Geological occurrence and accumulation mechanism of natural gas hydrates in the eastern Qiongdongnan Basin of the South China Sea: Insights from site GMGS5-W9-2018

Liang, Jin; Wei, Jiangong; Lu, Jingrang; Kuang, Zenggui; He, Yulin

doi:10.1016/j.margeo.2019.106042

Cited by 97 publications

(107 citation statements)

References 82 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…. N refers to the normalized concentration against the standard Post-Archaean Australian Shale [43].…”

Section: Methodsmentioning

confidence: 99%

“…δ 13 C and gas composition analysis indicated that the identified hydrate-bound gases are a mixture of biogenic and thermogenic gas. The paleo-uplift resulted in the differential compaction and formation of fractures and faults, which ultimately controlled the development of gas hydrate [43]. An intermediate gas reservoir lies beneath 190 mbsf, which has been suggested to bridge the deep gas reservoir and shallow gas hydrate system [36].…”

Section: Geological Settings and Site Descriptionmentioning

confidence: 99%

“…At GMGS5, carbonates were collected at 3, 52, and 53 mbsf layers of the Qiongdongnan Basin of the South China Sea. Gas hydrates have been found at 6 and 136 mbsf and the current sulfate and methane transition zone (SMTZ) is located at about 0.47 mbsf [43]. Therefore, GMGS5 is an ideal experimental site for studying the long history and the relationship between carbonate formation and methane leakage.…”

Section: Fluid Source and Environment Of Seep Carbonate Formationmentioning

confidence: 99%

See 2 more Smart Citations

Deeply Buried Authigenic Carbonates in the Qiongdongnan Basin, South China Sea: Implications for Ancient Cold Seep Activities

Wei

Zhang

et al. 2020

Minerals

Self Cite

View full text Add to dashboard Cite

Cold seep carbonates are important archives of pore water chemistry and ancient methane seepage activity. They also provide an important contribution to the global carbon sink. Seep carbonates at three sediment layers (3.0, 52.1, and 53.6 mbsf) were collected at site W08B in the Qiongdongnan Basin of the South China Sea. This study investigated the mineralogy, microstructure, stable carbon and oxygen isotopes, trace elements, and U-Th dates of these carbonates to identify the relationship between methane flux and authigenic carbonate precipitation. The results showed that the δ13C and δ18O values of all carbonates are similar, indicating that the carbon source for shallow carbonates and deep carbonates has remained constant over time and included biogenic and thermogenic methane. Although carbonates were found in three sediment layers, the two main stages of methane seepage events were discernible, which was likely caused by the dissociation of gas hydrates. The first methane seep took place at 131.1–136.3 ka BP. During a dramatic drop in the sea level, the seep carbonate at 52.1 mbsf formed at 136.3 ka BP through the anaerobic oxidation of methane (AOM). The carbonate at 53.6 mbsf resulted from the vertical downward movement of the sulfate-methane transition zone with decreasing methane flux at 131.1 ka BP. This is the reason for the age of carbonates at 52.1 mbsf being older than the age of carbonates at 53.6 mbsf. The second methane seep took place at 12.2 ka BP. Shallow carbonate formed at that time via AOM and is now located at 3 mbsf. Moreover, thin-section photomicrographs of deep carbonate mainly consisted of matrix micrite and biological debris and acicular aragonite occurred as vein cement filling the pore spaces between the matrix micrite. The acicular aragonite was mainly influenced by the timing of the carbonate precipitation of minerals. This research identified a long history of methane seep activity reflected by the vertical distribution of carbonates.

show abstract

“…. N refers to the normalized concentration against the standard Post-Archaean Australian Shale [43].…”

Section: Methodsmentioning

confidence: 99%

Section: Geological Settings and Site Descriptionmentioning

confidence: 99%

Section: Fluid Source and Environment Of Seep Carbonate Formationmentioning

confidence: 99%

See 1 more Smart Citation

Deeply Buried Authigenic Carbonates in the Qiongdongnan Basin, South China Sea: Implications for Ancient Cold Seep Activities

Wei

Zhang

et al. 2020

Minerals

Self Cite

View full text Add to dashboard Cite

show abstract

“…Deep‐water fans and channels are widely developed in this area. Seismic profiles show that a large number of gas chimneys and bottom simulating reflectors, indicators of gas migration and gas hydrate, were developed in the QDNB (Fang et al, ; Liang et al, ; Zhang et al, ). The fifth gas hydrate drilling expedition conducted in 2018 recovered natural gas hydrates within a gas chimney system (Wei, Liang, Lu, Zhang, & He, ; Ye et al, ).…”

Section: Geological Settingmentioning

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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

“…In terms of total carbon release, describing methane flow in mole values may lead to an underestimation since higher hydrocarbons are not considered, e.g., Mega Plumes 1 and 2 in [24]. However, because it was assumed that pure methane was released from the Site F and Haima cold seeps [57][58][59], the volume and gas amount (moles) were calculated separately for each bubble size measurement and then averaged for more accurate results. The estimated methane bubble flow rates for seeps 1-3 at Site F were 0.4, 4.4, and 0.1 L h -1 , respectively, and seep 1 of the Haima cold seeps yielded a rate of 12.6 L h -1 .…”

Section: Methane Bubble Fluxmentioning

confidence: 99%

Using Time-Series Videos to Quantify Methane Bubbles Flux from Natural Cold Seeps in the South China Sea

Dong

Tao

et al. 2020

Minerals

View full text Add to dashboard Cite

Natural cold seeps are an important source of methane and other greenhouse gases to the ocean and atmosphere in the marine environment. Accurate quantification of methane bubble fluxes from cold seeps is vital for evaluating their influence on the global methane budget and climate change. We quantified the flux of gas bubbles released from two natural cold seep sites in the South China Sea: one seep vent in the Haima cold seeps (1400 m depth) and three seep vents at Site F (1200 m depth). We determined bubble diameter, size distribution, and bubble release rate using image processing techniques and a semiautomatic bubble-counting algorithm. The bubble size distributions fit well to log-normal distribution, with median bubble diameters between 2.54 mm and 6.17 mm. The average bubble diameters and release rates (4.8–26.1 bubbles s−1) in Site F was lower than that in Haima cold seeps (22.6 bubbles s−1), which may be attributed to a variety of factors such as the nature of the gas reservoir, hydrostatic pressure, migration pathways in the sediments, and pore size. The methane fluxes emitted at Haima cold seeps (12.6 L h−1) and at Site F (4.9 L h−1) indicate that the Haima and Site F cold seeps in the South China Sea may be a source of methane to the ocean. However, temporal variations in the bubble release rate and the geochemical characteristics of the seeps were not constrained in this study due to the short observational time interval.

show abstract

Geological occurrence and accumulation mechanism of natural gas hydrates in the eastern Qiongdongnan Basin of the South China Sea: Insights from site GMGS5-W9-2018

Cited by 97 publications

References 82 publications

Deeply Buried Authigenic Carbonates in the Qiongdongnan Basin, South China Sea: Implications for Ancient Cold Seep Activities

Deeply Buried Authigenic Carbonates in the Qiongdongnan Basin, South China Sea: Implications for Ancient Cold Seep Activities

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

Using Time-Series Videos to Quantify Methane Bubbles Flux from Natural Cold Seeps in the South China Sea

Contact Info

Product

Resources

About