Casing pipe structure for preventing casing pipe from moving upwards during fracturing

Abstract

The utility model discloses a casing pipe structure for preventing casing pipes from moving upwards during fracturing, which comprises a production casing pipe arranged in a stratum, the lower portion of the production casing pipe is fixed in the stratum through well cementation cement, the periphery of the upper portion of the production casing pipe is sleeved with a surface casing pipe, the axis of the surface casing pipe coincides with that of the production casing pipe, and the upper edge of the surface casing pipe is flush with the ground. The surface casing is fixed in a stratum through well cementation cement, the upper end of the production casing is upwards pre-stretched by a certain height, and an annular steel plate is welded and fixed between the surface casing and the production casing. According to the casing pipe structure, the underground stability and sealing performance of the casing pipe can be guaranteed, the problem that the free section of the casing pipe deforms in the fracturing process is solved, a better pressure bearing environment is provided for fracturing, potential safety hazards caused by the upward moving problem of the casing pipe to fracturing are solved, and the fracturing success rate is increased.

Description

TECHNICAL FIELD

[0001] The utility model belongs to coal bed gas drilling technology field, and particularly relates to a casing structure for preventing casing channeling during fracturing. BACKGROUND

[0002] Coal bed gas well usually adopts casing perforation completion mode, cementing is needed after production casing is lowered into the well, cement return depth is designed to be 200 meters above the target coal bed, and the purpose is to seal and fix the production layer and aquifer and ensure normal fracturing construction.

[0003] After existing casing cementing, part of the free section casing is in a curved state due to the influence of self weight, and the wellhead is only fixed by spot welding of the annular steel plate, on the one hand, the pipe body is easy to be damaged, and on the other hand, during the fracturing process of the coal bed gas well, the casing is mainly in tensile deformation, the deformation point has the distribution characteristics of continuously increasing from the toe end to the heel end, and the deformation of part of the position continuously intensifies with time, the free section casing is easy to be elongated due to stress during the fracturing process, which leads to casing channeling and causes the fracturing construction to be unable to be normally carried out. CONTENT OF THE UTILITY MODEL

[0004] In order to solve the technical problem that the casing channeling is caused by the elongation of the free section casing due to stress deformation during the fracturing process, the utility model provides a casing structure for preventing casing channeling during fracturing.

[0005] The utility model adopts the following technical scheme: a casing structure for preventing casing channeling during fracturing, comprising a production casing arranged in the stratum, the lower part of the production casing is fixed in the stratum by cementing, the outer periphery of the upper part of the production casing is sleeved with a surface casing, the axis of the surface casing coincides with that of the production casing, the upper edge of the surface casing is flush with the ground, the surface casing is fixed in the stratum by cementing, the upper end of the production casing is pre-tensioned to a certain height upward, and an annular steel plate is welded and fixed between the surface casing and the production casing.

[0006] Further, the pre-tensioning height of the production casing is 30 cm.

[0007] Further, the upper end of the production casing is connected with a jointing section.

[0008] Further, the jointing section is connected with a drilling machine for pre-tensioning.

[0009] The casing structure of the utility model adopts the pre-tensioning of the casing to be seated on the annular steel plate, through the pre-tensioning, the stress change caused by the temperature and pressure change of the casing in the well can be balanced, so as to reduce the damage of the casing caused by stress concentration. Meanwhile, the pre-tensioning is helpful to the formation of the closer contact between the casing and the annular steel plate, so as to improve the sealing performance of the casing, and the mode is more firm than the original spot welding of the hoop and the annular steel plate.

[0010] The free section casing deformation problem in the fracturing process can be solved, a better pressure bearing environment for fracturing is provided, the safety hidden danger caused by the casing channeling problem to fracturing is solved, and the fracturing success rate is improved. The casing stability in the subsequent fracturing construction process is ensured, and the method has important theoretical and engineering significance for improving the safety of fracturing construction. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is the structural schematic diagram of the casing structure of the utility model;

[0012] Figure 2 is the structural schematic diagram of the casing before pre-stretching in the production of the utility model;

[0013] Figure 3 is the structural schematic diagram of the casing in the production of the utility model.

