The Importance of Overburden Stress Path in Assessment of Stress Dependence for 4D Applications

Abstract

This work demonstrates that for stress changes around the in situ stress, experimental stress sensitivity of a field shale core fits the linear stress path dependence that is expected on the basis of an assumed linear relationship between velocity changes and stress / pore pressure changes. This is based on ultrasonic laboratory measurements on a field shale core tested in undrained conditions along four different stress paths:Constant mean stress, isostatic, uniaxial strain, and triaxial. The in situ stress path depends on reservoir geometry, tilt, elastic contrast between reservoir and overburden, and possible non-elastic effects. Most often laboratory measurements are only carried out along one stress path, so the results from this work underline the significant importance of stress path for stress (and strain) sensitivity.