Sleeve-fracturing limitations for measuring in situ stress in an anisotropic stress environment

In order to determine the far-field in situ stress using the sleeve-fracturing technique, two and three discrete fractures must be produced for the double-fracture and single-fracture method, respectively. Numerical modelling of the sleeve-fracturing process, using the fracture mechanics code FRANC2D/L, showed that the initiation and propagation of discrete fractures, using the single or double sleeve-fracture method, was controlled by the far-field in-plane stress ratio. The numerical modelling also provided the characteristic shapes of the pressure-displacement curves for sleeve fracturing under various boundary conditions and highlighted the difficulty of detecting the inflection points in the pressure-displacement curves for the sleeve-fracture method, a key to the successful interpretation of the in situ stress data. (C) 2002 Elsevier Science Ltd. All rights reserved.