| The research area,including Xuanhan-Daxian,which is the key area in the study work, Yuanba,Tongnanba,lies in northeast of Sichuan Basin.The main content of this paper is geochemical characteristics of natural gases which includes chemical component,carbon isotope compositions,thermal maturity,etc.,geochemical characteristics of reservoir bitumen and analysis of source-gases.And the analysis of source-gases is mainly through two ways which are gas/gas and gas/rock.So with the analysis it is kown the origin of gases in northeast Sichuan.Base on the research consideraton,it is made research on the geochemical characteristics and origin of gases in northeast Sichuan.Now there are four conclusions to talk about as follow.(1) The gases' chemical component is dominant in hydrocarbon gases which are mainly made up of methane,and containe abundant no-hydrocarbon components with CO2 and H2S. And the gases of Ziliujing and Xujiahe Formations in Yuanba trap are also dominant in hydrocarbon gases,and containe many heavy hydrocarbon gases with a few of no-hydrocarbon components;The gases of Leikoupo Formation is belong to dry gas with an content of 99%of CH4;The gases of Feixianguan and Changxing Formations are drier than others',but Feixianguan Formation is in a lack of H2S.Jialingjiang and Changxing Formations in Hebachang trap in Tongnanba area also belong to dry gas with CH4 average concentration being 99%,and have a few of heavy hydrocarbon and no-hydrocarbon components.(2) Theδ13C1 values of Feixianguan and Changxing Formations' gases are heavy ranged mainly from -29‰to -33‰,suggesting a high level of thermal maturity,and theδ13C1 values are ranged from -28‰to -33‰,however theδ13C1 values of a part of samples' hydrocarbon gases from C1 to C3 are reversal relation to TSR.Lastly,theδ13C1 values ranged from -25.28‰to -30.5‰of Feixianguan and Changxing Formations' gases in Yuanba area are heavier than the same gas layer of Xuanhan-Daxian area,with the same as Tongnanba area, and theδ13C2 values ranged from -25.0‰to -27.6‰are also heavy.(3) About the types and causes of organic matter in gas and source rock,the parent material of gases is mainly organic matter of source rocks in typeⅡin Xuanhan-Daxian,and its gases of Feixianguan and Changxing Formations are gas-cracking from oil previously reservoired in the traps,and the same as Yuanba area,considered from terrestrial hydrocarbon souce rocks.But Tongnanba area's gases maybe directly from the matter in high thermal evolution organic matter of source rocks.(4) About origin of natural gases.The gases of Feixianguan and Changxing Formations in Xuanhan-Daxian besides cracked from oil previously reservoired in the traps,and also are mixed by other gases,and Feixianguan and Changxing Formations' gases reservoirs have the same source,which is mainly Permian source rocks.Xujiahe and middle Jurassic Formations' gases maybe from continental humic type gas-souce rocks in around.Feixianguan- Changxing Formations' gas are from(up) Permian marine hydrocarbon source rocks and Ziliujing-Xujiahe Formations' are from continental hydrocarbon source rocks of early Jurassic to late Triassic in Yuanba area,and Leikoupo Formation' gas is from marine hydrocarbon source rocks,Qixia Formation maybe from early Permian hydrocarbon source rocks.Lastly,the gases of Xuanhan-Daxian and Yuanba areas are viewed to have a same souce which is Permian hydrocarbon source rocks by analysis.
|
PDF Full Text Request