A New Method for the Measurement of In Situ Stress in Geothermal Fields

Abstract

A new method is proposed for the measurement of in situ stress in the deep earth's crust. The method utlizes hydraulic fracturing technique and measurements of AE signals emerging from the cracks created during the hydraulic fracturing. Its basic concepts are derived through considerations on crack initiation and crack curving in a rock mass under three dimensional stress states, so that the method is available to the case that the direction of the principal axes of stress is totally unknown; this is generally the case of most geothermal fields. Whereas the conventional hydraulic fracturing stress measurement, which is based on the two dimensional theory of elasticity, is not necessarily adequate to the above mentioned case, since the conventional method assumes that one of the principal axes of stress is vertical and the magnitude of the principal stress in the vertical direction is equal to the overburden pressure.