Double-layer combined casing and assembly method thereof

Abstract

The invention discloses a double-layer combined casing structure, comprising an internal threaded coupling joint and an external threaded coupling joint, an outer casing and an inner casing; the two ends of the outer casing are respectively threadedly connected with the internal threaded coupling joint and the external threaded coupling joint to achieve the sealing performance and connection performance of the casing, one end of the inner casing is connected with the internal threaded coupling joint in a threaded connection manner, and the other end is inserted into the inner hole groove of the external threaded coupling joint; at the same time, its assembly method is disclosed, and the invention can effectively solve the processing and assembly problems of the double-layer combined casing, make the double-layer combined casing structure stable and reliable, effectively improve the plastic deformation resistance of the inner casing, thereby improving the external extrusion strength of the entire double-layer combined casing, and is particularly suitable for shale gas horizontal section oil layer casing that requires multiple fracturing operations; during the service process, the drilling fluid enters the annular space to balance the pressure difference between the inner and outer walls of the outer casing, effectively improving the external extrusion resistance of the outer casing.

Description

Technical Field

[0001] The invention belongs to the technical field of casing structure and assembly used in oil and gas field exploration and development, and in particular relates to a double-layer combined casing and an assembly method thereof. Background Art

[0002] With the deepening of production and development of oil fields at home and abroad, most oil fields have experienced varying degrees of casing damage, which has had a great impact on the production and development of oil. Double-layer combined casing is an important means of early protection of casing. At present, most double-layer combined casings adopt the method of cementing between the inner and outer casings, which can improve the casing's anti-squeeze strength. However, in areas with large formation creep, the extrusion force of the formation is directly transmitted to the inner casing through the outer casing and cement ring, causing damage to the inner casing, resulting in the inability to carry out oil production projects. In addition, the construction is complicated and difficult to operate. At the same time, there is no specific assembly method for double-layer combined casing in existing literature and patents. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a double-layer combined casing and an assembly method thereof. The double-layer casing is assembled in the factory, and the well crew only needs to quickly connect the internal threaded coupling joint and the external threaded coupling joint at the operation site, thereby ensuring a safe and efficient casing lowering operation process. At the same time, the casing has high anti-extrusion strength and the inner casing is not easily damaged.

[0004] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is a double-layer combined casing, including an internal threaded coupling joint, an external threaded coupling joint, an outer casing and an inner casing, one end of the external threaded coupling joint connecting the casing is provided with an inner hole groove for connecting the inner casing, and the two ends of the outer casing are respectively connected to the internal threaded coupling joint and the external threaded coupling joint; the first end of the inner casing is provided with an inner casing external thread, the inner casing is threadedly connected with the internal threaded coupling joint through the inner casing external thread, the second end of the inner casing has a flat pipe wall, and the second end of the inner casing is inserted into the inner hole groove of the external threaded coupling joint.

[0005] Both ends of the outer casing are provided with outer casing external threads, and both the internal thread coupling joint and the external thread coupling joint are provided with internal threads for connecting the outer casing, and the two ends of the outer casing are respectively threadedly connected with the internal thread coupling joint and the external thread coupling joint.

[0006] The length of the outer casing is shorter than that of the inner casing.

[0007] An annular space is provided between the outer casing and the inner casing.

[0008] A gap is arranged between the end surface of the inner casing connected to the external thread coupling joint and the end surface of the inner hole groove.

[0009] The annular space is communicated with the inner side of the inner casing.

[0010] The assembly method of the double-layer combined casing of the present invention comprises the following steps:

[0011] The first end of the inner casing is connected to the internal threaded coupling joint;

[0012] One end of the outer casing is connected to the internal thread coupling joint;

[0013] The other end of the outer casing is connected to the external thread coupling joint, and the second end of the inner casing is inserted into the inner hole groove of the external thread coupling joint.

