Analysis of Coalbed Methane Stimulations in the Warrior Basin, Alabama

Abstract

Summary An objective of the U.S. DOE's in-house coalbed methane R&D effort has been to improve coalbed hydraulic fracturing techniques by improving the understanding of stimulation treatments. Current efforts focus on examining data from coal mine excavations to observe stimulation results, conducting Nolte-Smith analyses to characterize fracture behavior, and exercising DOE/METC's stimulation modeling codes. Test Wells DHM-6 and DHM-7, two research degasification wells located in the Oak Grove field, AL, were analyzed in this project. METC's hydraulic fracture models predicted Well DHM-6 coalbed wing lengths 3 to 5% greater than the excavated wing length. This modeling was based on observation of fluid penetration into the shale roof rock and on guidelines derived from the Nolte-Smith method, which indicated vertical propagation into the bounding strata. Results to date indicate that the Nolte-Smith method may provide adequate interpretation of coalbed fracture behavior when the effects of variable injection rates, natural fracture fluid interaction, and the interface effects of coalbed and bounding formations are considered. Further evaluation of hydraulic fracture models that predict the effects of geologic discontinuities on coalbed fracture propagation is recommended. Additionally, a future mine excavation to expose the coalbed roof rock and to assess the extent of vertical fracture propagation is suggested.