Anisotropy and fracture analysis for coalbed methane reservoir development in Bokaro coalfield, India

Abstract

ABSTRACTThe low permeability of coal seams is a constraint in the efficient production of coalbed methane. However, the presence of natural fractures in coal enhances the permeability, and prior knowledge of sub‐surface fractures in coal seams is vital to identify the prospective seam. This paper investigates the anisotropy and identifies fractures by processing the advanced sonic and resistivity image logs to mitigate challenges in the reservoir. Anisotropy is estimated from the difference in the travel time between fast and slow shear waves. The application of Alford's rotation technique determines the fast shear wave polarization angle which is consistent with the fracture orientation along the NE–SW or NW–SE direction in coal seams. Moreover, the crossover of fast and slow shear waves in the slowness versus frequency plot indicates stress‐induced anisotropy that originates from fractures. Besides, drilling‐induced fractures observed along NE–SW in the resistivity image log indicate the maximum horizontal stress direction. Results from this study compare coal seams based on fractures in adopting better operational activities for optimized production and future geomechanical studies in the Bokaro coalfield situated in India.