Abstract
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.
Highlights
Recognition of reservoir quality is an important objective in reservoir characterization process, the quality of a reservoir is defined by its hydrocarbon storage capacity, and storage capacity is a function of Porosity, whereas deliverability is a function of Permeability
Four rock types and groups have been identified in the Yamama formation, where the first group represents bad reservoir quality (FZI-1) (Mudstone Microfacies and Foraminiferal wackestone Microfacies), the second group reflects 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 shows a high trend of the Permeability and Porosity which represent a very good reservoir quality (FZI-4) (Peloidal–oolitic Grainstone Microfacies)
Capillary pressure analysis curves are presented for different rock types, curves samples at depths (3742 and 3705 m, Fig. 12), reflected a very good quality of reservoir and porous (Mega port type) (FZI-4) (Peloidal–oolitic Grainstone Microfacies), and with a low irreducible Water saturation (Swi)
Summary
Recognition of reservoir quality is an important objective in reservoir characterization process, the quality of a reservoir is defined by its hydrocarbon storage capacity, and storage capacity is a function of Porosity, whereas deliverability is a function of Permeability. These are as follows: oolitic–peloidal Grainstone, peloidal Packstone–Grainstone, Bioclastic wackestone–Packstone, Algal wackestone–Packstone, foraminifera wackestone, and Mudstone Microfacies Depending on these six cyclic types of Microfacies, the extension laterally for these Microfacies were identified by the similarity of logs curve characters (gamma ray, Spontaneous potential, neutron, density, and sonic) with of these Microfacies Mudstone Microfacies and Foraminiferal wackestone were characterized by a positive Spontaneous potential log deflection, high gamma ray log, low read values for resistivity, sonic and neutron logs, and high bulk density log, and these Microfacies reflected bad reservoir properties
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