UNCONVENTIONAL GAS SYSTEM OF UPPER PALEOZOIC IN ORDOS BASIN
鄂尔多斯盆地上古生界非常规含气系统

Upper Paleozoic of Ordos basin is prolific in unconventional natural gas. In the central-eastern basin, coal seam in Upper Paleozoic are characterized by thick layers, high vitrinite content and middlehigh coal rank. Influenced by the structural evolution and stress field, cleats are well developed within coal seam and thus the reservoir permeability is high. With the high absorption intensity, stable hydrodynamic field and coal-seam floor and roof, favorable coalbed gas system is formed. Abundant gas source rocks are develop in the central basin. Compaction process of sandstones is prior to the mass gas expulsion period of gas source rocks. Structure movement and hydrodynamics after the formation of reservoirs are relatively stable. Vast deep basin gas traps are formed in combination with these reservoir-forming conditions. Researches on reservoir-forming indicate that areas enriched with coalbed gas in Upper Paleozoic are important gas supplements to deep basin gas traps.