Genetic Types and Source of the Upper Paleozoic Tight Gas in the Hangjinqi Area, Northern Ordos Basin, China

The molecular and stable isotopic compositions of the Upper Paleozoic tight gas in the Hangjinqi area in northern Ordos Basin were investigated to study the geochemical characteristics. The tight gas is mainly wet with the dryness coefficient (C-1/C1-5) of 0.853-0.951, and delta C-13(1) and delta(2) H-C-1 values are ranging from -36.2% to -32.0% and from -199% to -174%, respectively, with generally positive carbon and hydrogen isotopic series. Identification of gas origin indicates that tight gas is mainly coal-type gas, and it has been affected by mixing of oil-type gas in the wells from the Shilijiahan and Gongkahan zones adjacent to the Wulanjilinmiao and Borjianghaizi faults. Gas-source correlation indicates that coal-type gas in the Shiguhao zone displays distal-source accumulation. It was mainly derived from the coal-measure source rocks in the Upper Carboniferous Taiyuan Formation (C(3)t) and Lower PermianShanxi Formation (P1s), probablywith aminor contribution fromP(1) s coalmeasures fromin situShiguhao zone. Natural gas in the Shilijiahan and Gongkahan zones mainly displays near-source accumulation. Thecoal-type gas component was derived from in situ C(3)t-P-1 s source rocks, whereas the oil-type gas component might be derived from the carbonate rocks in the Lower Ordovician Majiagou Formation (O(1)m).