The Effection of Authigenic Illite on Relatively High‐quality Tight Sandstones Reservoirs

The relatively high-quality tight sandstones reservoirs is the emphasis of oil exploration phase. Generally dense cases with high pore throat may gather a lot of oil. The quality of high-quality reservoirs is not only determined by the rock size, sedimentary environment and so on, clay minerals also affects the distribution of high quality reservoirs in great degree. The formation and distribution of authigenic illite has strong control function on reservoir physical properties. Authigenic illite is one of common clay minerals, which is generally formed in rich potassium water medium (Yu et al, 2009). The formation of authigenic illite can cause the jams of rock throat (Du et al, 2006; Huang et al, 2009). At the same time, the formation of authigenic illite can cause the dissolution of potassium feldspar (Song et al, 2006; Zhao et al, 2001). Large number of secondary porosity has greatly improved the reservoir property. Accordingly, it can be concluded that the formation, distribution and occurrence of authigenic illite has great significance on relatively highquality tight sandstone reservoirs. The study area is the 4th member of Quantou Formation in Daan oilfield. It is the low permeability reservoirs. Reservoir in the study area belongs to feldspar lithic sandstone and lithic feldspar sandstone. It mainly has fine sandstone and siltstone. The clay minerals in the study area mainly have illite, chlorite and illite mixed layer. Most of the clay minerals is illite. The authigenic illite exists in the pore throat. It narrowed the effective pore radius, increase bending degree of the reservoir throat. At the same time, the feldspar secondary dissolution pores formed, which increased the reservoir pore space. 2 Occurrence Characteristics of Authigenic Illite