Geochemical Characteristics Of The Natural Gas And The Contrast Between Western Sichuan And Middle Sichuan

Taking the gas of Upper Triassic and Cretaceous in the western and the middleSichuan basin as target, this dissertation researches the Geochemical characteristics andgas source of gas pools of Upper Triassic and Cretaceous in the western and themiddle Sichuan basin by the Characteristics of gas composition, carbon isotopecharacteristic, gently characteristics, and rare gas characteristics and mades the mainresearch results as follows:Natural gas in the western and the middle Sichuan is mainly composed ofhydrocarbon gas. They all both hydrogen sulfide-free. So they can not for the marineorigin. Dry gas is the main kind of natural gas in the western Sichuan, while moisture isthe main kind of the middle Sichuan. From the statistics of the carbon isotope,we cansee main alkane carbon isotopic of natural gas in the western Sichuan significantlygreater than in central Sichuan, showing that maturity of natural gas in the westernSichuan greater than in central Sichuan. The gas of Upper Triassic and Cretaceous inwestern Sichuan as a whole is in the stage of mature to high mature, only to ethanecarbon isotope values of some samples of Xu2are very low. Later, they were provedto be from higher maturity of Xu1of oil-type gas. While main alkane carbon isotopicof Upper Triassic in the middle Sichuan greater than Middle and lower Jurassic,showing that maturity of Upper Triassic in the middle Sichuan greater than Middle andlower Jurassic. In western Sichuan, Carbon isotopic of natural gas in Partial-layer isinverted. While, in middle Sichuan, carbon isotopic of natural gas shows normaldistribution. Showing that the relationship between the gas source and filling of middleSichuan is easier. This article using the relationship of benzene/hexane and benzene/cyclohexane separately analyses Gas migration phase of western and middle Sichuan.In western Sichuan, analysis shows that there are aqueous phase and free phase from Xu2to Middle Jurassic. While from Upper Jurassic to Cretaceous, there are only freephase. In middle Sichuan, aqueous phase is the main kind phase of UpperTriassic.While in Middle and lower Jurassic ree phase is the main kind phase.The component characteristics of natural gas shows that it is coal-type gas fromUpper Triassic to Cretaceous in middle Sichuan. The carbon isotope characteristics ofwestern Sichuan’s natural gas indicates that the main kind of natural gas is coal-type gas,only to be Xu2,there being little oil-type gas. Light hydrocarbon parameters of heptanevalue-isoheptane value, Mango light hydrocarbon parameters, methylcyclohexaneindex, Cyclohexane index, lipid hydrocarbon group composition, toluene/benzene andso on all show that the main kind of natural gas of western Sichuan is coal-type gas. Thenoble gas isotope analysis shows that the main kind of natural gas of western Sichuan isorganic origin gas of Shell source. Based on the above four kinds of results, I concludethe main kind of natural gas from Upper Jurassic to Cretaceous in western Sichuan iscoal-type gas with organic origin gas of Shell source. only to be Xu2,there being littleoil-type gas. In middle Sichuan, the component characteristics of natural gas indicatesthat all of natural gas are kerogen pyrolysis gas and the Upper Triassic’s natural gasbeing coal-type gas,the Middle and lower Jurassic’s natural gas being oil-type gas. Thecarbon isotope characteristics of middle Sichuan’s natural gas indicates that there areonly organic pyrolysis gas, without biogenetic gas.In Upper Triassic, there beingcoal-type gas,in Middle and lower Jurassic,there being oil-type gas and part of thecoal-type gas. The light hydrocarbon characteristics of natural gas indicates that it ishumic organic gas in Upper Triassic and the main kind is sapropelic organic gas, partlyto humic organic gas in Middle and lower Jurassic. So to sum up, I conclude in middleSichuan the natural gas of the Upper Triassic is coal-type gas of organic pyrolysis gas,the main kind of natural gas of the Middle and lower Jurassic is oil-type gas of organicpyrolysis gas, partly to coal-type gas of humic organic gas.After gas resource tracing by the Characteristics of gas composition, carbonisotope characteristic, gently characteristics, and rare gas characteristics,I Concludedthat In Upper Triassic of western Sichuan, the natural gas of Xu2mainly comes fromsource rocks of Xu2, partly coming from Marine source rocks of Xu1; the natural gasof Xu4mainly comes from source rocks of Xu4, then coming from Xu5, Xu3alsohave a certain contribution. In fault development areas, Xu2. also have a certaincontribution. In Jurassic of western Sichuan the natural gas mainly comes from sourcerocks of Xu5, then coming from Xu4, partly maybe coming from lower Jurassic. InUpper Triassic of middle Sichuan, the natural gas mainly comes from source rocks of Upper Triassic. In Middle and lower Jurassic, the natural gas mainly comes from sourcerocks of lower Jurassic, partly coming from source rocks of Upper Triassic.