CN110821415A - Combined casing pipe nipple for well cementation and well cementation method - Google Patents

Abstract

The invention discloses a combined casing short joint for well cementing and a cementing method. The combined casing short joint for well cementing is composed of a hollow casing short joint body and an outer sleeve. The diameter is smaller than the diameter of the outer sleeve, the casing short joint body is concentrically and fixedly connected to the outer casing through the outer casing, and a closed annular hollow is formed between the casing short joint body and the outer casing. Since the air interlayer is formed between the casing sub body and the outer sleeve, the pressure from the casing sub body will not be transmitted to the outer casing, so there will be no micro-gap between the outer casing and the cement, so Avoid the generation of gas channeling. The structure is simple to process, easy to use, and has the advantages of light weight, easy operation, and good economy.

Description

A combined casing pup joint for well cementing and method for well cementing

technical field

The invention belongs to the technical field of oil, natural gas and geological drilling, in particular to the structural design of a cementing casing string and a cementing method.

Background technique

Shale gas is a clean and efficient new energy source. Due to the continuous distribution of shale gas reservoirs and the characteristics of low porosity and low permeability, fracturing is required to form network fractures in order to form shale gas production. Shale gas wells usually use a cemented down-drillable bridge plug to achieve multi-stage fracturing, with pressures as high as 60-100 MPa. The purpose of cementing is to prevent fluid channeling between the drilled formations and ensure long-term interlayer isolation by injecting cement into the annular space of the drilled formation and casing, while the fracturing implemented in shale gas horizontal wells The casing is repeatedly squeezed during the reconstruction. During this process, the casing is subjected to repeated stress, which may cause micro-gap between the outer wall of the casing and the cement, or micro-cracks in the cement stone, which will destroy the integrity of the cement sheath and form gas channeling. channel, causing the gas in the well to escape to the wellhead, that is, the phenomenon of "wellhead pressure", which seriously affects the later mining and brings hidden dangers to safety production.

At present, the integrity of the cement sheath is mainly maintained by improving the mechanical properties of the cement stone, such as adding an elastic agent to the cement slurry to reduce the elastic modulus of the cement stone to cope with repeated external pressure shocks. However, this method can only maintain the integrity of the cement sheath as much as possible, and cannot prevent the gap between the casing and the cement sheath, so even if the cement sheath is not damaged at all during the fracturing process, the casing and cement The interface between the stones will peel off, and the gas channeling channel will still exist.

SUMMARY OF THE INVENTION

Aiming at the problem of annular pressure after fracturing of shale gas wells, the present invention provides a new solution. That is, a special hollow casing short joint is designed to connect between the two sections of oil layer casing to enhance the strain resistance of the casing, thereby blocking the gas channeling channel, maintaining the integrity of the wellbore, and avoiding the situation of annular pressure. occur.

The following are the specific technical solutions of the present invention:

A combined casing pup joint for well cementing is composed of a hollow casing pup joint body and an outer sleeve, the diameter of the casing pup joint body is smaller than the diameter of the outer sleeve, and the casing pup joint The body is concentrically and fixedly connected to the outer sleeve through the outer sleeve, and a closed annular hollow is formed between the sleeve short body and the outer sleeve, and the sleeve is short The diameter of the joint body is the same as that of the oil layer casing, and the short joint body of the casing is concentrically and fixedly connected with the adjacent oil layer casing.

Preferably, the radial width of the annular hollow is at least equal to or greater than 1 mm.

Preferably, the radial width of the annular hollow is 3 mm to 5 mm.

Preferably, each of the combined casing pup joints is 4m-6m long.

Using the combined casing pup joint cementing method, proceed as follows:

(1) Assemble the casing pup joint body and the outer sleeve together to form the combined casing pup joint;

(2) Install the combined casing short joints between the oil layer casings at intervals.

Preferably, at least two or more than two of the combined casing sub-sections are installed between the oil layer casings at intervals.

