Method for running a swellable rubber sleeve string into a well and swellable rubber sleeve string

Abstract

This invention belongs to the field of oil and gas development technology and discloses a method for inserting a water-swellable rubber casing string into a well and the water-swellable rubber casing string itself. The method for installing a water-swellable rubber casing string in the well includes the following steps: S1, hoist the water-swellable rubber casing at the wellhead; S2, clamp the section without rubber and perform the top connection; S3, install the opening and closing stabilizer on the coupling; S4, lower it into the wellbore; S5, repeat steps S1-S4, hoisting one string, connecting one string, and lowering one string into the well; S6, after the casing string is lowered into the well and before cementing operations, perform waterproofing operations to prevent water from entering the wellbore; during step S5, the following steps are also performed multiple times: S510, collect the current lowering friction force during the lowering process; S520, determine whether the current lowering friction force is less than the warning friction value, which is in the range of 5KN to 40KN. If yes, proceed to S540; if no, proceed to S530; S530, stop lowering into the well, perform cleaning and drag reduction operations, and return to step S510; S540, continue lowering into the well.

Description

Technical Field

[0001] This invention relates to the field of oil and gas development technology, and in particular to a method for inserting a water-swellable rubber casing string into a well and the water-swellable rubber casing string itself. Background Technology

[0002] As shale gas extends into deeper regions, the problem of casing deformation becomes more prominent, leading to increased fracturing costs and difficulties, a reduction in the number of fracturing stages, and serious consequences such as low single-well production and short well lifecycles.

[0003] Water-swellable rubber casing is made by vulcanizing a layer of water-swellable rubber onto a conventional casing, resulting in a larger outer diameter compared to conventional casing. During the wellbore installation process, the water-swellable rubber casing will come into contact with the well wall, causing wear and scratches due to friction. Furthermore, the water-swellable rubber casing will expand prematurely upon contact with moisture. All of these factors can lead to the abandonment of oil and gas wells and wellbore safety accidents.

[0004] To ensure the safe and smooth lowering of water-swellable rubber casing to the bottom of the well, a method for lowering a string of water-swellable rubber casing and a string of water-swellable rubber casing are proposed. Summary of the Invention

[0005] One objective of this invention is to provide a method for lowering a water-swellable rubber casing string into a well, enabling the water-swellable rubber casing string to be safely and smoothly lowered to the bottom of the well, avoiding premature expansion during the lowering process, and reducing rubber wear caused by contact friction with the well wall.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] The well insertion method for a water-swellable rubber casing string includes multiple water-swellable rubber casings connected by couplings. The water-swellable rubber casing string has staggered rubber-coated sections and non-rubber sections. The couplings correspond one-to-one with the non-rubber sections and are located on the corresponding non-rubber sections. The rubber-coated sections have a removable waterproof layer on their outer periphery. The well insertion method for the water-swellable rubber casing string includes the following steps:

[0008] S1. Use a hoisting device to hoist the water-swellable rubber casing to the wellhead;

[0009] S2. Use the upper and lower clip pliers to clamp the section without rubber and perform the upper clip;

[0010] S3. Install a retractable straightener on the coupling;

[0011] S4. Lower the shaft downwards;

[0012] S5. Repeat steps S1-S4, hoisting one, attaching one to the top, and lowering one into the well;

[0013] S6. After the tubing string is installed in the well and before cementing operations are carried out, waterproofing operations should be performed to prevent water from entering the wellbore.

[0014] During the execution of step S5, the following steps are also executed multiple times:

[0015] S510. Collect the current lowering friction force during the well lowering process;

[0016] S520. Determine whether the current downward friction force is less than the warning friction value, which is in the range of 5KN to 40KN. If yes, then execute S540; if no, then execute S530.

[0017] S530. Stop going downhole and perform cleaning and drag reduction operations, then return to step S510.

[0018] S540, continue going down the well.

[0019] Optionally, the wellbore includes several well sections connected at an angle. Step S5, and before step S510, further includes: step S500, when the lower end of the pipe string is lowered to the beginning of the current well section, obtaining the total frictional force on the pipe string, i.e., the total frictional force f of all well sections upstream of the current well section. p ;

[0020] Step S510 specifically includes:

[0021] S511. When the lower end of the tubing string is lowered to the current position of the current well section, obtain the current total frictional force f acting on the tubing string. n ;

[0022] S512. Obtain the current lowering friction force f for each sleeve according to the following formula:

[0023] f = (f n -f p ) / N (One)

[0024] In the above formula, N is the number of casings in the current well section.

