Various factors controlling the accumulation of natural gas hydrates (NGHs) form various enrichment and accumulation modes through organic combination. This study mainly analyzes the geological and geophysical characteristics of the NGHs occurrence in the uplifts and their slope zones within the deep-water area in the Qiongdongnan (QDN) Basin (also referred to as the study area). Furthermore, it investigates the dominant governing factors and models of NGHs migration and accumulation in the study area. The results are as follows. (1) The uplifts and their slope zones in the study area lie in the dominant pressure-relief direction of fluids in central hydrocarbon-rich sags in the area, which provide sufficient gas sources for the NGHs accumulation and enrichment through pathways such as gas chimneys and faults. (2) The top and flanks of gas chimneys below the bottom simulating reflectors (BSRs) show high-amplitude seismic reflections and pronounced transverse charging of free gas, indicating the occurrence of a large amount of gas accumulation at the heights of the uplifts. (3) Chimneys, faults, and high-porosity and high-permeability strata, which connect the gas hydrate temperature-pressure stability zones (GHSZs) with thermogenic gas and biogenic gas, form the main hydrate migration system. (4) The reservoir system in the study area comprises sedimentary interlayers consisting of mass transport deposits (MTDs) and turbidites. In addition, the reservoir system has developed fissure- and pore-filling types of hydrates in the pathways. The above well-matched controlling factors of hydrate accumulation enable the uplifts and their slope zones in the study area to become the favorable targets of NGHs exploration.

《地球科学》(ISSN 1000-2383;CN42-1874/P) (原刊名《地球科学——中国地质大学学报》ISSN 1000-2383;CN42-1233/P)，创刊于1957年，是由教育部主管、中国地质大学主办的综合性地学学术理论期刊，月刊，2015年改名为《地球科学》,她以反映中国地质大学教学与科研最新的、高水平的基础地质、应用地质、资源与环境地质及地学工程技术研究成果为主要任务。

Accurately identifying the Bottom Simulating Reflector (BSR) is a crucial and fundamental task in seismic exploration and the interpretation of gas hydrates in marine areas. During our seismic interpretation and inference work on a gas hydrate survey in the Qiongdongnan Sea area, we encountered a phenomenon that closely resembled the seismic reflection characteristics of BSR. By comparing and identifying various geological phenomena, we have determined that this unique seismic reflection phenomenon is, in fact, the reflection of the depositional bottom interface known as “mass transport deposits (MTDs)” as described by previous researchers. The physical properties of the MTDs developed on the shallow surface of the seafloor are similar to those of gas hydrate reservoirs in the seismic exploration of marine areas, particularly in the northern South China Sea’s Qiongdongnan Sea area. Due to the lack of active neotectonic movement in the area, most identified BSR reflection occurrences are parallel to the seafloor. Consequently, during the process of seismic interpretation of BSR in the Qiongdongnan Sea area, it may be confused with the bottom boundary reflection interface of MTDs. Accurately identifying MTDs’ sedimentary bodies in gas hydrate exploration activities in this area would greatly enhance the accurate identification of BSR and support the refined evaluation of gas hydrate resources. In this paper, the structural characteristics of MTDs are compared with the reflection characteristics of seismic profiles, the reflectors are identified as MTDs rather than BSR through analysis and interpretation, and the possible mechanism of hydrate accumulation in this region is discussed.