Distribution and characteristics of natural gas hydrates in the Shenhu Sea Area, South China Sea

Wei, Jiangong; Fang, Yuxiao; Lu, Hailong; Lu, Hongfeng; Lu, Jing; Jiang, Liang; Yang, Shengxiong

doi:10.1016/j.marpetgeo.2018.07.028

Cited by 126 publications

(59 citation statements)

References 34 publications

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“…Later, in 2010, Klapp et al reported the occurrence of sI and sII gas hydrates as coexisting phases from the Chapopote Knoll in the southern Gulf of Mexico [6]. Similar results were observed from the South China Sea by Wei et al [7], who analyzed gas hydrate samples and confirmed the coexistence of sI and sII gas hydrates. Even hydrate samples from Lake Baikal showed the coexisting hydrate phases with different structures and compositions [8].…”

Section: And Lighter Hydrocarbonsmentioning

confidence: 55%

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates

Pan

Schicks

2021

Molecules

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Natural gas hydrate occurrences contain predominantly methane; however, there are increasing reports of complex mixed gas hydrates and coexisting hydrate phases. Changes in the feed gas composition due to the preferred incorporation of certain components into the hydrate phase and an inadequate gas supply is often assumed to be the cause of coexisting hydrate phases. This could also be the case for the gas hydrate system in Qilian Mountain permafrost (QMP), which is mainly controlled by pores and fractures with complex gas compositions. This study is dedicated to the experimental investigations on the formation process of mixed gas hydrates based on the reservoir conditions in QMP. Hydrates were synthesized from water and a gas mixture under different gas supply conditions to study the effects on the hydrate formation process. In situ Raman spectroscopic measurements and microscopic observations were applied to record changes in both gas and hydrate phase over the whole formation process. The results demonstrated the effects of gas flow on the composition of the resulting hydrate phase, indicating a competitive enclathration of guest molecules into the hydrate lattice depending on their properties. Another observation was that despite significant changes in the gas composition, no coexisting hydrate phases were formed.

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Section: And Lighter Hydrocarbonsmentioning

confidence: 55%

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates

Pan

Schicks

2021

Molecules

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“…Two headspace gas samples from the shallow sediment (~20 cmbsf) recovered at HM‐2 using pushcorer contained more than 99.5% methane with δ 13 C of −71.5‰ to 72.3‰, indicating a biogenic origin (Wei et al, ). It has been reported that gas originated from shallower than 2.3 km are exclusively biogenic (Fang et al, ; Feng et al, ); therefore, it is speculated that “HaiMa” cold seeps are fuelled by gas from strata shallower than 2.3 km.…”

Section: Resultsmentioning

confidence: 99%

“…Pathways, such as faults, fractures, and gas chimneys, are often developed under the cold seeps which facilitate fluid migration (Bangs, Hornbach, & Berndt, ; Holbrook, Hoskins, Wood, Stephen, & Lizarralde, ; Posewang & Mienert, ; Riedel, Spence, Chapman, & Hyndman, ; Suo, Li, Dai, Liu, & Zhou, ). Natural gas hydrates are formed when gas‐charged (mainly methane) fluid moves into the gas hydrate stability zone (Bohrmann & Torres, ; von Huene & Pecher, ; Wei et al, ). In addition, methane undergoes sulphate reduction anaerobic methane oxidation which form authigenic minerals such as carbonate and pyrite (Bohrmann, Greinert, Suess, & Torres, ; Feng & Chen, ; Guan et al, ).…”

Section: Introductionmentioning

confidence: 99%

Geologically controlled intermittent gas eruption and its impact on bottom water temperature and chemosynthetic communities—A case study in the “HaiMa” cold seeps, South China Sea