[0014] The internal thread of the internal thread coupling joint is connected with the external thread of the external thread coupling joint to form a double-layer combined casing string.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: the assembly of a single double-layer casing is carried out in the production plant, ensuring the assembly accuracy and quality reliability. The outer casing is connected to the internal threaded coupling joint and the external threaded coupling joint by threads, which effectively ensures the connection strength and sealing performance of the double-layer casing; one end of the inner casing is threadedly connected to the internal threaded coupling joint, and the other end is inserted into the inner hole slot of the external threaded coupling joint, which effectively ensures the structural integrity of the double-layer casing. During field operations, the internal threaded coupling joint and the external threaded coupling joint are tightly connected by threads, which is the same as the conventional casing lowering method, ensuring safe, efficient and timely casing lowering operations. At the same time, since a gap is provided between the end face of the inner casing connected to the external threaded coupling joint and the end face of the inner hole slot, during the service process, the drilling fluid enters the annular space gap, balances the pressure difference between the inner and outer walls of the outer casing, and effectively improves the anti-external extrusion strength of the outer casing; in addition, the double-layer combined casing of the present invention also has the advantages and characteristics of simple, convenient, reliable assembly method and high production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of the present invention;

[0017] Figure 2 It is a schematic diagram of the structure of the internal thread coupling joint of the present invention;

[0018] Figure 3 It is a schematic diagram of the structure of the external threaded coupling joint of the present invention;

[0019] Figure 4 It is a schematic diagram of the outer sleeve structure of the present invention;

[0020] Figure 5 It is a schematic diagram of the inner sleeve structure of the present invention.

[0021] 1-internal thread coupling joint, 2-external thread coupling joint, 3-outer casing, 4-inner casing, 11-connecting internal thread of joint, 12-connecting thread of inner casing, 13-connecting thread of outer casing, 21-external thread of joint, 22-internal thread of external coupling joint, 23-inner hole slot, 41-external thread of inner casing, 31-external thread of outer casing; DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to the accompanying drawings and specific implementation modes.

[0023] like Figure 1 As shown, a double-layer combined casing comprises an internal threaded coupling joint 1, an external threaded coupling joint 2, an outer casing 3 and an inner casing 4. One end of the external threaded coupling joint 2 connected to the casing is provided with an inner hole groove 23 for connecting the inner casing, and the two ends of the outer casing 3 are respectively connected to the internal threaded coupling joint 1 and the external threaded coupling joint 2; the first end of the inner casing 4 is provided with an inner casing external thread 41, the inner casing 4 is threadedly connected to the internal threaded coupling joint 1 through the inner casing external thread 41, and the second end of the inner casing 4 is inserted into the inner hole groove 23 of the external threaded coupling joint 2; both ends of the outer casing 3 are provided with outer casing external threads 31, the internal threaded coupling joint 1 and the external threaded coupling joint 2 are both provided with internal threads for connecting the outer casing 3, and the two ends of the outer casing 3 are respectively threadedly connected to the internal threaded coupling joint 1 and the external threaded coupling joint 2.

[0024] like Figure 2 As shown, one end of the internal threaded coupling joint 1 is provided with a coupling connecting internal thread 11, and one end of the internal threaded coupling joint 1 connected to the casing is processed with an inner casing connecting thread 12 and an outer casing connecting thread 13 of different mid-diameters, and the inner casing connecting thread 12 and the outer casing connecting thread 13 are stepped threads.

[0025] like Figure 3 As shown, one end of the external threaded coupling joint 2 is provided with a joint external thread 21, and the joint external thread 21 is used to connect the internal threaded coupling joint 1, and one end of the connecting casing is provided with an external coupling joint internal thread 22 and an inner hole groove 23 for connecting the inner casing 4.

[0026] like Figure 4 As shown, both ends of the outer sleeve 3 are provided with outer sleeve external threads 31;

[0027] like Figure 5 As shown, the first end of the inner sleeve 4 is provided with an inner sleeve external thread 41, and the inner and outer walls of the second end are both flat.

[0028] like Figure 1In the structure shown, there is an annular gap between the inner casing 4 and the outer casing 3 , and the annular gap value is 3-10 mm; the outer casing 3 is 100-150 mm shorter than the inner casing 4 .

