The Prediction Of Massive Hydraulic Fracturing From Analyses Of Oriented Cores

An attempt has been made to predict the orientation of massive hydraulic fractures stimulated between depths of 2316 and 2464 m within the Muddy J Formation of the Wattenberg gas field, Colorado. Predictions were based upon a study of the properties of three oriented cores, one each from the west, central and eastern portion of the field and two unoriented cores from the central portion of the field. A preferred orientation of fractures induced in point load tests is found for all five wells. The two oriented cores from the western and eastern well show a primary trend of about 335° (# 25°), while that from the central sell showed a trend of about 110 ° (# 20°). The two unoriented cores also show a strong preferred orientation. This observed preferred orientation is corraborated by tensile strengths measured in Brazil tests. Additional support is obtained from triaxial compression tests done at confining pressure and temperatures simulating the hydrofracture depth. The strike of the induced shear fracture parallels (# 10 °) the orientation of the fracture produced by point loading. The second phase involves investigation of the composition, grain size, microfracture orientation, crystallographic orientation, grain dimensional orientation, and residual strain. Thin sections were cut parallel and perpendicular to the bedding plane and examined microscopically. In some cases sections were cut from two depths within the same well to determine vertical variability. The only two parameters that appear to possibly influence the fracture anisotropy are orientation of the dimensional axes of the quartz grains and the residual strain. In the wells on the east and west side of the field the long axes of the quartz are found to lie in the plane of the bedding and show a strong preferred orientation paralleling the direction of the fracture anisotropy.