Zoback, Mark D.1
(1) Stanford University, Stanford, CA
ABSTRACT: Determination of the Full Stress Tensor and Application to Problems of Fault Seal and Wellbore Stability
Over the past fifteen years, my colleagues and I have developed a suite of techniques for determination of in situ stress orientation and magnitude from observations routinely available in deep oil and gas. As these techniques can be utilized in both vertical and highly deviated wells, they have had extensive application in the petroleum industry where knowledge of stress orientation and magnitude at depth is important for addressing a wide range of problems. The techniques we have developed for estimation of the maximum horizontal principal stress make extensive use of observations of non-catastrophic failures of the wellbore wall - compressive failures (breakouts) and drilling-induced tensile fractures, as well as the stress perturbations associated with slip on faults cutting through the wellbore. The widespread use of wellbore imaging in the petroleum industry has been a critical development that makes utilization of these techniques possible. In addition to reviewing the theoretical basis for these techniques, we present case studies derived from oil and gas fields in different parts of the world. These case studies document the facts that the techniques described here yield i) consistent stress orientations and magnitudes over appreciable depth ranges, ii) stress magnitudes that are often consistent with absolute and relative stress magnitudes predicted by Coulomb faulting theories, iii) stress orientations and relative magnitudes that are consistent with regional stress indicators and tectonics and iv) sufficiently well-constrained estimates of the full stress tensor that are useful in application to problems such as fault seal evaluation and wellbore stability.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.