Study On The Controlling Factors Of Low Permeability Sandstone Reservoir Of The2^nd Section,Zhuhai Formation In Wenchang A Sag

Although oil and gas resources are rich, source-reservoir-caprock association arewell, but the exploration result shows that the Medium-low porosity, low-extra lowpermeability reservoir in in Wenchang A sag,Zhujiangkou basin.And control factors ofthis low permeability reservoir is unclear. This paper starting from sedimentarycharacteristics, divides to four types of lithofacies by core observation, thin sectionidentification. Conventional mercury, constant pressure mercury and NMR analysis allshow more coarse lithofacies has the better property, permeability is up to10×10-3μm2.The main types of reservoir pore are original intergranular pores, intergranulardissolved pore, intragranular dissolved pore, mold holes, debris dissolved pores,andpore combination type is mostly secondary pore. Regional sedimentary facies studiesshow estuary dam reservoir has the best properties, with an average porosity of14.8%and permeability up to7.5×10-3μm2. And sedimentary microfacies controll particlesize distribution of sandstone, coarse sandstone and medium sandstone depositedmainly in underwater distributary channel, tidal channels and estuaries dam,whileFine-grained sandstone and siltstone deposited mainly in the sand flat, sheet sand,andmixed flat microfacies.This paper detailed analyze the diagenesis processes of the2ndsection,Zhuhaiformation by compaction,cementation and dissolution, complete the division ofdiagenetic sequences and diagenetic facies.Fan delta area mainly develop mediumcompaction strong dissolution weak cementation and strong compaction strongdissolution weak cementation faces in shallow buried area, forming I-II reservoir.Whiledeeply buried reservoirs develop III class. Tidal flat mainly grow medium compactionmedium dissolution medium cementation face, when buried very deep,develop strongcompaction chlorite rims face,forming class III-IV reservoirs.We think this low permeability reservoir is mainly affected compaction strength,multi-stage control dissolution and cementation by deposition and diagenesis.Compaction is closely related to burial depth, sandstone size, chlorite rims. There arethree stages main dissolution, Atmospheric fresh water early dissolution, hydrothermal dissolution and CO2dissolution. Deeper depth, strong compaction is the key factor inthis low permeability reservoir development.“Dessert reservoir” develop in weakcompaction, strong dissolution or chlorite rims sandstones.