AN EXPERIMENTAL STUDY OF THE REACTIVE SURFACE AREA OF THE FONTAINEBLEAU SANDSTONE AS A FUNCTION OF POROSITY, PERMEABILITY, AND FLUID FLOW RATE - QUARTZ AND TUFF DISSOLUTION AT 240°C

Abstract

Reactive surface areas of Fontainebleau sandstone were measured as a function of porosity, permeability, and bulk fluid flow rate. Reactive surface areas were obtained by comparing the steady-state outlet Si concentration of flow-through experiments performed on sandstone cores with quartz dissolution rates normalized to BET surface areas obtained from ground cleaned samples of this sandstone. All experiments were performed at 80°C and far from equilibrium conditions using a 0.1 M NaCl + 0.01 M NaOH input solution having an in situ pH of 10.4. Measured reactive surface areas increase from ~20 to ~170 cm-1 with increasing porosity from 5.1 to 16.6%, respectively. These surface areas are similar to those predicted either by assuming the sandstone consists of a idealized spherical pore array or by using the Canals and Meunier (1995) intergrown sphere model. These geometric models, therefore, likely provide reasonable estimates of the reactive surface area of non-fractured porous media. Permeability measured in situ increases exponentially with increasing porosity, in good agreement with previous measurements. Both permeability and reactive surface area increased with increasing bulk flow rate. However, reactive surface area attained a steady-state at high flow rates whereas permeability increased continuously. This increase is probably due to a widening of connecting pore channels in response to increasing pore fluid pressure.