Evaluation of Oil Saturation in Reservoir Rocks Based on the Borehole-surface Electromagnetic Method

The Borehole-surface Electromagnetic Method (BSEM) is a controlled-source technique for oil and gas exploration, involving downhole excitation and surface observation to obtain resistivity and polarization data. By conducting excitations above and below target reservoirs and collecting time/frequency-domain electromagnetic data, BSEM complements seismic methods in delineating hydrocarbon boundaries and identifying fluids. A quantitative oil saturation evaluation model was developed using core experiments, Archie’s equation, and complex resistivity analysis. Applied in China’s W well zone, BSEM provided detailed resistivity and polarizability parameters, constrained by seismic and logging data. The results, validated by petrophysical experiments, offered clearer horizontal and vertical oil saturation profiles than traditional logging, enhancing reservoir evaluation and well placement optimization for deep and ultra-deep exploration.