Invistigation On Marine Oil And Gas Accumulation In The Carboniferous Reservoirs In The Northern Tarim Basin

Several oil and gas fields have been discovered in Carboniferous in the Northern Tarim Basin. However, its forming process is very complicated because of multistage tectonic movement and multi-period hydrocarbon accumulation. Therefore, invistigation on oil and gas accumulation will mean a lot for oil and gas exploration in this zone.In this paper, typical reservoirs have been studied according to the geological, geophysical and geochemical data, combined with previous research. The oil and gas origin, the accululation and controlling factors have been summarized.Oil-source correlation was discussed by the physical properties, biomarkers and carbon isotope of crude oil. The data indicat that hydrocarbon maily origined from the Mid-Upper Ordovician souce rocks, and origined from mixed sources in local areas, involving Cambrian-Lower Ordovician source rocks and Mid-Upper Ordovician source rocks. Meanwhile, gas composition and stable carbon isotopes abundance showed that in the east it is crude oil-cracking gas while it is crude oil associated gas in the west.According to inclusion data, authigenic illite K-Ar dating data, bitumen, etc., combined with previous research results, three periods for hydrocarbon charging are suggested to occur. In the Late Hercynian period, the oils failed to accumulate, only some asphalt residue was preserved in local areas; Since Yanshan period, formation begun to reverse, oil and gas experienced adjustment; And in late Himalayan period, natural gas invasion only affected Lunnan area, and the condensate reservoir was formed.The study results suggest that Ordovician carbonate reservoirs supplied oils and gas for the Carboniferous reservoir; the structural reversal, sedimentary facies, and gas invation has great affected the hydrocarbon accumulation and distribution.