The Coalfields of the Karst-Erosional Downcuttings of the Volga-Ural Oil and Gas Basin as a Factor of Geofluidodynamic Heterogeneity

摘要

This work considers the Early Carboniferous coal-bearing deposits of the karst-erosional paleo-downcuttings of the Volga-Ural oil and gas basin. The depth of their occurrence is 900-1400 m or more. The role of organic matter in coal as a fluid-generating component in the transformations of the geological environment is highlighted. It was noted that specific reservoirs (methane-coal and pyrometamorphic) may be formed in coal-bearing rocks. This work covers the concept of catagenetic fracturing, which is also caused by fluid-generated losses of organic matter and an unequal decrease in the thickness of coal-bearing layers. Attention is also drawn to the other factors of changes in the filtration properties and fracture fluid conductivity (aggressiveness of some products of organic matter transformation, deposition of epigenetic minerals, and variability of the ash distribution). It is concluded that the discrete occurrence of paleo-downcuttings affects circulation of stratal waters in the Visean deposits of the basin; the geochemical and geomechanical features of bulks of coal increase the geofluidodynamic heterogeneity of these deposits.