Influences of delta sandstone architecture on waterflooding sweep characteristics: A case study of layer J-II of Kumkol South oilfield in South Turgay Basin, Kazakstan

Taking layer J-II of Upper Jurassic of Kumkol South oilfield in South Turgay Basin, Kazakstan as an example, the article studied the architecture characteristics and heterogeneity of delta sandstones, and determined the influence of sandstone architecture on waterflooding sweep characteristics using fine characterization of sandstones, comprehensive interpretation of waterflooded layers, statistical analysis of production and injection profiles, reservoir numerical simulation methods. The result shows that the delta sandstones have a complex architecture of mosaic structure with mudstone baffles and mud-interbeds, and the sandstone architecture controls the sweeping characteristics of waterflood: due to impermeable or low permeable boundaries between single sand bodies, and lateral and vertical blocking of underwater distributaries bay mudstone, sands in delta have very complicated architecture, and the injected water flows priorly into underwater distributaries channel sand and estuary bar sand with better physical properties, making these two types of sands suffer stronger warterflooding, and have higher recovery degree and better waterflooding sweep effect in plane. Inside single sand bodies, on the one hand, underwater distributaries channel sand and estuary bar sand have high vertical producing degree and good waterflooding sweep effect because mud interbeds in the sands have vertical blocking and shunt effect on injected water; on the other hand, these two types of sands have inhomogeneous waterflood sweeping because of large permeability difference and high development of dominant water channels. In contrast, made up of thin homogeneous fine sand with poor physical properties, lateral sheet sand often has even water-flooding and poor waterflooding sweep effect.