Coalbed gas mining well body structure with high extrusion resistance and tensile strength

Abstract

The utility model belongs to the technical field of coalbed methane exploitation, and discloses a coalbed methane mining well body structure with high extrusion resistance and tensile strength, which comprises a first-opening drill hole, the first-opening drill hole vertically drills into a soft stratum by not less than 20 meters, a surface casing pipe is put into the first-opening drill hole and is sealed by well cementation cement, and the first-opening drill hole is connected with the first-opening drill hole. The second-opening drill hole vertically and downwards drills from the bottom of the first-opening drill hole to the target coal seam, the second-opening drill hole obliquely and downwards drills to the bottom of the well in the target coal seam, the distance between the bottom of the well and the main coal mining layer is 50-70 m, an outer-layer sleeve is put into the position above the top of the target coal seam, a packer is installed at the lower end of the target coal seam for well cementation, and an outer-layer screen pipe is put into the target coal seam section; an inner-layer casing pipe and an inner-layer screen pipe which are additionally provided with centralizers are respectively arranged in the outer-layer casing pipe and the outer-layer screen pipe; and a water stop plug is also arranged between the lower ends of the outer-layer casing pipe and the inner-layer casing pipe. According to the sleeve assembly, the aims of low cost and high yield can be achieved, the anti-extrusion tensile strength of the sleeve assembly is high, and under the condition that the sleeve assembly is extruded by strong ground stress, it is guaranteed that the sleeve is kept unblocked, and the dislocation phenomenon is avoided.

Description

Technical Field

[0001] The utility model belongs to the technical field of coalbed methane mining, and in particular relates to a coalbed methane mining well body structure with high anti-squeeze and anti-tensile strength. Background Art

[0002] my country's coal mines are rich in coalbed methane resources. The main problems in the development and utilization of coalbed methane are the scrapping of drilling and the decline of production capacity after underground production. At present, the industry widely uses hydraulic fracturing technology to transform coal seams. Through hydraulic fracturing, a seam network is formed in the coal reservoir to improve the permeability of the coal reservoir, and then the coalbed methane is produced by draining water and reducing pressure. Coalbed methane wells have the characteristics of rapid gas production decline, and are affected by underground production in coal mining areas, and the production cycle of drilling is limited.

[0003] Most of the coal mines in Xiyang County mainly mine the No. 15 coal seam of the Taiyuan Group, while the No. 8-1, 8-4, and No. 9 coal seams of the Taiyuan Group are unstable in development, have many layers, and have thin single-layer thickness, which is not conducive to underground mining or coalbed methane development, resulting in a huge waste of coal and coalbed methane resources. Utility Model Content

[0004] The utility model aims to provide a coalbed methane mining well body structure with high anti-squeezing and anti-tensile strength, which does not require fracturing to reduce construction costs and utilizes the underground mining pressure relief and permeability enhancement effect to extract gas from multiple coal seams.

[0005] The utility model provides the following technical scheme: a well body structure of a coalbed methane mining well with high anti-squeezing and anti-tensile strength, comprising a first borehole, the first borehole is vertically drilled into a soft stratum for not less than 20 meters, a surface casing is lowered into the first borehole and sealed with cement, a second borehole is vertically drilled from the bottom of the first borehole to a target coal seam, and is inclined downward in the target coal seam to a well bottom position, the well bottom position is 50 to 70 meters away from a main mining coal seam, an outer casing is lowered above and below the top of the target coal seam, and a packer is installed at the lower end for cementing, an outer screen is lowered into the target coal seam section, an inner casing and an inner screen equipped with a centralizer are respectively lowered into the outer casing and the outer screen, and a water stopper is also installed between the lower ends of the outer casing and the inner casing.

[0006] Furthermore, the casing and the screen pipe are both connected using a stepped buckle.

[0007] Furthermore, a nitrogen drill is used for the secondary drilling.

[0008] The utility model provides a coalbed methane mining well body structure, which is aimed at a low-inclination directional well constructed on the side of the return air tunnel in the working face being mined underground. The influence of underground mining is used to further release gas from the overlying thin coal seam of the main mining coal seam, thereby achieving the purpose of low cost and high return. The casing strength is improved, and the anti-squeezing and anti-tensile strength of the casing combination is improved by means of increasing the casing strength and adding a centralizer to the double-layer casing. When subjected to strong ground stress squeezing, the casing is guaranteed to remain unobstructed to avoid disconnection. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a structural schematic diagram of the utility model.

[0010] In the figure: 1-main mining coal seam; 2-bottom hole position; 3-target coal seam area; 4-outer screen; 5-inner screen; 6-packer; 7-Shanxi formation bottom plate; 8-water stopper; 9-inner casing; 10-outer casing; 11-surface casing; 12-centralizer. DETAILED DESCRIPTION

[0011] In order to better understand the purpose, structure and function of the utility model, the following is a further detailed description of a coalbed methane mining well body structure with high anti-squeezing and anti-tensile strength of the utility model in conjunction with the accompanying drawings.

