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Determination of Carbonate Rock Types at Multi-Scales

Abstract

Carbonate rocks are complex in their structures and pore geometries and often exhibit a real problem in their classification and behavior. Heterogeneity is a key issue in carbonates and the main challenge lies in defining rock types at different scales. Many petrophysical and fluid flow properties remain unexplained because of improper characterization of the reservoir rock. In this research, we propose a defined workflow for determining carbonate rock types at multi-scales: Thin-sections are used to define the structure of the rock together with its pore types. The structure is categorized into three distinct classes (grainy, muddy or mixed). The pore types can take different forms such as inter-particle, inter-crystalline, intra-particle, moldic or vuggy. This forms the basis of the rock types at the micro-scale. This (micro) rock typing scheme is then upscaled to the plug level by incorporating pore-throat size distribution and PoroPerm data. High resolution plug CT is also included at the plug level to confirm the (Macro) rock types and to explain heterogeneity effects. The presented rock typing scheme at multi-scales improved the understanding of reservoir heterogeneity and provided more insight into the effects of heterogeneity on petrophysical properties and fluid flow behavior. Imbibition dynamic data was used to validate the proposed rock typing scheme and gave consistent trends with the different rock types. Examples from several fields in the Middle East are demonstrated.