Du M.,Key Laboratory of Marine Mineral Resources of Ministry of Land and Resources |
Su J.,Dagang Oilfield Company |
Lu Y.,Wuhan University |
Chen L.,Wuhan University |
Shuai Q.,Key Laboratory of Marine Mineral Resources of Ministry of Land and Resources
Earth Science Frontiers | Year: 2013
According to core observation and considering drilling, well logging and seismic data, the sedimentary characteristics of the third member of Shahejie Formation in the Qishen area have been researched. The results show that four types of depositional systems composed of braided river delta, subaqueous fan, fan delta and lacustrine depositional system were developed in the third member of Shahejie Formation. Based on sedimentary lithofacies analysis of each borehole, taking seismic facies and attribute into account, and combined with conglomerate thickness, sand content rate and sand thickness, the sedimentary systems maps were made, in which the temporal and spatial distribution characteristics of each segment in the third member of Shahejie Formation were reconstructed in the Qishen area. The studies indicate that the dominate sources were from Zhouqinzhuang of the south, Shenqingzhuang of the northwest, and Xiaozhan-Gegu of the north. The distribution of sedimentary systems of the third member of Shahejie Formation in the Qishen area follows traditional filling model of fault basin, nevertheless extensive distal subaqueous fan is the representative characteristic in this study area. In the Qishen area, the types of depositional systems and their distribution are controlled by different types of structure-paleogeomorphology, whereas the fault transform zones dominate the redistribution of sand bodies. In the study area, the turbid channel deposits of distal subaqueous fan are the most favorable reservoir facies, followed by the underwater distributary channel and mouth bar deposits of braided river delta front, then the mouth bar and underwater distributary channel deposits of fan delta front are the third advantageous reservoir facies.
Chen F.,Guangzhou Marine Geological Survey |
Chen F.,Key Laboratory of Marine Mineral Resources of Ministry of Land and Resources |
Su X.,China University of Geosciences |
Lu H.-F.,Guangzhou Marine Geological Survey |
And 5 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2013
Based on studies of sedimentary features in the sediment interval containing high-saturation gas hydrate(HS-GHZ) in the Shenhu area, this paper presents results of Shenhu gas hydrates drilling site SH7B, at which HS-GHZ is observed at two major sediment intervals: between 155 and 166 m, and between 172 and 177 m. Our results suggest that the fine-grained sediments are foraminifera-contained clayey silt and silt; with very few siliceous microfossils. Two sediment intervals with high abundance of foraminifera coincide with two intervals of HS-GHZs, with high correlation coefficient up to 72%. Scanning electron microscope analysis on microstructure of sediments shows that existing of abundant sand-sized foramineral shells makes obvious contribution to the increase of sand fraction in these sediment intervals and shell-room space of foraminifers (intra-frame pore space) are significantly larger than pore space between silt-sized grains (inter-particle pore space). Only a few numbers of foraminiferal shell-rooms are filled with fine silt- or clay-sized grains or pyrites, suggesting slight influence of post-sedimentary diagenesis on foraminifera shells. In addition, shell-room spaces of foraminifers are generally in round-form with smooth pore-walls, which surely increases volume-containing capability in comparison with irregular and same diameter-sized inter-particle pore space. These evidences suggested that abundant foraminifers do not only increase in porosity of fine-grained sediments, but also provide high volume-containing capability of pore spaces for accumulating of gas hydrate in those two HS-GHZs at site SH7B. Furthermore, HS-GHZs are also well correlated to abundant foraminiferal intervals at two adjacent gas hydrates obtained sites, e.g. sites SH2B and SH3B, in the Shenhu area. All of these results lead to the assumption and explanation that a large portion of gas hydrates should be stored in shell-room spaces of abundant foraminifers in fine-grained sediment layers in Shenhu area, which are different from the results obtained by ODP gas hydrate drillings; and existence of abundant foraminifers is an important sedimentary factor for controlling accumulation and storage of high saturation of gas hydrates in Shenhu area.
Wang H.B.,Key Laboratory of Marine Mineral Resources of Ministry of Land and Resources |
Wang H.B.,CAS Guangzhou Institute of Energy Conversion |
Yang S.X.,Key Laboratory of Marine Mineral Resources of Ministry of Land and Resources |
Wu N.Y.,CAS Guangzhou Institute of Energy Conversion |
And 5 more authors.
Science China Earth Sciences | Year: 2013
Temperature and pressure on seafloor of the northern slope in the South China Sea are suitable for gas hydrate formation, but bottom simulation reflector (BSR), an indication of gas hydrate occurrence, only occurred in limited areas of the slope. Drillings in the BSR-distributed area (the District S) on the northern slope of the South China Sea suggested that gas hydrate only occurred at Sites SH2, SH3, and SH7 with high saturation (up to 20%-40%), and there is no hydrate at Sites SH1 and SH5 although the distance between SH1 to SH3 is only 500 m. In this paper, we investigated seafloor gradient, fault development, temperature, and pressure in the District S on the northern slope of the South China Sea to understand the possible factors controlling BSR distribution and gas hydrate occurrence. The District S is a structurally fractured continental slope zone and its seafloor gradient varied greatly. The BSR-occurred areas have an average gradient of 19. 89×10-2 whereas the BSR-free zone has the average gradient of 10. 57×10-2. The calculated relative structural intensities from fault densities and displacements show that the BSR-distributed areas tend to occur in the areas with a moderately high structural intensity, where faults frequently developed close to the seafloor that are possibly favored for lateral migration of gases. On the basis of temperatures and pressures at drilling sites, hydrate-occurred Sites SH2, SH3, and SH7 are located within the thermodynamically stable area for methane hydrate, and hydrate-absent Sites SH1 and SH5 are out of the thermodynamically stable area for methane hydrate formation, suggesting that both BSR and the thermodynamic stability are necessary for hydrate occurrence in the subsurface. © 2013 Science China Press and Springer-Verlag Berlin Heidelberg.
Yang Z.,Key Laboratory of Marine Mineral Resources of Ministry of Land and Resources |
Zhang G.,Key Laboratory of Marine Mineral Resources of Ministry of Land and Resources |
Zhang L.,Key Laboratory of Marine Mineral Resources of Ministry of Land and Resources
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2016
The reef and carbonate platform is one of the most important reservoirs in the south of South China Sea, and the reefs and the sedimentary facies of carbonate platform in the Wan'an basin should be further studied. The high-resolution seismic profiles associated with well data in this paper facilitate the understanding of the reefs and carbonate platforms in the study area. The evolution of reefs and carbonate platform can be divided into four stages. In Early Miocene, a few isolated carbonate platforms that were small in size firstly initiated in center of this basin. They flourished in Middle Miocene and mainly developed around the Northern Uplift, Central Uplift. Transversely, two bands there, namely western band and eastern band, were the distinct characteristic of its spatial distributions in this time. Platform-edge reef and massive reef were the main style of reef and there were also a few point reefs developing on the edge of carbonate platform. In Late Miocene, the carbonate platforms began to backstep to elevated topographic positions in response to a relative sea level rise. While, the number and style of reef increased in this stage, such as platform-edge reef, massive reef, atoll reef and point reef. Tectonics and eustasy are the two main controlling factors on platform development. Tectonics mainly controlled both the initial topography for reef growth and the distribution of platforms, and eustasy controlled carbonate sequence development. Since the Late Miocene, the rapid tectonic subsidence and the rise of relative sea-level should have led to the drowning of carbonate platform. © 2016, Editorial Department of Earth Science. All right reserved.