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Based on the analyses of hydrocarbon inclusions, K-Ar dating of authigenic illites and oil/gas-water contact retrospection as well as other methods, the marine primary reservoirs in the cratonic region of the Tarim Basin are found to have been formed in the late Caledonian to early Hercynian, late Hercynian, and Himalayan, and oil and gas adjusted and redistributed in the Yanshanian (Jurassic to Cretaceous) and Himalayan (Tertiary). The analyses also show that the remaining primary oil accumulations are mostly formed in the late Hercynian, and the secondary oil reservoirs resulted from the adjustment and redistribution of the earlier accumulations during the Yanshanian and Himalayan (especially late Himalayan), of which the Himalayan is also the major stage of gas accumulation. The primary oil reservoirs formed in the late Hercynian mostly occur within the Paleozoic formation, whereas the secondary reservoirs formed in the Himalayan in the Mesozoic. The late adjustment and redistribution of reservoirs in the craton region of the Tarim Basin is ubiquitous because of the intensified tectonic movements since the Mesozoic, especially Cenozoic and intrusion of the high-to overmature gas. Furthermore, the lower amplitude of reservoirs in the craton region also makes them easier to be adjusted and redistributed. Therefore, the remaining paleouplift and palaeoslope developed in relatively stable tectonic regions are the main potential areas for the middlelarge marine reservoirs in the Tarim Basin.

The Kela-2 gas field is located in the center of Kelasu structural belt in Kuqa Depression. This trap is one of a series of traps in the folded belts which are distributed in a string of pearls in the dual structure. The primary gas-bearing layers are sandstone of Lower Cretaceous K1bs while the secondary layers are dolomite member and glutenite member of Lower Tertiary E1–2km and sandstone of Lower Cretaceous K1b. The main component of natural gas is methane whose content is higher than 97%. It is characterized by dry gas whose source rock is Jurassic coal measure. The Kela-2 structural trap was formed during the Xiyu period and then became a reservoir in the late time. The reservoir formed late and the thick seal rock of Lower Tertiary gipsmantle are the avail reason why the giant Kela-2 gas field has been well kept. The abnormal high pressure of the Kela-2 gas field results from the strong structural compression in the northern part during the Xiyu period.