Principles and examples of CO2-ECBM site selection under the con-straints of multiple geological attributes

CO2-ECBM has attracted great attention from the natural gas industry,as it enhances the CBM recovery rate by injecting CO2 into coal seams and achieves the geological storage of CO2.In order to explore the technical adaptability of CO2-ECBM to a large number of existing low single well production wells in SZN block in the south of Qinshui Basin,and to enhance the gas production of low effective old wells and seal CO2 underground as well,some research have been conducted based on the geological settings and the anisotropy of physical properties in coal seams in the study area.This study proposes three key geological principles of location selection:injectability,stimulation and storage of selected wells in low efficiency old well area CO2-ECBM.On this basis,the paper explained the principle of the key geological conditions,such as the coal seams thickness,permeability,the dip angle of coal seams,structure curvature,groundwater flow field,geothermal field,burial depth,lithology of the roof and floor,faults,etc.The result show that appropriate coal seam thickness and simple seam structures,high gas production,less than 5 degree of dip angle,a flat fold which has approximate axis (structural curvature is less than 2.5×10-4),1 km away from the fault,relatively low ground stress and small difference of primary stresses,the cooperation of groundwater runoff and CO2 injection flow field in coal seam,and the roof and floor of the coal seam with a dense mudstone lithology are the evaluation parameters and indexes of potential engineering favorable areas of CO2-ECBM.Results Z-1~Z-100 in the north,Z-160~Z-170 in the middle and Z-180~Z-240 in the south are the favorable areas for CO2-ECBM.Through the above comparative analysis,on the basis of favorable areas,seven alternative well groups with good physical properties and low recovery degree are further selected.The implementation sequence of injection well group is T-7>T-2>T-1>T-3>T-6>T-4>T-5 by grey correlation analysis,and T-2 and T-7 are the most preferred injection well groups.