College of Safety Science and Engineering,Xi’an University of Science and Technology;Key Laboratory of Western Mine Exploitation and Hazard Prevention Ministry of Education,Xi’an University of Science and Technology;Western Engineering Research Center of Mine Gas Intelligent Drainage for Coal Industry

Most coal mining areas in China have a low coal seam permeability. Gas extraction technology by gas injec- tion displacement for increasing flow is one of effective methods to improve the efficiency of gas extraction in low-perme- ability coal seams. In this study,the gas occurrence characteristics of low-permeability coal seam in China were reviewed and classified. Five characteristics were summarized,including high resource reserves,low gas saturation,coexistence of multiple reservoir pressures, low-permeability, and complex partitioning. Based on the method of difference confidence,grey correlation and confidence interval calculation,the applicability of coal seam gas in China to the gas ex- traction technology by underground gas injection displacement for increasing flow was analyzed. Six direct factors affect- ing the effect of gas injection displacement were obtained. The influence degree was as follows:Platts coefficient > Gas pressure > Permeability > Ash content > Gas content > Langmuir pressure constant. A screening and evaluation method of coal seam parameters was established which was suitable for the gas drainage technology by underground gas injec- tion displacement for increasing flow. According to the different mechanisms of increasing gas flow in gas injection dis- placement,the gas flow increasing mechanism of gas injection displacement was clarified from two aspects:gas factor in- creasing flow (carry CH4 with filling energy to increase flow,promote CH4 desorption by sharing pressure to increase flow,promote CH4 diffusion by diluting to increase flow,and competitive adsorption to increase CH4 flow) and energy in- jection modification increasing flow (enlarge pores with filling energy to increase CH4 flow,enlarge pores with promo- ting desorption to increase CH4 flow,expand pores with promoting desorption to increase CH4 flow,and damaged pore structure/spread fracture network by pulse gas flow to increase CH4 flow). The influence of gas source and process pa- rameters on the gas injection displacement effect was summarized. A brief introduction to the key technology and equip- ment,application mode and application effect of the underground gas extraction technology by gas injection displacement for increasing flow. The future development trend of the underground gas extraction technology by gas injection displace- ment for increasing flow in China was prospected,including multidisciplinary deepening the theory of gas extraction by gas injection displacement for increasing flow,multimethod collaborative the technology of gas extraction by gas injec- tion displacement for increasing flow,precision of the parameters of gas extraction by gas injection displacement for in- creasing flow,intellectualization of the equipment of gas extraction by gas injection displacement for increasing flow,co- ordination of injection-pumping-excavation-mining connection layout in coal seam.

林海飞,季鹏飞,孔祥国,等.我国低渗煤层井下注气驱替增流抽采瓦斯技术进展及前景展望[J].煤炭学报,2023,48(2):730-749.
LIN Haifei,JI Pengfei, KONG Xiangguo, et al. Progress and prospect of gas extraction technology by under- ground gas injection displacement for increasing flow in low-permeability coal seam in China[J].Journal of China Coal Society,2023,48(2):730-749.