Gas hydrates have been considered as a new energy that could replace conventional fossil resources in the future because of their high energy density, environmental friendliness, and enormous reserves. To further analyze the potential distribution of gas hydrate stability zones (GHSZ) and the formation of a gas hydrate system in the Shenhu area of the South China Sea (SCS), a 3D petroleum simulation model (PSM) was built from 3D seismic interpretations and all available geological data. Based on the thermal calibration of the 3D model, the evolution of the GHSZ, hydrocarbon generation and migration, and the formation and accumulation of gas hydrates were simulated for the first time in the area. Thermal simulation shows that the methane source of gas hydrate originated from shallow biogenic gas and deep thermogenic gas. Most areas are dominated by shallow biogenic gas, while, only about 3% of the deep thermogenic gas derived from Enping Formation source rock and contributed to the gas hydrate formation within a few areas in the southeast. The thermogenic gas migrated vertically into the GHSZ through connecting faults, mud diapir, and/or gas chimney to form gas hydrate. The source rocks of the Wenchang Formation, a deep thermogenic gas source, began to enter the main hydrocarbon generation window at 28.4 Ma. The Enping source rock began to generate oil from 25 Ma on and gas from 16 Ma on. Since 5.3 Ma, most areas of the source rocks have generated a gas window, and only the shallower parts in the east still in the oil window, which had lasted until now. The shallow biogenic gas source rocks from the Hanjiang, Yuehai, and Wanshan formations generated gas in different periods, respectively. The Qionghai Formation began to generate hydrocarbon from 0.3 Ma and until now. Other results show that the GHSZ developed mainly during the Quaternary and Neogene (Wanshan Formation) and the GHSZ is thicker in the southern area and thinner in the northern part with a positive correlation with water depth. Starting at 11.6 Ma, the GHSZ developed in the Hanjiang Formation in the south of the Shenhu area and gradually expanded to the north to cover most of the study area at 5.3 Ma during the Yuehai Formation. From 1.8 Ma on, the GHSZ covered the entire study area. At the same time, the GHSZ in the Hanjiang Formation disappeared because of the change in temperature and pressure. At present, the GHSZ in the Yuehai Formation has disappeared, while the Quaternary and Wanshan are the two main formations for GHSZ development. The formation and distribution of gas hydrates are fundamentally controlled by the space-time coupling between the hydrocarbon generation and expulsion time and distribution of the GHSZ. The simulation results of gas hydrate accumulation and distribution were verified by drilling results and the matching rate is 84%. This is the first time that 3D simulation was successfully conducted with PSM technology in the Shenhu area and it provides important guidance for gas hydrate study in other areas of the SCS.

Since the onset of the Cenozoic, the South China Sea has experienced complex plate interactions including peripheral plate collisions, the demise of the Paleo-South China Sea, and the subsequent opening of the modern basin. These processes produced three major types of sedimentary basins: extensional, strike-slip, and compressional. The Beikang Basin represents a typical extensional continental-margin rift basin that preserves the stratigraphic and sedimentary record of the transition from syn-rift to post-rift stages. Subsidence happened mainly during the post-rift stage. Five structural styles exist: extensional, compressional-inversion, strike-slip–extensional, magmatic, and diapiric. While the first three are fault-related, the last two are mainly controlled by the volcanic phases. Using a seismic-facies-to-sedimentary-system workflow, we delineate a tectono-stratigraphic framework, comprising five seismic facies, seven lithofacies, and eight depositional facies. This framework indicates that the Beikang Basin evolved through four major tectonic stages including initial rifting, inherited rifting, climax rifting, and post-rift thermal subsidence. Each stage has primary control on sediment supply and accommodation development. Our findings refine the basin’s tectono-sedimentary evolution and improve predictions for sediment distribution and hydrocarbon exploration in the underexplored Beikang Basin.

The Beikang Basin is a large petroliferous sedimentary basin in the southern South China Sea, and is regarded as an important frontier area for deepwater hydrocarbon exploration in the Nansha region. Previous exploration by foreign oil companies has demonstrated its significant hydrocarbon potential. However, no wells have yet been drilled by China in the Beikang Basin. In this underexplored, well-free setting, sandstone reservoir prediction is hindered by several key challenges, including low velocity-picking accuracy, difficulty in constructing reliable low-frequency models, and limited inversion accuracy. These limitations collectively reduce the reliability of reservoir identification and thus increase exploration risk. To address the challenge of accurately predicting sandstone reservoirs in underexplored areas without well control, this study proposes a reservoir prediction workflow that integrates horizon-controlled gridded tomographic velocity modeling with seismic multiple integration. The workflow includes (1) pre-stack gather optimization, (2) tomographic velocity inversion to construct a precise velocity field, (3) multiple integration to supplement missing medium- to low-frequency information, and (4) pre-stack amplitude-versus-offset (AVO) simultaneous inversion to derive P-wave and S-wave impedances. Combined with petrophysical analysis from adjacent areas to establish a lithology interpretation framework, this integrated approach enables quantitative prediction of sandstone reservoirs in the Beikang Basin. Application to the study area demonstrates that the predicted sandstone thickness distribution is consistent with the regional geological conditions and is supported by drilling results from surrounding areas. The proposed method, therefore, provides a reliable technical approach for reservoir evaluation in the Beikang Basin, and has practical value for sandstone reservoir prediction in other underexplored frontier basins with limited or no well control.