Sonic Velocity in Dolostones. Examples from the Arabian Platform

This study investigates the main controlling factors on sonic velocity in dolostones by examining 100 outcrop samples from five different formations outcropping in Saudi Arabia. Thin-sections were prepared for all samples to analyze petrographic characteristics including lithology, pore types, and crystal/grain size. SEM analysis was conducted on selected samples to reveal the microstructure such as microporosity and pore occluding materials. XRD analysis was used to determine the mineralogical composition of each sample. Porosity, permeability, and sonic velocity were measured for the entire dataset. In general, porosity is the main factor controlling sonic velocity in the studied samples with an inverse porosityvelocity relation with a coefficient of determination R 2 of 0.82. However, other parameters contribute to deviations from the general porosity-velocity trendline. These parameters include texture, mineralogy, pore type, and crystal size. At high porosity (> 20 %), fabric-preserving dolostones have, relatively, higher velocities than non-fabric preserving dolostones. Although the majority of the studied samples are dominated by dolomite, calcite-, and quartz-rich samples show lower velocity values. Moldic and vuggy pore-dominated samples have, relatively, higher velocities than samples dominated by intercrystalline pores and microporosity. For non-fabric preserving dolostones, samples with larger crystals show, slightly, higher velocities than samples with smaller crystals. The result of this study might significantly help in interpretation and understanding the sonic logs and seismic data from dolostone strata.