The Role of Ultra-Deep Resistivity Tools in Detecting Oil-Water-Contact in a Faulted Regime While Geosteering

Abstract Geosteering horizontal wells in faulted carbonate reservoirs presents significant operational challenges, particularly in detecting variations in fluid contacts such as the oil-water contact (OWC). These variations are often influenced by complex fault systems, compartmentalized reservoir blocks, and historical production and water injection, which can displace fluid contacts and lead to undulating boundaries. Conventional resistivity-based Logging While Drilling (LWD) tools frequently lack the depth of investigation necessary to detect these contacts early, increasing the risk of water breakthrough and suboptimal well placement. This paper demonstrates the application of ultra-deep azimuthal resistivity (UDR) tools in accurately identifying OWC variations while geosteering in a structurally complex, mature carbonate dome structure. By integrating ultra-deep resistivity measurements—capable of imaging tens of meters from the wellbore—with real-time inversion algorithms and structural models, the geosteering team successfully identified bed boundary undulations, fault cuts, and fluid contact shifts during drilling. Operational results from this case confirm that the integration of UDR data with pre-existing models and real-time workflows significantly reduced subsurface uncertainty, improved wellbore positioning, and enhanced reservoir exposure while avoiding aquifer contact. The high-resolution inversion models enabled early detection of OWCs and compartment boundaries, providing valuable inputs for optimized well trajectories and future development planning.