Integrating well logs and microfacies analysis for reservoir facies characterization of the Mishrif Formation, Southern Iraq

The Mishrif Formation, a significant carbonate reservoir in southern Iraq, is characterized by complex depositional environments and diagenetic alterations that impact its reservoir quality. This study aims to understand the spatial distribution of facies and the influence of diagenetic processes on reservoir properties. Motivated by the need for accurate facies modeling and improved hydrocarbon recovery, this research integrates well log data, thin section analyses, and facies models to investigate the Mishrif Formation in the Faihaa oilfield. A total of 200 thin sections were analyzed using standard facies models, complemented by core and well log interpretations, to reconstruct depositional environments and identify diagenetic alterations. Various well logs, including Caliper, Gamma Ray (GR), Sonic (triangle t), Density (RHOB), Neutron (NPHI), and Resistivity logs were utilized to calculate shale volume, porosity, and water and hydrocarbon saturations. Computer Processed Interpretation (CPI) was conducted to evaluate and analyze petrophysical properties and identify reservoir units. Results confirmed that primary porosity is predominant in the formation, with very little secondary porosity at certain depths. The lower reservoir unit exhibits good effective porosity. Shale volume was analyzed using the gamma ray log, revealing an impermeable shale unit between the upper and lower parts of the Mishrif Formation. The study also included an analysis of water and hydrocarbon saturations, indicating that the formation contains varying amounts of water, residual hydrocarbons, and producible hydrocarbons. The lithology of the formation was mainly limestone with a small amount of dolomite. The classification of microfacies includes: wackestone microfacies, which encompasses submicrofacies like bioclastic foraminifera wackestone and bioclastic wackestone. packstone microfacies, which includes Alveolina bioclast packstone, bioclast packstone, and rudist rudstone-packstone submicrofacies. Grainstone microfacies, featuring submicrofacies such as peloidal grainstone and oolitic grainstone. Lastly, benthic foraminifera grainstone-packstone microfacies. The research delineates various depositional environments such as open marine, foreslope, rudist reef, shoal, and lagoon, by comparing them with standard facies models. It also correlates rock fabric with petrophysical properties, especially porosity and permeability, underscoring their importance in managing reservoirs and formulating production strategies. This thorough analysis improves the comprehension of the reservoir potential of the Mishrif Formation, contributing to the efficient management and optimization of hydrocarbon production.