Method for simulated evaluation of casing running difficulties with rubber composite casing

Abstract

The present application belongs to the technical field of oil and natural gas exploitation, and discloses a simulation evaluation method for casing running resistance of rubber combined casing, which comprises the following steps: placing rubber combined casing with closed ends in a steel pipe, injecting cement slurry into the annular part between the rubber combined casing and the steel pipe, and solidifying the cement slurry to form a cement stone, so as to obtain a simulation sample; setting a simulation resistance object at the outlet end of the steel pipe, the simulation resistance object extending radially inward along the steel pipe and being capable of contacting the rubber layer of the rubber combined casing, injecting a first liquid into the steel pipe at the inlet end, so that the first liquid pushes the rubber combined casing to move axially along the outlet end relative to the cement stone, and calculating the first friction resistance of the rubber combined casing; repeating the foregoing steps, and calculating the second friction resistance between the rubber combined casing and the cement stone when the rubber combined casing moves, without setting the simulation resistance object. The present application can systematically study the damage characteristics and friction resistance change law of casing running resistance of rubber combined casing.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, and in particular to a simulation evaluation method for casing obstruction encountered by rubber composite casing. Background Technology

[0002] In oil and gas extraction, casing is a key tubular structure run into the wellbore, primarily serving to support the wellbore to prevent collapse and to isolate fluids from different formations to avoid cross-flow interference with extraction. However, due to complex geological conditions or construction factors, casing is prone to deformation. Casing deformation not only increases the difficulty and cost of fracturing operations but also reduces the number of effective fracturing stages, thereby affecting single-well production and the final recovery rate.

[0003] To address the casing deformation problem, related technologies employ rubber composite casings that can absorb displacement loads, such as "filled high-strength fiber rubber outer layer composite casing" (CN106761442B) and "composite casing for oil and gas reservoir fracturing" (CN212671582U). These technologies add a layer of specially elastic rubber to the outer wall of traditional casings, utilizing the deformable properties of rubber materials to absorb displacement loads from formation slippage, thereby effectively alleviating the casing deformation problem.

[0004] However, due to the presence of the rubber layer, the outer diameter of rubber-coated casing is usually larger than that of conventional casing, making it more prone to obstruction during casing installation. If the rubber layer is scratched, torn, or completely detached during obstruction, it not only weakens the deformation resistance of the rubber-coated casing but also significantly increases the frictional resistance due to the accumulation of rubber debris, potentially preventing the casing from reaching the designed well depth. Currently, there is a lack of effective experimental methods, both domestically and internationally, to simulate the obstruction risk and frictional changes of rubber-coated casing during installation. Common frictional testing devices, such as the "Simulation Experimental Device for Casing String Installation Friction under Wellbore Collision Conditions" (CN115614021B), simulate the installation friction of conventional casing under complex wellbore conditions, but it is only applicable to conventional steel casing and has significant limitations when used to simulate rubber-coated casing.

[0005] Therefore, it is necessary to propose an effective simulation experiment evaluation method to address the obstruction problem encountered during the installation of rubber composite sleeves, so as to provide reliable theoretical support for the design optimization and field installation process of rubber composite sleeves. Summary of the Invention

[0006] The purpose of this invention is to provide a simulation evaluation method for the obstruction encountered during the lowering of rubber composite sleeves, which can systematically study the damage characteristics and friction change law of rubber composite sleeves encountering obstruction during the lowering process.

[0007] Based on the above concept, the technical solution adopted by this invention is as follows:

[0008] This invention provides a simulation evaluation method for obstruction encountered by the lower casing of a rubber composite casing, comprising:

[0009] S1. Place the sealed rubber combination sleeve inside the steel pipe, inject cement slurry into the annular space between the rubber combination sleeve and the steel pipe, and allow the cement slurry to solidify to form cement stone to obtain a simulated sample.

