Study On The Characteristic Of Sedimentology And Hydrocarbon Accumulation In Eastern Tarim Basin

The study area, which belongs to Tarim plate according to structural division, is located in the east of Tarim basin,and consists of Kongquehe slope,Yingjisu depression,Luobupo depression,and the north area of Tadong lower uplift and south-eastern depression.This area is nearly 25 percent of Tarim basin.Only the geologic ground survey had been completed before 1960 , including Kuluketage area and Aerjin area. Six exploratory wells had been drilled during 1960s with finding nothing, and it is the first time to drill for oil exploration in this area. The newly oil exploration work has been performing from the founding of Tarim headquarters to now. Oil and gas accumulations have been found in several wells, which indicates that the new era of oil and gas exploration is coming.The depositional cover incloudes Sinian system, Palaeozoic group, Mesozoic group, and Cainozoic group. The depositional thickness of all is nearly 10000 metres. Much tectogenesis had occurred in the past. The representation of tectogenesis is different in every geologic epoch, pull-apart depression in early Palaeozoic, uplift-denude area in late Palaeozoic, stable subsidence depression in Mesozoic era and Cenozoic era. There are six sedimentary evolution stages, such as, Sinian-Ordovician stage, Silurian-Devonian stage, Carboniferous-early Dias stage, late Triassic-middle Jurassic stage, Cretaceous stage,and Cenozoic stage. The change of sedimentary environment directly affects the distribution of sedimentary facies which determines the special distribution of oil sources, reservoirs and covers.Two oil source sets have been discovered. One comes from marine set of Cmbrian-lower Ordovician.The other comes from continental set of Jurassic. The Cmbrian-lower Ordovician source rock provides the mainly oil resource in study area which is thick,wide-ranging,lush and high maturation. The maturity index of Jurassic source rock, which comes from coal-measure strata, is lower. The thermal evolution of Jurassic source rock is in low-immature stage now. Partial mature source rock's product is mainly condensate. Middle-upper Ordovician maybe a potential oil source rock set.Two reservoir types are detrital reservoir rock and carbonate reservoir rock.The major reservoir sets are the detrital reservoir rock in lower Silurian, Jurassic, lower Cretaceous, and carbonate reservoir rock in Sinian and Palaeozoic in study area,among them the lower Silurian and Jurassic reservoir is better.The regional covers of study area are red mudstone in lower Silurian and the mudstone in Kezilenuer group of Jurassic.The other mudstone, argillaceous rock parting coal, as well as tight sandstone are local covers.There are ten reservoir-cover assemblages in study area,five in Sinian- Palaeozoic,the rest in Mesozoic whose assemblage is better.Three accmulation models have been summarized.The early accmulation model is Paleozoic source - Paleozoic reservoir. The late accmulation model is Paleozoic source -Mesozoic reservoir. The late accmulation model is Mesozoic source - Mesozoic reservoir or Paleozoic reservoir. There are seven favourable tectonic belts selected for exploration target in study area, five in Palaeozoic, the rest in Mesozoic .