Principal Investigator: William Griffith
Large, reservoir-scale sandstone dikes, 1-3 meters in thickness and hundreds of meters in length, intrude the shale-dominated Cretaceous Mowry formation at regular ~1 km intervals at Sheep Mountain Anticline. Source material for the dikes was a sandstone member of the overlying Frontier formation, thus the dikes represent significant potential fluid pathways through impermeable shales of the Mowry formation. The interior structure of the sandstone dikes is dominated by two pervasive sets of deformation bands (DB1 and DB2) representing significant (~10%) porosity loss. DB1 and DB2 bands maintain consistently distinct orientations, and DB1 bands are offset by shearing along DB2. A detailed study of the internal structure of the dikes will provide a better understanding of the hydraulic behavior of the dikes and the net potential effect of the dikes on fluid flow at the reservoir scale. In addition, detailed study of the development and deformation of the dikes will yield insights into the tectonic and stress history of Sheep Mountain Anticline. These insights will complement existing datasets based on fold-fracture relationships. Through coordinated research projects we will (1) reconstruct the 3D geometry of the dikes and surrounding country rocks using high precision Differential GPS and traditional geologic mapping techniques, (2) investigate fractures in the surrounding country rocks and deformation bands within the dikes, (3) study the petrophysical implications of the deformation bands using microscopy and image analysis, and (4) conduct geomechanical modeling of to gain insights into the mechanics of dike formation and deformation.