Preferably, at the position of the vertical well section at a distance of 1000m to 2000m from the wellhead, four of the combined casing sub-joints are installed between the oil layer casings at intervals.

The use of the combined casing pup joint of the present invention has obvious technical effects: the pup joint is a hollow casing, when fracturing the inside of the casing, the casing pup joint body will be slightly deformed. An air interlayer is formed between the casing and the outer casing, so that the pressure from the casing sub body will not be transmitted to the outer casing, so there will be no micro-gap between the outer casing and the cement, thereby avoiding the generation of gas channeling. The short section is simple to process, easy to use, light, easy to operate, and economical. It can be widely used in cementing operations of various high-pressure gas (oil) wells.

Description of drawings

Fig. 1 Schematic diagram of combined casing pup joint in cementing operation

Figure 2 Schematic diagram of the structure of the combined casing pup

Fig. 3 A schematic diagram of Fig. 1

Labels in the figure:

1 Combined casing pup 2 Oil layer casing 3 Outer casing 4 Casing pup body

5 Outer sleeve 6 Annular hollow.

Detailed ways

In order to better understand the technical solutions and effects of the present invention, the technical solutions of the present invention are described below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention.

It can be seen from Fig. 2 that the combined casing pup joint 1 for cementing is composed of a hollow casing pup joint body 4 and an outer sleeve 5. The diameter of the casing pup joint body 4 is smaller than the diameter of the outer sleeve 5, and the casing is short. The joint body 4 is concentrically connected to the outer sleeve 5 through the outer sleeve 5, and a closed annular hollow is formed between the casing short joint body 4 and the outer sleeve 5; as shown in Figure 1, the sleeve The pipe sub body 4 and the oil layer casing 2 have the same diameter, and the casing sub body 4 and the adjacent oil layer casing 2 are concentrically and fixedly connected together.

As shown in FIG. 2 , the assembly method of the combined casing pup joint 1 is that the casing pup joint body 4 passes through the outer sleeve 5 and is fixedly connected together, and the casing pup joint body 4 and the outer sleeve 5 have the same In this way, a closed annular hollow 6 is naturally formed between the casing sub body 4 and the outer sleeve 5 of different diameters, and the outer sleeve 5 can withstand a large pressure. In the present invention, it is required to The anti-extrusion strength is not lower than the formation pressure.

When the combined casing pup joint 1 is working, the two ends of the casing pup joint body 4 are fixedly connected with the adjacent oil layer casing 2 respectively. Since the casing pup joint body 4 and the oil layer casing 2 have the same diameter and have the same Therefore, it can achieve the same function as the oil layer casing 2 in cementing work. Naturally, in terms of mechanical properties, material selection, etc., the casing pup joint body 4 should have the same technical requirements as the oil layer casing 2 .

The connection between the casing pup joint body 4 and the outer sleeve 5, as well as the casing pup joint body 4 and the oil layer casing 2 can be threaded connection, or snap, slot, etc., which belong to the conventional mechanical connection method, which is not omitted here. detail.

Preferably, the radial width of the annular hollow 6 is preferably at least equal to or greater than 1 mm, so that there is a large space to offset the pressure from the casing sub body 4 and greatly reduce the gas from the casing sub body 4. Or the phenomenon that the wall of the outer casing 3 is deformed or even leaks gas (liquid) due to the strong pressure of the liquid, so as to maintain the integrity of the wellbore and avoid the occurrence of annulus pressure.

Preferably, in view of the phenomenon of annular pressure after fracturing of shale gas wells, when cementing at a vertical well section at a distance of 1000-2000 meters from the wellhead, the radial width of the annular hollow is preferably 3 mm to 5 mm.

Under normal circumstances, shale gas horizontal wells require multiple fracturing and high pressure. The cementing method, casing structure and strength of the vertical well section at the wellhead will directly affect the safety and normal operation of the vertical well section. The implementation of shale gas horizontal wells In the fracturing reconstruction, the casing is repeatedly squeezed, which may cause a micro-gap between the outer wall of the casing and the cement, resulting in the phenomenon of "wellhead pressure".