[0025] Optionally, in step S500, f p Obtained through the following steps:

[0026] The pipe string is raised at a constant speed to a preset depth to obtain the first lifting hook load F. p1 The pipe string is lowered at a constant speed to a preset depth to obtain the first lowering hook load F. p2 ,

[0027] F p1 -G p1 -f p =0 (II)

[0028] Gp1 -F p2 -f p =0 (III)

[0029]

[0030] In the above formula, G p1 This is the floating weight of the tube string at this time;

[0031] In step S511, f n Obtained through the following steps:

[0032] The pipe string is raised at a constant speed to a preset depth to obtain the second lifting hook load F. n1 The pipe string is lowered at a constant speed to a preset depth to obtain the second lowering hook load F. n2 ,

[0033] F n1 -G n1 -f n =0 (V)

[0034] G n1 -F n2 -f n =0 (VI)

[0035]

[0036] In the above formula, G n1 This is the buoyancy of the string at this time.

[0037] Optionally, the wellbore includes three sections: a vertical section, a directional section, and a horizontal section connected in sequence. In step S5:

[0038] When the lower end of the pipe string is lowered to the beginning of the inclined section, step S500 is performed;

[0039] The lower end of the pipe string is located within the inclined section, and steps S510-S540 are performed every time the pipe string is lowered to the first preset depth.

[0040] When the lower end of the string is lowered to the beginning of the horizontal segment, step S500 is executed;

[0041] The lower end of the pipe string is within the horizontal segment, and steps S510-S540 are performed every time the pipe string is lowered to the second preset depth.

[0042] Optionally, in step S5, when the tubing enters the open hole section of the vertical well section, it is lowered into the well at a constant speed, and the lowering speed is controlled not to exceed a preset speed value.

[0043] Optionally, the following steps may also be performed in step S5:

[0044] S550. After entering the open hole section of the vertical well section, cleaning and drag reduction operations are performed every third preset depth.

[0045] S560. After entering the horizontal section, a cleaning and drag reduction operation is performed every fourth preset depth. The fourth preset depth is greater than the second preset depth and less than the third preset depth.

[0046] Optionally, the water-swellable rubber sleeve includes a main pipe and a rubber sleeve. The main pipe includes a first reserved section, a wrapping section, and a second reserved section that are sequentially connected and integrally formed. The rubber sleeve is fitted onto the wrapping section to form a rubber wrapping section. In any two connected water-swellable rubber sleeves, the first reserved section of one water-swellable rubber sleeve is connected to the second reserved section of the other water-swellable rubber sleeve through a coupling. The sequentially connected first reserved section, coupling, and second reserved section together form a rubber-free section. The depth of the rubber-free section is not less than the depth of the upper and lower coupling clamps.

[0047] Optionally, the rubber cylinder is provided with a first structural protective layer and a second structural protective layer extending from both ends toward each other, and the lengths of the first structural protective layer and the second structural protective layer are both not less than the first length value.

[0048] Optionally, in step S6, when the tubing string is lowered into the well, the pump is continuously started to circulate oil-based mud to displace the water flowing into the wellbore from the formation; during cementing operations, the amount of pre-flush fluid is increased several times and cement trucks are used for the operation.

[0049] Another objective of this invention is to provide a water-swellable rubber sleeve string, which facilitates safe and smooth descent to the bottom of the well, avoids premature expansion during the descent process, and reduces rubber wear caused by contact friction with the well wall.

[0050] To achieve this objective, the present invention adopts the following technical solution:

[0051] The water-swellable rubber sleeve string includes multiple water-swellable rubber sleeves connected by couplings. The water-swellable rubber sleeve string has staggered rubber-wrapped sections and non-rubber sections. The couplings correspond one-to-one with the non-rubber sections and are located on the corresponding non-rubber sections. Each coupling is fixed with an openable stabilizer. The outer periphery of the rubber-wrapped section is provided with a removable waterproof layer.

[0052] Beneficial effects:

[0053] In the wellhead insertion method for water-swellable rubber casing provided by this invention, step S1 avoids rubber damage caused by friction when the casing is pulled through ramps or catwalks during conventional casing insertion operations. Step S2 uses a pliers to hold the rubber-free section, which does not affect the rubber structure of the rubber-wrapped section and avoids damage to the rubber. Step S3 uses an openable centralizer without rubber attachment, ensuring the integrity of the rubber casing. In steps S5, steps S510-S540 ensure that the friction force during insertion is always less than the warning friction value, thereby ensuring the structural integrity of the rubber on the rubber-wrapped section during insertion and preventing premature detachment or damage to the rubber. Step S6 increases the expansion efficiency of the rubber, improving its ability to absorb fault slippage in the later stages and effectively preventing casing deformation. The waterproof layer on the water-swellable rubber casing protects the rubber, preventing premature expansion of the rubber before insertion due to rain or external water at the wellhead. This invention ensures, on the one hand, that the casing can be safely installed and cemented, and on the other hand, it guarantees efficient expansion, allowing the rubber to fully function, thereby preventing casing deformation and improving the overall efficiency of shale oil and gas development. Attached Figure Description

[0054] Figure 1 This is a flowchart of the well insertion method for a water-swellable rubber casing string provided in an embodiment of the present invention;

[0055] Figure 2 This is a flowchart of the method for monitoring friction in the well insertion of a water-swellable rubber casing string provided in this embodiment of the invention;

[0056] Figure 3 This is a schematic diagram of the structure of the water-swellable rubber sleeve string of the present invention.

