CN109538167B

CN109538167B - Method for sectional step-by-step drainage and production of coal bed gas U-shaped well

Info

Publication number: CN109538167B
Application number: CN201811155504.5A
Authority: CN
Inventors: 陈召英; 郝春生; 李军军; 常会珍; 李进强; 赵晋斌; 姚晋宝; 王维; 杨昌永; 贾晋生
Original assignee: Shanxi Jincheng Anthracite Mining Group Co Ltd
Current assignee: Shanxi Jincheng Anthracite Mining Group Co Ltd
Priority date: 2018-09-30
Filing date: 2018-09-30
Publication date: 2021-11-12
Anticipated expiration: 2038-09-30
Also published as: CN109538167A

Abstract

The invention relates to the technical field of coal bed gas drainage and mining, in particular to a method for sectionally and gradually reducing pressure of a U-shaped well of coal bed gas, which is divided into three drainage and mining stages according to the track characteristics of the U-shaped well of a large inclination angle coal bed; taking the stage from the initial liquid level of the coal bed gas well to the critical desorption pressure point as a first drainage stage; taking the liquid level from the critical desorption pressure point to the position 20m above the target coal seam top plate as a second drainage and mining stage; the next row mining is the third row mining stage. Different stages of the U-shaped well drainage and production of the large-dip-angle coal seam are clearly divided, so that the coal seam gas well can be stably depressurized and desorbed; the U-shaped well fracturing points are used as key points for drainage and production control, drainage and production of the coal bed gas well can be controlled more accurately, each coal bed section can be fully desorbed, and large-area exposure of the coal bed due to the fact that the liquid level is reduced too fast is prevented, and desorption of the coal bed gas is not facilitated.

Description

Method for sectional step-by-step drainage and production of coal bed gas U-shaped well

Technical Field

The invention relates to the technical field of coal bed gas drainage and production, in particular to a method for sectionally and gradually reducing pressure of a U-shaped well of coal bed gas to drain and produce coal bed gas.

Background

The conventional vertical well development influence range is small, the single well yield is low, the economic benefit is poor, the horizontal well has the advantages that more cutting crack systems are penetrated, a large number of crack channels are communicated, the drainage and production pressure reduction and gas leakage area is enlarged, more gas can enter a main flow channel, and the horizontal well is increasingly applied to coal bed gas exploitation as the efficient development technology of a low-permeability coal reservoir.

However, the coal seam, as a gas-producing layer and a reservoir layer of the coal seam gas, has the characteristics of low porosity, small permeability, low mechanical strength, strong heterogeneity, low reservoir pressure and the like. These characteristics determine that the damage to the coal seam during drainage is much greater than in conventional reservoirs. Especially for low permeability coal reservoirs, this damage is more pronounced and irreversible. The damage directly affects desorption, diffusion, migration and drainage of the coal bed gas, and finally affects the development effect of the coal bed gas horizontal well.

Many scholars study from the aspects of horizontal well position deployment, drainage and mining curve characteristics, dynamic indexes, productivity influence factors and the like, but few people analyze drainage and mining characteristics and drainage and mining degree optimization of a low-permeability coal reservoir coal-bed gas well from the aspects of horizontal well drilling track, coal bed inclination angle and the like.

Disclosure of Invention

The invention mainly aims to provide a sectional step-by-step pressure reduction discharge and mining method for a U-shaped well of coal bed gas, which aims to solve the problems of unstable yield, poor gas production effect and the like caused by unreasonable discharge and mining degrees in the horizontal well discharge and mining process.

The invention adopts the following technical scheme:

a method for sectional step-by-step drainage and mining of a coal bed gas U-shaped well is divided into three drainage and mining stages according to the track characteristics of the U-shaped well of a large inclination angle coal bed; taking the stage from the initial liquid level of the coal bed gas well to the critical desorption pressure point as a first drainage stage; taking the liquid level from the critical desorption pressure point to the position 20m above the target coal seam top plate as a second drainage and mining stage; the next row mining is the third row mining stage.

And in the second drainage and mining stage, the coal seam elevation of the coal seam lamination crack point is calculated according to the coal seam lamination crack point, projected to the track of the vertical extraction well and divided into a plurality of key drainage and mining control points which are used as key points for drainage and mining control.

When the liquid level sequentially drops to each drainage and mining control key point, the liquid level is maintained at the key point for a period of time until the pressure drop funnel is fully expanded, and then the liquid level is stably dropped to the next key point.

