Geochemical characteristics of gases from the largest tight sand gas field (Sulige) and shale gas field (Fuling) in China

This study performed a detailed geochemical analyses of the components, stable carbon isotopes of alkane gas and CO2, stable hydrogen isotopes of alkane gas and helium isotopes of reproducing gas from the largest tight gas field (Sulige) and shale gas (Fuling) field in China. The comparative study shows that tight gas from the Sulige gas field in the Ordos Basin is of coal-derived origin, which is characterized by a positive carbon and hydrogen isotopic distribution pattern (delta C-13(1) > delta C-13(2) > delta C-13(3) > delta C-13(4); delta H-2(1) > delta H-2(2) > delta H-2(3)), i.e., the carbon and hydrogen isotopes increase with increasing carbon numbers. Carbon dioxide from this field are of biogenic origin and the helium is crust-derived. Shale gas from the Fuling shale gas field belongs to oil-derived gas which has complete carbon and hydrogen isotopic reversal of secondary alteration origin (delta C-13(1) < delta C-13(2) < delta C-13(3); delta H-2(1) < delta H-2(2) < delta H-2(3)), i.e., the carbon and hydrogen isotopes decrease with increasing carbon numbers. Such complete isotopic reversal distribution pattern is due to the secondary alteration like oil or gas cracking, diffusion and so on under high temperature. In that case, positive carbon or hydrogen isotopic distribution pattern will change into complete isotopic reversal as the temperature increases. Carbon dioxide is of abiogenic origin resulting from the thermal metamorphism of carbonates and helium is crust-derived. (C) 2016 Elsevier Ltd. All rights reserved.