Estimating Strain and Stress in Oriented Rock Cores Using a Diametral Deviation Method

摘要

A practical core-based method for estimating in situ stress was tested using 360° measurements of rock core diameter in a laboratory setting. In several mining districts across West Virginia, rock cores were recovered from exploration core holes and oriented using an acoustic televiewer (ATV) summary log. Measurements of diametral variation were performed at 0.1-foot depth intervals using a benchtop device comprised of a pair of diametrically opposed contact digital indicator gauges working in tandem. The diametral profiles were evaluated to determine strain direction and strain magnitude. Stress magnitudes were calculated when values for Young's modulus, and Poisson's ratio were available. Stress direction results are compared to other stress determination methods, including downhole overcores, drilling-induced fractures, and borehole breakouts. The testing and analytical methods used are similar to the diametrical core deformation analysis (DCDA) method (lto, Funato, and Shono, 2012), but with a number of important improvements. The diametral deviation method presented here was found to be a practical working approach for characterizing the local in situ horizontal stress field, although aspects of it are still considered to be experimental.