[0010] S2. A simulated obstruction is set at the outlet end of the steel pipe. The simulated obstruction extends radially inward along the steel pipe and can contact the rubber layer of the rubber composite sleeve. A first liquid is injected into the steel pipe at the inlet end of the steel pipe so that the first liquid pushes the rubber composite sleeve to move axially toward the outlet end relative to the cement stone, and the first frictional resistance of the rubber composite sleeve is calculated.

[0011] S3. Repeat steps S1 to S2, without setting the simulated obstacle when repeating step S2, to calculate the second frictional resistance between the rubber composite sleeve and the cement stone when the rubber composite sleeve moves.

[0012] In some embodiments, the method further includes the following steps after step S1 and before step S2:

[0013] A first baffle is fixedly connected to the inlet end, and a second baffle is fixedly connected to the outlet end. The first baffle is provided with an injection hole, and the second baffle is provided with an outlet hole. A second liquid is injected into the steel pipe through the injection hole so that the second liquid flows along the interface between the rubber combined sleeve and the cement stone until the second liquid flows out from the outlet hole; then the second baffle is removed.

[0014] In some embodiments, the simulation evaluation method for obstruction encountered by the lower casing of the rubber composite sleeve further includes temperature treatment; the temperature treatment specifically includes:

[0015] In step S1, when the cement slurry has not solidified, resistance wire is wrapped around the outer circumference of the steel pipe to heat it to a preset temperature and then kept at that temperature. After step S1, the simulated sample is kept at the preset temperature.

[0016] In some embodiments, the simulated obstruction is configured as an obstruction block to simulate point contact obstruction of the rubber composite sleeve.

[0017] In some embodiments, the obstruction block includes at least one of a triangular block, a rectangular block, a ring block, and a serrated block.

[0018] In some embodiments, the simulated obstruction is configured as an obstruction ring to simulate the narrowing obstruction of the rubber composite sleeve.

[0019] In some embodiments, the length of the rubber composite sleeve is less than the length of the steel pipe, and there is a reserved space between the rubber composite sleeve and the inlet end.

[0020] In some embodiments, in step S1, before injecting the cement slurry into the annulus between the rubber composite sleeve and the steel pipe, the reserved space is filled with a foam body with the same outer diameter as the rubber composite sleeve, and the foam body is removed after the cement slurry solidifies to form the cement stone.

[0021] In some embodiments, in step S1, the rubber composite sleeve is centrally placed inside the steel pipe.

[0022] In some embodiments, the displacement of the first liquid is set to 0.5 m³. 3 / min~0.8m 3 / min; the displacement of the second liquid is set to 0.1m. 3 / min~0.2m 3 / min.

[0023] The beneficial effects of this invention are:

[0024] The present invention provides a simulation evaluation method for obstruction during the running of rubber composite casing. By preparing simulated samples and simulating the obstruction state in the downhole environment during casing running, the method calculates the difference between the overall frictional resistance under obstruction conditions and the baseline frictional resistance under unobstructed conditions, accurately stripping away the additional frictional resistance after obstruction. This allows for a systematic study of the destructive characteristics and frictional resistance variation law of rubber composite casing during running. It can provide a scientific basis for the structural optimization and running process formulation of rubber composite casing, and provide quantitative indicators for judging the severity of obstruction on-site, avoiding empirical errors, so as to timely grasp the downhole condition of rubber composite casing and prevent wellbore blockage accidents. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the content of the embodiments of the present invention and these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of the simulated sample provided in the embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the obstruction block connected to the steel pipe according to an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the structure of the obstruction ring connected to the steel pipe according to an embodiment of the present invention;

[0029] Figure 4 These are friction curves under different resistance encounter methods provided in the embodiments of the present invention.