[0057] In the picture:

[0058] 1. Main pipe; 2. Rubber cylinder; 3. Male buckle; 4. Female buckle; 5. Opening and closing type centralizer; 6. First reserved section; 7. Second reserved section; 8. Warning line; 9. High-strength protective coating. Detailed Implementation

[0059] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0060] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0061] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0062] In the description of this embodiment, the terms "upper," "lower," "right," and "left," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, 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. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0063] Regarding the causes of casing deformation during fracturing, the inventors proposed a fluid channel-fault activation model based on the analysis of extensive field data. During fracturing, due to the characteristics of shale gas and shale oil reservoirs, including bedding, fractures, and faults, fracturing fluid enters the developed faults / fractures through channels such as fracture / bedding surfaces, fissures at the cement sheath-formation interface, and direct communication between the fracturing fluid and fractures / faults. The primary channel is through fracture / bedding surfaces and fissures at the cement sheath-formation interface. This increases the pore pressure of the developed faults / fractures, reduces the friction coefficient of the fault / fracture surfaces, triggers fault / fracture slippage, and consequently causes deformation of the oil reservoir casing.

[0064] To prevent casing deformation during fracturing, the inventors proposed the concept of "using flexibility to overcome rigidity." Based on this concept, they proposed using "low-modulus" cement stone, meaning that the compressive strength of the cement stone should meet requirements while its elastic modulus should be as low as possible. Using this method, a field test of "high-strength micro-bead cementing" was conducted, and the wellbore has been successfully fracturing without casing deformation. However, this method is more suitable for cases with small deformation amounts; for cases with larger deformation amounts, other methods need to be explored.

[0065] To address the issue of large casing deformation, the inventors considered adding an elastic rubber sleeve to the outside of the casing, creating a rubber composite casing. At high-risk fractures / faults / fault slippage areas, a limited number of rubber composite casings are run. During fracturing, if slippage occurs at a high-risk fracture / fault, the rubber can absorb the slippage deformation, thus protecting the inner casing from damage. Adding a rubber sleeve to the outside of the casing increases the resistance during casing descent. To reduce this resistance, a special water-swellable rubber is considered, meaning the rubber only absorbs water and expands during the thickening process of the cementing slurry.

[0066] Water-swellable rubber casing is made by vulcanizing a layer of water-swellable rubber onto a conventional casing. Compared to conventional casing, its outer diameter is larger, and it expands upon contact with water. Therefore, ensuring the safe and smooth lowering of this water-swellable rubber casing to the bottom of the well, preventing premature expansion during the lowering process, and avoiding contact friction with the well wall that could cause wear, scratches, or obstruction, thus preventing oil and gas well abandonment and wellbore safety accidents, requires specific technological methods.

[0067] like Figure 1 As shown, this embodiment provides a method for lowering a water-swellable rubber casing string into a well, which can safely lower the water-swellable rubber casing string into the wellbore. Figure 3 As shown, specifically, the water-swellable rubber sleeve string comprises multiple water-swellable rubber sleeves connected by couplings. The water-swellable rubber sleeve string has staggered rubber-coated sections and non-rubber sections. The couplings correspond one-to-one with the non-rubber sections and are located on the corresponding non-rubber sections. A removable waterproof layer is provided around the outer periphery of the rubber-coated sections. For ease of description, the water-swellable rubber sleeve string is referred to as the string, and the water-swellable rubber sleeve is referred to as the sleeve.

[0068] There are no restrictions on the size and structure of the casing. For example, for a common casing with an outer diameter of 139.7 mm, the length of the casing body is 11-12 m, the wall thickness is 9-13 mm, one end of the casing is a female thread 4 end, and the other end is a male thread 3 end. The coupling of the female thread 4 end is 25-30 cm long.

[0069] like Figure 1 and Figure 2 As shown, the method for inserting a water-swellable rubber casing string into the well includes the following steps:

[0070] S1. Use a hoisting device to hoist the water-swellable rubber casing to the wellhead;

[0071] S2. Use the upper and lower clip pliers to clamp the section without rubber and perform the upper clip;

[0072] S3. Install the opening and closing type straightener 5 on the coupling;

[0073] S4. Lower the shaft downwards;

[0074] S5. Repeat steps S1-S4, hoisting one, attaching one to the top, and lowering one into the well;

[0075] S6. After the tubing string is installed in the well and before cementing operations are carried out, waterproofing operations should be performed to prevent water from entering the wellbore.

[0076] During the execution of step S5, the following steps are also executed multiple times:

[0077] S510. Collect the current lowering friction force during the well lowering process;

[0078] S520. Determine whether the current downward friction force is less than the warning friction value. If the warning friction value is in the range of 5KN to 40KN, then execute S540; otherwise, execute S530.

[0079] S530. Stop going downhole and perform cleaning and drag reduction operations, then return to step S510.

[0080] S540, continue going down the well.

