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Multi-Scale Pore Network Evaluation of Bimodal Carbonates: Implications for Hydrocarbon Production


Microporosity in carbonate reservoirs is globally pervasive and commonly used to explain high porosity - low permeability reservoirs, higher than expected water saturations, low resistivity pay zones and poor sweep efficiency. The potential for micropores to store and produce hydrocarbons has long been recognized, yet limitations on tools to evaluate microporosity prevented rigorous evaluation. Here we demonstrate a workflow to investigate quantitative relationships among pore networks at multiple scales and their contribution to overall network connectivity and flow. This study focuses on a well-known, Jurassic age, productive carbonate reservoir in the Middle East. Key depositional lithofacies include micritic to very fine-grained mudstones; bivalve-coated grain pack- to grainstones; Cladocoropsis pack- to grainstones; stromatoporoid coralgal pack- to grainstones; and skeletal-oolitic grainstones. In total, 91 thin-sections with 40 corresponding core-plugs were available for study. In addition, laboratory measurements were provided to validate the pore network models. Multi-scale pore networks were generated from a combination of pore networks acquired at different scales (Jiang et al., 2013). The multi-scale networks consist of nodes (pore bodies) and bonds (pore throats) which honor the geometry and topology of the original networks. Centimeter scale networks were generated by direct extraction from CT images. Millimeter scale networks were extracted from pore architecture models (PAMs) (Wu et al., 2006) generated from 2D light microscopy images. Similarly, micron scale networks were extracted from PAM models generated from 2D Confocal Microscopy images. Pore Analysis Tools (Jiang et al., 2007) were then used to calculate network statistics, including porosity, permeability, pore-size distributions, and topological connectivity. Results of the Study indicate that while the macropore network is the dominant control on permeability, it is the micropore network that provides a significant source of porosity. Furthermore, no single pore network can account for the significant porosity and permeability of these samples, but rather it is the combination of pore networks that make these carbonates productive