The southern continental margin-slope area of the South China Sea is a complex passive continental margin with diverse tectonic structures and movements. This area is rich in gas hydrate resources and is also an area with a high incidence of potential geological hazards. Identifying and understanding the potential submarine geological hazards in this area is very important for disaster prevention and management during the future exploration and development of marine resources. In this paper, five types of potentially hazardous geological bodies are identified in the research area through high-precision two-dimensional seismic processing and interpretation, including submarine mounds, pockmarks, mass transport deposits, submarine collapses and faults. At the same time, the seismic reflection characteristics and the changes in its morphology and surrounding strata are described. In addition to the causes of geological hazards in this region and their influence on exploration and development, the research prospects of geological hazards in this region are also suggested. Special tectonic and sedimentary conditions, fluid activities and hydrate decomposition may be the conditions for geological hazards in this region, which pose a significant threat to the exploration and development of seabed resources and marine engineering construction in this region. Not only does our conclusion provide useful data for the development and utilization of gas hydrate, but it also presents theoretical suggestions for reducing geological hazards in the development process.

Recent breakthrough exploration wells in the Huagang Formation in the Y-area of the central anticlinal zone of the Xihu Sag have confirmed the significant exploration potential of structure–lithology complex hydrocarbon reservoirs. However, limited understanding of the provenance system, sedimentary facies, and microfacies has hindered further progress in complex hydrocarbon exploration. Analysis of high-precision stratigraphic sequences and seismic facies data, mudstone core color, grain-size probability cumulative curves, core facies, well logging facies, lithic type, the heavy-mineral ZTR index, and conglomerate combinations in drilling sands reveals characteristics of the source sink system and provenance direction. The Huagang Formation in the Y-area represents an overall continental fluvial delta sedimentary system that evolved from a braided river delta front deposit into a meandering river channel large-scale river deposit. The results indicate that the primary provenance of the Huagang Formation in the Y-area of the Xihu Sag is the long-axis provenance of the Hupi Reef bulge in the northeast, with supplementary input from the short-axis provenance of the western reef bulge. Geochemical analysis of wells F1, F3, and G in the study area suggests that the prevailing sedimentary environment during the period under investigation was characterized by anoxic conditions in nearshore shallow waters. This confirms previous research indicating strong tectonic reversal in the northeast and a small thickness of the central sand body unrelated to the flank slope provenance system. The aforementioned findings deviate from conventional understanding and will serve as a valuable point of reference for future breakthroughs in exploration.

During the Miocene, several reefs formed in the Beikang Basin, South China Sea, which may be potential targets for hydrocarbon exploration. This is due to the environment that developed as a result of the collision, splitting, and splicing of the Nansha Block, which was influenced by the Neogene expansion of the area. However, studies on the types, distribution, controlling factors, and evolution stages of these reefs are scarce. In this study, we used high-resolution seismic data and extensive well-drilling records to gain insights into the evolution of reefs in this particular area. Six distinct types of reefs, namely, the point reef, the platform-edge reef, the block reef, the bedded reef, the pinnacle reef, and the atoll reef, were identified based on our data. These reefs underwent four stages of development. During the initial stage, a few small-sized point reefs emerged in the basin and experienced significant growth during the early Middle Miocene. In the flourishing stage, the reefs predominantly thrived around the Central Uplift and Eastern Uplift areas. In the recession stage, the reefs began to deteriorate during the late Middle Miocene period as a result of the rapid increase in relative sea level caused by tectonic subsidence. In the submerged stage, since the Late Miocene, as the relative sea level continued to rise steadily over time, many reefs that had previously flourished surrounding the Central Uplift and Eastern Uplift areas became submerged underwater, with only a handful of atoll reefs surviving near islands located on the Eastern Uplift. This study indicated the presence of a significant number of well-preserved reefs in the Beikang Basin that have experienced minimal subsequent diagenesis and therefore exhibit high potential as reservoirs for oil and gas exploration.

