Characteristics And Reservoir Formation Mechanism Of Dichite Deposits In The Xiaxia Formation Of The Lower Permian In Northwestern

This paper aims at Qixia formation, early Permian, northwest of Sichuan Basin,utilizing drill data, core data, field outcrop data,thin section data,geochemical data and previous research data,based on principal theories sequence stratigraphy, sedimentary petrology, structural geology and Reservoir sedimentology,series of investigations have been studied on the stratigraphic and sedimentary features, reservoir characteristics and its genetic mechanism. Finally, it Summarizes the reservoir characteristics, diagenesis types and reservoir formation mechanism of Qixia formation’s karstic dolostone reservoirs which is control by grain beach facies.The present work ends with several following conclusionsr(1)According to lithological assemblage, Logging and geocyclic characteristics, Qixia formation was divided into two members:member Qil and member Qi2from top to bottom, meanwhile, member Qil can divided into two sub-member;the whole fomation was distributed stability, Has a tendency to gradually thinning to the north, characterized by development grain beach and barrier beach belong to open-semi-restricted platform.The barrier beach was controlled by the micro landform highland of Longmen mountain chain,however,the grain beach was controlled by the locality structural micro landform highland and upthrown side of syndepositional fault;(2)According to observation of rock sample, thin section and test data,we found two main reservoir rock type of Qixia formation:remnant grain dolostones and median-coarse crystal grain dolomite.Main types of reservoir space are pore,hole and fracture.Pore include intragranular pore, intergranular pore, intracrystal pore and intercrystal pore. Hole mainly demonstrates several types of solution pore and cavity. Fracture include construction joint and solution fracture;(3)Qixia formation had undergone several types of diagenesis.Compaction and cementation which are destructiveness diagenesis. Destructiveness grain beach facies control weathering crust karstification,mixed hydrothermal dolomitization,burial karstification which are constructive diagenesis;(4)The development of the reservoir was controlled by grain beach facies obviously, Destructiveness grain beach facies control weathering crust karstification was the key to The optimization of reservoir, mixed hydrothermal dolomitization was the important condition of reservoir preservation,the later structural fractures and burial karstification work an adjustment to the reservoirs.