High-quality lacustrine source rock and extensive sublacustrine fans are developed in deep-lacustrine depositional environment in lower section of the second member of Oligocene Dongying Formation(E3d2l)in southern Bozhong Sag,providing an exploration realm of lithological reservoirs.However,the generally poor porosity and permeability of the deep reservoirs severely hampered the progress for oil and gas exploration and development.Thus,there is an urgent need to elucidate the key factors and the pore evolutionary processes controlling the sandstone reservoir quality of the sublacustrine fans.Based on comprehensive analysis of drilling and logging data,rock grain-size,thin sections,scanning electron microscopy and fluid inclusions,this study has successfully identified the key factors controlling reservoir quality,and established quantitative models of pore evolution.The results show that:The sublacustrine fan reservoir of the E3d2l is characterized by predominantly medium-fine grained lithic feldspathic quartz sandstone with mainly dissolution pores.The favorable sedimentary units such as lobe axis and distributary channels in sublacustrine fan are the basis for the formation of high-quality reservoirs.Persistent compaction and early/late cementation are the main causes of continuous porosity loss.Organic acid dissolution and abnormally high pressure are the key factors for improving reservoir quality.The sublacustrine fan sandstone undergoes four stages during the burial process:rapid compaction in the early diagenesis A phase,rapid compaction and early cementation in the early diagenesis B phase,slow compaction and organic acid dissolution in the middle diagenesis A1 phase,and slow compaction and late cementation in the middle diagenesis A2 phase.During these phases the compaction and early cementation reduce porosity by 13.64，and 8.24，respectively,and organic acid dissolution increases porosity by 9.55，.In particular,the late cementation after the oil and gas accumulation results in a severe porosity decrease of 7.12，.This study will provide a theoretical basis for the oil and gas exploration and development of sublacustrine fan reservoirs in the deep-lacustrine basin of the Bohai Sea.