Method for mining coal bed gas by hydraulic washout of butted well in manner of pressure relief

Abstract

The invention discloses a method for mining coal bed gas by hydraulic washout of a butted well in the manner of pressure relief, which comprises the following steps: firstly, drilling a drainage vertical well (3); digging the section of a target coal bed (2); forming a pocket (4) after passing through the coal bed; drilling a vertical well section (9) and a deviating section (10) of a horizontal directional well (8) and laying a casing pipe for well cementation; then, drilling a channel of a horizontal section (11) by using a conventional measure; butting the channel of the horizontal section (11) with the drainage vertical well (3) for barefoot well completion; continuously injecting water into the horizontal directional well (8) to wash the coal bed of the horizontal section (11); gathering coal water into the pocket (4); discharging the coal water through lifting equipment (6); when pulverized coal does not exist in the pocket (4), laying a water spray hose (12); by means of the action of high-pressure water jet, ejecting out a plurality of branch boreholes (13) at the horizontal section (11); continuously injecting the water to wash until the pulverized coal does not exist in the pocket (4) any longer; closing the horizontal directional well (8); and entering a conventional water draining and gas mining stage. The invention provides a new resolution for ground gas mining from soft low-permeability coal beds.

Description

technical field [0001] The invention relates to the technical field of coalbed methane mining, and may also relate to the technical field of surface coal and gas co-mining, in particular to a method for mining coalbed methane by hydraulic scouring and pressure relief in butt joint wells suitable for soft, low-permeability, and high-gas coal seams. Background technique [0002] Drilling technologies for surface mining of coalbed methane are mainly vertical wells and horizontal wells. Vertical wells are drilled from the ground to pass through the coal seam, and cracks are created in the coal seam by means of fracturing, thereby releasing and extracting coalbed methane. The construction of vertical wells is simple and the cost is low, but this technology is mainly suitable for hard and thick coal seams with flat terrain and good permeability, and is not suitable for soft and low-permeability coal seams. A horizontal well refers to a well whose inclination angle reaches or is c...

AI Technical Summary

Problems solved by technology

However, there are a considerable number of soft, low-permeability, and high-gas coal seams in China. Conventional horizontal well drilling technology is difficult to achieve. It is difficult to complete the horizontal section of the well. Even if it is completed, it is easy to collapse and block, and it is difficult to maintain a stable pressure relief space.

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