FEATURES AND CONTROLLING FACTORS OF SANDSTONE RESERVOIR IN THE SOUTH PART OF THE XIHU DEPRESSION
Ren Zhengping Bao Zhu Qian Jianzhong(Shanghai Offshore Petroleum Exploration and Development Institute,Shanghai,200120,China)
Within the Eocene to Miocene series,we11-developed massive sandstones in our re-search area are from 2 to about 30m thick.The analytical results have indicated that the sandstone formations with a certain porosity and permeability lie mainly within thedepth range from 1900m to 3200m(within the Huagang and Longjing Formations).Their lithologies are substantially fine sandstones and siltstones with minor medium-coarse sandstones. The fine sandstones and siltstones are well-sorted,have low cementcontents(less than 10 percent),and are in a good porosity and permeability condition(φ10 percent to 28 percent,K from less than 1 to 1800×10￣(-3)um￣2).Their reservoir spaceconsists of secondary intergranular enlarged pores,intragranular pores ,moldic pores,mi- cropores in clay minerals,and a few primary pores. Clay minerals make up majority ofthe cements.and then there are carbonate and silica cements. Physical property of reservoirs in this area is controlled by composition structureand buried depth of reservoirs and primary geological conditions,and simultaneously af-fected by diagenetic epigenesis. Compaction and cementation bring about the reduction ofphysical property of reservoir rocks. Then corrosion of framework grains(mainlyfeldspar)and cements improves reservoir conditions of the rocks.