The Chaoshan Depression, situated in the northern South China Sea, is a Mesozoic residual depression beneath the Cenozoic Pearl River Mouth Basin. Borehole LF35-1-1 has confirmed the existence of marine Jurassic layers rich in organic carbon within this depression. However, the understanding of petroleum geology in this area is limited due to the complex interplay of Mesozoic and Cenozoic tectonic activities and the poor quality of seismic imaging from previous surveys, which have obstructed insights into the characteristics of Mesozoic reservoirs and the processes of oil and gas accumulation. Recent quasi-3D seismic data have allowed for the identification of Mesozoic bioherms and carbonate platforms in the Middle Low Uplift of the Chaoshan Depression. This research employs integrated geophysical data (MCS, gravity, magnetic) and well data to explore the factors that influenced Middle Jurassic reef development and their implications for reservoir formation. The seismic reflection patterns of reefs and carbonate platforms are primarily characterized by high-amplitude discontinuous to chaotic reflections, with occasional blank reflections or weak, sub-parallel reflections, as well as significant high-velocity, high Bouguer gravity and low reduced-to-pole (RTP) magnetic anomalies. Atolls, stratiform reefs, and patch reefs are located on the local topographic highs of the platform. Three vertical evolutionary stages have been identified based on the size of atolls and fluctuations in relative sea level: initiation, growth, and submergence. The location of bioherms and carbonate platforms was influenced by paleotectonic topography, while their horizontal distribution was affected by variations in relative sea level. Furthermore, the reef limestone reservoirs from the upper member of the Middle Jurassic, combined with the mudstone source rocks from the Lower Jurassic and the lower section of the Middle Jurassic, as well as the bathyal mudstone caprocks from the lower part of the Late Jurassic, create highly favorable conditions for hydrocarbon accumulation.

The Chaoshan Depression situated in the Dongsha Sea region, is an important Mesozoic residual depression beneath the Cenozoic Pearl River Mouth Basin in the northern South China Sea, showing significant potential for hydrocarbon exploration. However, current drilling efforts have not resulted in hydrocarbon finds due to the absence of high-quality reservoirs. Recent quasi-3D seismic data has allowed for the first identification of Mesozoic bioherms and carbonate platforms on the Middle Low Uplift of the Chaoshan Depression. A thorough analysis was performed on their horizontal sedimentary distribution and vertical evolution. The findings indicate that the seismic reflection patterns of reefs and carbonate platforms in this area are primarily characterized by high-amplitude discontinuous to chaotic reflections, sometimes showing blank reflections or weak, sub-parallel reflections, along with notable high-velocity anomalies. Atolls, stratiform reefs, and patch reefs are found on local topographic highs of the platform, with atolls mainly in the central part of the quasi-3D area, stratiform reefs in the northeast, and patch reefs in the central-eastern region. Four vertical evolutionary stages have been identified: initial development, flourishing, decline, and submergence. The spatial distribution of bioherms and carbonate platforms was influenced by paleotectonic topography, while their developmental scale was affected by changes in relative sea level. Furthermore, reefs limestone reservoirs within the upper part of the Middle Jurassic exhibit excellent conditions for hydrocarbon accumulation, following a "lower source, upper reservoir, and upper seal" model. These reservoirs have favorable geological conditions for the formation of medium- to large-scale hydrocarbon accumulations, suggesting significant exploration opportunities.