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Abstract: The Kela-2 gas field, located in the Kuqa Depression of Tarim Basin, is the most productive gas field in China, based on per unit surface acreage. The gas trap is a subsurface anticline formed along an E–W trending thrust belt in front of the southern Tianshan Mountains. The gas pay zones are located in fine-grained sandstones of a fan delta front facies in the Lower Cretaceous Bashijiqik Formation (Klbs), and Eogene evaporitic rocks serve as regional cap rocks. The gases were derived primarily from over-mature Jurassic coal measures. Peak gas generation and final shaping of the Kela-2 structure occurred relatively late, in the late Himalayan orogeny (5–0Ma). Thrust faulting appears to have played a significant role in the hydrocarbon generation, migration, accumulation and preservation in this foreland basin. Detailed delineation of the Kela-2 gas field indicates that high-quality regional cap rocks are essential for the formation of the super-rich, abnormally pressured, giant gas fields, while buried anticlines under the overthrust zone are the favorable gas habitat. Late gas accumulation is considered to be decisive for the conservation of the giant gas fields. [Copyright &y& Elsevier]

Reports that there is a gas-rich and well-charged petroleum system in the Kuqa Depression where Triassic and Jurassic source rocks play important roles. Distribution in an area of more than 10000 km² and with a thickness of up to 1000 m; Composition of dark mudstones, carbonaceous mudstones and coal seams containing 6%, 40% and 90% of TOC, respectively, mainly of humic organic matter; Statement that, as high-quality regional cap rocks, the Neogene and Eogene gypsum rocks and gypseous mudstones matched well with the underlying Neogene and Cretaceous-Eogene sandstones; Formation of the most favorable reservoir-seal assemblages in the Kuqa Depression; Formation of the Jurassic sandstones and mudstones into another favorable reservoir-seal assemblage; Shaping of the traps late in the fold-thrust belt, mainly fixed in the Tertiary-Quaternary, where ten structure styles have been distinguished; Reference to tge fact that these traps spread as a zone in N-S, are scattered like a segmental line in W-E and show tier-styled vertically; Statement that the best traps are gypsum-salt covered fault-bend anticlines related to the passive roof duplex; Characterization of this petroleum system by late accumulation; Distribution in the early Himalayan Movement of an accumulation of mainly gas condensate and oil in the outer circular region of the kitchen; Claim that in the middle and late Himalayan the gas accumulations mainly formed and were distributed in the inner circular region near the kitchen; Statement that the overpressure of gas pools is common and is formed by seal capacity of thick gypsum layers, extensive tectonic compression and large uplift; Suggestion that the well-preserved anticline traps underlying the high-quality regional cap rocks of the Tertiary gypsum rocks and gypseous mudstones are the main targets for the discovery of giant and medium-sized gas fields; Importance of the above conclusions for the petroleum geology theory and the exploratio