Sequence Stratigraphy, Depositional System, and Hydrocarbon Prospectivity of the Third Rifting-Sagging Cycle in Muglad Basin

Abstract

The Muglad basin, regarded as a typical passive rift, had undergone three-phase rifting-sagging cycles during Early Cretaceous, Later Cretaceous, and Tertiary respectively. The primary plays in the first cycle had been testified, and hydrocarbon was also discovered in the second one. However, the hydrocarbon prospectivity in the third cycle has been much less explored. Hence, the sequence stratigraphic framework of the third rifting-sagging cycle was built, and the depositional systems of each system tracts were thoroughly analyzed by using the comprehensive analysis of tectonic evolution, geological features, cores and cuttings, well logs, and seismic faices. Furthermore, favorable plays were also discussed. The third rifting-sagging cycle, approximately corresponding to Paleogene Nayil formation and Neogene Tendi formation, can be classified into five third-order sequences and eleven parasequence sets, meanwhile, five sedimentary faices and related sub-facies and micro-faices were identified. The braided delta and lacustrine deposits were widely distributed in SQ1 and SQ2, whereas fan delta and alluvial plain were locally developed. The braided delta was dominated in the western slope, and lacustrine was distributed in the Kaikang trough. The delta and alluvial plain deposits were massively developed during SQ3, while the braided delta was deposited in the western slope and northern Gudaim area. As a result, the lacustrine began to shrink in the north of the Kaikang trough and expanded to the southern Gurial area. The lacustrine continued to expand from SQ4 through SQ5, and the delta and braided delta were locally distributed. The hydrocarbon, generated in the first rifting-sagging cycle, migrated vertically for long distance along major or boundary faults, and finally accumulated again in SQ1 and SQ3, should be expected to have great hydrocarbon prospectivity.KeywordsRifting-sagging cycleSequence stratigraphyDepositional systemHydrocarbon prospectivityMuglad basin