A Study On Source-reservoir Configuration Of Xiagou Formation In The Qingxi Sag,Jiuquan Basin

It developed large sets of argillaceous dolomite,dolomitic mudstone,shale and mudstone in the Lower Cretaceous Xiagou Formation of the Qingxi Sag in Jiuquan Basin,representing complex and volatile lithologies and equipped with the characteristics of hybrid sedimentation.In this paper,the characteristics of source rocks have been systematically studied and three sets of effective source rock have been divided by employing the data of core,well logging and mud logging,and geochemistry.Combined with data of rock thin section,scanning electron microscope,and mercury porosimetry,the reservoir characteristics have been concretely studied,which include petrology characteristic,physical properties,pore structure and fracture developmental characteristics.Combined with oil-source correlation,the source-reservoir configuration features have been comprehensively analyzed and the types have also been confirmed and its control on oil and gas distribution was discussed.The study suggests that argillaceous dolomite,dolomitic mudstone,and mudstone all present rich organic matter,good organic matter type,and moderate maturity;and they represent great thickness,stable lateral distribution,and large covering area geologically,belonging to good source rock.The reservoir majorly contains argillaceous dolomite and dolomitic mudstone,a minor of siltstone and glutenite and represents poor physical property,belonging to the reservoir with a low porosity and permeability or extremely low porosity and permeability;it majorly develops the type of small pore and fine throat porosity structure and the fractures were well developed,mainly comprising of diagonal and intra-bedding fracture,having greater influence on hydrocarbon accumulations;longitudinally,source rock and reservoir intercalates or closely contacts with each other upwardly and downwardly,major source-reservoir configuration types are self-sourced and self-stored,and down-sourced and up-stored,and the laterally-changing type in the bottom;macroscopically,distribution of hydrocarbons is substantially predominated by the distribution of sedimentary facies and lithofacies.