Diagenesis and pore evolvement of the lower member of Xingouzui formation sandstone in Jiangling depression

The reservoir sandstone from lower member of Xingouzui formation in Jiangling depression is mainly composed of lithic arkose,feldspathic litharenite and quartz sandstone,and it belongs to low porosity and low permeability.Based on core observation,combining with thin section analysis,scanning transmission electron mi- croscope observation,cathodeluminescence analysis and physical property analysis,the sandstone is found to go through several diagenesises such as compaction,quartz overgrowth,cementation and dissolution of carbonate, anhydrite cementation,felspar lithic dissolution,filling of clay matrix,etc.At present,the sandstone has entered into stage-A of late diagenesis period.The compaction of early diagenesis and cementation of quartz,carbonate, anhydrite and clay minerals are the main reasons of de- creased porosity,the compaction makes 14% less,while the cementation reduces it by 16%.The nonresistance mineral is dissoluted by humic acids which come into being at the mature stage of organic matter and the well-devel- oped secondary pore zones generated is the beneficial dis- trict of hydrocarbon exploration.