Tectonic and stratigraphic controls of hydrocarbon systems in the Ordos basin: A multicycle cratonic basin in central China

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 forrn 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.