Publications

The application of oil based mud (OBM) for drilling in fractured reservoir is uncommon, but unavoidable for borehole stability reasons. Image log, as one of the most common and critical data acquired in fractured reservoirs, generally has lower resolution when it is run in the OBM compared to the water based mud (WBM). In the OBM, both log imager types of Electrical and Ultrasonic tools, have renowned resolution issues. Standard Electrical image tools (micro-resistivity tools) require water-based conductive muds to be effective: therefore in a non-conductive OBM environment, only specific tools can be used. The tools also have limited borehole coverage and the resulting image log is significantly affected by irregular logging speed (stick and pull). The application of Ultrasonic tools in OBM will reduce its effectiveness. Despite of its full borehole coverage advantage, Ultrasonic tools effectiveness are sensitive to tool eccentricity and drilling mud properties. Electrical images acquired in OBM system are suitable for bedding and identifying stratigraphic features, while Ultrasonic images are used for fracture identification. Both imaging tools should be run together for complete stratigraphic and fracture dataset. To anticipate inconclusive interpretation, collecting drilling data related to fracture penetration is also very essential. Rate of Penetration/Drilling Break, Gas Peak, Loss circulation, mud pit level, and else should be carefully and accurately monitored. Other type of data, such as Acoustic log and Core are important information in identifying open natural fractures and calibrating image logs interpretation. LM-3 well is an example of fracture data acquisition using OBM system drilled in West Natuna Basin. OBM was selected to anticipate the reactive shale. Electrical, Ultrasonic, and Acoustic tools were employed for data acquisition. Conventional core was also cut to verify any features observed in image logs. Image log interpretation was done by integrating different type of data (drilling, image logs, and core observation) to explain the presence of natural fractures in the target zone.