[0081] Compared to step S1, in conventional casing installation operations, a crane is typically used to pull the casing to the wellhead via a ramp or catwalk, then the casing is first placed into the mouse hole, and finally lowered into the well. This solution, using step S1, avoids rubber damage caused by friction when pulling the casing via the ramp or catwalk in conventional installation operations. It also avoids damage caused by friction due to misalignment during lifting and lowering into and out of the mouse hole. Specifically, a crane lifts the casing onto the drilling platform, initially horizontally. Then, the female thread end 4 is lifted, and the male thread end 3 is lowered. The female thread end 4 is secured with a clamp, and the casing is slowly and vertically lowered at the wellhead, maintaining a vertical position. It is important that the crane operator and driller operate slowly during the lifting operation to avoid collisions or impacts between the casing and other objects.

[0082] In step S2, the upper and lower clips clamp the section without rubber, which will not affect the rubber structure of the rubber-wrapped section and avoid damaging the rubber.

[0083] Compared to step S3, conventional centralizers are installed on the casing body and can move freely between the two ends of the casing during lifting and lowering operations. In this case, the centralizer may snag the rubber, causing it to detach from the casing, block the wellbore, and lead to obstruction during running and failure to cement safely. To solve this problem, in step S3, a retractable centralizer 5 is used to wrap around the casing coupling. The retractable centralizer 5 is installed on the coupling between each casing. During lifting and lowering of the casing string, the coupling can effectively restrict the movement of the retractable centralizer 5, thereby avoiding the risk of contact between the retractable centralizer 5 and the rubber sleeve 2. Moreover, the retractable centralizer 5 can still ensure that the casing remains centered during running and cementing, ensuring that the rubber does not contact the wellbore. The retractable centralizer 5 consists of two interlocking arc-shaped shells, which are directly installed in an openable manner on the section without rubber, without affecting the rubber on the rubber-wrapped section.

[0084] In this embodiment, the opening / closing stabilizer 5 is a rigid roller stabilizer. The rollers further reduce friction during casing lowering. The length of the opening / closing stabilizer 5 must be greater than the length of the coupling to ensure it can completely cover the coupling and prevent contact between the coupling and the wellbore. Preferably, the maximum outer diameter of the opening / closing stabilizer 5 is 202-220 mm, the main body outer diameter is 202 mm, the inner diameter is 165 mm, and the height is 40-50 mm.

[0085] In steps S510-S540, the warning friction value is not greater than the safe value of the rubber shear strength, which is determined by the rubber properties of the water-swellable rubber casing. Different rubbers have different shear strengths. Currently, the common shear strength of water-swellable rubber, i.e., the safe value of shear strength, is in the range of 5KN to 40KN. Therefore, the warning friction value is in the range of 5KN to 40KN. When the friction force between the casing and the wellbore wall is less than 5KN, the casing runs smoothly, and the rubber will not suffer structural damage due to friction. When the friction force between the casing and the wellbore wall exceeds 40KN, the rubber is prone to deformation and damage, causing blockage between the casing and the annulus. This can lead to a rapid increase in friction, further making casing installation difficult. Furthermore, during cementing, cement slurry injection becomes difficult, leading to pump stalling and excessively high pump pressure, preventing normal cementing.

[0086] In this embodiment, the shear strength between the rubber-wrapped section body and the interface between the rubber-wrapped section and the unrubber section is tested indoors. The smaller of the two values ​​is then divided by a safety factor to obtain the warning friction value. During the casing running into the wellbore, steps S510-S540 are executed multiple times to monitor the current running friction force and to perform timely cleaning and drag reduction operations. This ensures that the running friction force is always less than the warning friction value, thereby guaranteeing the structural integrity of the rubber on the rubber-wrapped section during the running process and preventing premature detachment or damage of the rubber.

[0087] In this embodiment, the shear strength of the rubber-wrapped section is 13-14 kN, and the shear strength at the interface between the rubber-wrapped section and the non-rubber section is 9-10 kN. The safety factor is not less than 1. Based on a safety factor of 1, the current lowering friction force on each sleeve should be less than the warning friction value of 9 kN. Preferably, the factor can be 1.5. Based on a safety factor of 1.5, during the lowering process, the current lowering friction force on each sleeve should be less than the warning friction value of 6 kN.

[0088] The cleaning and drag reduction operation specifically involves using oil-based drilling mud, circulating it with a pump at a certain displacement for a specific time to clean debris from the wellbore, ensuring unobstructed wellbore flow, reducing frictional resistance, and minimizing the risk of blockage. In this embodiment, each pump cycle involves 3-4 rotations, with a displacement of 1.5-2.0 m³ / h. 3 / min.

[0089] Between the completion of casing installation and the start of cementing, water from the formation may flow into the wellbore, causing premature expansion of the rubber and making safe cementing impossible later. Therefore, to prevent water from entering the wellbore between the completion of casing installation and the start of cementing, step S6 must be maintained to avoid premature rubber expansion. Specifically, in step S6, when the tubing string is completed, the pump is continuously operated to circulate oil-based mud to displace the water flowing into the wellbore from the formation.

