Reservoir characterization of the upper Turonian – lower Coniacian Khasib formation, South Iraq: Implications from electrofacies analysis and a sequence stratigraphic framework

Abstract

The Upper Turonian – Lower Coniacian Khasib Formation is a significant hydrocarbon reservoir in southern Iraq. The present study integrates multiple data sets of 33 wireline wells, available core, and thin sections from two important oilfields: Amara and Noor to interpret the lateral and vertical facies changes and petrophysical reservoir variability within a sequence stratigraphic framework. Cluster analysis based on well log data including gamma ray, sonic, neutron, bulk density data were used to classify the Khasib Formation into five carbonate electrofacies and determine the petrophysical properties. These electrofacies consists of compacted marly, argillaceous, chalky, porous, and vuggy limestones which are interpreted to have been deposited in a ramp setting. Sequence stratigraphic analysis shows that the Khasib Formation consists of two third-order sequences with three sequence boundaries refer to global sea-level changes: the Mishrif-Khasib regional unconformity, the intra-Khasib unconformity, and the Khasib-Tanuma formational boundary. Each sequence consists of a transgressive system tract (TST) and a highstand systems tract (HST) which are separated by a maximum flooding surface (MFS). Reservoir correlation and mapping of the Khasib Formation in both the Amara and the Noor oilfields show the best important oil-bearing zones are located dominantly in transgressive system tracts (TSTs).