Research About Geochemistry Characteristics Of The Holocene Shallow-biogenic Gas Source Sediments In Jiangzhe Coastal Plains Area

Research about Holocene shallow-biogenic gas has been received a lot of attention by scholars all over the world.Holocene shallow-biogenic gas could be found in lacustrine,floodplain,estuary,delta,shallow marine facies and so on.There are many advantages about shallow-biogenic gas,such as widespread,shallow buried,easier to predict,lower costs,yield quick returns and promise well.There are abundant shallow-biogenic gas resources in Jiangzhe coastal plains area which is widely distributed in Changjiang(Yangtze)River Delta and Hangzhou Bay but the degree of study and system are low.Research about geochemistry characteristics of the Holocene source sediments in this region is conducive to enrich the criteria and standards in the evaluation of source sediments.It provides evidence for the source of shallow-biogenic gas,enriches the theory of shallow-biogenic gas accumulation and petroleum geochemistry.Moreover,it has realistic directive significance to find new source sediments,zone of enrichment,calculate gas generated and deploy exploration.This paper conducts a systematic study on the Holocene sedimentary characteristics,depositional environment,petroleum geochemistry characteristics in Qidong area ZK01,Changjiang River Delta,and Xiaoshan area SE02,Hangzhou Bay,which are both belong to Jiangzhe coastal plains area.The TOC stands for the abundance of insoluble organic matter and the chloroform bitumen "A" stands for dissoluble organic matter.They both represent the abundance of organic matter.Identification of the types of insoluble organic matter is according to the element composition and precursors microscopy of Kerogen.The group composition of chloroform bitumen "A" and the gas facies chromatogram of saturated hydrocarbon can be used to determine the types of dissoluble organic matter.It is a comprehensive research to make sure the maturity of organic matter that combined with the gas facies chromatogram of saturated hydrocarbon,Rock-Eval data and Ro.What's more,this paper summarizes and investigates the geochemistry characteristics of late Quaternary shallow-biogenic gas and the control factors of generation in Jiangzhe coastal plains area.The muddy clay and silty clay of estuary-floodplain and shallow marine facies are both the source sediments of Holocene shallow-biogenic gas in Qidong area,Changjiang River Delta,and Xiaoshan area,Hangzhou Bay.It benefits the generation of shallow-biogenic gas because of source sediments in the favorable reduction environment.The abundance of organic matter in estuary-floodplain facies is more than that in shallow marine facies,and the former has stronger gas productivity.The abundance of Holocene organic matter in Changjiang River Delta is more than that in Hangzhou Bay.The terrigenous organisms predominate in the organic matter of the source sediments,and lower aquatic organisms are also present.The types of the organic matter are herbaceous sapropel-humic and herbaceous humic.The organic matter is still in immature stage and the shallow-biogenic gas is the result of the biochemical action.The late Quaternary shallow-biogenic gas is the result of CO2 reduction in Jiangzhe coastal plains area.It has provided the necessary geology conditions to generate shallow-biogenic gas since late Quaternary in Jiangzhe coastal plains area,such as big sea-level fluctuations,continuous tectonic subsidence,rapid deposition and favourable depositional environment in estuary region.Secondly,source sediments have good material conditions.Lastly,it is conducive to the growth of methanogens,such as reduction environment,fresh water-brackish water-salt water aqueous medium,low sulfate content and suitable pH.It is conducive to generate and accumulate shallow-biogenic gas,when these factors interact,influence and supply each other.