| Based on the analysis of core observation, conventional and cast slices, physical property analysis and mercury penetration, it is indicated that the Lower Cambrian Longwangmiao beach facies reservoirs that develop well in the central part of Sichuan Basin are composed of dolarenite, oolitic dolostone and the dolostone with residual particle texture. The pore space mainly includes intergranular dissolved pores, intragranular dissolved pores, intercrystalline dissolved pores, moldic pores, residual intergranular pores, fractures and vugs. Configuration between pores and throats are well in the reservoirs. The research on origin mechanism of the reservoirs indicates that beach-core and bank-wing microfacies are conducive to the development of the reservoirs. The feature of microfacies distribution in plane leads to the typical macroscopic heterogeneity of the reservoirs during early sedimentary stage, which provides good material foundation for formation and evolution of the beach facies reservoirs. It is suggested that the beach facies reservoirs went through three stages of karst diagenesis, i.e. the syndeposition, the epigenesis and the buried karstification. The syndepositional karstification controls the evolution of pores in the reservoirs formed during the early stage, which is critical to formation of good reservoirs. Epigenesis karstification determines the basic characteristics of reservoir distribution, when porosity increased in large scale. Buried karstification is favorable to the optimization of the porous beds formed previously. |