[0030] In the picture:

[0031] 1. Rubber combination sleeve;

[0032] 2. Steel pipe; 21. Outlet end; 22. Inlet end;

[0033] 3. Cement stone;

[0034] 4. Obstacle block; 41. Triangular block; 42. Rectangular block; 43. Ring block; 44. Sawtooth block;

[0035] 5. Obstruction loop;

[0036] 10. Simulated sample; 20. Reserved space. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0039] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0040] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are used only for the convenience of describing the invention and for 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. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0041] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0042] 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.

[0043] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0044] like Figures 1-3 As shown, the simulation evaluation method for obstruction encountered by the lower casing of the rubber composite casing provided in this embodiment includes:

[0045] S1. Place the sealed rubber combination sleeve 1 inside the steel pipe 2, inject cement slurry into the annular space between the rubber combination sleeve 1 and the steel pipe 2, and allow the cement slurry to solidify to form cement stone 3, so as to obtain the simulated sample 10.

[0046] S2. A simulated obstruction is set at the outlet end 21 of the steel pipe 2. The simulated obstruction extends radially inward along the steel pipe 2 and can contact the rubber layer of the rubber composite sleeve 1. A first liquid is injected into the steel pipe 2 at the inlet end 22 of the steel pipe 2 so that the first liquid pushes the rubber composite sleeve 1 to move axially toward the outlet end 21 relative to the cement stone 3, and the first frictional resistance of the rubber composite sleeve 1 is calculated.

[0047] S3. Repeat steps S1 to S2. When repeating step S2, do not set up simulated obstacles to calculate the second frictional resistance between the rubber combined sleeve 1 and the cement stone 3 when the sleeve moves.

[0048] In step S1, cement stone 3, solidified from cement slurry, is used to simulate the rock surrounding the formation wellbore. In step S2, the movement of the rubber casing 1 towards the outlet end 21, propelled by the first liquid, simulates the actual casing running process. Simulated obstructions at the outlet end 21 hinder the movement of the rubber casing 1. After passing the simulated obstructions, the rubber casing 1 will deform, scratch, etc., simulating the obstruction phenomenon during actual casing running. Step S2 allows for accurate observation of the rubber's damage morphology. Step S3 is a repetition of steps S1 to S2, except that simulated obstructions are not set up during the repetition of step S2. In other words, in step S3, only the first liquid propels the rubber casing 1, without simulated obstructions, simulating a no-obstruction phenomenon.

[0049] In step S2, the first frictional resistance f1 of the rubber composite sleeve 1 is the overall frictional resistance, including the frictional resistance between the rubber composite sleeve 1 and the cement stone 3, and the additional frictional resistance after encountering the simulated obstacle. In step S3, no simulated obstacle is set, and the second frictional resistance f2 is the frictional resistance between the rubber composite sleeve 1 and the cement stone 3. Therefore, the additional frictional resistance after encountering the obstacle during the lowering process of the rubber composite sleeve 1 can be calculated by f1-f2.

[0050] Specifically, the first frictional resistance f1 can be calculated using the following formula:

[0051] f1 = 1 / 4Pπd 2

[0052] In the formula, P is the injection pressure of the first liquid in step S2; d is the outer diameter of the rubber combination sleeve 1.

[0053] Similarly, the second frictional resistance f2 can also be calculated using the above formula, where P in the formula is the injection pressure of the first liquid in step S3.

[0054] In step S2, the damage morphology of the rubber includes minor scratches, scratches accompanied by the detachment of the rubber strip, and complete detachment. Generally speaking, minor scratches and scratches accompanied by the detachment of the rubber strip do not pose a safety risk to the wellbore, while complete detachment of the rubber does pose a safety risk to the wellbore.

[0055] The simulation evaluation method for obstruction during the running of rubber composite casing provided in this embodiment simulates the obstruction state of the downhole environment during casing running by preparing a simulated sample 10. By using the difference between the overall frictional resistance under obstruction conditions and the benchmark frictional resistance under unobstructed conditions, the additional frictional resistance after obstruction is accurately stripped away. This allows for a systematic study of the destructive characteristics and frictional resistance change law of rubber composite casing 1 during the running process. It can provide a scientific basis for the structural optimization and running process formulation of rubber composite casing 1, and can also provide quantitative indicators for judging the severity of obstruction on site, avoiding empirical errors, so as to timely grasp the downhole condition of rubber composite casing 1 and prevent wellbore blockage accidents.

