A New Method Developed for Rock Stress Measurement at Deep Depth in High Temperature Environment

Abstract

Core samples expand radially in anisotropic manner at core drilling by relief of anisotropic rock stresses, and as a result, they become to have a very slight elliptical cross section. In this study, we proposed and verified experimentally a new concept to modify the way of core drilling so that a partial section of the core sample expands to have elliptical cross section as described above but the other section maintains circular cross section before expansion. From this core sample, we can measure how much the core expands in any direction due to the stress relief with drilling, and the measured amount of expansion allows to estimate the magnitudes of in-situ stresses. This method does not require any in-situ test such as hydraulic fracturing and over-coring, it should be applicable to high temperature environment even in supercritical geothermal field, as long as the core samples can be obtained.