Determination of three-dimensional in-situ stress: Anelastic strain recovery method and an example of its application

For an intended application of stress measurement at great depth in the case of scientific drilling, a core-based, anelastic strain recovery (ASR) method was described in this paper. Then, an example of the application of the ASR method to an active fault drilling project was shown. The anelastic strain of a drilled core specimen in nine directions, including six independent directions, was measured after its in-situ stress was released. The core specimen used was sandstone taken from a depth of 592 m. Acquired anelastic strains reached several hundred microstrains that could be used for a three-dimensional analysis resulting in the determination of orientations and the estimation of magnitudes of the principal in-situ stresses. The obtained principal orientations and magnitudes can be considered to be valid. Consequently, it can be concluded that the anelastic strain recovery measurement is well suited for the task of directly determining the orientations of principal in-situ stresses and to estimate the magnitude of the stresses at great depth.