Tectonic development of Nahr Umr oil field southeastern Iraq: inferences from seismic reflection and borehole data

Abstract

Nahr Umr oil field is located in the southernmost of Mesopotamian foreland basin, southeast Iraq. Even though it is one of the largest and most important oil fields in south Iraq, the time sequence of its tectonic development is still equivocal. Therefore, pre-acquired two-dimensional seismic reflection profiles of total length 47.65 km, time and depth structure maps, well logs information, and calculated porosity distribution surfaces of Zubair and Mishrif formations were gathered to build a simplified tectonic development model. The suggested tectonic sequence model indicated that Nahr Umr oil field was formed during Late Cretaceous-Miocene synchronous to the dominant compressional stresses due to convergent plate boundaries, Arabian and Eurasian. These stresses of northeast-southwest direction formed the field anticline fold and affected the post-Cretaceous stratigraphic sequences. The stratigraphic sequence flexure is associated with fractures and faults, particularly in the axial zone. The fractured zones produced high porosity areas which played as pathways to move the Infra-Cambrian salts, upward. The salts stopped underneath Dammam formation of the Eocene-Miocene age because of either salt depletion or overburden weight. The Middle and Late Miocene-Recent time may show subtle anticline combined with few faults, but no free surface expressions.