A treatment string for a casing curved well and a construction method thereof

Abstract

This invention discloses a treatment process string and construction method for casing bends in wells. The treatment process string includes tubing, a hydraulic anchor, and a reversing force-boosting cylinder. The tubing is sequentially connected to the hydraulic anchor and the reversing force-boosting cylinder. The lower end of the reversing force-boosting cylinder is connected to a variable stiffness shaper, which is located at the bottom of the treatment process string for casing bends. The variable stiffness shaper, connected to the bottom of the treatment process string, can effectively perform variable stiffness extrusion shaping on the bend section. This invention provides a process string that can effectively treat casing bends. The string has a simple structure, and the tools included are highly targeted, solving the problem of the current lack of effective treatment process strings for casing bends, and also effectively solving the problem of rigid jamming in the treatment process string.

Description

Technical Field

[0001] This invention relates to a device and construction method for treating curved casing wells in the petroleum industry, and in particular to a treatment process string and construction method for curved casing wells. Background Technology

[0002] As major oilfields in China enter the later stages of exploitation, the service life of casings is approaching its limit, and various downhole problems are being fully exposed. More and more downhole casing damage issues are emerging, such as casing breakage, casing diameter reduction, casing bending, etc. Among them, casing bending is the most difficult to manage.

[0003] Currently, foreign oilfields mainly address oil and water wells with bends by using side-drilling.

[0004] There are many methods for treating trapped bends in wells in China, and they vary from oilfield to oilfield. However, sidetracking is the most effective method. Many oil and gas wells with minor trapped bends are essentially produced with the problem, while those with severe trapped bends can only be treated with sidetracking. However, due to recent low international oil prices and limited drilling investment, even though sidetracking is much cheaper than drilling a new well, it cannot be implemented on a large scale to meet the workover needs of the large number of trapped bend wells. Many trapped bend wells are simply abandoned because they cannot be treated economically and effectively. Therefore, once trapped bends occur in oil, gas, or water wells, no matter how they are handled, they will cause significant economic losses to oilfield production.

[0005] Many casing bends occur in the upper part of the production layer in wells. The reason for this is that the oilfield has been developed for a long time, and the formation outside the casing is severely depleted, resulting in a loss of support and causing the casing to bend. This type of bend is the most common and has the most serious impact on the oilfield, directly affecting normal production operations. However, after investigation and research, there is currently no good solution other than sidetracking. Therefore, it is urgent to tackle this problem. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a casing string and construction method for treating casing bend wells, to meet the requirements of casing bend well treatment technology, enabling casing bend wells to resume production, reducing economic losses in oilfields, and improving production efficiency.

[0007] To achieve the above objectives, the technical solution of the present invention is:

[0008] A treatment process string for a casing-bent well includes tubing, a hydraulic anchor, and a reversing force-enhancing cylinder. The tubing is connected sequentially to the hydraulic anchor and the reversing force-enhancing cylinder. The lower end of the reversing force-enhancing cylinder is connected to a variable stiffness shaper, which is located at the lowest end of the treatment process string for the casing-bent well.

[0009] Preferably, the variable stiffness shaper includes an anti-bending mandrel, an anti-bending outer cylinder, and a shaping head. The anti-bending outer cylinder is installed outside the anti-bending mandrel, and the lower part of the anti-bending mandrel is connected to the shaping head. The anti-bending outer cylinder and the anti-bending mandrel are connected by connecting shear pins. No hydraulic flushing channel is provided in the anti-bending mandrel and the shaping head.

[0010] Preferably, the anti-bending mandrel is a solid rod-shaped body with non-uniform diameter. The large-diameter end of the solid rod-shaped body is provided with a reversing and boosting hydraulic cylinder connecting cavity, which has an internal thread that can connect with the lower connector of the reversing and boosting hydraulic cylinder. The small-diameter end of the lower part of the solid rod-shaped body is provided with an external thread that connects with the shaping head. A shearing groove is provided on the outer wall of the rod above the external thread section of the small-diameter end. The shearing groove is an annular groove surrounding the outer wall of the rod. The lower part of the shaping head is a solid circular head, and the upper part of the head is provided with a mandrel connecting cavity. The mandrel connecting cavity has an internal thread that can connect with the threaded section of the small-diameter end of the anti-bending mandrel. The shaping head is threadedly connected to the anti-bending mandrel of the solid rod-shaped body.

