Optimization of Reservoir Mapping Technology for Horizontal Wells in 20 Degree Steeply Dipping Fault-Block Reservoirs

Abstract The Oilfield A is a highly complex fault-block reservoir segmented by 80 faults into over 40 small blocks, each averaging only 0.3 km2 in area. This structural complexity results in low recovery efficiency, with remaining oil primarily concentrated in the peripheral fault blocks. Certain blocks exhibit steep dips of up to 20° with significant variations, presenting substantial challenges for horizontal well trajectory design and reservoir exposure. To address these challenges, a resistivity reservoir mapping tool was deployed during horizontal drilling to provide real-time structural and stratigraphic insights, optimizing well placement. Steeply dipping formations introduce complex current pathways, significantly impairing resistivity measurement accuracy and imaging resolution. To mitigate these challenges, an enhanced resistivity reservoir mapping tool with four operational frequencies was employed. Geological models were constructed using offset well resistivity data, and frequency responses in steeply dipping formations were simulated to identify the optimal frequency combination for improved reservoir mapping resolution. Furthermore, the conventional inversion algorithm was improved to accommodate larger dip angles, increasing tool adaptability. Near-bit logging data were also integrated to identify abrupt local stratigraphic changes. The implementation demonstrated that the optimized frequency combination achieved excellent compatibility with the formation. The improved resistivity inversion algorithm effectively mapped structural variations, identifying dip changes from 15° to 21° and capturing a progressive thinning of the formation from 13 meters to a pinch-out. Reservoir exposure reached 85%, and production exceeded expectations by 50%. This successful application provides critical insights into horizontal well development in steeply dipping and complex reservoirs, offering significant potential for broader field applications.