[0056] For example, the specific composition of the cement slurry is: 100 parts of Grade G Jiahua cement, 30-40 parts of quartz sand, 0.8-2 parts of water loss reducer, 0.4-0.6 parts of drag reducer, and 50-60 parts of water (all by mass). This formula ensures that the cement slurry has good fluidity and curing strength. In step S1, the cement slurry prepared according to this formula is injected into the annulus between the rubber casing 1 and the steel pipe 2, ensuring that the annulus is filled with cement slurry. The entire sample is then cured for 7-10 days. The rubber casing 1 is wrapped with cement slurry for cementing, which can completely fix the rubber casing 1 and ensure that it can only move in one direction without shaking during subsequent movement.

[0057] In some embodiments, in step S1, the rubber composite sleeve 1 is placed centrally inside the steel pipe 2. That is, the rubber composite sleeve 1 is coaxial with the steel pipe 2 and centrally located inside the steel pipe 2, so as to simulate the centralized state during the process of lowering the rubber composite sleeve 1.

[0058] like Figure 1 As shown, in some embodiments, the length of the rubber composite sleeve 1 is less than the length of the steel pipe 2, and there is a reserved space 20 between the rubber composite sleeve 1 and the inlet end 22. This arrangement ensures that the reserved space 20 allows the first liquid injected into the inlet end 22 to smoothly propel the rubber composite sleeve 1. If the rubber composite sleeve 1 and the steel pipe 2 are of equal length, it increases the risk of the first liquid flowing along the interface between the cement stone 3 and the steel pipe 2, potentially disrupting the interface and leading to errors in the final measurement results.

[0059] Furthermore, in some embodiments, in step S1, before injecting cement slurry into the annulus between the rubber combined sleeve 1 and the steel pipe 2, the reserved space 20 is filled with foam with the same outer diameter as the rubber combined sleeve 1, and the foam is removed after the cement slurry solidifies to form cement stone 3.

[0060] With this setup, on the one hand, the foam body has the same outer diameter as the rubber combined sleeve 1, so that when cement slurry is injected, the foam body can fill the reserved space 20 and prevent the cement slurry from flowing and dispersing into the reserved space 20; on the other hand, the foam body is removable, and after the cement slurry solidifies to form cement stone 3, the foam body can be removed, which will not affect the forming quality of cement stone 3 and will preserve the original function of the reserved space 20.

[0061] Optionally, the length of steel pipe 2 is 1m to 1.5m, and the inner diameter is between 215mm and 220mm to simulate the actual wellbore dimensions. The length of rubber composite casing 1 is 0.5m to 1.2m, the maximum outer diameter thickness is designed to be 165mm to 180mm, the outer diameter of the inner casing is 140mm, and the thickness of the rubber layer is 12.5mm to 20mm to simulate the dimensions of the casing used in the field oil layer. The portion of rubber composite casing 1 smaller than steel pipe 2, i.e., the reserved space 20, is 0.2m to 0.3m in length. For example, if the length of steel pipe 2 is set to 1.5m and the length of rubber composite casing 1 is set to 1.2m, then the length of reserved space 20 is 0.3m. If the outer diameter of the inner casing of rubber composite casing 1 is 140mm and the thickness of the rubber layer is 20mm, then the overall outer diameter of rubber composite casing 1 is 180mm, the inner diameter of steel pipe 2 is set to 220mm, and the thickness of cement stone 3 is 20mm.

