ANALYSIS OF THE DIFFERENCES AND GENESIS FOR THE KEKEYA OIL IN TARIM BASIN

The oil-and gas-bearing strata are the Neogene Xihepu Formation(N₁x),the Paleogene Kalata Formation(E₂k)and the Cretaceous in Kekeya oilfield,Tarim Basin.Researches show that,in this area,the oil properties,group components,saturated hydrocarbon chromatograms,saturated hydrocarbon steranes,terpanes,carbon isotopes,nitrogen compounds etc.have regularly changed in spatial distribution.The density and the concentration of carbazole of the crude oil decrease gradually from the deep to the shallow,while some other parameters,such as content of saturated hydrocarbon,C₂₁-/C₂₂+,C₂₁₊₂₂/C₂₈₊₂₉,reset/regular steranes,carbon isotope and ratio of gas to oil,increase gradually from the deep to the shallow.These varying tendences in vertical were due to migration fractionation from the bottom to the top.Besides,the lateral differences between different strata or between the different oil-bearing formations in the same stratum are mainly controlled by the sedimentary facies belt and physical properties of reservoirs.And they are induced by grouped accumulation.