[0011] Preferably, the variable stiffness shaper includes an anti-bending mandrel, an anti-bending outer cylinder, and a shaping head. The anti-bending outer cylinder is installed outside the anti-bending mandrel, and the lower part of the anti-bending mandrel is connected to the shaping head. The anti-bending outer cylinder and the anti-bending mandrel are connected by connecting shear pins. The anti-bending mandrel and the shaping head are provided with hydraulic flushing channels.

[0012] Preferably, the anti-bending mandrel is a non-equal diameter rod-shaped body with a hydraulic flushing channel. The large-diameter end of the rod-shaped body has a reversing and boosting hydraulic cylinder connecting cavity, which has an internal thread and communicates with the hydraulic flushing channel. The internal thread in the reversing and boosting hydraulic cylinder connecting cavity can connect with the lower connector of the reversing and boosting hydraulic cylinder 3. The small-diameter end of the non-equal diameter rod-shaped body with the hydraulic flushing channel has an external thread that connects with the shaping head. A shearing groove is provided on the outer wall of the rod above the external thread section of the small-diameter end. The shearing groove is an annular groove surrounding the outer wall of the rod. The lower part of the shaping head is a circular head with a hydraulic flushing channel, and the upper part of the head has a mandrel connecting cavity. The mandrel connecting cavity communicates with the hydraulic flushing channel and has an internal thread that can connect with the threaded section of the small-diameter end of the anti-bending mandrel. The shaping head is threadedly connected to the anti-bending mandrel with the hydraulic flushing channel.

[0013] Preferably, the wall thickness of the anti-bending mandrel body is greater than the wall thickness of the casing in the well where the casing is bent, and the aperture of the hydraulic flushing channel in the anti-bending mandrel and the shaping head is set to be 8mm or more.

[0014] Preferably, the length of the anti-bending outer cylinder is less than the length of the anti-bending mandrel and both ends are chamfered; the length of the anti-bending mandrel is at least 50cm longer than the length of the anti-bending outer cylinder.

[0015] Preferably, a shearing pin hole is provided at the lower part of the anti-bending outer cylinder, and the position of the shearing pin hole corresponds to the position of the shearing pin groove at the lower part of the anti-bending mandrel. The connecting shearing pin can be inserted into the shearing pin groove at the lower part of the anti-bending mandrel from the shearing pin hole of the anti-bending outer cylinder. At least two shearing pin holes are provided in the anti-bending outer cylinder body.

[0016] A method for constructing a casing string for treating a casing bend well includes the following steps:

[0017] A. Connect the tubing, hydraulic anchor, reversing booster cylinder and variable stiffness shaper in the treatment process string of the casing bend well from top to bottom, and run them into the target well section of the casing bend well.

[0018] B. Slowly lower the tubing until it encounters resistance;

[0019] C. After the tubing is obstructed, immediately lift the tubing 1 meter and record the obstruction depth, suspended weight, and related operational data.

[0020] D. Then, slowly lower the tubing string to the obstructed section of the well. Use the weight of the tubing string to press down a weight of less than 2 tons. If the tubing string can pass through the obstructed section, continue lowering the tubing string. If it cannot pass through the obstructed section, release the full weight of the downhole tubing string and then use the reversing force-boosting cylinder and the variable stiffness shaping device to pressurize and shape the bent casing section.

[0021] When performing pressure testing and shaping on bent casing sections, the main steps are as follows:

[0022] A. When shaping the bent casing, let the weight of the upper tubing of the variable stiffness shaper press down on the obstruction position of the variable stiffness shaper, so that the reversing force-increasing hydraulic cylinder is under pressure and pressurizes from the oil pipe, so that the hydraulic anchor is fixed on the inner wall of the casing.

[0023] B. Continue to pressurize the tubing to push the reversing hydraulic cylinder downwards to straighten the bent casing section downhole.

[0024] C. When the variable stiffness shaping device gets stuck due to casing bending and cannot pass through the bent section of the casing, the connecting shear pin between the anti-bending outer cylinder and the anti-bending core tube in the variable stiffness shaping device is sheared off, and the shaping head continues to move forward under the push of the anti-bending core shaft.

[0025] D. After the variable stiffness shaper at the bottom of the tubing string passes through the curved section of the casing, the tubing string is depressurized and then lifted.