[0062] In some embodiments, the method further includes the following steps after step S1 and before step S2:

[0063] A first baffle (not shown in the figure) is fixedly connected to the inlet end 22, and a second baffle (not shown in the figure) is fixedly connected to the outlet end 21. The first baffle is provided with an injection hole, and the second baffle is provided with an outlet hole. A second liquid is injected into the steel pipe 2 through the injection hole, so that the second liquid flows along the interface between the rubber combined sleeve 1 and the cement stone 3 until the second liquid flows out from the outlet hole. Then the second baffle is removed. The removal of the second baffle is for setting a simulated obstacle at the outlet end 21 in the subsequent step S2.

[0064] With this setup, before the rubber sleeve 1 moves, the flow of the second liquid breaks the bonding between the rubber layer and the cement stone 3, thus avoiding the increase in friction caused by the bonding between the rubber layer and the cement stone 3 during the subsequent obstacle encounter simulation, which would affect the final calculation accuracy.

[0065] Optionally, the first baffle and the second baffle can be connected to the steel pipe 2 by welding. It should be noted that when welding the second baffle at the outlet end 21, the second baffle needs to be tightly attached to the inner rubber composite sleeve 1 and the outer steel pipe 2 to limit the displacement of the rubber composite sleeve 1 and prevent the rubber composite sleeve 1 from moving prematurely during the second liquid injection process.

[0066] In some embodiments, the displacement of the second liquid is set to 0.1 m³. 3 / min~0.2m 3 / min, for example, the displacement of the second liquid is 0.1m. 3 / min, 0.15m 3 / min or 0.2m 3 / min. With this setup, a small volume of the second liquid is slowly injected into the steel pipe 2 through the injection hole, ensuring that the second liquid flows slowly along the interface between the rubber combined sleeve 1 and the cement stone 3, effectively relieving the bonding between the rubber combined sleeve 1 and the cement stone 3. If the volume of the second liquid is too large, it may prematurely damage the rubber or cement stone 3.

[0067] It is understandable that the first liquid that propels the rubber sleeve 1 to move can also be injected into the steel pipe 2 through the injection hole.

[0068] In some embodiments, the displacement of the first liquid is set to 0.5 m³. 3 / min~0.8m 3 / min, for example, the displacement of the first liquid is 0.5m 3 / min, 0.6m 3 / min, 0.7m 3 / min or 0.8m 3 / min. By injecting the first liquid at a relatively large displacement, the rubber assembly sleeve 1 can be moved quickly, allowing observation of the damage pattern when the rubber encounters resistance and calculation of frictional resistance. If the displacement of the first liquid is too small, the first liquid tends to flow along the interface between the rubber assembly sleeve 1 and the cement stone 3, failing to move the rubber assembly sleeve 1.

[0069] Optionally, the first liquid and the second liquid may include, but are not limited to, water.

[0070] In some embodiments, the simulation evaluation method for obstruction encountered by the lower casing of the rubber composite casing further includes temperature treatment. Temperature treatment specifically includes:

[0071] In step S1, when the cement slurry has not solidified, resistance wire is wrapped around the outer circumference of the steel pipe 2 to heat it to the preset temperature and then keep it warm. After step S1, the simulated sample 10 is kept at the preset temperature.

[0072] For example, when the cement slurry has not solidified, resistance wire is wrapped around the outer circumference of the steel pipe 2 and heated to a preset temperature, which is between 90°C and 150°C. This temperature is then maintained for 4 to 6 hours to ensure sufficient heat transfer, allowing the simulated sample 10 to reach the same internal temperature. For example, the preset temperature is set to 100°C, and then maintained for 5 hours. Furthermore, after step S1, the simulation processes, including the breakdown of the interface between the rubber composite sleeve 1 and the cement stone 3, and the resistance encounter simulation of the rubber composite sleeve 1, are all maintained at the preset temperature by heating with resistance wire.

