| As a typical continental oil and gas bearing formation,Da'anzhai member in Yuanba area of Sichuan Basin has good exploration potential and prospect.Based on previous research,combined with field profile,drilling data,core observation,thin section identification,XRD diffraction analysis,scanning electron microscopy and other experiments,the petrological characteristics,physical characteristics,diagenesis and reservoir control factors of fine-grained sedimentary rocks in Da'anzhai member of Yuanba area are studied.The fine-grained sedimentary rocks in Da'anzhai member of the study area are mainly mudstone,shell mudstone and shell limestone,and the mineral components are mainly quartz,clay minerals,calcite and pyrite.Reservoir space types include pore and fracture.Pores include organic pore,intergranular pore,dissolution pore,intercrystalline pore and clay mineral micropore.Fractures include structural fracture,bedding fracture and diagenetic shrinkage fracture.Porosity distribution ranges from 0.92%?8.12%,and average porosity is 3.35%.Permeability is0.0020?147.2758 m D,and average permeability is 1.5367 m D,which belongs to typical ultra-low porosity and permeability tight reservoirs.Due to the development of fractures in individual samples,the average permeability is high.Porosity and permeability have a good positive correlation,and the pore is mainly nano-scale micropore and mesoporous.Compaction,cementation,dissolution,metasomatism,recrystallization,clay mineral transformation and organic diagenesis are developed in fine-grained sedimentary rocks.Da'anzhai member is in the stage B of middle diagenesis.Reservoir development is affected and controlled by petrological characteristics,diagenesis,tectonics and organic matter.Organic mudstone and organic shell mudstone are themost favorable reservoirs in Da'anzhai member of Yuanba area.The middle and lower mudstone sections are the favorable sections of Da'anzhai member. |
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