Local Rotations in Borehole Breakouts—Observed and Modeled Stress Field Rotations and Their Implications for the Petroleum Industry

Abstract

Existing borehole breakout techniques are used to estimate the orientation of maximum horizontal stress (SHmax) with depth at a single borehole location. This method often results in regional (between boreholes) and local (with depth) scatter. It is important to understand the reason for the variability rather than disregard data because it does not conform to a tight data set. SHmax variability can be due to rotations of the stress field caused by a stiffness differential between the fault plane and surrounding rock mass. A case study in the Penola Trough, Otway Basin, South Australia, is presented where the orientation of borehole breakouts rotate with depth. The stress field rotations at the well locations can be successfully modeled with the two-dimensional distinct-element code, and compared with borehole breakout data. It is, therefore, possible to use borehole breakouts to assist in the selection of fault parameters for input into simple computational stress models.