Improving Drilling Safety and Efficiency with 100% Reservoir Exposure in a Challenging Low Resistivity Mature Reservoir Associated with Structural and Geological Uncertainties by Integrating Extra Deep Azimuthal Resistivity Technology in a Source-Less Solution - A Case Study From UAE Offshore

Abstract

Abstract Improvement in drilling efficiency and maximum reservoir exposure are two key considerations in determining the success of a well. Detailed planning covering these aspects is critical, especially when the reservoir is associated with a complex geological setting. In this case study, oil producers in a complex low resistivity environment associated with high heterogeneity, karstification, caves, collapsed holes, fractured and faulting as common geological features were drilled on the flank of a mature field. Drilling challenges would be profound if the well bore passed through the sub-seismic karst features and the overlaying shale formation. Drilling into such features risk drilling complications that could potentially result in unwanted sidetracks and/or reduce reservoir exposure. The main challenge was to maximize reservoir exposure in the target interval, characterized by thin pay thickness, while maintaining a safety buffer of 15 to 20 ft between the overlying shale and the well trajectory. Maintaining a standoff from an uncertain oil-water contact (OWC) was also critical due to prolonged production in the field. Historically, a combination of a high-resolution resistivity-imaging service with nuclear magnetic resonance technologies was utilized for drilling the lateral sections in this area, primarily for fluid typing, permeability, porosity distribution, and detailed geological evaluation. However, this solution was insufficient for proactive geosteering to place the wellbore optimally in the reservoir and map the sub-seismic structural changes and the uncertain OWC. To overcome these challenges, Extra Deep Azimuthal Resistivity (EDAR), along with reservoir navigation services was integrated into the existing solution after completing feasibility studies based on the offset data. The feasibility study demonstrated that EDAR could map the structural and fluid changes from the wellbore satisfying drilling and well placement requirements. EDAR inversion mapped the structural changes on top of the reservoir, reducing the geological uncertainty related to sub-seismic faults, karsts, and the OWC. This enabled informed geosteering decisions to achieve 100% reservoir exposure in the optimum target zone and helped to maintain a smooth well profile facilitating a trouble-free completion operation. Placing the well in the best porous zone of the reservoir resulted in a 28% increase in ROP. The completion design was optimized based on fluid distribution analysis and structural information from EDAR inversion. The acquired data improved the knowledge of the geological setting of this area.