An Integrated Geological Model of Selective Carbonate Reservoir Wells, in Mishrif Formation in the Ratawi Oilfield, Southern Iraq

The majority of petroleum studies have traditionally focused on rocks that store hydrocarbons due to their economic significance, particularly in a period where oil is the primary global energy source. In the Cretaceous period, Iraq, and the Middle East, in general, are of particular interest due to the presence of formations that are significant for hydrocarbon storage and generation. The Mishrif Formation, dating to the Cenomanian-Early Turonian period, is a notable oil reservoir in southern Iraq. This formation’s distinctive features and extensive surface area make it a significant hydrocarbon repository, ranking second economically after the Zubair Formation in the region. This study analyzed six oil wells from the Mishrif Formation using various well logs (gamma ray, density, neutron, spontaneous potential, acoustic and resistivity) to extract petrophysical properties. The study identified rock types, layer boundaries, thicknesses, formation depths, and hydrocarbon-bearing zones. Through qualitative interpretation of these logs, the reservoir's characteristics were evaluated, including porosity, shale distribution, water and oil saturation. The results were visualized in three-dimensional models using the Petrel software, showing the distribution of these characteristics across the study wells. The Mishrif Formation is composed of four units (MA, CR-1, MB-1, and MB-2), with varying properties that were detailed in this study. Shale volume, averages between 0.04 % and 0.16%. Effective porosity ranges from 0.09% to 0.19%, indicating good reservoir quality; permeability ranges from 0.001 to 10 mD. Hydrocarbon saturation varies from 0.1to 0.7, while water saturation ranges from 0.3 to 0.9. The distribution of effective porosity in the Middle Mishrif reservoir unit is good throughout the field. In the Lower Mishrif reservoir unit, the effective porosity distribution is good in the central part of the field but poor in the northern and western parts. The formation thickness is homogeneous, indicating stable deposition. Hydrocarbon accumulations are present in both the Lower and Middle Mishrif reservoir units.