Prediction of permeability trends and origins in coal-bed methane reservoirs of the Raton Basin, New Mexico and Colorado
— Jay C. Close and Russell R. Dutcher

The purpose of this paper is to propose methods for identifying trends and origins of inferred fracture permeability in potential Cretaceous-Tertiary coal-bed methane reservoirs of the Raton basin, northeastern New Mexico and southeastern Colorado. Permeability is a crucial reservoir characteristic that strongly influences the producibility of natural gas from coal seams. The regional trends of inferred primary and secondary permeability in potential coal-bed methane reservoirs of the central and southern Raton basin are approximately east and north, respectively. Published emplacement models for middle Tertiary syenite and syenodiorite dikes of West Spanish Peak in the northwestern Raton basin show that the trend of maximum principal horizontal regional stress during magmatic invasion was approximately N80°E (roughly perpendicular to the trend of the Sangre de Cristo Mountains thrust front along the western basin flank). Field evidence indicates that dike magmas south of the Spanish Peaks intruded pre-existing fractures, which are thus interpreted to have formed in the same stress regime as that calculated for the dikes. Therefore, primary extensional and secondary compressional release fractures and the corresponding inferred permeability freeways in potential central and southern Raton basin coal-bed methane reservoirs formed parallel and perpendicular, respectively, to eastdirected Laramide compressional forces.