[0026] E. If the tubing string requires greater lifting force to release the jamming, lift the tubing string more than 2 tons above its own weight. Continue to pressurize the tubing to fix the hydraulic anchor to the inner wall of the casing. Continue to pressurize the tubing and use the reversing force-increasing hydraulic cylinder to lift the variable stiffness shaper located below to remove the tubing string.

[0027] Compared with the prior art, the present invention has the following advantages;

[0028] The process tubing and its supporting tools proposed in this invention have a reliable working principle, simple and practical structure, convenient construction and operation, and a high safety factor, specifically manifested in:

[0029] (1) This invention provides a process tubing string that can effectively control casing bending. The tubing string has a simple structure and the tools in the tubing string are highly targeted, which solves the problem that there is currently no effective process tubing string for controlling casing bending.

[0030] (2) The variable stiffness shaping tool provided in this invention has two implementation methods. This tool can not only effectively expand and shape the curved section of the casing, but also overcome the problem of tool jamming caused by the rebound after casing shaping through the adaptive change of its own stiffness, which greatly improves the safety of downhole construction of the process tubing.

[0031] (3) The construction method in this invention, in conjunction with the reversing force-enhancing hydraulic cylinder and the variable stiffness shaper in the process tubing, can effectively achieve the shaping and treatment of the bent section of the downhole casing, and at the same time effectively solve the problem of rigid jamming of the process tubing.

[0032] (4) The variable stiffness shaper in this invention is connected to the bottom of the treatment process tubing, which can effectively perform variable stiffness extrusion shaping on the curved section. While ensuring effective extrusion shaping of the casing in the curved section, it adaptively adjusts the stiffness to meet the shape changes in the curved casing shaping process in real time, ensuring the construction safety of the entire process tubing when it is lifted and lowered during operation.

[0033] In summary, compared to existing technologies, this invention addresses the lack of effective tools and methods for treating curved casing wells, reduces the risk of the casing string getting stuck in the curved casing during the treatment process, and enables the well to resume production after treatment. It effectively fills the gap in construction technology for this type of operation. It reduces economic losses in oilfields, improves production efficiency, and generates significant economic and social benefits, while also possessing enormous potential for widespread application. Attached Figure Description

[0034] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0035] In the attached diagram:

[0036] Figure 1 This is a schematic diagram of the casing string structure for a treatment process of a casing-bent well according to the present invention.

[0037] Figure 1In the middle: 1. Oil pipe; 2. Hydraulic anchor; 3. Reversing force-boosting hydraulic cylinder; 4. Variable stiffness shaping device.

[0038] Figure 2 for Figure 1 A schematic diagram of the structure of Embodiment 2 of the medium-stiffness shaper.

[0039] Figure 2 In the middle: anti-bending mandrel 41, anti-bending outer cylinder 42, shaping head 43, connecting shear pin 44.

[0040] Figure 3 for Figure 2 A schematic diagram of the structure of the bending mandrel. Detailed Implementation

[0041] The accompanying drawings are for reference and illustration only and are not intended to limit the scope of protection of this invention. The technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0043] In the description of this invention, it should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, in the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0044] See Figure 1 - Figure 3 A treatment process string for casing-bent wells includes tubing 1, a hydraulic anchor 2, and a reversing booster cylinder 3. The tubing 1 is sequentially connected to the hydraulic anchor 2 and the reversing booster cylinder 3, wherein:

[0045] The lower end of the reversing and boosting hydraulic cylinder 3 is connected to the variable stiffness shaper 4, which is located at the bottom of the treatment process string for curved casing. The reversing and boosting hydraulic cylinder 3 drives the variable stiffness shaper 4 to shape the curved casing. The reversing and boosting hydraulic cylinder 3 in the treatment process string can be a reversible boosting device for downhole workover operations in oil, gas and water wells, as described in application number 202111195491.6.

[0046] The variable stiffness shaper 4 of this invention has the following two embodiments:

[0047] Example 1 of the variable stiffness shaper 4

[0048] The variable stiffness shaper 4 is provided with an anti-bending mandrel 41, an anti-bending outer cylinder 42, and a shaping head 43. The anti-bending outer cylinder 42 is installed outside the anti-bending mandrel 41. The lower part of the anti-bending mandrel 41 is connected to the shaping head 43. The anti-bending outer cylinder 42 and the anti-bending mandrel 41 are connected by connecting shear pins 44. No water flushing channel is provided in the anti-bending mandrel 41 and the shaping head 43.

