Hydrocarbon migration and accumulation history in deep reservoirs: a case study of Mesozoic sandstone gas reservoirs in the Kelasu-Yiqikelike structural belt of the Kuqa Depression, Tarim Basin

Numerous deep oil and gas reservoirs have recently been discovered in the Kelasu-Yiqikelike structural belt of the Kuqa Depression in the northern Tarim Basin, north-western China. The sources and accumulation processes of the oil and gas are determined in this study through a series of biomarker geochemical parameter analyses and fluid inclusion analyses, respectively. The geochemical parameters show that the oil of the Kela 2 gas field originated from the Triassic Huangshanjie (T3h) Formation lacustrine source rock and that the oil of the Jurassic reservoirs in the Dibei gas field was sourced from Jurassic coal measures, with some contribution from the T3h source rock. Furthermore, the gas in the Kela 2, Keshen and Dibei gas fields was derived from the Jurassic coal measures. Based on petrographic and fluid inclusion analyses, combined with a reconstruction of the reservoir burial history, timing estimates and charge models of the hydrocarbon accumulation have been obtained. Two stages of oil charging and one stage of gas charging were identified in the Kela 2 gas field. The two stages of oil charging occurred in the middle–late Miocene and in the early Pliocene. The gas charge occurred in the middle–late Pliocene. Additionally, one stage of gas charging occurred in the Keshen gas field in the late Pliocene to Quaternary. In contrast, two hydrocarbon charging stages were identified in the Dibei gas reservoirs, with the first occurring in the early Miocene and the second occurring in the Pliocene.