A large diameter wellbore freezing method using circumferential freezing

Abstract

The present invention discloses a freezing method for a large-diameter wellbore, which is suitable for use in underground engineering. Directional follow-up pipe drilling is used to arrange spiral freezing pipes in an annular manner outside the excavation range of the large-diameter wellbore that needs to be excavated. The spiral freezing pipes surround and cover the entire outer area of ​​the wellbore. A liquid supply pipe with a matching structure is provided in the freezing pipe. Refrigerant circulates through the liquid supply pipe to generate a layer of cylindrical freezing curtain that wraps the wellbore outside the pre-excavation range of the wellbore, thereby providing maintenance for the surrounding soil for the wellbore excavation. According to the wellbore depth, formation conditions, and maintenance requirements, the spacing between the spiral freezing pipes can be adjusted to form freezing walls of different thicknesses and strengths. When the required freezing wall thickness is too large, two or more circles of spiral freezing pipes are arranged around the wellbore to shorten the construction time. The freezing process of the large-diameter wellbore can be completed with a small number of freezing pipes.

Description

Technical Field

[0001] The invention relates to a shaft freezing construction method, in particular to a large-diameter shaft freezing method for circumferential freezing used in underground engineering, and belongs to the technical field of mine construction. Background Art

[0002] During the shaft construction in coal mine engineering construction, when the shaft excavation position passes through the water-rich soft soil layer, it is necessary to use artificial freezing technology to freeze and reinforce the soil around the shaft excavation range. During construction, it is generally necessary to construct a circle of freezing holes vertically around the shaft, and arrange freezing pipes in the freezing holes to circulate the low-temperature refrigerant. After a circle of closed freezing curtains is formed around the shaft, the soil inside the shaft is excavated while maintaining the stability of the surrounding soil. When the shaft diameter is large, the required freezing wall thickness is large, and it is often necessary to arrange multiple circles of freezing pipes around the shaft excavation range. This not only requires longer freezing pipe materials, but also makes the freezing system connection complicated, and it is necessary to consider the balance of low-temperature refrigerant circulation between different circles. More importantly, the freezing pipes arranged vertically from the ground around the well excavation range have consistent freezing wall effects formed around the wellbore, so the thickness and strength of the freezing wall formed at different depths are the same. When the geological conditions of the strata at different depths are different, the quality of the freezing wall cannot be adjusted according to the characteristics of the strata conditions. The thickness and strength of the freezing wall can only be designed according to the worst geological conditions, resulting in a waste of freezing resources. Summary of the invention

[0003] In view of the shortcomings of the prior art, a large-diameter wellbore freezing method with circumferential annular freezing is provided. In the large-diameter wellbore freezing method with circumferential annular freezing of the large-diameter wellbore, a single spiral freezing pipe is arranged along the wellbore excavation range to form the required freezing wall. The freezing system is simple in organization, and the pitch of the spiral freezing pipe can be differentially adjusted according to the requirements of the freezing effect, thereby achieving differential freezing of strata at different depths.

[0004] To achieve the above technical objectives, the present invention provides a large-diameter wellbore freezing method with circumferential annular freezing. Directional follow-up pipe drilling is used to arrange spiral freezing pipes in an annular manner outside the excavation range of the large-diameter wellbore that requires excavation. The spiral freezing pipes surround and cover the entire outer area of ​​the wellbore. A liquid supply pipe with a matching structure is provided in the freezing pipe. Refrigerant circulates through the liquid supply pipe to generate a cylindrical freezing curtain that wraps the wellbore outside the pre-excavation range of the wellbore, thereby providing protection for the surrounding soil for the wellbore excavation.

[0005] The specific steps are as follows:

[0006] a. Arrange a directional drilling rig at the ground location of the wellbore to be excavated, and use the pipe-following drilling method to perform spiral drilling in the soil layer around the wellbore to be excavated. Use the freezing pipe as a drill rod and use a directional drill bit to drill according to the pre-designed spiral freezing pipe curve, so as to complete the arrangement of the spiral freezing pipe outside the wellbore;

[0007] b. Use a directional drill to lower a spiral liquid supply pipe with a matching structure of a smaller diameter into a single spiral freezing pipe to form a freezing cycle, that is, the low-temperature refrigerant flows into the spiral liquid supply pipe from the liquid supply pipe opening of the spiral liquid supply pipe, and flows into the bottom of the spiral freezing pipe along the matching spiral liquid supply pipe with a smaller diameter, and then flows out of the spiral freezing pipe opening along the annular space between the spiral freezing pipe and the spiral liquid supply pipe, and is connected to the ground liquid supply system;

[0008] c. During the circulation of the low-temperature refrigerant in a single spiral freezing pipe, the low-temperature refrigerant absorbs heat from the ground around the spiral freezing pipe and turns the surrounding ground into frozen soil, thereby increasing the ground strength and forming a freezing curtain. As the low-temperature refrigerant continues to circulate, the thickness of the freezing curtain gradually increases;

[0009] d. After a closed freezing curtain that meets the design requirements is formed around the shaft, the shaft will be excavated and subsequent structures will be constructed under the protection of the freezing curtain.

