Fracture detection in oil-based drilling mud using a combination of borehole image and sonic logs

摘要

The deeply buried (5.5-7.1 km) Lower Cretaceous Bashijiqike sandstones are important fractured reservoirs in the Kuqa depression. In these high temperature-high pressure drilling environments, oil-based muds are used to limit drilling risks and improve efficiency, making facture detection using resistivity based image logs difficult. The maximum horizontal stress (SHmax) trends close to North-South(0-10 degrees) based on orientations of the drilling-induced fractures and borehole breakouts. Core descriptions, thin sections and image logs used to describe the fractures in the Bashijiqike sandstone reservoirs show that opening-mode natural fractures are common, and the fractures range from fully open to sealed by calcite and clay minerals. The open fractures are dominantly steeply dipping or vertical and primarily strike north-south. Locally horizontal fractures or fractures with low angle dip are detected.