Determination of In-Situ Stress From Anelastic Strain Recovery Measurements of Oriented Core

A reliable method for determining the in situ stress state in deep formations is of great importance to the gas industry in designing massive hydraulic fracture treatments of low permeability reservoirs. Knowledge of the horizontal in situ stress directions and magnitudes would allow prediction of fracture azimuth and height. In this paper a method using anelastic strain recovery measurements of oriented core will be presented as a reliable and practical tool for determining both the directions and magnitudes of the principal horizontal in situ stresses in deep formations. The principal horizontal stress directions are determined directly from the principal horizontal strain recovery directions. The principal horizontal stress magnitudes are calculated from the principal strain recovery magnitudes, overburden stress, and Poisson's ratio of the rock using a viscoelastic model by Blanton. In addition, petrophysical measurements of the core parallel to the principal directions of strain recovery, at atmospheric pressure and at elevated confining pressure, suggest that the strain recovery process is a consequence of microcrack formation and expansion.