Characteristics of Tectonic Transition Zone in the Western Segment of the Bonan Low Uplift and the Formation of Giant Buried Hill Oil and Gas Field in the Offshore Bohai Bay Basin

ABSTRACT The western segment of the Bonan Low Uplift (WBLU), situated in the southern Offshore Bohai Bay Basin and bounded by the Ludong Uplift and the Chengning Uplift, represents a significant tectonic transition zone that records the Mesozoic tectonic events. This study investigates the tectonic evolution and hydrocarbon accumulation mechanisms of the region through three‐dimensional seismic interpretations, petrographic analysis and imaging log data. Our findings demonstrate that the WBLU functions as a strike‐slip transition zone, accommodating differential movements along strike‐slip fault systems. The tectonic evolution of the region is characterised by four distinct stages: Indosinian orogenic uplift, early Yanshanian compressional thrusting, late Yanshanian strike‐slip deformation and Himalayan reverse faulting and subsequent burial. The early Yanshanian compressional‐torsional regime played a critical role in initiating differential block movements, thereby laying the foundation for the current tectonic framework. As an inherited structural high positioned between major uplifts, the WBLU has significantly contributed to the formation of extensive buried hill closures. Multi‐phase tectonic activity generated fault breccia, enhancing seal integrity and reactivated internal fractures, facilitating fluid dissolution and mineral alteration. Collectively, these processes created favourable conditions for the development of buried hill fracture reservoirs. This study provides a comprehensive framework for understanding the tectonic and hydrocarbon evolution of the transition zone in the Offshore Bohai Bay Basin, offering insights that may guide the exploration of buried hill oil and gas reservoirs in complex fault systems.