Hydrocarbon sources and charge history in the Southern Slope Region, Kuqa Foreland Basin, northwestern China

Abstract

Numerous oil and condensate gas reservoirs have recently been discovered in the Southern Slope Region of the Kuqa Foreland Basin in the northern Tarim Basin, northwestern China. However, their hydrocarbon sources and charge history are still unclear. In this study, oil-source correlation was firstly used to ascertain the sources of oils in different tectonic belts. The hydrocarbon charge history was then investigated using an integrated fluid inclusion analysis and basin modelling approach. On the basis of a variety of oil-source correlation geochemical parameters, two distinct oil groups were delineated in this region: Group I including oils in the Yaha and Yingmai-7 tectonic belts, while Group II comprising oils from the Yangtake, Hongqi, and Yudong-2 tectonic belts and the YM-21 well. Oil-source correlations show that Group I oil is sourced from the Upper Triassic Huangshanjie Formation (T3h), while Group II oil is mainly sourced from the lower part of the Middle Jurassic Qiakemake Formation (J2q). Both source rocks are located in the middle and northern parts of the Kuqa Foreland Basin.Basin modelling shows that the T3h source rock began to generate early mature to mature oil at 34 Ma and continued until around 3 Ma. The J2q source rock began to generate early mature to mature oil between after 34 Ma and continued to 12 Ma, mainly in the central part of the J2q source rock. Oil migration modelling indicates that the T3h-sourced oils did not accumulate in the Southern Slope Region until 12–5 Ma, whereas the J2q-sourced oils began to charge into the Southern Slope Region around 5–3 Ma. Coupled with fluid inclusion analysis, the modelling shows that oils originated from the T3h source rock began to charge into the Yaha tectonic belt as early as 6 Ma, and subsequently to the Yingmai-7 tectonic belt which received its initial charge around 4.8 Ma. Oils sourced from the Lower J2q source rock began to charge into the Yangtake tectonic belt around 4 Ma, and then into the Yudong-2 tectonic belt around 3.7 Ma. Oils first charged into the Hongqi and YM-21 areas after 4 Ma. Oils from the T3h and the Lower J2q source rocks continued to charge into the Southern Slope Region until 3 Ma.