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ON RADICAL RULES OF OIL AND GAS DISTRIBUTION IN THE EASTERN AREA OF JUNGGAR BASIN
Peng Xiling
1989, 10 (4):
1-14.
The eastern Part of Junggar basin is a new oil and gas-bearing area with principal source bed being upper Permian series. The Distribution of oil and gas here was controlled by late-palaeozoic depressions. The north Dajin g depression and east of the south Changji depression seperated by an uplift appear to be two independent oil and gas-bearing units, resembling two independent oli and gas-bearing basins where distribution patterns of oil and gas are not uniform. The Dajing depression, located in the north area is an oil-bearing depression where source rock and reservoir rock are the same bed.Pindiquan formation is only srratigraphic unit bearing industrial oil and gas. The formation itself is source bed and reservoir rock as well as caprock. Therefore, the centre of depression was the centre of source area. In the centre of source area anticlines with middle uplift size and mature synchronous with hydrocarbon are the best oil-bearing traps. The lithologic characters, however, is a faactor which should not be neglected. They are tyoal strucral-lithologic oil pools in which oil-water interfaces are uneven whereas reservoir pressures uniform. In the south area, the east part of Changji depression is characterized with source and reservoir rocks are not the same beds. Here, more oil - bearing stratigrraohic units exist, and formation course of oil and gas reservoir is very complicated. Variations of the thickness of Permian source rock are very rapid laterally, and times when the source rock came into maturity threshold are not uniform. Porous sand-stones were so tack in the source rock that expulsion of hydrocarbons was impeded. This resulted in great difficulty of oil-gas migration. The main centre of source area of Permian was only situated within the limite of a long, narrow piedmont of Bogeda mountain. After early Yenshan movement this zone rose, becoming an erosional area, hence lost meaning of a source area. In the west depression Mesozoic coal-series was a kind of source rocks. From the south slope of north Santai uplift to the downthrow of Fukang fault, oil and gas came from source centre of the piedmont and gathered into traps before Cretaceaus, and then were eroded Here. heavy. viscous oil of remaining old oil reservoirs was principal with part of oil and gas came in late. In Jimusar depression heavy and viscous oil came from the unmature-low mature source rocks within the depression. The oil and gas in north faulted-nose at north Shantai uplift came from Permian in the north part of Fukang depression, and was a sort of exotic petroleum experienced secondary migration. It is still well preserved and isn't remanent reservoir, The oil and gas in the west slope of north Shantai uplift is characteristic of low density and low viscosity.This is a kind of late mature and late arriving oil and gas coming from Fukang depression. It is not the remainders of destroyed oil depositeither. It is anticipated that some small oil and gas reservoirs might be discove-red in Wucaiwan depression and Hodong syncline of the northern area. In the southern area where Fukang fault zone has greater potential unfortunately,however, there are only many scattered, complex, middle and small oil and gas reservoir. Oil potential in Jimusar depression can not be neglected. Later oil and gas accumulations in the west slope of north Shantai uplift might be so
important that it could change significance of the southern area.
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