[0010] Furthermore, the spiral freezing pipes arranged outside the excavation range of the shaft are configured into a multi-layer nested structure as needed to increase the area of ​​the freezing curtain; when the required freezing curtain thickness is large, the freezing effect of a single spiral freezing pipe cannot meet the need, then one or more multi-layer spiral freezing pipes concentric with the shaft are constructed in the soil outside the spiral freezing pipe and surrounding the spiral freezing pipe. Through the joint freezing action of multiple spiral freezing pipes, a thick freezing curtain required by the freezing design is formed.

[0011] Furthermore, multiple spiral freezing pipes are arranged in multiple layers outside the wellbore, and the spiral directions of the spiral freezing pipes are alternately reversed to improve the freezing effect and the firmness of the freezing curtain.

[0012] Furthermore, the pitch of each spiral freezing pipe is adjusted according to actual freezing needs, thereby forming areas with different freezing effects on the outside of the wellbore. The areas with closer pitches have thicker and higher strength frozen curtains, while the areas with farther pitches have thinner and lower strength frozen curtains.

[0013] Beneficial effects:

[0014] This method constructs spiral freezing boreholes around the wellbore within the excavation range of the soil layer outside the wellbore. Compared with the existing freezing pipes set close to the wellbore wall, or the straight freezing pipes driven horizontally into the soil layer around the wellbore, only a small number of freezing pipes need to be arranged to complete the freezing construction process. The freezing system is simple to connect, which greatly shortens the drilling construction period and reduces the construction cost. During the construction process, the freezing pipes are drilled into the formation with a directional drill bit. The spiral spacing of the boreholes is adjusted at any time according to the actual situation of the formations at different depths to achieve differential freezing at different depths, thereby effectively reducing energy loss and being highly economical. In addition, circumferential annular freezing is adopted, and each freezing pipe only needs one brine inlet and one brine outlet, which greatly reduces the brine return connection work of traditional straight pipe freezing, and the freezing system is simpler and easier to operate. Since the freezing system is simple, the geothermal refrigerant circulating in the freezing pipe can be adjusted at any time during construction. That is, ultra-low temperature liquid nitrogen can be circulated in the freezing pipe to quickly form a freezing wall, and then low-temperature brine can be circulated in the freezing pipe to maintain the freezing wall from melting. This can achieve rapid freezing and save construction time and costs, and can also reduce engineering investment by freezing brine in the later stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the main structure of the spiral freezing process of an embodiment of the present invention.

[0016] In the figure: 1-wellbore; 2-spiral freezing pipe opening; 3-liquid supply pipe opening; 4-spiral freezing pipe; 5-spiral liquid supply pipe. DETAILED DESCRIPTION

[0017] The embodiments of the present invention are further described below in conjunction with the accompanying drawings.

[0018] like Figure 1 As shown, 1. a method for freezing a large-diameter wellbore 1 by circumferential annular freezing of the present invention is characterized in that: spiral freezing pipes 4 are arranged in an annular manner on the outside of the excavation range of the large-diameter wellbore 1 that requires excavation by using directional follow-up pipe drilling, and the spiral freezing pipes 4 surround and cover the entire outer area of ​​the wellbore 1. A liquid supply pipe with a matching structure is provided in the freezing pipe. Refrigerant circulates through the liquid supply pipe to generate a cylindrical freezing curtain that wraps the wellbore 1 on the outside of the pre-excavation range of the wellbore 1, thereby providing protection for the surrounding soil for the excavation of the wellbore 1.

[0019] The specific steps are as follows:

[0020] a. Arrange a directional drilling rig at the ground position of the wellbore 1 to be excavated, and use the pipe-following drilling method to perform spiral drilling in the soil layer around the wellbore 1 to be excavated. Use the freezing pipe as a drill rod and use a directional drill bit to drill according to the pre-designed spiral freezing pipe curve, so as to complete the arrangement of the spiral freezing pipe 4 outside the wellbore 1;

[0021] b. Use a directional drill to lower a spiral liquid supply pipe 5 with a matching structure of a smaller diameter into the arranged single spiral freezing pipe 4 to form a freezing cycle, that is, the low-temperature refrigerant flows into the spiral liquid supply pipe 5 from the liquid supply pipe port 3 of the spiral liquid supply pipe 5, and flows into the bottom of the spiral freezing pipe 4 along the matching spiral liquid supply pipe 5 with a smaller diameter, and then flows out of the spiral freezing pipe port 2 along the annular space between the spiral freezing pipe 4 and the spiral liquid supply pipe 5, and is connected to the ground liquid supply system;

[0022] c. During the circulation process of the low-temperature refrigerant in the single spiral freezing pipe 4, the low-temperature refrigerant absorbs heat from the ground around the spiral freezing pipe 4 and turns the surrounding ground into frozen soil, thereby increasing the ground strength to form a freezing curtain. As the low-temperature refrigerant continues to circulate, the thickness of the freezing curtain gradually increases;

[0023] d. After a closed freezing curtain that meets the design requirements is formed around the shaft 1, the shaft 1 is excavated and the subsequent structure is constructed under the protection of the freezing curtain. When part of the stratum does not need to be frozen, a straight pipe can be used to pass through the stratum at that depth, thereby reducing the loss of cold.