And in the third drainage and production stage, when the water yield is not enough to carry the pulverized coal for production, intermittent drainage and production or reinjection water treatment is carried out on the coal-bed gas well.

The drainage and mining method has the following advantages:

(1) different stages of the U-shaped well drainage and production of the large-dip-angle coal seam are clearly divided, so that the coal seam gas well can be stably depressurized and desorbed;

(2) the U-shaped well fracturing points are used as key points for drainage and production control, drainage and production of the coal bed gas well can be controlled more accurately, each coal bed section can be fully desorbed, and large-area exposure of the coal bed due to the fact that the liquid level is reduced too fast is prevented, and desorption of the coal bed gas is not facilitated.

Drawings

FIG. 1 is a schematic diagram of division of different drainage and production stages of a horizontal well;

FIG. 2 is a schematic diagram of key point division in the horizontal well drainage stage II;

in the figure: i, a first drainage stage; II, a second stage; III-third stage.

Detailed Description

Aiming at the characteristics of a large-dip-angle coal seam, the invention takes a U-shaped well fracturing point as a key point for drainage and mining control, and reduces pressure layer by layer in a segmented manner, wherein the specific process comprises the following steps:

(1) and (3) carrying out remote butt joint on the engineering well of the horizontal well to generate gas firstly. Because the horizontal section of the remote butt-jointed well is generally drilled in a downhill mode, the coal seam section near the engineering well reaches desorption conditions firstly, and if the inclination angle of the coal seam is larger, the phenomenon is more obvious.

(2) And a three-stage drainage and mining stage. Taking the stage from the initial liquid level of the coal bed gas well to the critical desorption pressure point as a first drainage stage; taking the liquid level from the critical desorption pressure point to the position 20m above the target coal seam top plate as a second drainage and mining stage; the next row mining is the third row mining stage.

(3) And (5) arranging and collecting key points. And in the second drainage and mining stage, calculating the coal seam elevation of the coal seam fracture point, and projecting the coal seam elevation onto the track of the vertical extraction well to be used as a key point for drainage and mining control.

(4) When the liquid level sequentially drops to each drainage and mining control key point, the liquid level is maintained at the key point for a period of time until the pressure drop funnel is fully expanded, and then the liquid level is stably dropped to the next key point.

(5) The third stage is a high gas yield stage and a low water yield stage, and the liquid level position is maintained to be about 20m above the coal seam roof;

(6) if the coal bed drainage water in the later period is less, the coal bed drainage water is not enough to carry out the generated coal powder, and the coal bed gas well needs to be subjected to water re-injection measures for avoiding accidents such as low pump efficiency, pump blockage and the like.

As shown in fig. 1, when the production reaches stage i, the bottom hole flow pressure should be continuously and smoothly reduced according to the reservoir characteristics (or sensitivity experiment);

as shown in fig. 2, when the drainage and production reaches stage ii, the elevation of the coal seam fracture point is projected onto the vertical well trajectory as a key point for drainage and production control. When the liquid level sequentially drops to each drainage and mining control key point, the liquid level is maintained at the key point for a period of time until the pressure drop funnel is fully expanded, and then the liquid level is stably dropped to the next key point;

when the drainage and mining reaches the stage III, the liquid level is kept above the drainage pump, and the water yield can meet the requirement of carrying the pulverized coal to return to the ground. If the water discharge is too small, intermittent drainage or reinjection water measures are adopted.

Claims

1. A method for sectional gradual drainage and mining of a coal bed gas U-shaped well is characterized in that three drainage and mining stages are divided according to the track characteristics of the large-inclination coal bed U-shaped well; taking the stage from the initial liquid level of the coal bed gas well to the critical desorption pressure point as a first drainage stage; taking the liquid level from the critical desorption pressure point to the position 20m above the target coal seam top plate as a second drainage and mining stage; the subsequent drainage and mining is a third drainage and mining stage;

in the second drainage and mining stage, coal bed elevations of the coal bed laminated fracture points are calculated according to the coal bed laminated fracture points, projected onto a vertical extraction well track and divided into a plurality of key drainage and mining control points which are used as key points for drainage and mining control;

when the liquid level sequentially drops to each drainage and mining control key point, the liquid level is maintained at the key point for a period of time until the pressure drop funnel is fully expanded, and then the liquid level is stably dropped to the next key point;