Exploring the Impact of Mineralogy on Pore Structure and Fluid Dynamics in Tight Reservoir Rocks: Insights for Enhanced Oil Recovery and Gas Storage

Abstract

This study investigates the influence of mineralogy, particularly anhydrite relative to dolomite content, on the pore structure, petrophysical characteristics, and fluid flow potential of six rock samples (S-1 to S-6) from a Middle East outcrop reservoir. The main purpose of this research is to give novel perception into the interplay of the rock mineralogy, petrophysical properties, and fluid flow in tight formations, which are candidates for EOR/EGR processes as well as CO₂ subsurface storage. To achieve this, experimental techniques included XRD analysis, petrophysical measurements, and NMR experiments were performed. In addition, oil recovery potential was also assessed using imbibition, seawater, surfactant and CO₂ flooding experiments to mimic the primary, secondary and tertiary oil recovery processes, respectively. Results show that the rocks predominantly consist of anhydrite and dolomite, having varying pore types with broad distributions. Higher dolomite compared to anhydrite content correlates with better reservoir quality. Fractal analysis reveals complex pore structures, with macropores exhibiting medium complexity and mesopores being the most complex. Inverse correlations between the fractal dimensions with porosity and permeability were observed. In addition, rocks predominated by anhydrite (S-1 to S-3) showed water-wet behavior, whereas samples (S-4 to S-6), primarily consisting of dolomite, displayed oil-wet characteristics. Moreover, it was noted that CO₂ flooding proved to be more effective than surfactant flooding in rocks containing anhydrite. These findings offer a quantitative assessment of microscopic pore structures linked to macroscopic rock properties and oil recovery enhancing our understanding of reservoir dynamics and implications for oil and gas storage.