[0090] In step S6, during the cementing operation, the amount of pre-flush fluid used is increased several times, and a cement truck is used for the operation. Cementing fluids generally consist of pre-flush fluid, cement slurry, and displacement fluid; the amount of pre-flush fluid used is typically 15-20 ml. 3 The displacement is 1.0-1.2m. 3 / min; Cement grout is generally 120-140m 3 The displacement is 1.6-2.0m. 3 / min; displacement solution is 50-60m 3 The displacement is 1.6-2.0m. 3 / min. In this embodiment, in order for the rubber to fully absorb the water in the pre-fluid and swell, the amount of pre-fluid can be increased from the conventional 15-20m. 3 Increased to 50-60m 3 This volume is close to that of a wellbore, which increases the rubber's expansion efficiency and enhances its ability to absorb fault slippage later. Cement trucks are used for cementing operations instead of mud pumps, primarily to prevent excessive pump pressure during cement injection due to excessive rubber expansion, which could overwhelm the mud pump's operational capacity.

[0091] The waterproof layer protects the rubber from premature expansion before it is lowered into the well due to rain or water ingress at the wellhead. The waterproof layer can be removed before cementing operations. In one embodiment, wax can be applied to the surface of the rubber cylinder 2 to form a waterproof layer. Preferably, a low-melting-point wax (40-50°C) is used, so that the paraffin wax protective layer will automatically dissolve due to the formation temperature during the lowering process, without affecting the subsequent expansion of the rubber. In another embodiment, a waterproof membrane can be used to wrap around the rubber cylinder 2 as a waterproof layer. The waterproof membrane protects the rubber cylinder 2 in steps S1-S3 and is removed before step S4.

[0092] In summary, by implementing steps S1-S6 and S510-S540 in this embodiment, on the one hand, the casing can be safely lowered and cemented, and on the other hand, efficient expansion can be ensured so that the rubber can play its full role, thereby preventing casing deformation and improving the overall efficiency of shale oil and gas development.

[0093] During on-site construction, the types of well casings vary. When a well casing comprises several well sections connected at an angle, the specific method for collecting the current lowering friction force of any well section is as follows: In step S5 and before step S510, step S500 is also included: when the lower end of the pipe string is lowered to the beginning of the current well section, the total friction force on the pipe string is obtained, that is, the total friction force f of all well sections upstream of the current well section on the pipe string. p Step S510 specifically includes: S511, when the lower end of the pipe string is lowered to the current position of the current well section, obtaining the current total frictional force f acting on the pipe string. n S512. Each casing is equipped with an opening / closing stabilizer 5. Therefore, the lowering friction force of each opening / closing stabilizer 5 represents the current lowering friction force of each casing. The current lowering friction force f of each casing is obtained according to the following formula:

[0094] f = (f n -f p ) / N (One)

[0095] In the above formula, f represents the lowering friction force of each opening and closing stabilizer 5 in the current well section. n f is the current total frictional force acting on the string. p N is the total frictional force exerted on the pipe string by all upstream well sections in the current well section; N is the number of centralizers (i.e., the number of casings) in the current well section of the pipe string.

[0096] By collecting f p and f nSubstituting these values ​​into Formula (I), the current lowering friction force f for each casing at any position can be obtained. In this embodiment, it is necessary to ensure that f is always less than the warning friction value of 6 kN. Otherwise, a cleaning and drag reduction operation is performed to ensure unobstructed wellbore flow, reduce frictional resistance, and mitigate the risk of encountering obstruction in advance.

[0097] Furthermore, in order to obtain f p and f n This facilitates obtaining the current downward friction force f. In step S500, f p Obtained through the following steps:

[0098] The pipe string is raised at a constant speed to a preset depth to obtain the first lifting hook load F. p1 The pipe string is lowered at a constant speed to a preset depth to obtain the first lowering hook load F. p2 ,

[0099] F p1 -G p1 -f p =0 (II)

[0100] G p1 -F p2 -f p =0 (III)

[0101]

[0102] In the above formula, F p1 For the first lifting hook load, F p2 For the first lower enlarged hook load, G p1 This is the floating weight of the tube string at this time;

[0103] In step S511, f n Obtained through the following steps:

[0104] The pipe string is raised at a constant speed to a preset depth to obtain the second lifting hook load F. n1 The pipe string is lowered at a constant speed to a preset depth to obtain the second lowering hook load F. n2 ,

[0105] F n1 -G n1 -f n =0 (V)

[0106] G n1 -F n1 -f n =0 (VI)

[0107]

[0108] In the above formula, F n1For the second lifting hook load, F n2 For the second lower amplified hook load, G n1 This is the buoyancy of the string at this time.

[0109] In other words, the total frictional force on the pipe string is calculated by using two processes: partially lifting the sleeve and partially lowering the sleeve, and by varying the load on the large hook. In this embodiment, the preset depth value is preferably the length of one sleeve.

