Research advances in theory and technology of the stress release applied extraction of coalbed methane from tectonically deformed coals

The efficient exploitation of coalbed methane (CBM) in tectonically deformed coals (TDC) is the choice of China’s resource endowment of CBM. Current CBM exploitation theory of dewatering-depressure-desorption is unfit for tectonically deformed coal seams,which determined by the characteristics of TDC and the occurrence characteristics of CBM in TDC. The stress release applied extraction of CBM is a new theory and technology,which is expected to transform TDC from the forbidden zone of CBM exploitation into a new field. Meanwhile,it will be a fundamental solution of coal and gas outburst control and greenhouse gas emissions (methane) in coal mine. Supported by the National Key Project for Scientific Instrument and Equipment Research and Development,the work took the key experimental platform and engineering equipment prototype of the stress release applied extraction of CBM as the basic positioning,took exploitation theory innovation and technical principle exploration as the forerunner,and took the device,engineering equipment,and technology of the stress release applied extraction of CBM as the core research content. Based on this research,the theory and technology of the stress release applied extraction of CBM has been made important and substantial progress. Currently,the theoretical and technical basis of the stress release applied extraction of CBM has been explored,which expounds the mechanical principles of the TDC in-situ CBM recovery by horizontal well cavern completion and stress relief. The design of analogue experiment system for the TDC in-situ CBM recovery by horizontal well cavern completion and stress relief has been completed,and entered the processing,based on which some important results have been obtained according to a series of supporting basic experiments,including the establishment of relation model between the stress relief of TDC and the desorption and diffusion of CBM,and the reveal of the variation rules of TDC permeability caused by the stress release applied extraction. Based on the design of the analogue experiment system,some key technologies of the stress release applied extraction of CBM in TDC haves been developed,including the large diameter horizontal well drilling technology for TDC with two-way reciprocating drilling+multistage reaming+complex circulating drilling fluid,the stress relief and permeability increase technology with horizontal well pumping+ejection-induced controllable cavitation,the efficient lifting technology of mixture of water,gas,and high concentration coal powder in vertical wells with jet pump+supporting bottom hole device,the efficient ground gravitational separation+recycle+water circulation technology,and the data acquisition and control system for the device and engineering equipment of the stress release applied extraction of CBM.