[0014] In the drawing: 1-ground, 2-production casing, 3-surface casing, 4-production casing cementing surface, 5-cementing cement, 6-production casing movable section, 7-formation, 8-production casing out of surface casing distance, 9-annular steel plate, 10-production casing pulling distance, 11-union top section, 12-drilling machine. DETAILED DESCRIPTION

[0015] In order to better understand the purpose, structure and function of the utility model, the casing structure for preventing casing channeling during fracturing will be further described in detail below in combination with the drawings.

[0016] As shown in Figure 1 , a casing structure for preventing casing channeling during fracturing, comprising a production casing 2 placed in the formation, the lower part of the production casing 2 is fixed in the formation 7 by cementing cement 5, the upper part of the production casing 2 is sleeved with a surface casing 3, the surface casing 3 coincides with the axis of the production casing 2, and the upper edge of the surface casing 3 is flush with the ground 1, the surface casing 3 is fixed in the formation 7 by the cementing cement 5, the upper end of the production casing 2 is pre-stretched to a certain height, and the annular steel plate 9 is welded and fixed between the surface casing 3 and the production casing 2.

[0017] As shown in Figure 2 , in the embodiment, before pre-stretching, the production casing 2 slightly lower or flush with the surface casing 3 after being lowered into the wellbore. Then, the cementing joint is connected, and the cementing operation is carried out, and after the cementing is completed according to the design requirement, the waiting time is more than 48 hours. The section above the production casing cementing surface 4 of the production casing 2 is the casing free end, and the lower part of the casing free end is in a curved state under the influence of gravity to form a production casing movable section 6.

[0018] As shown in Figure 3As shown, in the embodiment, the jointing section 11 is installed on the production casing 2, the jointing section 11 is connected with the drilling machine 12, the jointing section 11 is lifted by the drilling machine 12 to pre-tension the free section of the casing in the well, the lifting height is preferably 30 cm more than the production casing pulling distance 10 of the surface casing 3, and the production casing 2 is ensured to be centered in the surface casing 3, after the annular steel plate 9 is welded between the surface casing 3 and the production casing 2, the pre-tensioned production casing 2 is slowly lowered until the upper end collar of the production casing 2 is tightly seated on the annular steel plate 9, the production casing 2 has a certain distance of the production casing out of the surface casing distance 8, finally, the jointing section 11 is disassembled, the wellhead cap is installed, and the pre-tensioning of the production casing 2 is completed.

[0019] The casing structure of the utility model can ensure the stability and sealing property of the casing in the well, solve the deformation problem of the free section casing in the fracturing process, provide a better pressure bearing environment for the fracturing, solve the safety hidden danger caused by the casing channeling problem to the fracturing, and improve the fracturing success rate.

[0020] It can be understood that the utility model is described through some embodiments, and those skilled in the art know that various changes or equivalent replacements can be made to these features and embodiments without departing from the spirit and scope of the utility model. In addition, these features and embodiments can be modified to adapt to specific conditions and materials under the guidance of the utility model without departing from the spirit and scope of the utility model. Therefore, the utility model is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the application belong to the scope protected by the utility model.

Claims

1. A casing structure to prevent casing from shifting upwards during fracturing, characterized in that, The production casing (2) is placed in the formation (7). The lower part of the production casing (2) is fixed in the formation (7) by cementing cement (5). A surface casing (3) is fitted around the upper outer periphery of the production casing (2). The axis of the surface casing (3) coincides with that of the production casing (2), and the upper edge of the surface casing (3) is flush with the ground (1). The surface casing (3) is fixed in the formation (7) by cementing cement (5). The upper end of the production casing (2) is pre-stretched upward to a certain height. A ring steel plate (9) is welded and fixed between the surface casing (3) and the production casing (2).

2. The casing structure for preventing casing upward movement during fracturing according to claim 1, characterized in that, The pre-stretch height of the production sleeve (2) is 30cm.

3. The casing structure for preventing casing slippage during fracturing according to claim 1 or 2, characterized in that, The upper end of the production sleeve (2) is connected to the top joint (11).

4. The casing structure for preventing casing upward movement during fracturing according to claim 3, characterized in that, The top joint (11) is connected to the drilling rig (12) for pre-stretching.

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