Method of extracting gas from tectonically-deformed coal seam in-situ by depressurizing horizontal well cavity

摘要

The invention relates to the field of coal seam gas extraction. Disclosed is a method of extracting gas from a tectonically-deformed coal seam in-situ by depressurizing a horizontal well cavity. A horizontal well drilling and reaming subsystem (1, 10) constructs a U-shaped well in which a horizontal well adjoins a vertical well, and performs a reaming process on a horizontal section of the horizontal well (11) to enlarge hole diameter. A horizontal well hole-collapse cavity-construction depressurization excitation subsystem (14, 15, 16) performs pressure-pulse excitation and stress release on the horizontal well of tectonically-deformed coal seam gas, and hydraulically displaces a coal-liquid-gas mixture such that the mixture is conveyed towards a vertical well section along a depressurizing space. A product lifting subsystem (8) further pulverizes the coal and lifts the mixture towards a wellhead of a vertical well (7). A gas-liquid-solid separation subsystem (5, 4) separates the coal, liquid and gas. A monitoring and control subsystem detects and controls the operation conditions and the execution processes of technical equipment in real time. The method enables the completion of a large-diameter horizontal well in a loose tectonically-deformed coal reservoir, horizontal well cavity-constructing stress release, effective lifting of mixed fluids, and efficient separation of produced mixtures, thereby achieving efficient in-situ extraction of tectonically-deformed coal seam gas.