[0049] The specific working principle of the variable stiffness shaper 4 is as follows: when the variable stiffness shaper 4 enters the curved section of the casing, its outer diameter is jammed by the curved casing, causing the connecting shear pin 44 between the anti-bending outer cylinder 42 and the anti-bending mandrel 41 to be shear off, thus achieving axial unlocking between the anti-bending mandrel 41 and the anti-bending outer cylinder 42. Because the shaping head 43 is restricted by the casing trajectory, it can only move along the axis of the casing curvature under the push of the anti-bending mandrel 41. Therefore, the anti-bending outer cylinder 42 can also perform extrusion operations on the casing wall at the inner bend of the curved casing section under the push of the anti-bending mandrel 41, achieving straightening treatment of the curved casing. The variable stiffness shaper 4 in this embodiment has high bending strength and a significant effect on treating curved casing sections.

[0050] Based on the above embodiment one, the variable stiffness shaper 4 of this structure also has the following embodiments:

[0051] The bending mandrel 41 is a solid rod-shaped body with a non-uniform diameter. The large-diameter end of the solid rod-shaped body has a reversing and force-enhancing hydraulic cylinder connecting cavity, which has an internal thread that can connect to the lower connector of the reversing and force-enhancing hydraulic cylinder 3. The small-diameter end of the lower part of the solid rod-shaped body has an external thread that connects to the shaping head 43. A shearing groove, an annular groove surrounding the outer wall of the rod-shaped body, is provided above the external thread section at the small-diameter end. The lower part of the shaping head 43 is a solid circular head, and the upper part of the body has a mandrel connecting cavity. The mandrel connecting cavity has an internal thread that can connect to the threaded section at the small-diameter end of the bending mandrel 41. The shaping head 43 is threadedly connected to the bending mandrel 41 of the solid rod-shaped body. In this embodiment, the solid shaping head 43 and the bending mandrel 41 of the solid rod-shaped body cooperate to enhance the overall strength of the variable stiffness shaping device 4. The anti-bending mandrel 41 and the shaping head 43 have sufficient bending strength to ensure that the shaping head 43 can forcefully pass through the bent sleeve section. If the shaping head 43 cannot forcefully pass through the bent sleeve section, the anti-bending mandrel 41 and the anti-bending outer cylinder 42 can easily repair and straighten the bent sleeve section under the action of the reversing force-boosting cylinder 3. When using this embodiment, a hydraulic flushing hole needs to be added to the side wall above the threaded section of the lower connector of the upper reversing force-boosting cylinder 3 to avoid local dead space during reversal of the cylinder.

[0052] The length of the anti-bending outer cylinder 42 is less than the length of the anti-bending mandrel 41, and both ends are chamfered; the length of the anti-bending mandrel 41 is at least 50cm longer than the length of the anti-bending outer cylinder 42. This allows the anti-bending mandrel 41, which passes through the anti-bending outer cylinder 42, to move forward along the sleeve axis with the shaping head 43, forcing the anti-bending outer cylinder 42, which is blocked by the bending of the sleeve, to be squeezed, straightened, and shaped in the inward bending direction of the bent sleeve.

[0053] A shearing pin hole is provided at the lower part of the anti-bending outer cylinder 42, which corresponds to the position of the shearing pin groove at the lower part of the anti-bending mandrel 41. The connecting shearing pin 44 can be inserted into the shearing pin groove at the lower part of the anti-bending mandrel 41 from the shearing pin hole of the anti-bending outer cylinder 42.

[0054] The outer cylinder 42 of the anti-bending cylinder has at least two shear nail holes, which can ensure the connection strength between the anti-bending mandrel 41 and the outer cylinder 42 of the anti-bending cylinder, and ensure that they do not detach during the process of going down into the well.

[0055] Example 2 of the variable stiffness shaper 4

[0056] The variable stiffness shaper 4 is provided with an anti-bending mandrel 41, an anti-bending outer cylinder 42, and a shaping head 43. The anti-bending outer cylinder 42 is installed outside the anti-bending mandrel 41. The lower part of the anti-bending mandrel 41 is connected to the shaping head 43. The anti-bending outer cylinder 42 and the anti-bending mandrel 41 are connected by connecting shear pins 44. The anti-bending mandrel 41 and the shaping head 43 are provided with water flushing channels.