[0029] The assembly method of a single double-layer combined casing is as follows:

[0030] The first end of the inner casing 4 is connected to the internal threaded coupling joint 1;

[0031] One end of the outer casing 3 is connected to the internal thread coupling 1;

[0032] The other end of the outer casing 3 is connected to the external thread coupling joint 2, and the second end of the inner casing 4 is inserted into the inner hole groove 23 of the external thread coupling joint 2;

[0033] The double-layer combined casing string is assembled in such a way that the internal thread 11 of the internal thread coupling joint 1 is connected with the external thread 21 of the external thread coupling joint 2 .

[0034] An annular space is formed between the assembled inner casing 4 and the outer casing 3 , and the annular space is communicated with the inner wall annular space of the inner casing 4 .

[0035] The double-layer combined casing assembled by the above-mentioned implementation method ensures the assembly accuracy and quality reliability because the assembly of a single double-layer casing is carried out in the production factory. The outer casing is connected to the internal threaded coupling joint and the external threaded coupling joint by threads, which effectively ensures the connection strength and sealing performance of the double-layer casing. The first end of the inner casing 4 is threadedly connected to the internal threaded coupling joint 1, and the second end of the inner casing 4 is inserted into the inner hole groove 23 of the external threaded coupling joint 2, which effectively ensures the structural integrity of the double-layer casing. During field operations, the internal threaded coupling joint 1 and the external threaded coupling joint 2 are tightly connected by threads, which is the same as the conventional casing lowering method, ensuring safe, efficient and timely casing lowering operations. At the same time, since there is a gap between the end face of the inner casing 4 connected to the external threaded coupling joint 2 and the end face of the inner hole groove 23, during the service process, the drilling fluid enters the annular space gap to balance the pressure difference between the inner and outer walls of the outer casing 3, effectively improving the anti-external extrusion strength of the outer casing. In addition, the double-layer combined casing of the present invention also has the advantages and characteristics of simple, convenient and reliable assembly method and high production efficiency.

Claims

1. A double-layer combined casing, characterized in that: The invention comprises an internal thread coupling joint (1), an external thread coupling joint (2), an outer casing (3) and an inner casing (4); one end of the external thread coupling joint (2) connected to the casing is provided with an inner hole groove (23) for connecting to the inner casing; the two ends of the outer casing (3) are respectively connected to the internal thread coupling joint (1) and the external thread coupling joint (2); the first end of the inner casing (4) is provided with an inner casing external thread (41); the inner casing (4) is connected to the internal thread through the inner casing external thread (41); The threaded coupling joint (1) is threadedly connected, the second end of the inner casing (4) has a flat pipe wall, and the second end of the inner casing (4) is inserted into the inner hole groove (23) of the external threaded coupling joint (2); an annular space gap is provided between the outer casing (3) and the inner casing (4); the annular space gap is connected to the inner side of the inner casing (4); a gap is provided between the end face of the inner casing connected to the external threaded coupling joint and the end face of the inner hole groove, and during service, drilling fluid enters the annular space gap to balance the pressure difference between the inner and outer walls of the outer casing.

2. The double-layer combined casing according to claim 1, characterized in that: Both ends of the outer casing (3) are provided with outer casing external threads (31), the internal thread coupling joint (1) and the external thread coupling joint (2) are both provided with internal threads for connecting the outer casing (3), and the two ends of the outer casing (3) are respectively threadedly connected with the internal thread coupling joint (1) and the external thread coupling joint (2).

3. The double-layer combined casing according to claim 1, characterized in that: The length of the outer sleeve (3) is shorter than the length of the inner sleeve (4).

4. The method for assembling the double-layer combined casing according to claim 1, characterized in that: The assembly process is as follows: The first end of the inner casing (4) is connected to the internal thread coupling joint (1); One end of the outer casing (3) is connected to the internal thread coupling joint (1); The other end of the outer casing (3) is connected to the external thread coupling joint (2), while the second end of the inner casing (4) is inserted into the inner hole groove (23) of the external thread coupling joint (2).

5. The method for assembling the double-layer combined casing according to claim 4, characterized in that: The joint connection internal thread (11) of the internal thread coupling joint (1) is connected with the joint external thread (21) of the external thread coupling joint to form a double-layer combined casing string.

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