Therefore, in order to better realize the technical effect of the present invention, correspondingly, the present invention also provides a cementing method using the combined casing pup joint 1 . In the embodiment shown in FIG. 1 , prior to the cementing construction, the casing sub body 4 and the outer sleeve 5 in the combined casing sub 1 are assembled in advance for backup. Then, after installing the first section of oil layer casing 2, connect and fix the end of the first combined casing short joint 1 with the end of the first section of oil layer casing 2, and then the first combined casing The other end of the casing pup joint 1 is installed with the second section of the oil layer casing 2, and then the end of the second combined casing pup joint 1 is connected to the other end of the second section of the oil layer casing 2. Fix, then install the third section of oil layer casing 2 at the other end of the second combined casing pup joint 1, and so on, install the combined casing pup joint 1 on the adjacent oil layer casing 2 at intervals. until all required combined casing sub joints 1 are installed according to the design requirements.

Due to structural strength, manufacturing, installation and many other factors, the length of the combined casing pup joint 1 is preferably 4 to 6 meters each.

In order to achieve a better technical effect, the number of combined casing short joints 1 should be at least 2, and they must be installed between the oil layer casings 2 at intervals. Especially for the phenomenon of annular pressure after multi-stage fracturing in shale gas wells, multiple combined casing sub-sections 1 are installed at intervals between the oil layer casings 2, which can effectively block the gas channeling channel and prevent the gas in the well from penetrating into the well. The wellhead will seriously affect the later mining.

As a more preferable example, in the embodiment of FIG. 1 , four combined casing sub joints 1 can be installed between the oil layer casings 2 at intervals in the vertical well section at a distance of 1000-2000 meters from the wellhead.

The combined casing short joint 1 and the cementing method using the combined casing short joint 1 disclosed in the present invention can well avoid the generation of micro-gap in the cement sheath after cementing, and eliminate the problem of casing annulus pressure, and is suitable for Cementing operations for all kinds of high-pressure gas and oil wells, not limited to shale gas production cementing operations.

It is hereby declared that the above-mentioned embodiments and accompanying drawings do not mean that all situations of the technical solutions of the present invention are completely presented, and all other embodiments obtained by those of ordinary skill in the art without creative work are all within the protection of the present invention. range.

Claims (7)

1. A combined casing pup joint for well cementing is composed of a hollow casing pup joint body and an outer sleeve, the diameter of the casing pup joint body is smaller than the diameter of the outer sleeve, and the casing pup The short joint body passes through the outer sleeve and is concentrically and fixedly connected to the outer sleeve, and a closed annular hollow is formed between the casing short joint body and the outer sleeve, and the sleeve The pipe sub body and the oil layer casing have the same diameter, and the casing sub body and the adjacent oil layer casing are concentrically and fixedly connected together. 2 . The combined casing sub for cementing according to claim 1 , wherein the radial width of the annular hollow is at least equal to or greater than 1 mm. 3 . 3 . The combined casing pup for well cementing according to claim 1 , wherein the radial width of the annular hollow is 3 mm to 5 mm. 4 . 4 . The combined casing pup joint for well cementing according to claim 1 , wherein each of the combined casing pup joints is 4m-6m long. 5 . 5. Using the combined casing pup joint cementing method, proceed as follows: (1) Assemble the casing pup joint body and the outer sleeve together to form the combined casing pup joint; (2) Install the combined casing short joints between the oil layer casings at intervals. 6 . The method for cementing well using combined casing pup joints according to claim 5 , wherein at least two or more of the combined casing pup joints are installed between the oil layer casings at intervals. 7 . . 7. The method of adopting combined casing pup joint cementing according to claim 5, characterized in that, at the position of the vertical well section at a distance of 1000m to 2000m from the wellhead, four said Combined casing nipple.

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