Geochemical characteristics and genesis of tight sandstone gas in Xinguang area, Junggar Basin

Abstract

Based on the study of natural gas geochemical characteristics, combined with carbon isotope composition distribution of n-alkanes in condensate oil associated with tight sandstone natural gas, the source of natural gas in Jiamuhe Formation tight sandstone reservoir from Xinguang area of Zhongguai uplift in Junggar Basin was determined. The result shows, hydrocarbon generation potential of three sets of source rocks in Permian is: Fengcheng Formation > Lower Wuerhe Formation > Jiamuhe Formation. Lower Wuerhe Formation source rocks generate oil and gas. And C7 light hydrocarbons composition of the natural sandstone reservoir of Jiamuhe Formation in Xinguang area is dominated by n-heptane, with content more than 40%, content of methylcyclohexane is less than 40%, and carbon isotope distribution of ethane is between -29.0‰ and -27.0‰. which shows the gas origin from sapropelic source rock. The carbon isotope composition distribution of n-alkanes in condensate oil associated with the tight sandstone natural gas of Jiamuhe Formation is “valley” type, which is consistent with source rock of Lower Wuerhe Formation, indicating that the condensate oil from Xinguang area is derived from Lower Wuerhe Formation source rock. According to comprehensive analysis, the tight sandstone gas of Jiamuhe Formation in Xinguang area of Junggar Basin is mainly derived from high-mature Lower Wuerhe Formation source rock.