The Origin And Distribution Of High Quality Reservoir Of Longwangmiao Formation In Central Sichuan Basin

Taking the reservoir of the lower Cambrian Longwangmiao formation in the Sichuan basin as the research object,and based on observation of outcrops,cores,thin sections,logging and experimental data,then analyzing the features,main controlling factors,evolution and distribution of the Longwangmiao formation reservoirs in the Lower Cambrian,Sichuan Basin,finally can predict the distribution of favorable reservoirs.The high-quality reservoirs were controlled by the distribution of carbonatite grain shoal.Studying the temporal and spatial distribution rule of grain shoal in this area has great significance for predicting reservoir distribution in the Longwangmiao formation.Therefore,it was conducted the research of vertical superimposed relationship and horizontal distribution rule of the grain beaches in Longwangmiao formation.The results were as follow:(1)During the deposition period of the Longwangmiao formation,the depositional environment of the inner-ramp was mainly developed,and the grain beach was relatively developed in this environment.Grain shoal could be subdivided into shoal core,shoal flank and interbank sea.(2)The types of reservoir rock in the Longwangmiao Formation are mainly granular dolomite,crystalline dolomite and variegated dolomite.The main reservoir spaces include dissolved pores,residual intergranular pores and intercrystalline pores.The major diagenesis types are seabed cementation,penecontemporaneous dissolution,penecontemporaneous dolomitization,burial compaction,uplift karstification,cementation of dolomite,burial corrosion and petroleum filling,formation of bituminous membranes,cracking and hydrothermal mineral filling;(3)The major controlling factors such as sedimentary facies,dissolution and tectonic cracking have important influences on the development and evolution of high-quality reservoirs.The shallow water and high-energy areas on the seabed paleogeomorphology determine the primary spatial distribution of the sub-facies of grain shoal.The decline in sea level is beneficial to the development and evolution of the reservoir.The epigenetic dissolution is beneficial to the properties of the reservoir.(4)Based on the analysis of the main controlling factors of the reservoir,the prediction of Anyue-Longnusi-Nanchong area is the most favorable reservoir development area.