Wei

et al. 2020

Geological Journal

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In 2018, the Institute of Deep Sea Science and Engineering investigated the “HaiMa” cold seeps in the northwestern part of the South China Sea using R/V “TanSuoYiHao” with manned submersible “ShenHaiYongShi.” Ten dives were conducted to make seafloor observations at six cold seeps (HM‐1 to HM‐6). By combining multibeam echosounder data and seismic profiles, a systematic study was made to understand fluid migration, accumulation, and eruption and their impact on the ecosystem. Location of gas flares observed in the multibeam echosounder data obtained in 2016 and 2018 is different, indicating a year‐level spatiotemporal variation of the cold seep activities. Seafloor observation shows that massive carbonates occur in HM‐1 and HM‐5, indicating two long‐term existed cold seeps (several thousands of years). Mussels covered large areas of HM‐2, HM‐3, and HM‐6, suggesting young active seeps. Elevated seabed with broken edges, mud cones, clay pools, and sudden increased water turbidity and temperature was encountered in multiple areas, which are inferred to be associated with shallow gas accumulation and eruption. Methane content of the headspace gas from shallow sediment at HM‐2 is higher than 99.5% with δ13C‐CH4 of −71.5‰ to 72.3‰, indicating a biogenic gas origin. It is inferred that the gas is sourced by reservoirs at ~1,280 mbsf, which are characterized by low frequency in the seismic profiles. Gas migrates from the gas reservoir to the top of the Basel uplift along the slope. High‐angle faults are widely developed between 800 and 240 mbsf, facilitating gas migration from the top of the Basel uplift to the shallow sediment. Most of the faults did not reach the seafloor; therefore, gas accumulated at shallow depth exhibits bright spots in the seismic profiles. When the pore pressure overcomes the overburden sediment, fractures will be created for gas entering the water column. Gas emission provides a pressure release mechanism; therefore, most fractures did not reach the seafloor as observed in the seismic profiles. However, it is speculated that gas emission will stop with growth of gas hydrates and authigenic carbonates, which continuously decrease the permeability of the original fractures. Pressure will be built up, and new fractures will be generated, leading to the formation of new seeps. This mechanism is inferred to result in the spatiotemporal variation of cold seep activity and affects the development of the cold seep ecosystem.

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“…The northern SCS experienced continuous evolution from an active continental margin in the late Mesozoic to a stable passive continental margin in the Cenozoic (Hui et al, ). Gas hydrate has been widely discovered in the northern slope of the SCS, and the gas source and origin have been well studied (Hui et al, ; J. Wang, Wu, Kong, Li, et al, ; J. Wang, Wu, Kong, Ma, et al, ; J. Wang, Wu, & Yao, ; Wei et al, ). The north‐eastern slope of the SCS is developed between the continental shelf and the abyssal plain at 300–3,700 m water depth (Figure ).…”

Section: Geological Settingsmentioning

confidence: 99%

Characteristics and formation mechanism of seafloor domes on the north‐eastern continental slope of the South China Sea

Wei

Liu

et al. 2018

Geological Journal

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Multibeam echo-sounding and seismic data were obtained during three geophysical surveys by Guangzhou Marine Geological Survey (GMGS) on the north-eastern slope of the South China Sea (SCS). Nineteen seafloor domes and numerous elongated pockmarks were distinguished in the study area. The seafloor domes vary on number of summits, shape, and spatial interrelation, based on which they were classified into four types which are single-summit, double-summits, elongated, and connected. Bottom simulating reflectors and blanking zone underneath were observed in the seismic profiles, indicating the potential existence of gas hydrate and free gas. Multiple faults and diapirs exist beneath the seafloor domes and pockmarks, which were inferred to provide efficient pathways for fluid migrating from deep subsurface. The seafloor domes exhibits high backscatter feature, which is potentially associated with the seep-related gas hydrate and authigenic carbonate in the shallow sediment. It is speculated that fault and diapir activity, fault sliding caused by region extension and the interaction between neighbour domes control and affect the activity and formation of the domes. However, further investigations, including geological sampling and seafloor observation, are still needed to confirm whether they are mud volcanoes.

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Distribution and characteristics of natural gas hydrates in the Shenhu Sea Area, South China Sea

Cited by 126 publications

References 34 publications

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates

Geologically controlled intermittent gas eruption and its impact on bottom water temperature and chemosynthetic communities—A case study in the “HaiMa” cold seeps, South China Sea

Characteristics and formation mechanism of seafloor domes on the north‐eastern continental slope of the South China Sea

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