Comprehensive pore structure characterization and permeability prediction of carbonate reservoirs using high-pressure mercury intrusion and X-ray CT

The heterogeneity of carbonate reservoirs, influenced by sedimentary environments and diagenetic processes, leads to the development of microfractures and vugs, posing significant challenges for reservoir evaluation. This study investigates the complex pore structures of Y-type carbonate reservoirs in the Middle East. We assess the performance of classical permeability prediction models and introduce a novel approach that incorporates a bimodal pore size distribution (PSD) derived from High-Pressure Mercury Injection (HPMI) measurements, accounting for gas slip flow effects. Our results, based on CT imaging, categorize carbonate rock core samples into matrix, fracture, and vuggy. Matrix-type carbonate rocks show a strong correlation between permeability and pore-throat radius, while fracture-type carbonate rock cores exhibit weaker correlations. Traditional model permeability predictions without core categorization yield suboptimal results, with the Winland model achieving the highest R² of only 0.365. However, after categorization, classical model permeability predictions significantly improve in accuracy. Notably, the introduced bimodal Gaussian PSD model outperforms traditional permeability prediction models, with an R² of 0.8138, providing a valuable tool for predicting the permeability of carbonate rocks characterized by complex pore structures.