Abstract: Lacustrine beach-bar sandstone is generally adjacent to source rocks, and it is favorable for hydrocarbon accumulation under high differential pressure between the source rock and reservoir.In recent years, a large number of oil and gas reservoirs have been discovered in the Cenozoic lacustrine beach bar sandstones in eastern China.Distribution of beach-bar sands in the 3^rd Member of the Funing Formation was studied on the basis of the core observation.Mercury data, cast thin sections and scanning electron microscope were integrated to analyze the distribution of pore throat and the combinations of porosity types in reservoirs of different genetic types.The following results were obtained.①Three kinds of lithofacies were recognized in beach-bar sand and they can be organized into four kinds of lithofacies associations, which correspond to four kinds of logging facies;②The beach-bar sand has the characteristics of fine grain size, thin single layer, as well as interbedding, overlapping and lateral connection of the beach and barsands, and the potato-shaped bar sands are distributed in parallel with the lake shoreline;③The bar sands are dominated by fine sandstone with low matrix content;Primary pore and secondary pore are well developed, and clay minerals are rich in kaolinite and poor in chlorite and mixed layer;the beach sands are generally dominated by siltstone and very fine sandstone with high matrix content;Their pore structures are poor and secondary pores are underdeveloped, and the clay minerals are rich in mixed layer and poor in kaolinite and chlorite.

Key words: beach bar sand, reservoir, diagenesis, 3^rd Member of the Funing Formation, Zhangjiaduo oilfield, northern Jiangsu Basin