Main controlling factors of Paleogene sandstone reservoirs in the Huimin subbasin

Abstract：The physical properties of Paleogene sandstones reservoirs in the Huimin subbasin are mainly controlled by compaction, carbonate cementation, dissolution and depositional environment. The controlling factors of physical properties of reservoirs are analyzed based on the data from analyses of mold thin sections, cathode luminescence thin sections, scanning electron microscopy, physical properties and carbonate contents of rocks. Preliminary quantitative evaluation of the degrees of influences of these factors has been carried out. It is suggested that：① the porosity decreases by 8％–9% per 1000 m of descent due to compaction at the early burial stage or the stage of low degrees of carbonate cementation; ② the influence of carbonate cementation on the physical properties of reservoirs is related to the diagenetic evolution stages：the higher the degree of diagenetic evolution, the greater the influence of the cements on physical properties will be; and ③ dissolution plays an important role in improving the properties of the reservoirs and the secondary porosity produced by dissolution is up to 20%. However, the dissolution is mainly controlled by the regional tectonic setting and the position of the hydrocarbon-producing subbasin and the dissolution is relatively stronger in the central uplift zone ａｎｄ the south slope zone near the hydrocarbon-producing center (Linnan subbasin)where faults are better developed. The sandstones that are coarser in grain size and well-sorted, with low matrix contents have been subjected to stronger dissolution. The influence of the depositional environment on physical properties of reservoirs is manifested by the development degree of primary porosity and its controls on such diagenesis as dissolution and cementation.