Physical property evolution of Huagang formation in central inversion tectonic belt in Xihu depression

LIN Chengyan; SUN Xiaolong; MA Cunfei; ZHANG Xianguo; ZHAO Zhongxiang

Abstract：Based on the studies of reservoir physical property,reservoir-seal association and burial history,the physical property evolution and controlling factors of south and middle Huagang formation in central inversion tectonic belt of Xihu depression were investigated by using analysis of casting thin section,scanning electron microscopy,X-ray,mercury intrusion and vitrinite reflectance.The results show that different reservoir-seal associations undergo different diagenetic evolutions by the control of burial history.The southern region is far away from early subsidence center.Primary pores are preserved during the slow subsidence period,which benefits the dissolution in the rapid subsidence and tectonic uplift stage.Late cementation is not abundant in the period of steady subsidence.Values of ΦCOM (compaction porosity loss),ΦCEM(cementation porosity loss) and ΦDIs (dissolution porosity increase) are 20.86％,7.65％ and 7.78％ respectively.Shallow buried and half-open diagenetic environment leads to conventional and low permeability reservoir with relatively weak compaction,weak cementation and intensified dissolution.By comparison,the central region is close to the early subsidence center.Primary pores are completely destroyed during slow subsidence.The compaction is inhibited by the undercompaction overpressure resulting from beneficial reservoir-seal association during rapid subsidence.The dissolution is apparently different during tectonic uplift.Late cementation is comparatively rich in steady subsidence.For upper members of Huagang formation,the values of ΦCoM,ΦCEM and ΦDIS of are 21.82％,9.01％ and 5.64％;for lower members,the values are 23.84％,9.05％ and 4.50％ respectively.Deep buried and closed diagenetic environment leads to low permeability and tight reservoir in upper member and tight reservoir in lower member,both with relatively intensified compaction,strong cementation and weak dissolution.