A cement sheath crushing and sectioning method

Abstract

The present application relates to oilfield workover process technical field, especially a kind of cement sheath broken segmented sleeve taking process method.This cement sheath broken segmented sleeve taking process method includes the following steps: first, breakage tool is lowered into casing extrusion casing to make cement sheath broken separation;Then change the position of breakage tool and repeat extrusion casing;Next, casing cutter is lowered into casing and cut casing along the circumference again, and the cut casing is fished to wellhead until the casing of target well section is all fished and recovered;Finally, cement scraping tool is lowered to clean the residual cement of surface casing inner wall.The cement sheath broken segmented sleeve taking process method proposed in the present application, by extruding casing to break cement sheath first, then cutting casing and fishing, when fishing tool mills cement sheath during casing fishing work, the resistance generated by broken cement sheath is reduced, avoiding the occurrence of milling no footage and milling losing fish phenomenon during fishing process, improving the efficiency of sleeve taking work and shortening the working time.

Description

Technical Field

[0001] This invention relates to the field of oilfield well workover technology, and in particular to a method for segmented removal of cement sheaths by crushing them. Background Technology

[0002] During oilfield operation, production wells are prone to casing damage after prolonged operation. The best solution is to work over the damaged well. Current technology primarily relies on conventional PDC milling heads and milling barrels to reach the damaged area and retrieve the casing. However, this method of milling the cement sheath is inefficient. When the retrieval tool contacts the cement sheath during milling, excessive milling speed or force can lead to excessive resistance from the cement sheath, affecting the tool's operation and resulting in poor cement sheath fragmentation. This can easily lead to insufficient milling progress and lost casing in the cement-sealed section, prolonging the downhole casing retrieval process and reducing efficiency. Therefore, to address these shortcomings, a segmented cement sheath fragmentation method for casing retrieval is proposed. Summary of the Invention

[0003] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a process and apparatus for crushing and segmenting cement rings, which solves the problems of low working efficiency and poor crushing degree in the existing method of milling cement rings, resulting in milling failure and loss of material during milling in the cement-sealed section inside the surface layer.

[0004] (II) Technical Solution To address the above problems, this invention provides a method for segmented crushing and sheath removal of cement rings, comprising: Step S1: After lowering the breaking tool into the casing to the specified depth, drive the breaking tool to squeeze the casing at the target location to break and separate the cement ring on the outer wall of the casing. Step S2: Eliminate the working pressure of the breaking tool, change the position of the breaking tool and repeat step S1 until the cement sheath outside the target well section is completely broken. Step S3: After removing the breaking tool, insert the casing cutter into the casing and cut the casing circumferentially. Step S4: Lower the casing retrieval tool to retrieve the cut casing to the wellhead; Step S5: Lower the casing cutter and repeat steps S3 and S4 until all the casing in the target well section is retrieved and recovered. Step S6: Use a cement scraper to clean the residual cement on the inner wall of the surface casing.

[0005] Furthermore, in step S1, the depth to which the breaking tool is inserted into the casing is 3-5m above the bottom corner of the surface casing.

[0006] Furthermore, in step S2, the breaking tool moves from bottom to top during operation, and the distance it moves each time is the length of the breaking tool.

[0007] Furthermore, when the breaking tool is compressing the sleeve, it performs multiple compressions along the circumferential direction at the same height to completely compress the sleeve at the same height.

[0008] Furthermore, in step S5, the distance by which the casing cutter moves downward is determined based on the casing deformation.

[0009] Furthermore, in step S6, circulating well-washing fluid needs to be injected into the well when cleaning residual cement.

[0010] Furthermore, in step S6, a solids control system is installed at the wellhead. After the circulating well-washing fluid flows out from the well, it flows through the solids control system to remove impurities and filter them before being reinjected into the well.

[0011] Furthermore, in step S6, when cleaning the residual cement, it is necessary to change the cement scraper tool with different working diameters multiple times to clean the residual cement.

