Determination of reservoir properties for Nahr Umr Formation based on core plugs, lithofacies, and well logs in Noor oilfield, southern Iraq

Abstract

The Nahr Umr Formation, one of the most important Cretaceous formations and one of the main generating reservoirs in southern Iraq and neighboring regions, was chosen to study and estimate its petrophysical properties using core plugs, lithofacies, and well logs from five wells in the Noor oilfield. Reservoir properties and facies analyses are used to divide the Nahr Umr formation into two-member (limestone in the upper part and main sandstone in the lower). Limestone members are characterized by low reservoir properties related to low effective porosity and permeability while the main sandstone member is considered as a reservoir. Four lithofacies were recognized in the main sandstone member of the Nahr Umr Formation according to petrographic observation with gamma-ray. They are well-sorted quartz arenite sandstone, poorly sorted Quartz arenite sandstone, Sandy shale, and Shale Lithofacies.

Calculation of the various reservoir properties (shale volume, effective porosity, permeability, and water saturation) using the (Interactive Petrophysics v3.5) program and linking them with the lithofacies by computer processed interpretation (CPI) of available of the available wells. Divided the sandstone member into three units are A, B, and C. Each unit consists of many reservoir sandstone subunits separated by shale and streaks of limestone. Average reservoir properties of units A and B are good to very good related to high porosity, permeability, and economy hydrocarbon saturation (low water saturation). While these properties are decreased in unit C. The Sandston member of borehole No-5 was the best reservoir characterization, especially in the thickness of the reservoir units and the low shale content.