[0012] like Figure 1 As shown: a coalbed methane mining well body structure with high anti-squeezing and anti-tensile strength, including a borehole, the first borehole is vertically drilled into the soft stratum for not less than 20 meters, the surface casing 11 is lowered into the first borehole and sealed with cement, the second borehole is vertically drilled from the bottom of the first borehole to the target coal seam, and is inclined downward to the bottom position 2 in the target coal seam, the bottom position 2 is 50 to 70 meters away from the main mining coal seam 1, the outer casing 10 is inserted above and below the top of the target coal seam and a packer 6 is installed at the lower end for cementing, the outer screen 4 is lowered into the target coal seam section, the inner casing 9 and the inner screen 5 equipped with a centralizer 12 are respectively lowered into the outer casing 10 and the outer screen 4, and a water stopper 8 is also installed between the lower ends of the outer casing 10 and the inner casing 9.

[0013] The coalbed methane well of the utility model is a mining well, the main gas source comes from the target coal seam above the main mining coal seam 1 of the coal mine, and no fracturing is performed, but the gas is produced by the effect of underground mining on the target coal seam to create fractures and increase permeability. The well body structure of the well is generally divided into two parts, upper and lower. In the well section from the wellhead to the target coal seam, in order to improve the casing's resistance to mining effects, a two-opening double-layer casing well body structure is adopted, and a double-layer screen pipe well body structure is adopted in the target coal seam area 3, and the effect of underground mining is used to release gas from the target coal rock layer, so as to achieve the purpose of high and stable production without fracturing, small investment and high profit.

[0014] The coalbed methane well of this embodiment is a low-inclination directional well with a two-opening well body structure. It is aimed at the working face being mined underground. The target coal seam is the Taiyuan Group, and the Shanxi Group is above the Taiyuan Group. According to the well body structure, the mining well is constructed several months in advance. The surface casing 11 is lowered in the first opening, and the second opening is bounded by the Shanxi Group bottom plate 7. The inner casing 9 and the outer casing 10 of the production double-layer casing are lowered in the upper part, and the outer sieve 4 and the inner sieve 5 of the double-layer screen are lowered in the lower part. The casings all use skew buckles, and a centralizer 12 of matching specifications is installed every other casing to further improve the casing strength. In order to avoid the influence of underground aquifers on the mining well, the possible water inflow in the well is blocked by using the packer 6 cementing and the water stopper 8. When the well is mined underground, the influence of underground mining is used to further release gas from the overlying thin coal seam of the main mining coal seam 1, so as to achieve the purpose of low cost and high return.

[0015] The specific process steps are:

[0016] 1) Moving: Move into the well site and prepare for work.

[0017] 2) Primary drilling: Drill 20m below the soft stratum with a 425mm drill bit (in order to further improve the strength, the primary drilling depth can be deepened), insert a 377mm surface casing 11 with a J55 steel grade and a wall thickness of 10.03mm, and return the cement to the surface for solidification.

[0018] 3) Secondary drilling: Use a 311.1mm drill bit and nitrogen to drill to the bottom of the well 2. Insert a 339.7mm outer casing 10 with Q125 steel grade and 13.06mm wall thickness above the top of the Taiyuan Formation, and insert a 339.7mm outer screen 4 into the Taiyuan Formation section. Install a packer 6 on the bottom plate 7 of the Shanxi Formation to cement and solidify the well above the Shanxi Formation. Then, insert a 139.7mm inner casing 9 and inner screen 5 into the outer casing 10. The inner casing 9 is for the Shanxi Formation and above, and the inner screen 5 is for the Shanxi Formation and below. The pipes are all made of P110 steel grade. A water stopper 8 is installed between the two pipes at the bottom plate 7 of the Shanxi Formation to seal the water. When lowering the casing and screen, install a centralizer 12 of matching specifications for every other casing or screen.

[0019] 3) Install flame arresters and one-way valves and connect to the ground pipeline system.

[0020] Several coalbed methane mining wells were constructed in the Sijiazhuang coal mining area, with significant production increase effects, low economic investment and high cost performance. As the coal mine is about to be mined to the drilling area, mining wells were constructed several months in advance according to the well structure, and the pressure relief and permeability enhancement effect of underground mining on the 8-1, 8-4, and 9 coal seams of the Taiyuan Group was used to further release the coalbed methane in the coal seams.

[0021] It is understood that the present invention is described by some embodiments, and those skilled in the art are aware that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A coalbed methane mining well body structure with high anti-collision and tensile strength, characterized in that: The invention comprises a first borehole, wherein the first borehole is vertically drilled into a soft stratum for not less than 20 meters, a surface casing (11) is lowered into the first borehole and sealed with cement, a second borehole is vertically drilled downward from the bottom of the first borehole to a target coal seam, and then inclined downward in the target coal seam to a well bottom position (2), wherein the well bottom position (2) is 50 to 70 meters away from a main mining coal seam (1), an outer casing (10) is lowered above and below the top of the target coal seam and a packer (6) is installed at the lower end for cementing, an outer screen (4) is lowered into the target coal seam section, an inner casing (9) and an inner screen (5) equipped with a centralizer (12) are respectively lowered into the outer casing (10) and the outer screen (4), and a water stopper (8) is also installed between the lower ends of the outer casing (10) and the inner casing (9).

2. The coalbed methane mining well body structure with high anti-collision and anti-tensile strength according to claim 1 is characterized in that: The casing and screen are connected by ladder buckles.

3. The coalbed methane mining well body structure with high anti-collision and anti-tensile strength according to claim 1 is characterized in that: Nitrogen drill is used for secondary drilling.

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