Beach-bar sandstone reservoirs from the fourth member of the Shahejie Formation in the Boxing Oil Field,Dongying depression,Shandong

The beach-bar,submarine fan and gravity flow channel sandstone reservoirs are well displayed on the southern slope of the Dongying depression,Shandong,constituting a composite oil and gas accumulation zone with many types of oil reservoirs and oil and gas pools.The oil reservoirs in the fourth member of the Shahejie Formation consist of the littoral and shallow lacustrine beach-bar sandstone reservoirs including lithologic and structural-lithologic oil and gas pools,and thus are considered as the main exploration targets in the study area.These sandstone reservoirs are composed of feldspathic coarse siltstone and lithic siltstone with low to moderate textural maturity.The porosity types of the sandstone reservoirs significantly consist of residual intergranular pores,intergranular solution openings and intragranular solution openings.The pore structures are dominated by low permeability-micropore throats,indicating the medium-to low-porosity and low-permeability reservoirs.The sedimentary microfacies and diagenesis are considered as the main controlling factors of physical properties of the beach-bar sandstone reservoirs in the study area.