Abstract:

The north part of Tarim Basin,including Kuche depression,Shayar uplift and Awati-Manjiar depression,has an area of more than 100,000 sq km.On Sept.22,1984,more than 1,000m³ oil and 2,000,000m³ natural gas per day have been tested from well Shacan-2 on Yakela structure of Shayar uplift.Between Kuche and Awati-Manjiar depression,there is east-west extending Shayar uplift which is 460km long and 10-50km wide.It existed as a suc-cesional uplift during early Paleozoic to Mesozoic time.In the south of the uplift,Awati-Manjiar depression contains the Cambrian-Ordovician,Carboniferous-Permian and Triassic-Jurassic source rocks,among which the thick Cambrian-Ordo-vician and Triassic-Jurassic source rocks are widespread with better oil-generationpotential.North of the uplift,the Kuche depression contains mainly Triassic-Ju-rassic source rocks.The Shayar uplift,with many structural,stratigraphic,lithologic and combination traps,is in close proximity to those source rocks and in the direction of oil and gas migration.Therefore,it is favourable for searching gaint oil and gas fields.The oil and gas in well Shacan-2 are produced from the weathering zone of the Cambrian-Ordovician dolomites.The oil has high vanadium content(5.88 ppm),high nickel content(0.76 ppm)and high V/Ni ratio(17.76).The GC analysis of the saturated hydrocarbon in the crude oil indicates thatthe oil has even carbon predominance of C₂₈,C₃₀ and C₃₂ and its CPI is 0.988.It is considered that hydrocarbons from the well Shacan-2 were probablyderived from the Cambrian-Ordovician marine source rock.However,the Triassic sporo-pollen fossils have been found in the crude oil and many Acri-tarch fossils have been examined in the Triassic sediments of the well Yoacan-1on Shayar uplift,therefore,marine intercalations might exist in Triassic,hydrocarbons from the well Shacan-2 were also probably derived from the Triassic-Jurassic source rock.From above,the authors consider that the Yakela pool is of multi-source origin.