Hydrocarbon Sources of the Carboniferous System in the Central and Peripheral Areas of the Junggar Basin

Carboniferous volcanic reservoirs are widely developed in the central part and surrounding areas of the Junggar Basin. These reservoirs are closely associated with underlying Carboniferous and overlying Permian major source rocks, providing favorable source–reservoir configurations. Determining the hydrocarbon sources of the Carboniferous System is therefore critical for understanding hydrocarbon accumulation mechanisms. In this study, the Fukang Sag and Penyijingxi Sag in the central basin and the Wucaiwan Sag, Dinan Uplift, and Zhongguai Uplift in the surrounding areas were selected as research targets. Based on a systematic analysis of geochemical characteristics of source rocks, biomarker compounds and stable isotopes were integrated to conduct oil–source and gas–source correlation studies for Carboniferous petroleum systems. The results show significant variations in hydrocarbon sources among different tectonic units. Carboniferous crude oils in the central basin are mainly derived from Permian source rocks, with minor contributions from Carboniferous source rocks. In contrast, Carboniferous oils in the Wucaiwan Sag are mainly sourced from Carboniferous source rocks, whereas those in the Zhongguai and Dinan Uplifts are primarily derived from Permian source rocks. Natural gases in the Penyijingxi Sag and Dinan Uplift are mainly supplied by Permian source rocks, while gases in the Fukang Sag and Wucaiwan Sag are predominantly derived from Carboniferous source rocks. Overall, the Carboniferous petroleum system in the central and marginal areas of the Junggar Basin exhibits mixed-source characteristics, with significant differences in dominant source strata among tectonic units. Further analysis indicates that Carboniferous oils in the central basin and Dinan Uplift are mainly sourced from Permian source rocks. The Wucaiwan Sag is dominated by Carboniferous-derived hydrocarbons. For gas–source correlation, gases in the Penyijingxi Sag and Dinan Uplift are mainly derived from Permian source rocks, whereas those in the Fukang Sag and Wucaiwan Sag originate primarily from Carboniferous source rocks. However, gases in the Zhongguai Uplift show poor correlation with known source rocks in the area.