Sedimentary microfacies characteristics and their control on reservoirs in Daanzhai Member, Lower Jurassic, Sichuan Basin

The Daanzhai Member of the Lower Jurassic in the Sichuan Basin is an important exploration target with complicated petrogeologic features. The Daanzhai Member includes eight lithofacies: thick blocks of recrystallized limestone, sparry shell limestone blocks, micritic shell limestone blocks or thin sections, argillaceous shell limestone thin sections, interbedded mudstones and shale shell limestones, shell mudstone thin sections, black mudstones, and red to green mudstones. A depositional model was established, consisting of five sedimentary microfacies: mud from littoral to shallow lake, back beach shell, shell beach core, beach front shell, and mud from shallow to intermediate depth lake. The controls of sedimentary microfacies on reservoir properties were determined according to the relationship between porosity/permeability and depositional environment. The beach front shell facies was favorable for tight oil accumulation.