[0012] (III) Beneficial Effects The cement sheath fragmentation and segmented casing retrieval method provided by this invention involves first lowering a crushing tool into the well to compress the casing, causing it to vibrate and deform, thereby breaking and separating the cement sheath on the outer wall of the casing. Then, a casing cutter is used to divide the casing into several segments, which are then retrieved segment by segment. This significantly reduces the resistance of the already broken cement sheath to the retrieval tool when milling the cement sheath outside the casing during casing retrieval. This avoids the occurrence of insufficient milling depth and lost casing due to excessive resistance from the cement sheath during milling, thereby improving the efficiency of cement sheath segment retrieval and well workover operations and reducing the difficulty of the retrieval work. Attached Figure Description

[0013] Figure 1 This is a flowchart of the cement ring crushing and segmented sleeve removal process of the present invention; Figure 2 This is a schematic diagram of the action of the breaking tool in the cement ring crushing and segmented removal process of the present invention. Detailed Implementation

[0014] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] In the description of this invention, it is necessary to understand that the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "outer", "top", and "bottom" are based on the orientation or positional relationship shown in the accompanying drawings. The purpose is only to facilitate the description of this invention and to simplify the description. It is not intended to indicate or imply that the component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0016] like Figure 1-2 As shown, the present invention provides a process for segmented crushing and sheath removal of cement rings, specifically including: Step S1: After lowering the breaking tool into the casing to the specified depth, drive the breaking tool to squeeze the casing at the target location to break and separate the cement ring on the outer wall of the casing.

[0017] After the breaking tool is lowered to the designated depth inside the casing, power is supplied to it to actuate. The output end of the breaking tool applies pressure to the inner wall of the casing. This pressure is simultaneously transmitted outward through the inner wall to the cement ring outside the casing. As the pressure increases, the inner wall of the casing gradually deforms and squeezes the cement ring. Under this pressure, the cement ring gradually breaks apart. Simultaneously, the crushing process generates vibrations, which are transmitted upwards and downwards along the cement ring. Cement rings that have not yet been squeezed gradually loosen under the influence of these vibrations, weakening their connection to the outer wall of the casing and improving the success rate and efficiency of subsequent casing recovery. When the cement ring is subjected to pressure, it gradually breaks apart when the pressure exceeds the bearing limit of the cement ring. At this point, the cement ring is almost completely separated from the outer wall of the casing, with only a small amount of cement adhering to the outer wall of the casing. When the casing is recovered, the bonding force between the cement ring and the outer wall of the casing is reduced, which reduces the operational difficulty of the subsequent casing recovery work.

[0018] Step S2: Eliminate the working pressure of the breaking tool, change the position of the breaking tool and repeat step S1 until the cement sheath outside the target well section is completely broken.

[0019] By continuously changing the position of the breaking tool, the cement sheath outside the target well section is completely crushed. The adhesion of the cement sheath inside the target well section to the casing nearly disappears, leaving only a small amount of residual cement adhering to the outer wall of the casing. In this state, retrieving the casing only requires overcoming the casing's own weight and the friction between the residual cement and the crushed cement sheath, thus significantly reducing the workload and difficulty of casing recovery and improving its efficiency. Typically, hydraulic breaking tools such as hydraulic breakers or hydraulic picks are used. During operation, after the breaking tool is lowered into the casing, its output end acts on the inner wall of the casing. Injecting pressurized fluid into the breaking tool serves as its power source, driving its action to crush the inner wall of the casing.

[0020] To ensure safe operation during the crushing of the cement sheath, the breaking tool typically crushes the inner wall of the casing and the cement sheath from bottom to top within the target well section. Once the outer cement sheath of the casing within the target well section is completely crushed, the breaking tool simultaneously reaches the wellhead. At this point, the breaking tool can be directly removed from the wellhead, and other downhole tools can be lowered into the wellhead for subsequent operations, saving time during casing retrieval. Simultaneously, the crushed cement sheath will deposit downwards under gravity. Crushing the cement sheath from top to bottom causes the weight of the already crushed cement sheath above to accumulate on the bottom cement sheath. The bottom cement sheath, under the weight and accumulation of the upper cement sheath, crushes the outer wall of the casing. This increased adhesion of the cement sheath at the bottom of the target well section to the outer wall of the casing increases the difficulty of retrieval of the casing at the bottom of the target well section. Typically, the initial working position of the breaking tool in step S1 is 3-5m above the bottom corner of the inner surface casing within the target well section. In actual work, the initial working position of the breaking tool can be adjusted according to different site conditions and work requirements.

