The current work is focused on the rock typing and flow unit classification for reservoir characterization in carbonate reservoir, a Yamama Reservoir in south of Iraq (Ratawi Field) has been selected, and the study is depending on the logs and cores data from five wells which penetrate Yamama formation. Yamama Reservoir was divided into twenty flow units and rock types, depending on the Microfacies and Electrofacies Character, the well logs pattern, Porosity-Water saturation relationship, flow zone indicator (FZI) method, capillary pressure analysis, and Porosity-Permeability relationship (R35) and cluster analysis method. Four rock types and groups have been identified in the Yamama formation depending on the FZI method, where the first group represents the bad reservoir quality (FZI-1) (Mudstone Microfacies and Foraminiferal wackestone Microfacies), the second group reflects a moderate quality of reservoir (FZI-2) (Algal wackestone-Packstone Microfacies and Bioclastic wackestone-Packstone Microfacies), the third group represents good reservoir quality (FZI-3) (Peloidal Packstone-Grainstone Microfacies), and the fourth group represents a very good reservoir quality (FZI-4) (Peloidal-oolitic Grainstone Microfacies). Capillary pressure curves and cluster analysis methods show four different rock types: a very good quality of reservoir and porous (Mega port type) (FZI-4) (Peloidal-oolitic Grainstone Microfacies) with a low irreducible Water saturation (Swi), good quality of reservoir and porous (Macro port type) (FZI-3) (Peloidal Packstone-Grainstone Microfacies), moderate quality of reservoir (Meso port type) (FZI-2) (Algal wackestone-Packstone Microfacies and Bioclastic wackestone-Packstone Microfacies), and a very fine-grained with bad reservoir quality (Micro port type) (FZI-1) (Mudstone Microfacies and Foraminiferal wackestone Microfacies) and with the higher displacement of pressure). These capillary pressure curves support the subdivision of the main reservoir unit to flow units.

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The objective of this paper is determining the petrophysical properties of the Mauddud Formation (Albian-Early Turonian) in Ratawi Oil Field depending on the well logs data by using interactive petrophysical software IP (V4.5). We evaluated parameters of available logs that control the reservoir properties of the formation, including shale volume, effective porosity, and water saturation. Mauddud Formation is divided into five units, which are distinguished by various reservoir characteristics. These units are A, B, C, D, and E. Through analyzing results of the computer processed interpretation (CPI) of available wells, we observed that the main reservoir units are B and D, being distinguished by elevated values of effective porosity (10%-32%) and oil saturation (95%-30%) with low shale content (6%-30%). Whereas, units A, C, and E were characterized by low or non-reservoir properties, due to high water saturation and low values of effective porosity caused by increased volume shale.

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Mishrif carbonates formation, is a major reservoir in southeast of Iraq and is one of the principle carbonate reservoir in central and southern Iraq, which is of Late Cenomanian to Early Turronian. A petrographic and depositional Environment study has been carried out by examining available thin sections in the Ministry of Oil for wells (No-1, No-2 (Noor field), Am-1(Amara field) and Hf-1 (Halfaya field)).      The main skeletal grains of the Mishrif formation include coral, Rudist, large and small benthonic Foraminifera & planktonic Foraminifera (Planktonic Foraminifera are common in the lower part of the Mishrif Formation), ostracods, echinoderms, and molluscs. The Rudist were found in small to large fragments; and as a complete fossil covering the whole thin section. The Non-skeletal grains included peloids, and micrite.      The most important diagenetic processes affecting on the Mishrif Formation are dolomitization, dissolution, cementation, micritization, recrystallization and Stylolite. Mishrif succession comprises six paleoenvironments which are deep marine, shallow open marine, rudist biostrome, shoal, back shoal, and lagoon.