Study on sedimentary sand body hierarchy of Ⅱ+Ⅲ low permeability reservoir of Baozhong block

Baozhong block of Baolang oilfield belongs to typical reservoirs with low porosity and low permeability. II and III oil formations are main oil-bearing formations. Controlled by sedimentary microfacies, three levels of sedimentary sand bodies differences have been reflected. As for oil formation level, the sand bodies have obvious configuration and different connectivity, with narrow and short striped, isolated potato-shaped and lenticular sand bodies and poor connectivity in II oil formation, while thick and uniform sand bodies and good connectivity in III oil formation. As for layer level, the sand bodies present NE-SW distribution and there is no regularity on thickness variation, with unstable interbedded layers developed in II formation and restraining barriers developed in III formation. As for single sand bodies level, the phase and pinchout of sand bodies change quickly, forming complicated lithology. The suddenly pinchout is caused by the thick thickness of channel bar and dveloped bay phase in shallow water.