Studies On Reservoir Characteristics Of The Cambrian Xixiangchi Group In Northern Sichuan Basin

The Sichuan Basin Cambrian has great potential for oil and gas resources.This paper takes the Xixiangchi Group in the northern Sichuan Basin as the study object.Integrated with discipline knowledge such as structural geology,sedimentology,reservoir physics,reservoir geology;took field outcrop section measurement,drilling core and cuttings observation,thin section microscopic analysis,physical property analysis,etc.as methods;Collected previous research results and drilling core data,studied the layers,sedimentary facies,and reservoir characteristics of Xixiangchi Group in northern Sichuan,and clarified the main development of the reservoir Controlling factors,obtained the following results.Studies on outcrop and drilling data shows that the top and bottom boundaries of strata are clear in most areas of Xixiangchi Group in northern Sichuan,The layers contacted with the Cambrian Douposi Formation in the underlying layers conformity,in the northern part of the study area,the overlying Ordovician layers lacked the Middle and Lower System,showing unconformity contact.In terms of electrical characteristics,the natural gamma curve of the Xixiangchi Group and the overlying and underlying strata show a step down,and the lateral resistivity curve of the depth and shallowness shows a certain amplitude difference.The thick boundary of the Xixiangchi Group in the northern Sichuan area is between 10 meters and 400 meters,the Strara thickness is thin in the west and thick in the east.The sedimentary facies of the Xixiangchi Group in northern Sichuan are dominated by restricted platform facies,and open platform facies are developed to the east;the upper vertical section in the east is restricted platform deposition,and the lower section is mainly open platform deposition.Restricted platform facies can be subdivided into three subfacies,such as mixed tidal flats,intra-platform beaches and lagoon,and open platform facies developed intra-platform beach and inter-beach subfacies.The reservoir of Xixiangchi Group in northern Sichuan are dominated by residual grain dolomite and Powder-fine crystal dolomite,and the main types of the reservoir spaces are intergranular dissolution pores,intercrystalline pores and intercrystalline dissolution pores.The reservoir has experienced mechancial compaction and pressure dissolution,cementation,recrystallization,dissolution,and dolomization.The pore structure is small pore throat,mostly reservoirs have low porosity and low permeability,and fractured reservoirs are underdeveloped.The reservoir of Xixiangchi Group in northern Sichuan is controlled by sedimentary facies,diagenesis and tectonic action.The intergranular pores and intercrystalline dissolution pores are more developed in granite dolomite and residual granule dolomite,which belong to the intra-platform beach subfacies of the restricted platform has the best physical properties,and the tidal flat subfacie has the worst physical properties.Pressure dissolution,cementation filling and excessive dolomization are destructive diagenesis,which makes the rock compact and reduces reservoir porosity and permeability.Dissolution and moderate dolomitization play a constructive role on the reservoir,optimize the storage space,and improve the porosity and permeability of the reservoir.