Method for exploiting coal-bed methane by utilizing water force of horizontal pinnate well of double well-shaft to scour, drill and relieve pressure

Abstract

The invention discloses a method for exploiting coal-bed methane by utilizing a water force of a horizontal pinnate well of a double well-shaft to scour, drill and relieve pressure. The method comprises the following steps: drilling a straight drainage well (3), digging a hole in a section of a target coal-bed (2) and forming a pocket (4) after passing through the coal-bed; drilling a straight well section (9) and a building section (10) of a horizontal pinnate well (8) and placing a casing pipe for fixing the well; placing a water-spraying hose (12) connected with a high-pressure water pump (11) into the horizontal pinnate well (8); passing through a cave (5), scouring the coal-bed with a high-pressure jetted water and drilling along a horizontal direction, thereby forming a horizontal sectional main well hole (14); changing a jetting direction, and jetting a plurality of branched well holes (16) around the horizontal sectional main well hole (14); causing coal water to flow back to the pocket (4) during a jetting process, and discharging the coal water through a lifting device (6); separating through a methane, coal and water separating device (7); collecting and storing the coal and methane; and reusing the water to jet flow and scour under the well. The invention provides a new solution for ground gas production on a mellow and low-seepage coal bed.

Description

technical field [0001] The present invention relates to the technical field of coalbed methane mining, and may also relate to the technical field of co-mining of ground coal and gas, in particular to a double-shaft horizontal pinnate well hydraulic flushing drilling pressure relief suitable for soft, low-permeability, and high-gas coal seams Coal bed gas mining method. Background technique [0002] Drilling technologies for surface mining of coalbed methane are mainly vertical wells and horizontal wells. The construction of vertical wells is simple and the cost is low, but it 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; the technology of horizontal wells is more complicated than that of vertical wells, but it can greatly increase the exposed area of ​​coal seams , to increase coalbed methane production. At present, there are mainly three types of horizontal wells: the...

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Problems solved by technology

[0003] The construction of horizontal directional well is simple, but the exposed area of ​​coal seam is limited, and the water accumulation in the well cannot be solved during the gas production process; the horizontal butt joint well can solve the problem of water accumulation in the well, but because of the remote connection, the horizontal section generally needs to be supported by screen pipes. The hardness of the coal seam and the requirements for construction technology are relatively high; the exposed area of ​​the coal seam has increased significantly due to the addition of branch boreholes in the horizontal pinnate well, but the horizontal pinnate well with single wellbore also faces the problem of water accumulation in the well, and the horizontal pinnate well with double wellbore has increased the special Vertical wells for drainage of coal water and coalbed methane can effectively solve the problem of water accumulation in the well, but the horizontal well section is located in the target coal seam. In order to prevent the coal seam from collapsing and blocking the wellbore, it is generally necessary to select a hard coal seam for construction and install a screen pipe Cementing

[0004] 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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