Genesis of freshwater limestone of Paleogene Nadu Formation in Nakun area, Baise Basin

Abstract： On the basis of core observation,the authors studied the features and genesis of freshwater limestone by acoustic emission technology, stable isotopic analysis, fluid inclusion homogenization temperature of filled components in fractures. The results show that the main fractures of the freshwater limestone reservoir are of three types： vertical fissures, high-angle fissures, and oblique fissures. The tectoclase and non-tectoclase constitute two main fissure types. The complex fracture can be formed by tectoclase overlying diagenetic fractures. Some fissures are completely or partly filled with calcite, whereas others are effective fractures without fillings. The development and evolution of fractures have been affected considerably by three different tectonic stress fields. The tectoclase has exerted important contribution to improving porosity and permeability of the reservoir.