[0073] With this setup, temperature processing helps simulate the high-temperature environment of the formation, ensuring that the rubber casing 1 is under similar temperature and thermodynamic conditions as the actual downhole conditions during the experiment, which helps to make the final data more closely resemble the real downhole situation.

[0074] like Figure 2 As shown, in some embodiments, the simulated obstruction is set as an obstruction block 4 to simulate point contact obstruction of the rubber composite sleeve 1. In specific implementation, the point contact obstruction can be simulated by partially welding the obstruction block 4 onto the steel pipe 2. In this way, the point contact obstruction scenario during the lowering process of the rubber composite sleeve 1 can be accurately reproduced.

[0075] For point-contact obstruction scenarios, different point-contact schemes can be designed based on various possible situations in actual downhole contact. Optionally, the obstruction block 4 includes at least one of a triangular block 41, a rectangular block 42, an annular block 43, and a sawtooth block 44. Different shapes of obstruction blocks 4 can specifically simulate different point-contact scenarios in the well (e.g., triangular block 41 simulates sharp protrusions, annular block 43 simulates localized annular obstacles, etc.), comprehensively reproducing the diversity of actual obstruction, making the simulation results more consistent with various real working conditions, and improving the comprehensiveness of the evaluation.

[0076] Various shapes of obstruction blocks 4 can be set with different heights (i.e., the distance the obstruction block 4 extends radially inward along the steel pipe 2), which can be designed according to the required rubber embedding depth. Taking the size of the simulated sample 10 mentioned above as an example, due to the thickness of the rubber layer, a maximum embedding thickness of 20 mm can be achieved.

[0077] like Figure 3 As shown, in some embodiments, the simulated obstruction is set as an obstruction ring 5 to simulate the obstruction caused by the reduction in diameter of the rubber composite casing 1. In specific implementation, the obstruction ring 5 can be welded along the circumference of the steel pipe 2 to reduce the inner diameter of the steel pipe 2, simulating the situation of the wellbore diameter being reduced in the field. Taking the size of the simulated sample 10 mentioned above as an example, the reduced inner diameter of the steel pipe 2 is between 140mm and 180mm.

[0078] This configuration allows the simulation and evaluation method for obstruction during casing installation provided in this embodiment to further assess the damage morphology of the rubber in the rubber composite casing 1 under different obstruction modes and the additional frictional resistance during casing installation. This enables on-site guidance to predict obstruction modes based on the actual increase in additional frictional resistance during casing installation, and to obtain the damage morphology of the rubber under different obstruction modes. This allows for timely monitoring of the installation status of the rubber composite casing 1, preventing rubber detachment and blockage of the wellbore, thus avoiding wellbore safety risks. Furthermore, based on different frictional resistance increments, different embedding depths of the obstruction block 4 or obstruction ring 5 can be correlated with different rubber damage morphologies, forming a graded early warning mechanism. For different damage characteristics, it can guide the analysis of critical safety thresholds for parameters such as rubber layer thickness and hardness, providing a basis for the selection of rubber materials and the design of structural parameters such as thickness and morphology of the rubber composite casing 1.

[0079] For example, such as Figure 4 The figure shows the friction curves under different obstruction modes obtained from the experiment. As can be seen from the figure, the overall friction caused by obstruction due to reduced diameter is higher than that caused by point contact obstruction. Furthermore, the peak friction of obstruction due to reduced diameter is higher and lasts longer, while the friction of point contact obstruction is relatively gentler. These curves visually present the differences in mechanical response under different obstruction modes. Combined with the aforementioned simulation scheme of obstruction block 4 and obstruction ring 5, the stress and failure characteristics of the rubber composite casing 1 under complex working conditions can be analyzed more accurately, providing data reference for obstruction judgment and casing optimization design in downhole construction.