The first oil and gas well in the South Yellow Sea Basin was completed in 1961. In 1984, 2.45 tons of light oil were obtained from the Cenozoic strata. However, it remains the only large oil and gas basin in China’s offshore area without industrial oil and gas discoveries. Although the consensus is that the South Yellow Sea Basin is a foreland basin, and the oil and gas exploration prospects are promising, the research on the regional structure and the tectonic evolution of the foreland basin system is weak, which seriously hinders the process of industrial oil and gas discoveries. This paper reports the results of over 30 years of onshore and offshore investigations and well-seismic joint interpretation in the study area: for the first time, the mountains and basins formed by the collision of the North China and Yangtze plates were discovered in the geological survey of the northern islands of the South Yellow Sea Basin; the C-type eclogite chronology of Qianliyan Island, the characteristics of the foreland basins and intracontinental foreland basins around the South Yellow Sea, and the tectonic evolution characteristics and models of the basins were clarified. Through the zircon/phosphate fission track analysis of the deep black Jurassic strata in the Qianyuan S-2 well, it was revealed that the collision and subduction of the Pacific Plate against the Eurasian Plate since the Late Cretaceous–Paleogene led to large-scale uplift movements, and more than 3000 m of strata were eroded in the basin area. This is consistent with the multiple unconformities of E/N, K/N, and T₂/N identified by well-seismic joint interpretation, and is also the main reason why oil and gas have been difficult to preserve in the South Yellow Sea Basin since the Middle Triassic–Jurassic. Deep prototype oil and gas exploration in the basin may be the preferred option for current oil and gas exploration deployment, which is conducive to achieving industrial oil and gas discoveries.

Submarine natural gas hydrate accumulation requires deep methane to enter the gas hydrate stability zone, become immobilized within a reservoir, and remain confined beneath a caprock. The long-term coupling among reservoir supply, caprock retention, and hydrate self-sealing remains poorly resolved. We developed a mass-conservative synthetic two-dimensional Darcy flow and reactive-transport model that couples a quasi-steady potential field, mobile methane transport, supply- and pore-capacity-limited hydrate formation, and saturation-dependent permeability reduction. Single-factor, full-factorial, global-sensitivity, numerical-convergence, and long-term experiments showed that reservoir and caprock permeability both controlled methane supply; hydrate mass was more sensitive to caprock permeability (PRCC = 0.919) than to reservoir permeability (PRCC = 0.738), and the reservoir response plateaued above approximately 100 mD. Caprock permeability and thickness jointly regulate flux and leakage, with maximum conversion occurring at intermediate caprock permeability rather than at maximum flux. In the 30 kyr reference case, self-sealing reduced source-zone flow by 7.14%. In the 500 kyr extension, hydrate-mass growth and source-flow change first remained simultaneously below 1% over the preceding 10 kyr at approximately 338 kyr. The parameter combinations maximizing hydrate mass, conversion efficiency, and sustained accumulation differed, and, at 30 kyr under the stated thresholds, only 8 of 81 combinations jointly achieved high conversion, elevated reservoir saturation, and low leakage. Favorable accumulation therefore reflects dynamic matching among supply, retention, and self-sealing under specified boundary conditions, rather than an isolated extreme in any single property.

Clay-surface conduction in fine-grained, weakly consolidated marine sediments, together with the scale mismatch between core and logging observations, often causes resistivity- and acoustic-based estimates of gas hydrate saturation to diverge. For Well GMGS5-W08, we develop a core-constrained, scale-matched electroacoustic fusion method (CC-SMEF) for gas hydrate saturation estimation. The method derives a low-frequency clay background from gamma-ray and core clay data. An optimizable vertical window then summarizes the logs around each core reference depth as robust neighborhood features. A low-dimensional, regularized kernel map integrates deep resistivity, P-wave velocity, gamma ray, and the clay background on this common representation scale. Chlorinity-derived saturation provides the geochemical reference, and the model was compared with the Archie and Simandoux methods at all reference points and with the isotropic three-phase acoustic method at available matched depths. Pointwise leave-one-out evaluation indicated lower observed error than Archie, although the uncertainty interval included no improvement and explanatory capability remained moderate. The fixed-parameter ablation is exploratory. Under the stricter four-block protocol, saturation-model tuning and fitting were restricted to training blocks while the clay background remained calibrated from all 22 core clay measurements; CC-SMEF RMSE was 17.89 percentage points versus 15.87 for Archie, so superiority in held-out-depth prediction was not established. CC-SMEF is therefore interpreted as a local interpolation framework for the represented W08 intervals; application elsewhere requires independent calibration and validation.