Abstract:

The petrologic features, diagenesis characteristics and reservoir characteristics of the Es₃ reservoirs in Wen’an slope were systematically studied by core observation, thin section observation and physical property analysis. It can be seen that the study area mainly developed lithic arkose, which contains a few matrixes and its component maturity and structure maturity are in the middle. The reservoir spaces of the lithic arkose are primary pores, which occupy 72.81% of the total pores. The reservoirs possess comparatively bad reservoir characteristics, and belong to middle-low porosity, low to ultra-low permeability reservoirs. The reservoirs sequently underwent a series of diagenetic stages as follows: consolidation and early carbonate cementation→feldspars and rock debris dissolution, quartz enlargement, kaolinite fillings →quartz dissolution and carbonate cementation→pyrite cementation. On basis of analyzing the lower limits of effective reservoir properties, this study systemically analyzed the controlling factors of effective reservoirs, which include sedimentary microfacies, particle size, sorting, diagenesis and formation pressure. Better reservoirs developed in coarser grains in underwater distributary channels and estuary dams, which have better sorting and fewer matrixes. Cementation has distinct control effect on reservoir characteristics, and is the major controlling factor of characteristics of mid-deep reservoirs. Dissolution is mainly shown as the corrosion of silicate minerals such as feldspars, in which the average increasing of pore volume is 3.42%. The overpressure of early phase restrained compaction, protecting the pores, and became the favorable factor of the development of effective reservoirs.

Key words: reservoir characteristic, effective reservoir, controlling factor, third section of Shahejie Formation, Wen’an slope, Baxian Sag