[0024] The spiral freezing pipes 4 arranged outside the excavation range of the shaft 1 are arranged into a multi-layer nested structure as required to increase the area of ​​the freezing curtain; when the required freezing curtain thickness is large, the freezing effect of a single spiral freezing pipe 4 cannot meet the requirement, then one or more multi-layered spiral freezing pipes concentric with the shaft 1 are constructed in the soil outside the spiral freezing pipe 4, surrounding the spiral freezing pipe 4, and through the joint freezing action of the multiple spiral freezing pipes 4, a thick freezing curtain required by the freezing design is formed. The multiple spiral freezing pipes arranged in multiple layers outside the shaft 1 have their spiral directions alternately reversed to improve the freezing effect and the firmness of the freezing curtain. The pitch of each spiral freezing pipe is adjusted according to the actual freezing needs, so as to form areas with different freezing effects outside the shaft 1. The freezing curtain formed by freezing in areas with closer pitches is thicker and has higher strength, while the freezing curtain formed in areas with farther pitches is thinner and has lower strength.

[0025] The outer freezing pipe is a steel pipe, which can be drilled by directional drill bit. The inner liquid supply pipe is also made of hard carbon steel. Since it is suitable for the construction of large-diameter wellbore with a diameter of about 20m, the lowering of the inner liquid supply pipe will not be affected by the large curvature of the freezing pipe.

Claims

1. A method for freezing a large diameter wellbore (1) by circumferential freezing, Features: A spiral freezing pipe (4) is arranged in an annular direction outside the excavation range of the large-diameter wellbore (1) by means of directional follow-pipe drilling, wherein the spiral freezing pipe (4) surrounds and covers the entire outer area of ​​the wellbore (1), and a liquid supply pipe with a matching structure is provided in the freezing pipe, through which a refrigerant circulates, thereby generating a cylindrical freezing curtain that wraps around the wellbore (1) outside the pre-excavation range of the wellbore (1); The specific steps are as follows: a. Arrange a directional drilling rig at the ground position of the wellbore (1) to be excavated, and use the pipe-following drilling method to perform spiral drilling in the soil layer around the wellbore (1) to be excavated, use the freezing pipe as a drill rod, and use a directional drill bit to drill according to a pre-designed spiral freezing pipe curve, thereby completing the arrangement of the spiral freezing pipe (4) outside the wellbore (1); b. Using a directional drilling rig to lower a matching spiral liquid supply pipe (5) with a smaller diameter into the arranged single spiral freezing pipe (4) to form a freezing cycle, that is, the low-temperature refrigerant flows into the spiral liquid supply pipe (5) from the liquid supply pipe opening (3) of the spiral liquid supply pipe (5), flows along the spiral liquid supply pipe (5) to the bottom of the spiral freezing pipe (4), and then flows out of the spiral freezing pipe opening (2) along the annular space between the spiral freezing pipe (4) and the spiral liquid supply pipe (5) to be connected to the liquid supply system on the ground; c. During the circulation of the low-temperature refrigerant in the single spiral freezing pipe (4), the low-temperature refrigerant absorbs heat from the ground around the spiral freezing pipe (4) and turns the surrounding ground into frozen soil, thereby increasing the ground strength to form a freezing curtain. As the low-temperature refrigerant continues to circulate, the thickness of the freezing curtain gradually increases; d. After a closed freezing curtain that meets the design requirements is formed around the shaft (1), the shaft (1) is excavated and the subsequent structure is constructed under the protection of the freezing curtain.

2. A method for freezing a large diameter wellbore (1) by circumferential freezing according to claim 1, Features: The spiral freezing pipes (4) arranged outside the excavation range of the shaft (1) are arranged into a multi-layer nested structure as required to increase the area of ​​the freezing curtain; when the required freezing curtain thickness is relatively large, the freezing effect of a single spiral freezing pipe (4) cannot meet the requirement, then one or more multi-layered spiral freezing pipes concentric with the shaft (1) are constructed in the soil outside the spiral freezing pipe (4) and surrounding the spiral freezing pipe (4), so that a thick freezing curtain required by the freezing design is formed through the joint freezing effect of the multiple spiral freezing pipes (4).

3. The method for freezing a large diameter wellbore (1) by circumferential freezing according to claim 2, Features: A plurality of spiral freezing pipes are arranged in a multi-layer distribution outside the wellbore (1), and the spiral directions of the spiral freezing pipes are alternately reversed to improve the freezing effect and the firmness of the freezing curtain.

4. The method for freezing a large diameter wellbore (1) by circumferential freezing according to claim 1, Features: The pitch of each spiral freezing pipe is adjusted according to actual freezing needs, so as to form areas with different freezing effects outside the wellbore (1). The areas with closer pitches have thicker freezing curtains and higher strength, while the areas with farther pitches have thinner freezing curtains and lower strength.

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