[0057] Based on the above embodiment one, the variable stiffness shaper 4 of this structure also has the following embodiments:

[0058] The anti-bending mandrel 41 is a non-equal diameter rod-shaped body with a hydraulic flushing channel. The large-diameter end of the rod-shaped body has a reversing and boosting hydraulic cylinder connecting cavity. The reversing and boosting hydraulic cylinder connecting cavity has an internal thread and communicates with the hydraulic flushing channel. The internal thread in the reversing and boosting hydraulic cylinder connecting cavity can connect with the lower connector of the reversing and boosting hydraulic cylinder 3. The small-diameter end of the non-equal diameter rod-shaped body with the hydraulic flushing channel has an external thread that is threadedly connected to the shaping head 43. A shearing groove is provided on the outer wall of the rod above the external thread section of the small-diameter end. The shearing groove is an annular groove surrounding the outer wall of the rod. The lower part of the shaping head 43 is a circular head with a hydraulic flushing channel, and the upper part of the body has a mandrel connecting cavity. The mandrel connecting cavity communicates with the hydraulic flushing channel and has an internal thread that can connect with the threaded section of the small-diameter end of the anti-bending mandrel 41. The shaping head 43 is threadedly connected to the anti-bending mandrel 41 with the hydraulic flushing channel. In this embodiment, both the anti-bending mandrel 41 and the shaping head 43 are provided with a hydraulic flushing channel, which can be connected to the hydraulic flushing channel of the reversing booster cylinder 3 connected above, making operation more convenient and eliminating the need to set a hydraulic flushing hole on the side wall above the threaded section of the lower connector of the reversing booster cylinder 3.

[0059] The wall thickness of the anti-bending mandrel 41 is greater than the wall thickness of the casing in the well where the casing is bent. The aperture of the hydraulic flushing channel in the anti-bending mandrel 41 and the shaping head 43 is set to be 8 mm or more. In this embodiment, the anti-bending mandrel 41 and the shaping head 43 have sufficient bending strength to repair and straighten the bent casing, and the operation is convenient.

[0060] The length of the anti-bending outer cylinder 42 is less than the length of the anti-bending mandrel 41, and both ends are chamfered; the length of the anti-bending mandrel 41 is at least 50cm longer than the length of the anti-bending outer cylinder 42. This allows the anti-bending mandrel 41, which passes through the anti-bending outer cylinder 42, to move forward along the sleeve axis with the shaping head 43, forcing the anti-bending outer cylinder 42, which is blocked by the bending of the sleeve, to be squeezed, straightened, and shaped in the inward bending direction of the bent sleeve.

[0061] A shearing pin hole is provided at the lower part of the anti-bending outer cylinder 42, which corresponds to the position of the shearing pin groove at the lower part of the anti-bending mandrel 41. The connecting shearing pin 44 can be inserted into the shearing pin groove at the lower part of the anti-bending mandrel 41 from the shearing pin hole of the anti-bending outer cylinder 42.

[0062] The outer cylinder 42 of the anti-bending cylinder has at least two shear nail holes, which can ensure the connection strength between the anti-bending mandrel 41 and the outer cylinder 42 of the anti-bending cylinder, and ensure that they do not detach during the process of going down into the well.

[0063] A method for constructing a casing string for treating a casing bend well includes the following steps:

[0064] A. Connect the tubing 1, hydraulic anchor 2, reversing force-enhancing cylinder 3 and variable stiffness shaping device 4 from top to bottom in the treatment process string of the casing bend well and run them into the target well section of the casing bend well.

[0065] B. Slowly lower the tubing until it encounters resistance;

[0066] C. After the tubing is obstructed, immediately lift the tubing 1 meter and record the obstruction depth, suspended weight, and related operational data.

[0067] D. Then, slowly lower the tubing string to the obstructed section of the well. Use the weight of the tubing string to press down a weight of less than 2 tons. If the tubing string can pass through the obstructed section, continue lowering the tubing string. If it cannot pass through the obstructed section, release the full weight of the downhole tubing string and then use the reversing force-boosting cylinder 3 and the variable stiffness shaping device 4 to pressurize and shape the bent casing section.

[0068] When performing pressure testing and shaping on bent casing sections, the main steps are as follows:

[0069] A. When shaping the bent casing, let the weight of the upper tubing of the variable stiffness shaper 4 press down on the obstruction position of the variable stiffness shaper 4, so that the reversing force-increasing hydraulic cylinder 3 is under pressure and pressurizes from the oil pipe 1, so that the hydraulic anchor 2 is fixed on the inner wall of the casing.

