Fracture Density Of Units In The Brushy Canyon Formation, Whitehorse Group And Winchell Formation Of The Permian Basin.

Abstract

This study tests the theoretical equation(Fd Ua)/μ=A v/(1-2v)+B, where Fd equals the fracture density present in a geologic unit under constant strain conditions. The material properties in the equation were measured using acoustic velocities and density from samples taken from outcrops. Fracture density was measured from those same outcrop layers. If the equation is valid the measured data should plot as a straight line. The validity of the equation can be estimated using the correlation coefficient of the straight line graph. Fracture density measurements were made within the Permian age Brushy Canyon formation, Whitehorse Group and Winchell Formation of the West Texas Permian Basin. Material properties were obtained from P and S wave velocity measurements made by the Geomechanics Lab at UTA from samples collected from the Permian units mentioned above. Density was also measured from samples taken from the Brushy Canyon Formation, Whitehorse Group and Winchell Formation. Supplemental data for the observed formations were obtained from Wickham (1985) to support and expand the data set collected for this study. The results from the Whitehorse group have a correlation coefficient ≥ .90 indicating that the equation above is valid for those particular outcrops, and may be a good predictor of brittleness. I was unable to get more than three data samples for the other units, so the high correlations may be unreliable. Using the evaluation criteria in this study the fracture density of a unit has an exponential increase as the unit experienced increasing uniaxial extension. In addition, some units have significantly greater fracture density at a particular strain than others, identifying those layers that are more brittle.