Characteristics Of Microbialite Reservoir Of Sinian Dengying Formation In The Southwestern Sichuan Basin

Microbialite is a hot topic in the world.Microbialite develop in Sinian Dengying Formation in the Southwestern Sichuan Basin.Thesis is based on Hanshen 1,Jinkouhe section and Xianfeng section,using thin slice identification,cathodoluminescence,scanning electron microscopy,carbon and oxygen isotopes and strontium isotopes to study Microbialite sedimentary microfacies and combination characteristics,the types of reservoir space,pore evolution and lithogeneous sequence to lead to the main controlling factors of the high-qualigy reservior in the study area.Microbialite of Sinian Dengying Formation is mainly developed in the subtidal-intertidal zone,and a small amount is developed in the supratidal zone.Eight types of sedimentary microfacies are dicided: thrombolite(MF1),stromatolite(MF2),foamed cavernous microbialite(MF3),clot cohesive aggregate granular rock(MF4),oncolite floating rock(MF5),bright crystalline cemented oncolite dolomite(MF6),window lattice cohesive rock(MF7),and grape-lacelike dolomite(MF8).There are five types of reservoir space in the Sinian Dengying Formation in the study area:(a)microbiological shelf(solution)hole;(b)the grape-lacelike dissolution hole;(c)karst cave;(d)intergranular pore,intergranular dissolution hole;(e)fractures.The pore evolution is divided into the evolution of primary pores and secondary pores.The former was cemented by fibrous and crystalline dolomite in the syngenetic period,and continues to be cemented to lead to the vanishing of primary pores in the burial period;the latter was cemented by fibrous dolomite in the syngenetic period,then the cementation was dissolved in syngenetic period karst and supergene period karst,the foliate and fine-microtek dolomite was filled.The dolomite,which was cemented in the burial period,might be metasomatism by hydrothermal fluid to form siliceous,and then cemented with coarse-grained dolomite.Finally,it formed fractures under structural uplift,and part of the fractures were filled with fibrous and crystalline dolomite.The diagenesis of the Sinian Dengying Formation are including dolomitization,dissolution,cementation,recrystallization,pressure dissolution,silicification,filling and fracturing.The diagenesis sequence is dolomitization in the sea water environment? cementation in the sea water subsurface zone where the primary pore of is cemented? syngenetic period karstification ? cementation under the shallow burial period? supergene period karstification(the first and second stage of the Tongwan movement)? the filling,recrystallization,pressure dissolution and silicification in the shallow burial period? dissolution and filling in the middle deep burial period? filling in the deep buried period? fracturing in Yanshan-Himalaya period which improves reservoir physical preperty.The controlling factors of microbialite reservoir in the Dengying group are:(a)different sedimentary microfacies under different sedimentary environments have different reservoir properties;(b)dissolution plays an important role in the development of reservoir space in the study area.Under the control of Mianyang-Changning intracratonic sag,the distribution of high-quality reservoirs is affected.(c)tectonic movement provides channel for oil and gas migration and connects isolated dissolved pores,finally,increases reservoir permeability,and improves reservoir physical property.