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

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.