Abstract: In recent years, two 100 million-ton class subtle reservoirs were found in the Shijiutuo uplift within the Bohai Sea. Exploration practices have proved that new geological understandings provide theoretical guidance and scientific deployment for hydrocarbon exploration discoveries. The mechanism of ternary-factor (ridge-trap-sand) coupling for controlling reservoir in low-amplitude structure guided the significant discovery of the Neogene structural-lithologic reservoir in extra-shallow water delta in the Shijiutuo uplift. The differential hydrocarbon accumulation mode of subtle reservoirs in basin-margin fault transfer zone in steep slope belt facilitated the discovery of the first 100 million-ton class the Palaeogene stratigraphic-lithologic reservoir in the medium-deep layers in the Bohai oilfield. These new geological understandings further promoted technical researches and innovations. As a result, six key technologies have been developed, including the variable-velocity mapping for shallow low-amplitude structure, the description of lithologic traps in sand-rich extra-shallow water delta, the semi-quantitative fault-sand coupling analysis, the exquisite palaeogeomorphic restoration under the tectonic-sedimentary simulation in medium-deep layers, the identification of stratigraphic-lithologic traps in medium-deep layers, and the testing of complex lithologies in medium-deep layers. These technologies provide technical support and assurance for discovering large subtle reservoirs in the Bohai Sea, playing a prospective role for future promotion and application.

Key words: Archaeozoic, covered region, magmatic rock, rock type, quantitative identification, Jiyang depression