Characters And Formation Mechanism Study For Lower Ordovician Carbonatite Reservoir In Sichuan Basin

Sinian and Cambrian reservoir exploration in Sichuan basin and the peripheral area in recent years is a horizon question,but the ordovician reservoir development characteristics and mechanism lacks system research and understanding.In this paper,structural geology,sequence stratigraphy,sedimentary petrology,reservoir geology as theoretical guidance,combining with drilling and logging data,seismic data,field work and laboratory work,etc.,were used to study carbonate reservoir,and explore its reservoir characteristics and formation mechanism.As a result,some points have been got as below:The Ordovician limestone away from the beach facies reservoir is mainly distributed in the ancient uplift area,limeestone reservoir mainly includes the oolitic limestone,bioclastic limestone,its pore space types are mainly intergranular and intragranular dissolution pores and microcracks,table and buried karst composite area often developed seam hole reservoir.Beach facies limestone aggregate is relatively dense,microfracture reservoir to improve significantly.Main beach grainstone atmospheric precipitation,water,rock formation water generation calcite cementation filling,residual only a few primary pores,tectonic fracture development.The Ordovician dolostone type mainly includes two major categories of grain dolostone and crystalline dolostone,is the product of grain beach.Dolomite is given priority to with low permeability reservoir,the local development of high permeability.Maximum porosity 13.9%,average 3.33%,maximum 86.3 md,permeability,on average,1.65 md.Geochemical characteristics indicate that dolomite by penecontemporaneous reformation atmospheric precipitation.The typical zebra structure features of the Ordovician dolomite in central guizhou was noticeably compared with surrounding rock filling light carbon and oxygen isotopic compositions,in addition,rare earth elements and fluid inclusions analysis also show that filling dolomite belongs to tectonic hydrothermal origin.Combined with background of geological evolution,hydrothermal dolomite reservoir development is: the early ordovician sedimentary during penecontemporaneous dolomite diagenesis,the late ordovician,exposed to the surface by atmospheric precipitation karstification,burial period of tectonic hydrothermal reformation,solution pores formed by the current natural gas is the main reservoir space.