[0070] B. Continue to pressurize the tubing 1 to push the reversing hydraulic cylinder 3 downward to straighten the curved casing section downhole.

[0071] C. When the variable stiffness shaping device 4 becomes stuck due to casing bending and cannot pass through the bent section of the casing, the connecting shear pin 44 between the anti-bending outer cylinder 42 and the anti-bending core tube 41 in the variable stiffness shaping device 4 is sheared off, and the shaping head 43 continues to move forward under the push of the anti-bending mandrel 41. This is because the force of the anti-bending outer cylinder 42 being stuck in the bent section of the casing causes it to shear off the connecting shear pin 44 between it and the anti-bending core tube 41, thus achieving axial unlocking between the anti-bending outer cylinder 42 and the anti-bending core tube 41. The anti-bending outer cylinder 42 becomes stuck and cannot move forward, while the shaping head 43 continues to move forward under the push of the anti-bending mandrel 41. During this process, the overall stiffness of the variable stiffness shaper 4 increases due to the separation of the two large-diameter components, the shaping head 43 and the anti-bending outer cylinder 42. This increases the overall stiffness of the tool as it passes through the curved casing. Under the constraint of the curved section of the casing, the shaping head 43 moves along the trajectory of the casing or wellbore. The resulting deviation will exert a lateral force on the anti-bending outer cylinder 42, causing the anti-bending outer cylinder 42 to squeeze and treat the inner bend of the curved section of the casing, thus straightening and shaping the curved well.

[0072] D. When the variable stiffness shaper 4 at the bottom of the tubing string passes through the curved section of the casing, the tubing string is depressurized and then lifted. If the casing bends and springs back, causing the outer anti-bending cylinder 42 to get stuck, the shaping head 43, driven by the anti-bending core tube 41, will move towards one end of the anti-bending cylinder 42, making the large diameter section of the entire variable stiffness shaper 4 shorter and reducing the stiffness of the variable stiffness shaper 4 as a whole as it passes through the curved casing. This achieves the variable stiffness release function of the present invention and ensures the safety of lifting the tubing string.

[0073] E. If the tubing string requires greater lifting force to release the jamming, the lifting force exceeds the tubing string's own weight by 2 tons. Pressure can be continued to be applied into tubing 1 to fix the hydraulic anchor 2 to the inner wall of the casing. Continue to apply pressure into tubing 1 to lift the variable stiffness shaping device 4 located below by the reversing force-boosting cylinder 3. The reversing force-boosting cylinder 3, in conjunction with the variable stiffness shaping device 4, releases the jamming and removes the tubing string.

[0074] The embodiments described above are merely typical examples, but the present invention is not limited to these embodiments. Those skilled in the art can make modifications without departing from the spirit and teachings of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the inventive spirit and concept of the present invention should be included within the protection scope of the present invention. Therefore, the protection scope is not limited to the above description.

Claims

1. A treatment string for a curved wellbore comprising a tubing (1), a hydraulic anchor (2) and a reverse force augmentation cylinder (3), the tubing (1) being connected in series with the hydraulic anchor (2) and the reverse force augmentation cylinder (3), characterised in that, The lower end of the reversing force-boosting hydraulic cylinder (3) is connected to the variable stiffness shaping device (4), which is located at the lowest end of the treatment process string for the casing bend well. The variable stiffness shaping device (4) is equipped with an anti-bending mandrel (41), an anti-bending outer cylinder (42), and a shaping head (43). The anti-bending outer cylinder (42) is installed outside the anti-bending mandrel (41), and the lower part of the anti-bending mandrel (41) is connected to the shaping head (43). The anti-bending outer cylinder (42) is connected to the anti-bending mandrel (41). The mandrels (41) are connected by connecting shear pins (44); there is no water flushing channel in the anti-bending mandrel (41) and the shaping head (43); the length of the anti-bending outer cylinder (42) in the variable stiffness shaping device (4) is less than the length of the anti-bending mandrel (41), and the anti-bending outer cylinder (42) and the anti-bending mandrel (41) are connected by connecting shear pins (44); the length of the anti-bending mandrel (41) is at least 50cm longer than the length of the anti-bending outer cylinder (42). When the variable stiffness shaping device (4) becomes stuck due to casing bending and cannot pass through the bent section of the well, the connecting shear pin (44) between the anti-bending outer cylinder (42) and the anti-bending mandrel (41) in the variable stiffness shaping device (4) is sheared off, and the shaping head (43) continues to move forward under the push of the anti-bending mandrel (41); the separation of the two large-diameter components, the shaping head (43) and the anti-bending outer cylinder (42), makes the large-diameter section of the variable stiffness shaping device (4) longer, thus making the variable stiffness shaping device (4) more flexible and efficient. The stiffness of the stiffness shaper (4) increases as it passes through the curved casing; the anti-bending mandrel (41) is provided with a reversing force-enhancing hydraulic cylinder connecting cavity, which can be connected to the lower connector of the reversing force-enhancing hydraulic cylinder (3); the reversing force-enhancing hydraulic cylinder (3) can push the variable stiffness shaper (4) downward to straighten the curved casing section downhole and can also lift the variable stiffness shaper (4) located below upward through the reversing force-enhancing hydraulic cylinder (3).

