushing process, liquid enters from the casing annulus. When the sand flushing well string approaches the sedimentary formation sand at the bottom of the well, the liquid is converted from the casing annulus into the oil pipe, and the sedimentary formation sand is impacted and flushed from the oil pipe. The flow rate is relatively high, which can easily loosen the compacted sedimentary formation sand in the screen pipe. During the upward return process, the liquid carries the formation sand and is converted from the casing annulus into the oil pipe to flow upward. The speed is relatively high, the formation sand is not easy to settle, and the sand carrying effect is good. The effect of the bottom sand flushing device 2 is that after the design of the sand flushing nozzle 24, the negative pressure chamber 22 and the water eye 23, the fluid has a higher speed and a greater impact force after passing through the bottom sand flushing device 2, and the water eye 23 has a cleaning effect on the formation sand around the bottom sand flushing device 2, and the sand flushing effect is better.

[0100] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

[0101] It should be understood that the above description is for illustration and not for limitation. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but rather with reference to the appended claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the foregoing claims is not intended to be a disclaimer of such subject matter, nor should it be assumed that the inventors did not consider such subject matter to be part of the disclosed inventive subject matter.

Claims

1. A sand flushing and well washing string suitable for secondary sand control horizontal wells, comprising an oil pipe lowered into a casing, an oil casing annulus is formed between the casing and the oil pipe, and is characterized in that: A forward and reverse circulation sand flushing conversion device (1) is connected to the oil pipe, so that the liquid entering the well from the oil casing annulus and the liquid carrying formation sand and moving upward along the oil casing annulus after sand flushing can complete the flow channel conversion from the oil casing annulus to the oil pipe after passing through the forward and reverse circulation sand flushing conversion device (1); an expansion seal (3) is sleeved on the lower part of the outer wall of the forward and reverse circulation sand flushing conversion device (1) to seal the oil casing annulus at this position; The forward and reverse circulation sand flushing conversion device (1) comprises a fixed pipe and an internal driving pipe which are slidably connected. When the internal driving pipe is in a first position relative to the fixed pipe, the upper part and the lower part of the inner cavity of the forward and reverse circulation sand flushing conversion device (1) are connected, and the inner cavity of the forward and reverse circulation sand flushing conversion device (1) is isolated from the external oil casing annulus; when the internal driving pipe slides to a second position relative to the fixed pipe, the fixed pipe and the internal driving pipe are connected, the inner cavity of the forward and reverse circulation sand flushing conversion device (1) is connected to the external oil casing annulus, and the upper part and the lower part of the inner cavity of the forward and reverse circulation sand flushing conversion device (1) are isolated; The fixed pipe comprises an upper joint (4), a cylinder sleeve (6), an outer protective sleeve (5), an inner pipe (8), a flow pipe (10), and a lower joint (11); the internal driving pipe is a sliding inner pipe (7), wherein: The outer wall of the upper joint (4) is provided with a plurality of groove flow channels a (18), and the top ends of the groove flow channels a (18) are connected to the interior of the upper joint (4) through through holes a (19) provided on the wall of the upper joint (4); The cylinder sleeve (6) is connected to the lower end of the upper joint (4), and a plurality of groove flow channels b are provided on the outer wall of the cylinder sleeve (6). The top ends of the groove flow channels b are aligned and communicated with the groove flow channels a, and the bottom ends of the groove flow channels b are communicated with the through holes b provided on the wall of the cylinder sleeve (6); The outer protective sleeve (5) is connected to the upper joint (4) and the outer wall of the liquid cylinder sleeve (6), and the groove flow channel a and the groove flow channel b are encapsulated into a closed flow channel; the outer protective sleeve (5) and the liquid cylinder sleeve (6) are provided with a communication port a (15) and a communication port b (17) formed by correspondingly communicating the notches; The inner tube (8) is connected to the inner wall of the bottom of the cylinder sleeve (6), and a through hole c communicating with the through hole b is formed on the inner tube (8); The flow tube (10) is connected to the inner wall of the inner tube (8), a cavity is formed between the two, and the through hole c is correspondingly connected to the cavity; The sliding inner tube (7) is slidably connected to the upper joint (4) and the inner wall of the liquid cylinder sleeve (6); a compression chamber (13) is formed between the sliding inner tube (7) and the liquid cylinder sleeve (6); a liquid chamber (14) connected