<i>In situ</i> stress prediction using differential strain analysis and ultrasonic shear-wave splitting

Abstract

Abstract Knowledge of the in situ states of stress in rock masses is of considerable importance to a number of subsurface engineering activities, including those involved in exploiting petroleum and geothermal energy reserves. In this paper, a comparison is made of two laboratory techniques, based upon stress-relief microcracks, for determining the in situ state of stress: differential strain analysis (DSA) and ultrasonic shear-wave splitting (USWS). Measurements on ten sandstone samples recovered from deep boreholes, made using the well-established technique of DSA, have been compared to those made by the comparatively new technique of USWS and to sleeve fracturing measurements of in situ stress made in the corresponding boreholes. The results obtained indicate that the USWS technique, with its ability to test a large number of samples quickly, provides a useful adjunct to DSA and sleeve fracturing in determining trends in in situ stresses. Used in combination, the two laboratory techniques have also proved useful for examining rock micro-structural features.