[0021] It is important to note that in step S2, the breaking tool moves from bottom to top during operation, and the distance it moves each time is equal to the length of the breaking tool. Dividing the casing into several segments based on the length of the breaking tool ensures that the breaking tool completely breaks the cement sheath outside the target well section during its working process, while also reducing the time spent breaking the cement sheath. During operation, if the distance the breaking tool moves each time is greater than its length, a "safe zone" without complete crushing will exist between adjacent working positions of the breaking tool, preventing the cement sheath outside the casing from being completely broken and increasing the difficulty of casing recovery. If the distance the breaking tool moves is less than its length, there will be too many working positions of the breaking tool during the cement sheath breaking process, leading to a longer working time for breaking the cement sheath and reducing the efficiency of casing recovery. However, in actual work, the force applied by the breaking tool in a single action during the crushing of the cement ring varies along the range of action of the cement ring depending on factors such as the type of breaking tool used, the force application area of ​​the output end, the magnitude of the output force, and the shape of the output end. Workers can adjust the moving distance of the breaking tool in the casing according to the various parameters of the breaking tool used so that the pressure of the breaking tool can be transmitted to all corners of the cement ring outside the casing, so that the cement ring can be completely broken and separated.

[0022] In addition, to improve the crushing effect on the cement ring and prevent any uncrushed parts from remaining, the crushing tool performs multiple compressions along the circumference at the same height while compressing the casing, completely crushing the casing at that height. Generally, at the same height, the crushing tool rotates 120° circumferentially after each compression and performs another compression, repeating this process twice. This results in three evenly distributed compression points along the circumference within the same height on the inner wall of the casing, ensuring complete crushing and separation of the cement ring outside the casing at that height. In actual operation, the number and angle of the compression points within the same height can be adjusted according to the working parameters of the crushing tool and the casing size.

[0023] Step S3: After removing the breaking tool, insert the casing cutter into the casing and cut the casing circumferentially.

[0024] After the casing cutter is inserted into the casing, it cuts the casing circumferentially. Since the cement ring outside the casing has been squeezed and broken apart, the cut casing can be directly retrieved from the wellhead by the retrieval equipment.

[0025] Step S4: Lower the casing retrieval tool to retrieve the cut casing to the wellhead.

[0026] After the casing is cut, the casing retrieval tool immediately retrieves the cut-off casing from the wellhead. Since the casing being retrieved is the cut-off portion, the frictional force generated by the residual cement on the outer wall of the casing during retrieval is negligible, thus reducing the difficulty of the retrieval process. Because the cement ring outside the casing has already been crushed and separated before retrieval, the casing retrieval tool only needs to apply a tangential force to the cement ring during the milling drilling operation to remove the broken cement ring. The resistance generated by the broken cement ring on the rotation of the milling head during milling is greatly reduced, thus avoiding the occurrence of insufficient milling depth and lost casing due to excessive resistance from the cement ring during milling. This improves the stability and efficiency of the casing retrieval operation.

[0027] Step S5: Lower the casing cutter, repeating steps S3 and S4 until all the casing in the target well section is retrieved. This workflow of retrieving the cut casing from the wellhead before proceeding with the next cut avoids the accumulation of cut casing in the well, which could negatively impact subsequent casing retrieval. Generally, each section of casing cut is 3-5 meters in length. During casing retrieval, the casing may tilt or deform over time. Therefore, the distance the casing cutter should be lowered depends on the casing deformation. Greater deformation and tilt require a shorter lowering distance to ensure the cut casing is nearly vertical, reducing the difficulty of subsequent retrieval.

