Petroleum geologic characteristics of Wushi Sag in Tarim Basin

The integrated explanations of gravity-magnetic data and the characters of seismic sections of Wushi Sag were carried out. The basin filling sequence, structure framework and fault system were determined. The characters of Mesozoic stratigraphic distribution and structural play of Wushi Sag were analyzed. It shows that the structure pattern of Wushi Sag is different from west to east. Wushi Sag can be divided into western,central and eastern sub-sags as well as western and eastern low rise beam belts. The Mesozoic stratigraphy is chiefly distributed in the east Wushi Sag. The geology characters of Well Wucan-1 and adjacent sedimentary reservoir show that the provenance of Cretaceous fan-delta sandstones and conglomerates of Well Wucan-1 is Wen-Su Bulge. The depositional systems of Well Wucan-1 are very different from those of northern and eastern areas. The total thickness of the Cretaceous sandstone reservoir developed in Wushi Sag is approximately from 200 to 300 meters. The heterogeneity of reservoir in vertical sense is relatively strong. A new better source rock of gray dark politic micrite dolomite was found in the Jurassic Qiakemake Formation of Awate river profile. The source rock of the Jurassic Qiakemake Formation has good parent materials,moderate maturity and great oil-bearing potential. The western source rock of the Permo*$-Carboniferous marine facies has poor oil-bearing potential,because of their lower abundance of organic matters and higher degree of thermal evolution of Well Wucan-1.Gas was originated from the Jurassic humic type source rock of continental facies,and oil came from the Jurassic Qiakemake Formation sapropelic type source rock of lacustrine facies. Well Wucan-1 belongs to the rich condensate gas pool with normal temperature,super-pressure and bedded style. The pool-forming mechanism of Well Wucan-1 was characterized by abnormal pressure compartment,feed from lateral hydrocarbon kitchen,charged along fault or unconformity surface,accumulation in high-quality reservoir,pool-forming in late stage. The eastern low bulge belt and the southern belt of Wushi Sag are the most favorable areas for oil and gas accumulation. The pool-forming condition in these areas is similar to the Quele area of Kuqa Basin.