In-situ stress distribution and coalbed methane reservoir permeability in the Linxing area, eastern Ordos Basin, China

摘要

Understanding the distribution of in-situ stresses is extremely important in a wide range of fields such as oil and gas exploration and development, CO~(2)sequestration, borehole stability, and stress-related geohazards assessment. In the present study, the in-situ stress distribution in the Linxing area of eastern Ordos Basin, China, was analyzed based on well tested parameters. The maximum horizontal principal stress ( S ~( H max)), minimum horizontal principal stress ( S ~( h min)), and vertical stress ( S ~( v )) were calculated, and they were linearly correlated with burial depth. In general, two types of in-situ stress fields were determined in the Linxing area: (i) the in-situ stress state followed the relation S ~( v )> S ~( H max)> S ~( h min)in shallow layers with burial depths of less than about 940 m, indicating a normal faulting stress regime; (ii) the S ~( H max)magnitude increased conspicuously and was greater than the S ~( v )magnitude in deep layers with depths more than about 940 m, and the in-situ stress state followed the relation S ~( H max)> S ~( v )> S ~( h min), demonstrating a strike-slip faulting stress regime. The horizontal differential stress ( S ~( H max)– S ~( h min)) increased with burial depth, indicating that wellbore instability may be a potentially significant problem when drilling deep vertical wells. The lateral stress coefficient ranged from 0.73 to 1.08 with an average of 0.93 in the Linxing area. The coalbed methane (CBM) reservoir permeability was also analyzed. No obvious exponential relationship was found between coal permeability and effective in-situ stress magnitude. Coal permeability was relatively high under a larger effective in-situ stress magnitude. Multiple factors, including fracture development, contribute to the variation of CBM reservoir permeability in the Linxing area of eastern Ordos Basin.