Use of nonlinear chaos inversion in predicting deep thin lithologic hydrocarbon reservoirs: A case study from the Tazhong oil field of the Tarim Basin, China

Abstract

With the gradual disappearance of traditional structural reservoirs, widely distributed deep thin lithologic reservoirs developed in continental and transitional sedimentary environments may offer significant petroleum reserves. Reservoir characterization through conventional impedance inversion methods without appropriate selection of regularization parameters and other empirical constraints cannot easily detect and assess these reserves, however, due to their size, variation, and features that conceal them. We have evaluated a nonlinear chaos inversion method that uses well data and seismic facies to characterize the oil and gas reservoirs of the Tazhong oil field in the Tarim Basin, China. The inverted results exhibited high agreement with the well data in highlighting the interfaces and lithologic bodies. This integrated method also provided enhanced resolution of depositional contacts and variable lithologic bodies. Specifically, the approach was able to describe a highly variable, approximately 5 m thick Carboniferous formation at depths greater than 3400 m. Borehole and core data provided a complementary hydrocarbon accumulation model. We used background information on hydrocarbon-bearing units within the main structure (an anticline) to detect and access (drill) ultra-thin lithologic reservoirs located in deeper areas of the structural high. Two wells drilled according to predictions derived from this new approach have each reached production rates of more than 30 tons of oil per day. Thus, we have determined the effectiveness of combining chaos inversion methods with empirical constraints in exploration of deep thin hydrocarbon reservoirs.