Conception of coordinated development technology system for coalbed methane and underground coal gasification in inclined coal seams

Coalbed methane (CBM) development and underground coal gasification (UCG) are important sources for coal-based natural gas production in China, and coal and CBM resources are abundant in the inclined coalbed development area of the Xinjiang foreland thrust belt. To deeply analyze the feasibility of coordinated development of CBM and UCG in inclined coal seams, the existing key technologies of CBM and UCG and their significances for coordinated development of CBM- UCG was systematically analyzed, the advantages, the technical routes, major problems and future research directions of coordinated development of CBM and UCG in inclined coal seams were also elaborated, the major problems faced and the direction of future research were proposed, and the following understanding was obtained. ① The coordinated development of CBM-UCG under the “CBM development dredging effect”, “UCG thermal desorption effect”, and “UCG mining pressure releasing effect” can form a virtuous cycle of mutual promotion. ② The coordinated development technology routes was proposed, such as vertical wells + inclined well along coal seam with “first drainage and then gasification”, multiple inclined wells along the coal seam with “simultaneous drainage and gasification”, directional L-typed CBM wells + UCG wells along the coal seam direction with “simultaneous gasification and drainage”, UCG wells along inclined wells in the lower coal + directional L-typed CBM wells in the upper coal seam with “first drainage, then gasification, and then drainage again”, and the “well factory” arrangement of complex well type. ③ The coordinated development of CBM and UCG faces theoretical issues such as weak theoretical foundation research on geological constituency evaluation, unclear expansion range of UCG thermal action under the condition of fracture network, and the undetermined range of rock movement and pressure relief in the UCG process of inclined coal seams. It also faces the engineering issues such as coordinated development of CBM-UCG “well factory” drilling technology, coordinated development of CBM wells and UCG wells production system, coordinated development of CBM and UCG wells geodynamic measurement and control, and the sealing and high-temperature-resistant protection of CBM wells. ④ It is necessary to strengthen the study on the evaluation of geological site selection for the coordinated development of CBM and UCG in inclined coal seams, the theoretical research on the development dynamics, and the pioneering experimental study on engineering coordination technology, so as to ensure that the coordinated development is safe, orderly, controllable and efficient.