[0080] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A simulation evaluation method for obstruction encountered by the lower casing of a rubber composite sleeve, characterized in that, include: S1. Place the sealed rubber combination sleeve (1) inside the steel pipe (2), inject cement slurry into the annular space between the rubber combination sleeve (1) and the steel pipe (2), and let the cement slurry solidify to form cement stone (3) to obtain a simulated sample (10). S2. A simulated obstacle is set at the outlet end (21) of the steel pipe (2). The simulated obstacle extends radially inward along the steel pipe (2) and can contact the rubber layer of the rubber composite sleeve (1). A first liquid is injected into the steel pipe (2) at the inlet end (22) of the steel pipe (2) so that the first liquid pushes the rubber composite sleeve (1) to move axially toward the outlet end (21) relative to the cement stone (3), and the first frictional resistance of the rubber composite sleeve (1) is calculated. S3. Repeat steps S1 to S2. When repeating step S2, do not set the simulated obstacle to calculate the second frictional resistance between the rubber combined sleeve (1) and the cement stone (3) when the rubber combined sleeve (1) moves.

2. The simulation evaluation method for obstruction encountered by the lower casing of the rubber composite sleeve according to claim 1, characterized in that, The steps following step S1 and before step S2 include: A first baffle is fixedly connected to the inlet end (22), and a second baffle is fixedly connected to the outlet end (21). The first baffle is provided with an injection hole, and the second baffle is provided with an outlet hole. A second liquid is injected into the steel pipe (2) through the injection hole so that the second liquid flows along the interface between the rubber combined sleeve (1) and the cement stone (3) until the second liquid flows out from the outlet hole; then the second baffle is removed.

3. The simulation evaluation method for obstruction encountered by the lower casing of the rubber composite sleeve according to claim 2, characterized in that, The simulation evaluation method for the obstruction encountered by the lower casing of the rubber composite sleeve also includes temperature treatment; the temperature treatment specifically includes: In step S1, when the cement slurry has not solidified, resistance wire is wound around the outer circumference of the steel pipe (2) to heat it to a preset temperature and then keep it warm. After step S1, the simulated sample (10) is kept at the preset temperature.

4. The simulation evaluation method for obstruction encountered by the lower casing of the rubber composite sleeve according to claim 1, characterized in that, The simulated obstruction is set as an obstruction block (4) to simulate point contact obstruction of the rubber composite sleeve (1).

5. The simulation evaluation method for obstruction encountered by the lower casing of the rubber composite sleeve according to claim 4, characterized in that, The obstruction block (4) includes at least one of a triangular block (41), a rectangular block (42), a ring block (43), and a sawtooth block (44).

6. The simulation evaluation method for obstruction encountered by the lower casing of the rubber composite sleeve according to claim 1, characterized in that, The simulated obstruction is set as an obstruction ring (5) to simulate the narrowing obstruction of the rubber composite sleeve (1).

7. The simulation evaluation method for obstruction encountered by the lower casing of the rubber composite sleeve according to claim 1, characterized in that, The length of the rubber composite sleeve (1) is less than the length of the steel pipe (2), and there is a reserved space (20) between the rubber composite sleeve (1) and the inlet end (22).

8. The simulation evaluation method for obstruction encountered by the lower casing of the rubber composite sleeve according to claim 7, characterized in that, In step S1, before injecting the cement slurry into the annulus between the rubber combined sleeve (1) and the steel pipe (2), the reserved space (20) is filled with foam with the same outer diameter as the rubber combined sleeve (1). After the cement slurry solidifies to form the cement stone (3), the foam is removed.

9. The simulation evaluation method for obstruction encountered by the lower casing of the rubber composite sleeve according to claim 1, characterized in that, In step S1, the rubber composite sleeve (1) is placed centrally inside the steel pipe (2).

10. The simulation evaluation method for obstruction encountered by the lower casing of the rubber composite sleeve according to claim 2, characterized in that, The displacement of the first liquid is set to 0.5m. 3 / min~0.8m 3 / min; the displacement of the second liquid is set to 0.1m. 3 / min~0.2m 3 / min.

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