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

摘要

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 depo-sitional systems and the development of erosional surfaces and ultimately governed the distribution of oil and gas fields and trap types.