Comparison Between the Impact of Mineralogy and Pore Geometry on Acoustic Velocity in Carbonates: Insights from Global Dataset and Rock-Physics Modeling

The characterization of carbonate subsurface reservoirs, which host significant natural resources such as water and hydrocarbon, is crucial for earth scientists and engineers. Key characterization methods include seismic and downhole sonic techniques. This study explores the relative influence of mineralogy versus pore geometry on acoustic velocity and velocity–porosity relationships in carbonate rocks, which is important for seismic and sonic interpretation in reservoir characterization. A global dataset from ten localities encompassing different carbonate lithologies—including limestones, fabric-preserving (FP) and non-fabric-preserving (NFP) dolostones, and siliceous carbonates—was analyzed using laboratory measurements and Differential Effective Medium (DEM) modeling. Results show that the mineralogy influence decreases with porosity, so it is limited only to tight rocks where dolostones show higher velocity than limestones while siliceous carbonates show the least velocity. As porosity increases, FP dolostones retain higher velocities, whereas NFP dolostones have comparable or lower velocities than limestones, contrary to expectations from mineral elastic properties. This behavior is mainly governed by pore geometry, as supported by petrographic analysis and DEM modeling. Siliceous carbonates display notably lower velocities, which is entirely attributed to smaller pore aspect ratios (about 50% less than in limestones) rather than mineralogical effects. Overall, this study highlights that pore geometry dominates over mineralogy in determining acoustic velocity within porous carbonates, providing a valuable framework for improving seismic and sonic-based porosity estimation across variable carbonate lithologies.