to the communication port b (17) is formed between the sliding inner tube (7) and the liquid cylinder sleeve (6); the bottom of the sliding inner tube (7) slides vertically in the cavity between the flow tube (10) and the inner tube (8); and a slider (9) is connected to the bottom end of the sliding inner tube (7); the slider (9) is connected to the inner wall of the inner tube (8). The sliding inner tube (7) is connected with the outer casing annulus by sliding; a connecting cavity (16) is also provided on the wall of the sliding inner tube (7) for communicating with the connecting port a (15) when the sliding inner tube (7) moves to the second position, so that the inner cavity of the positive and negative circulation sand flushing conversion device (1) is connected with the outer casing annulus; a plug structure is provided on the top of the sliding inner tube (7) for sealing the inner cavity of the upper joint (4) when the sliding inner tube (7) moves to the second position, so that the upper part and the lower part of the inner cavity of the positive and negative circulation sand flushing conversion device (1) are separated; The lower joint (11) is connected to the outer wall of the inner tube (8), a liquid inlet (12) is formed between the lower joint (11) and the flow tube (10), and the liquid inlet (12) is communicated with a plurality of groove flow channels c formed on the outer wall of the flow tube (10); It also includes a bottom sand flushing device (2) connected to the bottom end of the oil pipe for increasing the flow rate of the liquid; the outer diameter of the bottom sand flushing device (2) is larger than the outer diameter of the oil pipe; the bottom sand flushing device (2) includes a joint (20), a sand flushing device body (21), and a sand flushing nozzle (24); one end of the joint (20) is connected to the oil pipe, and the other end is connected to the sand flushing device body (21); the inner wall of the sand flushing device body (21) is connected to the sand flushing nozzle (24); a negative pressure cavity (22) is formed between the outer wall of the sand flushing nozzle (24) and the inner wall of the sand flushing device body (21); the inner diameter of the sand flushing nozzle (24) gradually decreases from top to bottom; a plurality of water holes (23) connected to the negative pressure cavity (22) are provided on the side wall of the sand flushing device body (21); the inner diameter of the water holes (23) gradually increases from outside to inside; a plurality of water grooves (25) are provided on the side wall of the sand flushing device body (21) for serving as channels for the liquid to flow upward; The sand flushing fluid is pumped from the surface into the well through the annulus of the casing, and after passing through the positive and negative circulation sand flushing conversion device (1), the fluid enters the oil pipe from the annulus of the casing and flows downward into the bottom sand flushing device (2); The sand flushing liquid enters the sand flushing nozzle (24), the flow rate increases, and impacts the accumulated formation sand from the lower outlet; When the sand flushing liquid enters the sand flushing nozzle (24), the flow rate increases, a negative pressure is formed in the negative pressure chamber (22), and the formation sand and debris around the water eye (23) are sucked into the negative pressure chamber (22) by the negative pressure in the water eye (23) and mixed with the high-speed water flow, so as to prevent the formation sand from accumulating again at the bottom and sides when the bottom sand flushing device (2) is in a horizontal state; The sand flushing fluid carries the formation sand and flows upward along the water tank (25) outside the sand flushing device body (21), and enters the process of returning to the ground.

2. A sand flushing and well washing string suitable for secondary sand control horizontal wells according to claim 1, characterized in that: When the sliding inner tube (7) is in the first position, the slider (9) blocks the through hole c; when the sliding inner tube (7) moves upward to the second position, the slider (9) moves upward out of the through hole c.

3. The sand flushing and well washing string suitable for secondary sand control horizontal wells according to claim 1, characterized in that: The expansion seal (3) is threadedly connected to the outer wall of the lower joint (11).

4. A sand flushing and well washing string suitable for secondary sand control horizontal wells according to claim 3, characterized in that: The expansion seal (3) is a leather cup packer.

5. The sand flushing and well washing string suitable for secondary sand control horizontal wells according to claim 3, characterized in that: A compression spring is arranged in the compression chamber (13).

6. The sand flushing and well washing string suitable for secondary sand control horizontal wells according to claim 1, characterized in that: The diameter of the notch on the outer protective sleeve (5) is larger than the diameter of the notch on the cylinder sleeve (6).

7. A sand flushing and well washing string suitable for secondary sand control horizontal wells according to claim 6, characterized in that: The outer protective sleeve (5) and the cylinder sleeve (6) are respectively connected to the upper joint (4) via positioning pins.

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