Fracture Modeling and Fault Zone Characteristics Applied to Reservoir Characterization of the Rulison Gas Field, Garfield County, Colorado

Jeff Jackson¹ and Bruce Trudgill^2
1XTO Energy, Ft. Worth, TX
²Geology and Geological Engineering, Colorado School of Mines, Golden, CO

Structural modeling is a potentially valuable reservoir characterization tool. A good structural model is grounded in geologic data but incorporates many aspects from other disciplines. This work presents a structural model that incorporates geologic well data, 3D seismic data, geomechanical analysis, and well production data to characterize the Cretaceous stratigraphic interval of the Rulison Field area in the Piceance Basin of northwestern Colorado. The structural evolution of the Rulison Field was derived from the interpretation of 3D seismic. Shale Gouge Ratios along the seismically mapped fault surfaces have been calculated based on available well data. Incorporation of geomechanical stresses allows the dilation tendency of faults and fractures within the field to be calculated and analyzed. The mapped faults and horizons were used to create an elastic dislocation model of the reservoir. This elastic dislocation model yields a 3-D fracture model, which predicts qualitative fracture densities and shear failure types from the known geomechanical properties of the reservoir interval.

Ultimately, this model highlights compartmentalization within key reservoir intervals in the Rulison Field. It also confirms that the fault zones are pathways for fluid migration through their dilation, and that predicted 3-D fractures can be correlated to areas of known fracture production. On a larger scale, the interpreted tectonic history of early Cretaceous extension followed by Laramide aged inversion is a new interpretation of the structural evolution of the Piceance Basin. Thus, the structural model could be used to better optimize drilling locations and therefore production from within Rulison Field.

AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado