An experimental study of the reactive surface area of the Fontainebleau sandstone as a function of porosity, permeability, and fluid flow rate

Reactive surface areas of Fontainebleau sandstone were measured as a functi on of porosity, permeability, and bulk fluid flow rate. Reactive surface ar eas were obtained by comparing the steady-state outlet Si concentration of Bow-through experiments performed on sandstone cores with quartz dissolutio n rates normalized to BET surface areas obtained from ground cleaned sample s of this sandstone. All experiments were performed at 80 degrees C and far from equilibrium conditions using a 0.1 M NaCl + 0.01 M NaOH input solutio n having an in situ pH of 10.4. Measured reactive surface areas increase fr om similar to 20 to similar 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 ar ray or by using the Canals and Meunier (1995) intergrown sphere model. Thes e geometric models, therefore, likely provide reasonable estimates of the r eactive surface area of non-fractured porous media. Permeability measured i n situ increases exponentially with increasing porosity, in good agreement with previous measurements. Both permeability and reactive surface area inc reased with increasing bulk flow rate. However, reactive surface area attai ned a steady-state at high flow rates whereas permeability increased contin uously. This increase is probably due to a widening of connecting pore chan nels in response to increasing pore fluid pressure. Copyright (C) 1999 Else vier Science Ltd.