Depositional model and diagenetic evolution of hydrocarbon reservoirs in deep dolomites of the Ordos Basin, China

Natural gas reservoirs in the intracratonic Ordos Basin have been examined for their sedimentological and geochemical characteristics in order to get a better insight into their depositional conditions and diagenetic evolution. The dolomite reservoir rocks originated in a tidal flat that extended by cyclic progradation on an epeiric platform. The tidal flat successions extended laterally as a progradational wedge in each cycle of sea-level fluctuation. The peritidal shoal facies in the wedge represent potential dolomite reservoirs. They can be recognized by the presence of dolo-arenites that have been altered by diagenesis. Although continuing destructive diagenesis has led to reservoir densification, burial- and facies-dependent dolomitization and dissolution mostly continued in peritidal shoal facies, thus improving the reservoir quality of the dolomites. The findings help targeting deep dolomite gas reservoirs.