[0110] In this embodiment, the wellbore includes three sections: a vertical section, a directional drilling section, and a horizontal section connected in sequence. The rubber sleeve 2 is most likely to come into contact with the well wall in the directional drilling and horizontal sections, leading to rubber damage. Therefore, in step S5:

[0111] When the lower end of the tubing string is lowered to the beginning of the build-up section, step S500 is performed to obtain the frictional resistance f of the entire vertical well section to the tubing string. p1 ;

[0112] The lower end of the pipe string is located within the inclined section. Steps S510-S540 are executed every time the pipe string is lowered to a first preset depth. Specifically, by executing steps S511 and S512 in step S510, the current total friction force f at each time the inclined section is lowered to the first preset depth is obtained. n1 , will f n1 and f p1 Substituting into formula (1), that is, the current lowering friction force of the casing in each skew section is f1 = (f n1 -f p1 ) / N1, where N1 is the number of casings in the inclined section.

[0113] Further in steps S520-S540, depending on whether the current lowering friction force f1 of each casing in the directional section is greater than the warning friction value, the option is to continue lowering or perform cleaning and drag reduction operations to ensure unobstructed wellbore and avoid rubber damage.

[0114] Similarly, in the horizontal section, when the lower end of the tubing string is lowered to the beginning of the horizontal section, step S500 is performed to obtain the total frictional force f of the vertical well section and the directional drilling section on the entire tubing string. p2 ;

[0115] The lower end of the pipe string is within the horizontal section. Steps S510-S540 are executed every time the pipe string is lowered to a second preset depth. Specifically, by executing steps S511 and S512 in step S510, the current total frictional force f for each time the horizontal section is lowered to a first preset depth is obtained. n2 , will f n1 and f p2 Substituting into formula (1), that is, the current lowering friction force of the casing in each horizontal segment is f2 = (f n2 -f p2) / N2, where N2 is the number of sleeves in the horizontal section.

[0116] Further in steps S520-S540, depending on whether the current lowering friction force f2 of the horizontal section is greater than the warning friction value, the option is to continue lowering or perform cleaning and drag reduction operations to ensure unobstructed wellbore and avoid damage to the rubber.

[0117] In this embodiment, in step S5, when the tubing string enters the open hole section of the vertical well, it is lowered at a constant speed, and the lowering speed is controlled not to exceed a preset speed value. This is to prevent pressure surges that could cause formation leakage, and to reduce the risk of encountering obstruction.

[0118] During actual operations, after the casing enters the open hole, the casing lowering speed must be strictly controlled. Sudden lowering is prohibited, and each casing should be lowered for at least 40 seconds to keep the lowering speed within the preset value. After the vertical well section is completed (i.e., at the beginning of the build-up section), localized short-range lifting and lowering are performed to calculate the frictional resistance f of the entire vertical well section. p1 Ensure that the friction force is less than the warning friction value of 6 kN. After entering the inclined section, calculate the friction force f every time the first preset depth (5 casing lengths) is reached. n1 Ensure that the frictional resistance f1 of each casing is less than the warning friction value of 6 kN; after the build-up section is completed, calculate the total frictional force f of the vertical well section and the build-up section. p2 After entering the horizontal section, calculate the frictional resistance f2 every second preset depth (5 casing lengths) to ensure it is less than the warning frictional value of 6 kN. If the frictional resistances f1 and f2 increase to the warning frictional value of 6 kN, perform a cleaning and drag reduction operation. First, start the pump to circulate and clean the well for 3-4 cycles, with a displacement of 1.5-2.0 m³ / h. 3 / min, then perform short-distance lifting and lowering to ensure the wellbore is unobstructed, and then perform local lifting and lowering to ensure that the friction force is less than the warning friction value of 6KN.

[0119] In this embodiment, the following steps are also performed in step S5:

[0120] S540. After entering the open hole section of the vertical well, a cleaning and drag reduction operation is performed every third preset depth to prevent damage to the rubber due to obstruction during descent. Specifically, after each third preset depth, the pump needs to be started for circulation at a displacement of 1.0-1.5m. 3 The process of circulating the mud for a certain period of time ( / min) serves two purposes: firstly, it improves the flowability of the oil-based mud, and secondly, it cleans away any loose material from the wellbore, preventing accumulation that could lead to casing blockage later. For example, the third preset depth is the length of 80-100 connected casing sections.

[0121] S550, after entering the horizontal section, a cleaning and drag-reducing operation is performed every fourth preset depth to prevent damage to the rubber due to obstruction during descent. Specifically, a jacking operation is performed once every time the vehicle descends to the fourth preset depth, with a displacement of 0.5-1.0m each time. 3 / min, time 20-30min. The fourth preset depth is greater than the second preset depth and less than the third preset depth. For example, the fourth preset depth is the length after 30-50 sleeves are connected.

