Timing and history of marine hydrocarbon accumulation in Tarim craton

Abstract

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.