Reservoir Properties of the Upper Sand Member of the Zubair Formation in North Rumaila Oil Field

Abstract

The Zubair Formation is main prolific reservoirs in the Rumaila oilfield in southern Iraq. The petrophysical assessment of the Zubair Formation was carried out using a suite of open-hole logs from eight wells along with the Rumaila North oil fields, in Basra. Based on THE neutron, density and Gamma Ray logs, the Upper Sand Member of the Zubair Formation is divided into the alternate units of the sand and shale and defining their boundaries. Based on the obtained results, the Upper Sand Member was divided into three main pay units: AB, DJ, and LN, separated by two insulating shale units designated C and K. The unit DJ was subdivided into four secondary reservoir units: D, F, G, H, and the LN unit, which is split into L, M, and N. High porosity, high oil saturation and a high net-to-gross ratio were found in the petrophysical investigation. The porosity types are good (from 15 to 20%), very good (20-25%) and excellent (more than 25%) except wells R-559 and R-256, which has medium permeability, all the wells have good to excellent permeability. The net pay for the reservoir unit thickness ranges from 5 to 59m in all wells, resulting in significant hydrocarbon productivity due to strong hydrocarbon saturation, good effective porosity, and low shale volume.