Reservoir Characteristics of Epimetamorphic Rock Gas Reservoir in Pingxi Area, Qaidam Basin

Abstract

Metamorphic rock gas reservoirs whose protolithic is sedimentary rock were found for the first time in Pingxi area, Altun foreland, Qaidam Basin. Comprehensive analysis containing core data, thin section analysis, X-ray diffraction analysis, scanning electron microscopy and confocal laser scanning shows that there are three types of shallow metamorphic rock reservoirs in Pingxi area, such as slate, “metamorphic limestone” and calc-schist which have good responses in logging and seismic data. Fractures and pores develop in epimetamorphic rock reservoir, and there are five types and eight subcategories of reservoir space. Industrial CT shows that there are differences in pores and throats of the three types of metamorphic rock reservoirs, and the fractures have a significant impact on the development of pore throats. The protolithic type is the genetic basis of epimetamorphic rock reservoirs in Pingxi area, and thin section, mineral characteristics and carbon and oxygen isotopes data show that the protolithic of epimetamorphic rock is Palaeozoic Ordovician marine sedimentary rock. Five kinds of actions, such as metamorphism, weathering, structural fragmentation, dissolution and filling, are external mechanisms of reservoir genesis. Metamorphic, weathering and structural fragmentation form fractures, and dissolution is the main cause of matrix porosity.