Structure Characteristics and Deep Shearing in M Field, South Iraq, First Evidence from 3D Seismic and Integrated Gravity Study

Abstract The South Iraq is one of the most prolific hydrocarbon-producing regions in the world. Most of fields in this area are elongated in N-S, NW-SE and characterized as four-way dip closure. The kinetic and dynamic mechanisms of these structures are reported as deep salt diapir or regional shear but lack clear evidence in field scale. To robust understanding of structure origination and growth, a dedicated study with the integration of seismic and gravity illustration was carried out. This study was conducted based on high-quality 3D seismic as well as field-scale gravity investigation in M field. Tectonically, this field locates in transition zone of N-S trending and NW-SW trending. The basement depth and tectonic lineament were delineated through gravity-based inversion with different scenarios to figure out the influence of Hormuz salt. Under the recognition of gravity, faults in Jurassic and Cretaceous were interpreted according to dedicated seismic interpretation through geometric attributes and AI techniques. Geometric, kinetic as well as dynamic mechanisms of structure were organically analysed. The anticline growth history is also quantitatively demonstrated through 2D seismic horizon flattening and 3D paleo-structure reconstruction. These understandings of fault features, anticline evolution history as well as basement condition give a clear delineation on the generation and growth procedure of M field. Generally, two sets of faults develop in M field and are separated by Gotnia anhydrite. The fault systems are generated in same stress regime and show different patterns. The Jurassic faults perform as sinistral trans-compression with two N-S trending major faults and eighteen NW-SE subordinate faults. The Cretaceous faults distribute as right-stepping en echelon series. The Gotnia formation adjusts the deformation differentiation through ductile flow and results in the lateral thickness variation. The coincidence of Cretaceous anticline crest and Jurassic fault-constraint area indicated the contribution of fault activity to growth of the anticline. Paleo-structure through 2D horizon flattening and 3D methods indicated the continuous growth of since the early Cretaceous. Conclusively, this is the first time to explicitly display the fault configuration in South Mesopotamian basin and prove the dextral shearing of Jurassic formation in 3D seismic and gravity. The study provides insight into the relationship between tectonic movement and field growth. The achievement of this study would enhance the understanding of hydrocarbon accumulation in South Mesopotamian basin and give inspiring information on hydrocarbon accumulation.