Main controlling factors and favorable reservoir prediction of low permeability reservoir in the third Member of Liushagang Formation in Wushi W Oilfield, Beibu Gulf Basin

By using cast thin section, scanning electron microscope, cathodoluminescence, and other technical means, an in-depth study was conducted on the causes of heterogeneity of reservoir physical properties of thick sandy conglomerate low-permeability reservoir in the third member of Eocene Liushagang Formation in the Wushi W Oilfield, Beibu Gulf Basin, South China Sea, and reservoir physical property prediction models were established for different well areas via geological modeling with logging parameters, so as to predict the distribution characteristics of favorable oil-gas reservoirs. Result shows that: ① The Ⅱ oil group of reservoir in the third member of Liushagang Formation has medium porosity and low permeability in general. The reservoir in near provenance area is characterized by medium porosity and ultra-low permeability, while in the middle area between near and far provenance areas is characterized by medium porosity and low permeability. The far provenance area is characterized by medium to low porosity and permeability, and the trend of permeability variation is different from that of porosity variation. ② The physical properties of the reservoir are controlled jointly by sedimentary microfacies and diagenesis. The main controlling factors are burial depth (compaction), shale content, lithology (grain size, rock composition), heterogeneity of dissolution and fracture et and so on. ③ The relatively high porosity reservoir area was located in the areas of Wells 2, 3, and 5, and in small fault-block to the south of Well 7, which is a favorable reservoir development area, while the relatively high permeability reservoir area is located mostly in Wells 8 and 9, which is a potential oil-gas reservoir development area.