Abstract

The Ordos basin is the oldest and still an important hydrocarbon province in central China. It is a typical cratonic basin developed on the Archean granulites and lower Proterozoic greenschists of the North China block. The development of the Ordos basin during the Paleozoic–Mesozoic can be divided into three evolutionary stages: Cambrian–Early Ordovician cratonic basin with divergent margins; Middle Ordovician–Middle Triassic cratonic basin with convergent margins; and Late Triassic–Early Cretaceous intraplate remnant cratonic basin. Two hydrocarbon systems are present in the basin: the Paleozoic gas and Mesozoic oil systems. In the Paleozoic gas system, the Lower Ordovician marine carbonates and Pennsylvanian–Lower Permian coal measures serve as source rocks. The Lower Ordovician karst-modified dolomites and Pennsylvanian bauxitic mudstones form a significant reservoir-seal association, and the Pennsylvanian–Lower Permian deltaic sandstones and Upper Permian lacustrine mudstones form another effective reservoir-seal association. In the Mesozoic oil system, the Upper Triassic lacustrine mudstones are mature source rocks. The Upper Triassic deltaic sandstones and overlying shallow-lacustrine and swamp mudstones form a reservoir-seal association, and the Lower Jurassic fluvial sandstones and overlying shallow-lacustrine and swamp mudstones form another reservoir-seal association. In both hydrocarbon systems, the stratigraphic variations provide the principal traps. The Ordos basin is characterized by a stable tectonic setting that controlled the distribution of depositional systems and the development of erosional surfaces and ultimately governed the distribution of oil and gas fields and trap types.

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