Evaluation of geological controlling factors of CO2-ECBM in complex coal seams and optimization of favorable areas

SHI Suzhen; ZHAO Kang; GAO Weixu; LIU Zuiliang; LI Li; ZHANG Xin

Abstract：In order to explore the feasibility of implementing CO2-ECBM in heterogeneous coal seams under com-plex geological conditions,taking the No.15 coal seam bifurcation merging area in Xinjing Mining area as an example,the spatial distribution characteristics of coal seams were finely characterized by logging constrained wave im-pedance inversion and time-depth conversion technology,and then integrated fracture prediction was realized by com-bining eigencoherence and intelligent ant technology.The evaluation parameters(thickness,structure,capping condi-tions,etc.)of CO2-ECBM geological favorable area are also described.The results show that the higher the thickness of coal reservoir,the better the effect of CO2 storage.The thickness of No.15 coal seam bifurcation area is small and there is dirt inclusion,and the existence of coal-mudstone system leads to the reduction of reservoir,which is not conducive to the recovery of coalbed gas and CO2 storage.The coal rock thickness in the coalescing area of No.15 is larger than that in the bifurcation area,the geological structure is relatively simple,and the content of coal-bed methane is higher.Starting from the sealing conditions of the surrounding rock,the top and bottom of the No.15 coalseam area develop thick mudstone and limestone,which is poor in permeability,conducive to the large-scale and long-term effective storage of gas,and belongs to a typical closed tectonic environment.In terms of geological structure,the gently inclined coal seam helps to slow down the CO2 escape rate and make CO2 spread more even-ly throughout the coal seam,and the reservoir effect is the best in areas with undeveloped faults,and the reservoir effect in areas with developed reverse faults is better than that in areas with developed normal faults.Therefore,the zone with inclination less than 10°,undeveloped fault or reverse fault development in the No.15 coalseam area is se-lected as the potential favorable area for CO2-ECBM implementation.The study is helpful to promote the application of this technology in similar complex coal seams,and provide a basis for the storage and injection and production of CO2 in complex coal seams.