35 hp://jpst.ripi.ir Journal of Petroleum Science and Technology 2017, 7(1), 35-41 © 2017 Research Instute of Petroleum Industry (RIPI) ABSTRACT Knowledge of the orientaon of horizontal in situ stresses is important to some areas of oil and gas field development plans. Borehole breakouts observed in image logs and drilling-induced fractures are the main parameters for the determinaon of the stresses’ direcons in situ. In this work, the orientaons of borehole breakouts were invesgated as a funcon of depth in oil wells A and B in Lali oilfield, in the Southwest of Iran. Borehole breakouts were detected from FMI logs. By the stascal analysis of the borehole breakouts’ orientaon in the foregoing two wells, it was found that, while a mean orientaon of minimum horizontal stress in well A is NE-SW, the azimuth of breakout in well B is different with a mean azimuth of 312˚±10˚. The result reveals that the orientaon must be different in these two wells due to some geological abnormality. Therefore, accurate and reliable geomechanical analyses are crucial steps toward minimizing the costs of drilling and compleon programs and migang borehole instability problems. Keywords: In Situ Stresses, Borehole Breakout, Drilling-induced Fractures, Lali Oilfield Mohammadreza Zare Reisabadi and Seyyed Saeed Ghorashi* Faculty of Research and Development in Upstream Petroleum Industry, Research Instute of Petroleum Industry (RIPI), Tehran, Iran The Effect of Fault Plane on the Horizontal In Situ Stresses Orientation: a Case Study in one of Iranian Oilfield *Corresponding author Seyyed Saeed Ghorashi Email: ghorashis@ripi.ir Tel: +98 21 48255325 Fax: +98 21 44739746 Arcale history Received: February 23, 2015 Received in revised form: December 23, 2015 Accepted: January 31, 2016 Available online: February 20, 2017 Journal of Petroleum Science and Technology INTRODUCTION Borehole breakouts and drilling-induced fractures (DIF’s) are important indicators of horizontal stress orientations [1]. Knowledge of the orientation of horizontal in situ stresses derived from the analysis of borehole breakouts is important for planning hydrocarbon exploration strategies; developing production strategies; engineering reservoirs, drilling, and wellbore mechanics; and studying crustal stress and rock mechanics [1]. Borehole breakouts are stress-induced enlargements of the wellbore cross-secon [2]. When a borehole is drilled, the material removed from the subsurface is no longer supporng the surrounding rock. As a result, the stresses become concentrated across the surrounding rock (including the wellbore wall). Borehole breakouts occur when the stresses around the borehole exceed the compressive strength of the borehole wall [3]. The enlargement of the wellbore is caused by the development of intersecng conjugate shear planes that cause spalling of the fragments of the formaon being drilled. Around a vercal borehole, stress concentraon is generally greatest in the direcon of the minimum horizontal stress. Hence the long axes of borehole breakouts are oriented approximately perpendicular to the maximum horizontal stress orientaon [4].