Four types of lithofacies are identified in the 3rd member of Funing Formation in Zhangjiaduo oilfield

the Subei Basin

including dark mudstone

bioturbated siltstone

siltstone-fine sandstone lithofacies with argillaceous laminates and burrow as well as fine sandstone with parallel bedding. Upward-coarsening reverse rhythm is the main section structure

followed by first upward-coarsening and then upward-thinning composite rhythm

while positive rhythm is very rare. All the features of lithofacies

section structure

logging facies and cumulative grading curve show that the 3rd member of Funing Fm is typical shallow lake beach-bar facies. According to the sedimentary characteristics and spatial distributions

the reservoirs are further divided into sandstone of bar microfacies and sandstone of beach microfacies. A beach-bar sedimentary model is proposed. The sandstone reservoirs of bar microfacies are high in hydrocarbon fullness

due to its low shale content and high porosity. In contrast

the sandstone reservoirs of beach microfacies show great variance in hydrocarbon fullness as argillaceous laminations are well developed

heterogeneity is week

and hydrocarbons mainly fill in the fine sandstone lithofacies with parallel bedding and argillaceous laminates + burrow fine sandstone lithofacies.