Rock Properties of Complex Lithologies - Similarities Between Offshore Brazil and West Siberia

Rift related basins represent an important part of hydrocarbon bearing areas worldwide. In basins containing large flood basalts, volcanic rocks occur as major sediment source for potential reservoir sandstones. Examples from Cretaceous sediments in the Santos Basin, offshore Brazil, and Jurassic sediments in the West Siberian Basin are presented here. In contrast to pure quartz arenites, these sandstones contain a significant amount of feldspars, lithics and their diagenetic products which have a significant impact on reservoir properties. Although diagenetic products may preserve porosity at relatively deep burial, they normally reduce permeability and therefore production rates. The acoustic and elastic properties of the reservoirs are also affected. These types of complex reservoirs are rarely documented. Therefore, learning from case studies helps to understand similar reservoirs and to predict their properties in order to optimise exploration and production potential.