[0122] Specifically, the water-swellable rubber sleeve includes a main pipe 1 and a rubber cylinder 2. The main pipe 1 includes a first reserved section 6, a wrapping section, and a second reserved section 7 that are sequentially connected and integrally formed. The rubber cylinder 2 is sleeved on the wrapping section to form a rubber wrapping section. In any two connected water-swellable rubber sleeves, the first reserved section 6 of one water-swellable rubber sleeve is connected to the second reserved section 7 of the other water-swellable rubber sleeve through a coupling. The sequentially connected first reserved section 6, coupling, and second reserved section 7 together form a rubber-free section. The depth of the rubber-free section is not less than the depth of the upper and lower coupling clamps.

[0123] In this embodiment, to ensure safe lowering, a certain distance needs to be reserved at both ends of the rubber sleeve 2, namely the male thread 3 and the female thread 4, forming the first reserved section 6 and the second reserved section 7, thus creating a rubber-free section to facilitate threading and unthreading operations at the wellhead. Since the slip height on site is 40-60cm, the threading / unthreading pliers (hydraulic pliers) are 100-120cm above the ground, and the hydraulic pliers are 20-30cm thick, the length of the unvulcanized rubber reserved in the second reserved section 7 at the female thread 4 end is 100-150cm, and the length of the unvulcanized rubber reserved in the first reserved section 6 at the male thread 3 end is 50-100cm. Therefore, the length of the rubber sleeve = casing length - first reserved section length - second reserved section length - coupling length. For example, the slip is 40cm long, the hydraulic pliers are 110cm high above the ground, the hydraulic pliers are 20cm thick, the first reserved section 6 is 1m long, the second reserved section 7 is 1.2m long, and the rubber cylinder 2 is 9-10m long.

[0124] Optionally, the rubber sleeve 2 is provided with a first structural protective layer and a second structural protective layer extending from both ends towards each other on its outer periphery. The lengths of both the first and second structural protective layers are not less than a first length value. That is, a high-strength protective coating 9, namely the first and second structural protective layers, is sprayed onto both ends of the rubber sleeve 2 to improve the strength of the rubber and prevent premature breakage of the ends of the rubber sleeve 2 during drilling operations using slips and hydraulic tongs, which could lead to obstruction during well running and cause wellbore risks. Preferably, the materials for the first and second structural protective layers can be Line-X material. Line-X is a high-performance elastomer spraying material composed of a two-component system: component A (isocyanate) and component B (resin). When the two components are mixed in a 1:1 volume ratio, a spraying thickness of 1-2 mm can form a high-strength protective layer. Preferably, the first length value is 10-20 cm.

[0125] Optionally, to prevent contact with the rubber when placing the slips, a warning line 8 is marked on the female thread 4 of the casing. The slips are placed only after the drill bit surface has passed the warning line 8, ensuring that the slips do not get stuck on the rubber. In this embodiment, the warning line 8 is fluorescent to ensure visibility during nighttime operations.

[0126] This embodiment also provides a water-swellable rubber sleeve string, which is beneficial for safely and smoothly descending to the bottom of the well, avoiding premature expansion during the descent process, and reducing rubber wear caused by contact friction with the well wall.

[0127] The water-swellable rubber casing string is the water-swellable rubber casing string in the aforementioned water-swellable rubber casing string insertion method. It includes multiple water-swellable rubber casings connected by couplings. The water-swellable rubber casing string has staggered rubber-wrapped sections and non-rubber sections. The couplings correspond one-to-one with the non-rubber sections and are located on the corresponding non-rubber sections. Each coupling is fixed with an openable centralizer 5. The outer periphery of the rubber-wrapped section is provided with a removable waterproof layer.

[0128] The rubber-wrapped section utilizes the water-absorbing and swelling properties of the outer rubber layer to absorb sliding deformation caused by slippage in high-risk cracks / faults during fracturing, thus protecting the inner tubular structure from damage. The rubber-free section is used during coupling and uncoupling operations, held in place by coupling clamps to prevent damage to the rubber and the generation of rubber debris. The removable waterproof layer prevents premature swelling of the rubber upon contact with water.

[0129] Specifically, the water-swellable rubber sleeve includes a main pipe 1 and a rubber cylinder 2. The main pipe 1 includes a first reserved section 6, a wrapping section, and a second reserved section 7 that are sequentially connected and integrally formed. The rubber cylinder 2 is sleeved on the wrapping section to form a rubber wrapping section. In any two connected water-swellable rubber sleeves, the first reserved section 6 of one water-swellable rubber sleeve is connected to the second reserved section 7 of the other water-swellable rubber sleeve through a coupling. The sequentially connected first reserved section 6, coupling, and second reserved section 7 together form a rubber-free section. The depth of the rubber-free section is not less than the depth of the upper and lower coupling clamps.

