Characteristics of light hydrocarbons of tight gases and its application in the Sulige gas field, Ordos basin, China

Tight gas plays an important role in the unconventional natural gas, and the researches of origin and migration of tight gas is of great importance to find the “sweet spots” for exploration and development. Combining the carbon isotopic analysis with light hydrocarbon analysis, it is concluded that the Upper Paleozoic tight gases in the Sulige gas field, Ordos basin are typical coal-derived gas with δ13C2 values ranging from -25.3‰ to -22.1‰ (average value = -23.7‰). In addition, methycyclohexane enrichment and a small amount of benzene and toluene are observed in light hydrocarbon composition. The C7 light hydrocarbons are predominated by methylcyclohexane accounting for 44% to 68% while the content of the naphthene and isoparaffin is relatively higher in C5-7 compounds. According to the Mango parameters K1 and K2, the Upper Paleozoic tight gases in the Sulige gas field are derived from the Carboniferous- Permian coal measures. Besides, the light hydrocarbon parameters such as the content of aromatics, benzene/n-hexane, toluene/n-heptane and other light hydrocarbon indicators show little differentiation which is inferred that the Upper Paleozoic tight gases of the Sulige gas field accumulated near the source rocks without long distance migration. Hence, it is reasonable to regard the district nearby the coal measures as the “sweet spots” in the Sulige gas field.