Mechanism of gas hydrate accumulation and its potential geological hazard risk in the northern accretionary wedge of Manila Trench
Natural gas hydrates have received widespread attention due to their enormous resource potential,but previous researches have focused mostly on the passive continental margin in the northern South China Sea,while rarely on the active continental margin in the eastern South China Sea.Based on the analysis of multi-channel seis-mic profiles in the active continental margin area of the Manila Trench in northeast of the South China Sea,this pa-per identified typical gas hydrate indicators such as bottom simulating reflector,blanking zone,polarity-reversal,and fluid migration channels,such as reverse fault and mud diapir are identified in this paper.The Orogenic Belt in southwestern Taiwan is an extension of the accretionary wedge of the Manila Trench.The associated gas of mud volcano is mainly CH4 and minorly showing high nitrogen anomaly.The geochemical characteristics of the associ-ated gas show that natural gas in this area is mainly mature hydrocarbon gas of pyrolysis origin,and is mainly the contribution of Neogene thick marine sedimentary source rock.According to the analysis,the cause is that the plate subduction brought deep hydrocarbon into the accretionary wedge and formed a high-pressure environment.The thermally generated hydrocarbon gas migrated upward along mud diapir and reverse fault.During the migration,some natural gas was gradually transformed by decomposition of microorganisms and mixed with in-situ microbial gas.The thermogenic and biogenic methane eventually mixed in the suitable stable zone to form a mixed gas hy-drate reservoir dominated by thermogenic and partly biogenic.In addition,with the change of external environment and the continuous activities of subduction movement,the stability of natural gas hydrate is damaged and decom-position leakage occurs,which may cause landslide.In the further exploration and development of natural gas hy-drate resources in this area,we must pay attention to the potential geological disaster risk.
gas hydrateaccumulation mechanismaccretive wedge of Manila Trenchactive continental marginSouth China Sea
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