Identification of Stresses on Near-Borehole Field Using Cross-Dipole Sonic Tool and Image Logs: Case Study in Deepwater Carbonate

Abstract

Near-borehole stress analysis is performed from an integrated interpretation of sonic, imaging, and caliper tools to determine the magnitude and orientation of stresses around the borehole. These stresses can affect the wellbore stability because the tectonic stress field is disturbed during the well drilling. This paper presents a case study in which integrated information from borehole acoustic logs, image logs, and caliper tools were used to identify stresses in the near-borehole region of a deepwater presalt formation, offshore Brazil. The objectives were to extract the maximum (SH) and minimum stress (Sh) orientations in the near-borehole region for a particular zone of interest and identify fractures due to tectonic stresses. The Sh orientation was determined by the presence of induced fractures and borehole breakouts (both created during drilling), which were observed in the ultrasonic and resistive imaging log data. The SH orientation can be characterized using cross-dipole sonic anisotropy processing when borehole conditions are favorable. Tectonic fractures were identified using ultrasonic and resistive imaging log data information and the Stoneley reflection method was used to support the conductivity interpretation from these image logs.