2. A remedial work string for a cased deviated well according to claim 1, characterised in that, The bending mandrel (41) is a solid rod-shaped body with non-uniform diameter. The large-diameter end of the solid rod-shaped body is provided with a reversing and boosting hydraulic cylinder connecting cavity. The reversing and boosting hydraulic cylinder connecting cavity is provided with an internal thread that can be connected to the lower connector of the reversing and boosting hydraulic cylinder (3). The small-diameter end of the lower part of the solid rod-shaped body is provided with an external thread that is threaded to the shaping head (43). The outer wall of the rod above the external thread section of the small-diameter end is provided with a shearing groove. The shearing groove is an annular groove surrounding the outer wall of the rod. The lower part of the body of the shaping head (43) is a solid circular head, and the upper part of the body is provided with a mandrel connecting cavity. The mandrel connecting cavity is provided with an internal thread that can be connected to the threaded section of the small-diameter end of the bending mandrel (41). The shaping head (43) is threaded to the bending mandrel (41) of the solid rod-shaped body. Both ends of the bending outer cylinder (42) are provided with chamfers.

3. A treatment string for a curved wellbore comprising a tubing (1), a hydraulic anchor (2) and a reverse force augmentation cylinder (3), the tubing (1) being connected in series with the hydraulic anchor (2) and the reverse force augmentation cylinder (3), characterised in that, The lower end of the reversing force-boosting hydraulic cylinder (3) is connected to the variable stiffness shaping device (4), which is located at the lowest end of the treatment process string for the casing bend well. The variable stiffness shaping device (4) is equipped with an anti-bending mandrel (41), an anti-bending outer cylinder (42), and a shaping head (43). The anti-bending outer cylinder (42) is installed outside the anti-bending mandrel (41), and the lower part of the anti-bending mandrel (41) is connected to the shaping head (43). The anti-bending outer cylinder (42) is connected to the anti-bending mandrel (41). The mandrels (41) are connected by connecting shear pins (44); the anti-bending mandrel (41) and the shaping head (43) are provided with a hydraulic flushing channel; the length of the anti-bending outer cylinder (42) in the variable stiffness shaping device (4) is less than the length of the anti-bending mandrel (41), and the anti-bending outer cylinder (42) and the anti-bending mandrel (41) are connected by connecting shear pins (44); the length of the anti-bending mandrel (41) is at least 50cm longer than the length of the anti-bending outer cylinder (42). When the variable stiffness shaping device (4) becomes stuck due to casing bending and cannot pass through the bent section of the well, the connecting shear pin (44) between the anti-bending outer cylinder (42) and the anti-bending mandrel (41) in the variable stiffness shaping device (4) is sheared off, and the shaping head (43) continues to move forward under the push of the anti-bending mandrel (41); the separation of the two large-diameter components, the shaping head (43) and the anti-bending outer cylinder (42), makes the large-diameter section of the variable stiffness shaping device (4) longer, thus making the variable stiffness shaping device (4) more flexible and efficient. The stiffness of the stiffness shaper (4) increases as it passes through the curved casing; the anti-bending mandrel (41) is provided with a reversing force-enhancing hydraulic cylinder connecting cavity, which can be connected to the lower connector of the reversing force-enhancing hydraulic cylinder (3); the reversing force-enhancing hydraulic cylinder (3) can push the variable stiffness shaper (4) downward to straighten the curved casing section downhole and can also lift the variable stiffness shaper (4) located below upward through the reversing force-enhancing hydraulic cylinder (3).