[0130] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for inserting a water-swellable rubber casing string into a well, characterized in that, The water-swellable rubber casing string includes multiple water-swellable rubber casings connected by couplings. The string has staggered rubber-coated sections and non-rubber sections. The couplings correspond one-to-one with the non-rubber sections and are located on the corresponding non-rubber sections. The rubber-coated sections have a removable waterproof layer on their outer periphery. The method for inserting the water-swellable rubber casing string into the well includes the following steps: S1. Use a hoisting device to hoist the water-swellable rubber casing to the wellhead; S2. Use the upper and lower clip pliers to clamp the section without rubber and perform the upper clip; S3. Install a retractable stabilizer (5) on the coupling. S4. Lower the shaft downwards; S5. Repeat steps S1-S4, hoisting one, attaching one to the top, and lowering one into the well; S6. After the tubing string is installed in the well and before cementing operations are carried out, waterproofing operations should be performed to prevent water from entering the wellbore. During the execution of step S5, the following steps are also executed multiple times: S510. Collect the current lowering friction force during the well lowering process; S520. Determine whether the current downward friction force is less than the warning friction value, which is in the range of 5KN to 40KN. If yes, then execute S540; if no, then execute S530. S530. Stop going downhole and perform cleaning and drag reduction operations, then return to step S510. S540, continue going down the well.

2. The method for inserting a water-swellable rubber casing string into a well according to claim 1, characterized in that, The wellbore comprises several well sections connected at an angle. Step S5, and prior to step S510, further includes: step S500, when the lower end of the pipe string is lowered to the beginning of the current well section, obtaining the total frictional force on the pipe string, i.e., the total frictional force f of all well sections upstream of the current well section. p ; Step S510 specifically includes: S511. When the lower end of the tubing string is lowered to the current position of the current well section, obtain the current total frictional force f acting on the tubing string. n ; S512. Obtain the current lowering friction force f for each sleeve according to the following formula: (one) In the above formula, N is the number of casings in the current well section.

3. The method for inserting a water-swellable rubber casing string into a well according to claim 2, characterized in that, In step S500, f p Obtained through the following steps: The pipe string is raised at a constant speed to a preset depth to obtain the first lifting hook load F. p1 The pipe string is lowered at a constant speed to a preset depth to obtain the first lowering hook load F. p2 , (two) (three) (Four) In the above formula, G p1 This refers to the buoyancy of the tubing string when its lower end is lowered to the beginning of the current well section. In step S511, f n Obtained through the following steps: The pipe string is raised at a constant speed to a preset depth to obtain the second lifting hook load F. n1 The pipe string is lowered at a constant speed to a preset depth to obtain the second lowering hook load F. n2 , (five) (six) (seven) In the above formula, G n1 This is the buoyancy of the tubing string when the lower end of the tubing string is lowered to the current position of the current well section.

4. The method for inserting a water-swellable rubber casing string into a well according to claim 3, characterized in that, The wellbore comprises three sections: a vertical section, a directional section, and a horizontal section, which are connected sequentially. In step S5: When the lower end of the pipe string is lowered to the beginning of the inclined section, step S500 is performed; The lower end of the pipe string is located within the inclined section, and steps S510-S540 are performed every time the pipe string is lowered to the first preset depth. When the lower end of the string is lowered to the beginning of the horizontal segment, step S500 is executed; The lower end of the pipe string is within the horizontal segment, and steps S510-S540 are performed every time the pipe string is lowered to the second preset depth.

5. The method for inserting a water-swellable rubber casing string into a well according to claim 4, characterized in that, In step S5, when the tubing enters the open hole section of the vertical well, it is lowered into the well at a constant speed, and the lowering speed is controlled not to exceed the preset speed value.

6. The method for inserting a water-swellable rubber casing string into a well according to claim 5, characterized in that, In step S5, the following steps are also performed: S550. After entering the open hole section of the vertical well section, cleaning and drag reduction operations are performed every third preset depth. S560. After entering the horizontal section, a cleaning and drag reduction operation is performed every fourth preset depth. The fourth preset depth is greater than the second preset depth and less than the third preset depth.

7. The method for inserting a water-swellable rubber casing string into a well according to claim 1, characterized in that, The water-swellable rubber sleeve includes a main pipe (1) and a rubber sleeve (2). The main pipe (1) includes a first reserved section (6), a wrapping section and a second reserved section (7) that are connected in sequence and integrally formed. The rubber sleeve (2) is fitted on the wrapping section to form a rubber wrapping section. In any two water-swellable rubber sleeves connected together, the first reserved section (6) of one water-swellable rubber sleeve is connected to the second reserved section (7) of the other water-swellable rubber sleeve through a coupling. The first reserved section (6), the coupling and the second reserved section (7) that are connected in sequence together form a rubber-free section. The depth of the rubber-free section is not less than the depth of the upper and lower clamps.

8. The method for inserting a water-swellable rubber casing string into a well according to claim 7, characterized in that, The rubber cylinder (2) is provided with a first structural protective layer and a second structural protective layer extending from its two ends toward each other. The lengths of the first structural protective layer and the second structural protective layer are not less than the first length value.

9. The method for inserting a water-swellable rubber casing string into a well according to any one of claims 1-8, characterized in that, In step S6, when the tubing string is lowered into the well, the pump is continuously started to circulate oil-based mud to displace the water flowing into the wellbore from the formation; during cementing operations, the amount of pre-flush fluid is increased several times and cement trucks are used for the operation.

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