Reservoir conditions of Carboniferous- Permian strata in Ejin Banner and its vicinities, western Inner Mongolia: a study of Carboniferous-Permian petroleum geological conditions (part 2)

Based on the characteristics of vertical variation and plane distribution of Carboniferous-Permian clastic rock sedimentary facies, petrological features, diagenesis and pore types, the authors hold that the development degree and compositional and structural maturity of Carboniferous-Permian glutenite are controlled by two sedimentary derivations of Alxa ancient land and Mazongshan-Guaizihu central uplift belt. The sedimentary derivation in the south is Alxa ancient land, with the development of glutenite, and the compositional and structural maturities are both high. The effect of Alxa ancient land central uplift as the material source is decreased from south to north, with the gradual worsening of the glutenite development and the compositional and structural maturities. Based on clay mineral content and authigenic mineral characteristics, the authors divided the diagenesis into stages: most sections belong mainly to A stage of middle diagenesis, and the diagenesis of northern study area, Beishan area and Yagan area affected by Altun fault belongs to B stage of middle diagenesis, affected by tectonic dynamometamorphism or magmatic-thermal contact-metamorphism. Because pore evolution of the clastic rock reservoir is controlled by diagenesis, the pores are mostly dissolved pores (fractures), with only a few residual intergranular pore, and the pores are on the whole poorly-developed. Carbonate, volcanics and Variscan Stage weathering crust are likely to become important reservoir types.