Relationship between hydrocarbon distribution and fault network system under multi-stage rifting: a case study from the Tanhai area, Bohai Bay Basin, Eastern China

Multi-phase rifting creates complex fault networks that strongly influence hydrocarbon distribution. This study examines the offshore to shallow-marine eastern Jiyang Depression, Bohai Bay Basin, analyzing fault geometries across stratigraphic intervals using node/branch analysis and fractal dimensions to quantify topology and spatial scaling, and relating these to reservoir distribution. Results show a clockwise stress rotation (NW–SE to near NS), reorienting the dominant fault strike from NE–SW to NEE–SWW. High topological values cluster near tips of major NNE-trending faults (Gudong, Kendong, Changdi) and in linkage zones. Upward, I-nodes increase while Y- and X-nodes decrease; I-I branches increase at the expense of I-C and C-C connections, indicating poorer connectivity at shallower depths. Fractal dimensions remain high near principal NE-striking faults and decline from deep to shallow, reflecting reduced structural complexity. Both measures correspond closely with hydrocarbon occurrence, with high-value zones matching the most favourable accumulation fairways.