[0028] Step S6: Lower a cement scraper to clean the residual cement from the inner wall of the surface casing. Typically, the casing retrieved during operation is the oil layer casing, with an additional oil-free layer casing surrounding it. The cement sheath is located between the oil layer casing and the oil-free layer casing. After retrieving the oil layer casing, some residual cement sheath adheres to the inner wall of the oil-free layer casing. At this point, a cement scraper is needed to clean the residual cement from the inner wall of the oil-free layer casing to provide conditions for normal production operations of the oil well. To remove residual cement from the well, circulating well-washing fluid is injected into the well during the cleaning process in step S6. The circulating well-washing fluid circulates within the well under the action of the wellhead drive device, carrying away the scattered and cleaned residual cement from the wellhead, thereby maintaining the cleanliness of the well.

[0029] In step S6, a solids control system is installed at the wellhead. The circulating well-washing fluid flows out of the well and passes through the solids control system to remove and filter impurities before being reinjected into the well. The solids control system filters and removes solid impurities such as cement particles carried in the circulating well-washing fluid, preventing these impurities from flowing back into the well and causing secondary pollution. The solids control system typically includes a vibrating screen, a desander, and a centrifuge. The circulating well-washing fluid, carrying impurities, flows sequentially through these three components. Through their combined action, solid impurities are removed from the circulating well-washing fluid, improving its ability to remove cement solids and viscous phases, ensuring stable performance and cleaning efficiency, and increasing its working efficiency during the cleaning process.

[0030] In step S6, when cleaning residual cement, it is necessary to change cement scraping tools with different working diameters multiple times to clean the residual cement. During the cleaning process, a cement scraper with a smaller working diameter is usually used first to clean the residual cement in the well. Then, the cement scraper is gradually replaced with a larger diameter tool to clean the residual cement. By using cement scrapers of different working diameters in sequence from small to large, the cleaning efficiency of the residual cement in the well can be maximized. This prevents the cement scraper from being damaged by excessive resistance when it comes into contact with the residual cement after directly lowering a large working diameter tool, thus improving the stability and efficiency of the device during cement scraping.

[0031] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit 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 spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for segmented crushing and sheath removal of cement rings, characterized in that, Includes the following steps: Step S1: After lowering the breaking tool into the casing to the specified depth, drive the breaking tool to squeeze the casing at the target location to break and separate the cement ring on the outer wall of the casing. Step S2: Eliminate the working pressure of the breaking tool, change the position of the breaking tool and repeat step S1 until the cement sheath outside the target well section is completely broken. Step S3: After removing the breaking tool, insert the casing cutter into the casing and cut the casing circumferentially. Step S4: Lower the casing retrieval tool to retrieve the cut casing to the wellhead; Step S5: Lower the casing cutter and repeat steps S3 and S4 until all the casing in the target well section is retrieved and recovered. Step S6: Use a cement scraper to clean the residual cement on the inner wall of the surface casing.

2. The cement ring crushing and segmented removal process according to claim 1, characterized in that, In step S1, the depth to which the breaking tool is inserted into the casing is 3-5m above the bottom corner of the surface casing.

3. The method for segmented crushing and sheath removal of cement rings according to claim 1, characterized in that, In step S2, the breaking tool moves from bottom to top during operation, and the distance it moves each time is the length of the breaking tool.

4. The method for segmented crushing and sheath removal of cement rings according to any one of claims 1-3, characterized in that, When the crushing tool is crushing the sleeve, it performs multiple crushing operations along the circumferential direction at the same height to completely crush the sleeve at the same height.

5. The method for segmented crushing and sheath removal of cement rings according to claim 1, characterized in that, In step S5, the distance the casing cutter moves downward is determined based on the casing deformation.

6. The method for segmented crushing and sheath removal of cement rings according to claim 1, characterized in that, In step S6, circulating well-washing fluid needs to be injected into the well when cleaning residual cement.

7. The cement ring crushing and segmented sleeve removal process according to claim 6, characterized in that, In step S6, a solids control system is installed at the wellhead. After the circulating well washing fluid flows out from the well, it flows through the solids control system to remove impurities and filter the fluid before re-injecting it into the well.

8. The cement ring crushing and segmented sleeve removal process according to claim 7, characterized in that, In step S6, when cleaning the residual cement, it is necessary to change the cement scraper tool with different working diameters multiple times to clean the residual cement.

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