Deciphering multi-phase inversion tectonics in the southern Dezful Embayment: insights from the Rag-e-Sefid Oilfield, SW Iran

Abstract

ABSTRACT Identification of inversion tectonics and inverted structures is very important in petroleum exploration and production due to the positive or negative impacts they can exert on the hydrocarbon traps. In order to characterize the occurrence of multi-phase inversion tectonics and its effect in the Rag-e-Sefid Oilfield, located in the southern Dezful Embayment (SW Iran), this research describes the structural style and deformation history through structural and tectono-sedimentary analyses. The results obtained from the interpretation of seismic profiles and the investigation of the geometry of the sedimentary layers across the growth structures indicate that the Rag-e-Sefid anticline is created from multiple fault-propagation folds. The final shape and geometry of the Rag-e-Sefid anticline are affected by the Rag-e-Sefid and Nourooz-Hendijan-Izeh Faults activity. The deformation history in the north-western part of the Rag-e-Sefid anticline is older than the south-eastern part of it. The Rag-e-Sefid Fault set in the north-western and south-eastern parts of the Rag-e-Sefid Oilfield experienced activity at least during seven and four tectonic phases, respectively. Multiple fault-propagation folding and the fold axis rotation in the north-western part of the Rag-e-Sefid anticline controlled by the presence of several décollement surfaces and the occurrence of inversion tectonics along the pre-existing basement structures. Three-phase inversion tectonics along the Nourooz-Hendijan-Izeh Fault and the Rag-e-Sefid Fault set in the north-western part of the Rag-e-Sefid Oilfield occurred at the Late Devonian-Carboniferous (positive inversion), Permian-Early Triassic (negative inversion), and Late Cenomanian-Early Turonian (positive inversion) boundaries and modified the evolutionary history of the sedimentary basin. The inversion affected hydrocarbon trap development at the Late Cretaceous and controlled their current conditions in the southern Dezful Embayment. Based on the hydrocarbon migration in these regions from the Late Miocene to the present day, the N-S trending (Pan Africa trend) north-western part of the Rag-e-Sefid anticline has a larger share of oil and gas compared to the NW-SE trending (Zagros trend) south-eastern part. The results of this study could add data to worldwide examples of the positive impact of tectonic inversion on the hydrocarbon traps development in the foreland of a collisional orogen.