In this study, we use petroleum systems modeling (PSM) to quantitatively simulate the uncertainty of biogenic gas generation modes and their impact on the spatial distribution and resource assessment of gas hydrates in the Baiyun Sag, South China Sea. The results are as follows: (1) Biogenic gas generation is significantly affected by thermal state and organic matter type. Low temperature is a primary reason for gas hydrate occurrence in shallower sediments when sufficient methane gas is present. This may be due to higher thermal conductivity of the overlying sediments, slower sediment burial rates, or other geological processes. (2) Natural gas hydrate resources are significantly controlled by biogenic gas generation. In addition to the thermal conditions of the source rock or sediment, the nature of the organic matter is another crucial factor. Generally, low-temperature methanogens produce more methane gas because they require less energy, whereas high-temperature methanogens require more energy and thus produce less methane gas. (3) The biogas generation thermal model is key to controlling the location and quantity of natural gas hydrate resources. The three possible gas-phase models, K0, K1, and K2 (representing different methanogens), produce varying amounts of methane gas over time, resulting in different amounts of natural gas hydrate resources. Additionally, the preservation of various methanogens in biogas source rocks can alter reservoir formation locations, influencing the scale and genetic model of natural gas hydrate resources.

Accurate evaluation of the distribution characteristics and physical properties of gas hydrate reservoirs is crucial for estimating gas hydrate resources,guiding development and utilization strategies,and understanding environmental impacts.Based on high-precision 3D seismic and well-logging data acquired in the Shenhu area,this paper presents a comprehensive method for discriminating between hydrate layers,free gas layers,and coexistence layers using integrated logging-seismic responses.Our results show that the gas hydrate layer and free gas layer at the W17 station can be accurately identified by combining post-stack seismic profiles with detailed analysis of logging curves.Above the BSR,a hydrate layer is characterized by relatively high seismic velocity,strong amplitude reflections,poor transverse continuity,and high resistivity and velocity values.In contrast,the underlying free gas layer exhibits low seismic velocity,low-frequency weak amplitude reflections,and low resistivity and velocity values.This study provides a robust basis and valuable reference for informed decision-making regarding gas hydrate reservoir identification,resource evaluation,exploration,and trial production activities.

塔中—顺托果勒地区油气勘探不断取得重大突破已表明该区域蕴藏着丰富的油气资源,而颗粒滩沉积刻画对于沉积环境分析和储层预测具有理论和实践意义.本文通过大量的岩心薄片分析,发现该地区颗粒滩类型主要为内碎屑滩,生物礁体不发育,岩性主要以亮晶碎屑灰岩为主,部分发生白云岩化作用,并且随着深度增加其作用增强.内碎屑滩通常含有一些鲕粒、藻粒和少量生物碎屑,其中鲕粒较小,见低能环境放射鲕.连井对比分析显示:鹰山组可以划分为两个三级层序,并且能在整个塔中地区进行对比,上升半旋回期间颗粒滩沉积以薄层退积为主,下降半旋回期间则以厚层加积为主,而最大海泛面时期颗粒滩发育规模较小.鹰山组沉积时期,颗粒滩在开阔台地和局限台地广泛发育,但两者沉积特征不同,开阔台地颗粒滩沉积厚度较大,呈团块状沿开阔台地外围分布,而局限台地内颗粒滩一般厚度较小,呈小团块或条带状分布.

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.

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.

The amount of natural gas contained in the world’s gas hydrate accumulations is enormous, but these estimates remain highly speculative. So far, it is still challenging to locate spatial distribution of marine gas hydrate and quantitatively characterize the evaluation parameters and systematic improvement of evaluation systems. Considering the systematic review of the key accumulation factors, such as heat flow, deposition rate and total organic carbon in the typical passive continental margin, the evaluation results of global marine gas hydrate resources were analyzed based on the characteristics of gas hydrate geology, geophysics and geochemistry anomalies in the South China Sea. We analyze the problems on the evaluation of marine gas hydrate resources, probing into the geological characteristics and distribution laws of marine gas hydrate resources in the South China Sea, and estimate the parameters for in-place resource evaluation, in which the volume method based on Monte Carlo probability was used to evaluate the gas hydrate potential resources in the South China Sea. The probability distribution ranges from 37.6 billion (with 90% probability) to 117.7 billion (with 10% probability) tons of oil equivalent, with an expected value of 74.4 billion tons of oil equivalent. The study results show that the gas hydrate resource density in the South China Sea is similar to that in the typical sea areas, and the estimated global resources are basically consistent with the assessment results at this stag; this shows that the South China Sea has great potential for gas hydrate resources. The research results can provide guidance for the evaluation of global climate change and the exploration and development of hydrate resources.