The change in pore size distribution from surface reactions in porous media

Abstract

AbstractWhen a porous solid is penetrated by a reactive fluid which changes the pore geometry, the macroscopic properties of that porous material may be greatly changed. A model is proposed in which the matrix is visualized as being a number of short cylindrical pores dispersed randomly throughout the solid. The change in the distribution of these cylindrical pores is then represented by a integrodifferential equation which is solved for two special cases.The evolution of the pore size distribution is determined by the particular way in which the solid‐liquid boundary takes place. The case considered here is that of a surface reaction which dissolves the solid thus continuously enlarging the pores. The rate of reaction is calculated theoretically using a laminar flow diffusion model and this growth rate expression is then taken as the basis for numerical calculations relating to the action of dilute hydrochloric acid on limestone.A comparison is made with experimental results and it is found that the model behaves in much the same way as the real system although the observed rate of pore growth was two to three times that predicted by the diffusion model. Several possible explanations for this discrepancy are being tested.An exact solution of the integrodifferential equation for highly retarded reaction rates has been found with the change in permeability being given in terms of the change in porosity. This result will permit a prediction of the stimulation that can be achieved in acidizing oil wells with retarded acids.