This study examines problems that are related to large spatial variations in the physical properties of fan-delta sandstone in the Baikouquan Formation on the western slope of the Mahu Sag. This study conducts high-resolution sequence stratigraphy, sedimentary-microfacies identification, seismic-sedimentology analyses, and seismic inversions of high-quality reservoirs by comprehensively utilizing geophysical log data, cores, thin sections, and three-dimensional seismic data. A fourth-order sequence stratigraphic framework of the study area is established through these methods, enabling us to define the sedimentary filling processes that were related to multistage transgression and regression in the Huangyangquan and Xiazijie fan deltas. According to this study's results, the fourth-order sequences SSQ3 and SSQ5 were the development sequences of high-quality reservoirs. Feldspar-dissolution effects produced a secondary porosity-development zone, which favors relatively high-porosity and -permeability physical traps. Sedimentary microfacies, such as distributary and interdistributary channels in the fan-delta plain, alongside subaqueous distributary channels, estuarine mouth bars, and sheet sand in the fan-delta frontal areas, are successfully identified. The results suggest that the fan-delta front is the most favorable subfacies belt for reservoir development in the study area. By using the vertical boundary of the fourth-order sequence stratigraphy and the horizontal boundary of the sedimentary subfacies as the constraint conditions, we perform a facies-controlled seismic impedance inversion, in which the layers are divided to improve the accuracy of the reservoir predictions. Subsequently, five potential regions of high-quality reservoir development are predicted in the fourth-order sequences SSQ3 and SSQ5, and three well positions are proposed. Subsequent exploration drilling achieved industrial oil flow, thereby confirming these predictions from seismic sedimentological analysis.