4. A remedial work string for a cased deviated well according to claim 3, characterised in that, The bending mandrel (41) is a non-equal diameter rod with a hydraulic flushing channel. The large diameter end of the rod has a reversing and boosting hydraulic cylinder connecting cavity. The reversing and boosting hydraulic cylinder connecting cavity has an internal thread and communicates with the hydraulic flushing channel. The internal thread in the reversing and boosting hydraulic cylinder connecting cavity can be connected to the lower connector of the reversing and boosting hydraulic cylinder (3). The small diameter end of the non-equal diameter rod with a hydraulic flushing channel has an external thread and is threadedly connected to the shaping head (43). A shearing groove is provided on the outer wall of the rod above the external thread section of the small diameter end. The shearing groove is an annular groove surrounding the outer wall of the rod. The lower part of the shaping head (43) is a circular head with a hydraulic flushing channel, and the upper part of the body has a mandrel connecting cavity. The mandrel connecting cavity communicates with the hydraulic flushing channel and has an internal thread that can be connected to the threaded section of the small diameter end of the bending mandrel (41). The shaping head (43) is threadedly connected to the bending mandrel (41) with a hydraulic flushing channel.

5. A remedial work string for a cased deviated well according to claim 4, characterised in that, The wall thickness of the anti-bending mandrel (41) is greater than the wall thickness of the casing in the well where the casing is bent. The diameter of the hydraulic flushing channel in the anti-bending mandrel (41) and the shaping head (43) is set to be above 8 mm. Both ends of the anti-bending outer cylinder (42) are chamfered.

6. The casing string for treating a casing bend well as described in claim 5, characterized in that, The lower part of the anti-bending outer cylinder (42) is provided with a shearing nail hole, which corresponds to the position of the shearing nail groove at the lower part of the anti-bending mandrel (41). The connecting shearing nail (44) can be inserted into the shearing nail groove at the lower part of the anti-bending mandrel (41) from the shearing nail hole of the anti-bending outer cylinder (42). There are at least two shearing nail holes in the cylinder body of the anti-bending outer cylinder (42).

7. A method for constructing a casing string for treating a casing bend as described in any one of claims 1 or 3, comprising the following steps: A. Connect the tubing (1), hydraulic anchor (2), reversing booster cylinder (3), and variable stiffness shaper (4) in the treatment process string of the casing bend well from top to bottom, and run them down to the target section of the casing bend well; B. Slowly lower the tubing string until it encounters resistance; C. After the tubing string encounters resistance, immediately raise the tubing string by 1 meter and record the resistance depth, suspended weight, and related operation data; D. Then, slowly lower the tubing string to the section of the well where resistance is encountered, and use the weight of the tubing string to press down a weight of less than 2 tons. If the tubing string can pass through the section of the well where resistance is encountered, continue lowering the tubing string. If it cannot pass through the section of the well where resistance is encountered, release the full weight of the downhole tubing string and then use the reversing booster cylinder (3) and variable stiffness shaper (4) to pressurize and shape the bend section of the casing.

8. The method for constructing a casing string for treating a curved well as described in claim 7, characterized in that, When performing pressure shaping on a curved casing section, the main steps are as follows: A. When shaping the curved casing, the weight of the upper tubing of the variable stiffness shaper (4) is pressed onto the obstructed position of the variable stiffness shaper (4), so that the reversing force-boosting cylinder (3) is under pressure, and pressure is applied from inside the tubing (1) to fix the hydraulic anchor (2) on the inner wall of the casing; B. Continue to apply pressure to the tubing (1) so that the reversing force-boosting cylinder (3) pushes the variable stiffness shaper (4) downward to straighten the curved casing section downhole; C. When the variable stiffness shaper (4) is stuck due to the curved casing and cannot pass through the curved casing section, the variable stiffness shaper ( 4) The connecting shear pin (44) between the anti-bending outer cylinder (42) and the anti-bending mandrel (41) in the process is cut off, and the shaping head (43) continues to move forward under the push of the anti-bending mandrel (41); D) When the variable stiffness shaping device (4) at the bottom of the tubing passes through the curved section of the casing, the tubing is depressurized and then lifted; E) If the tubing needs a greater lifting force to release the jamming, the tubing is lifted more than 2 tons above its own weight, and pressure is continued to be applied into the tubing (1) to fix the hydraulic anchor (2) on the inner wall of the casing. Pressure is continued to be applied into the tubing (1), and the variable stiffness shaping device (4) located below is lifted upward by the reversing force-enhancing hydraulic cylinder (3) to remove the tubing.

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