Summary
This paper elucidates the influence of pH and ion exchange on formation damage caused by fines migration. The experimental results affect waterflooding, design of drilling muds, and alkaline flooding. In-situ release of naturally existing fines (generally clays) results from changes in colloidal conditions of the permeating fluid. Such processes can cause extensive formation damage in sandstones, thereby reducing oil production. Our recent studies clearly indicate that the release process is started by a combination of high pH and low salinity. We present experimental results that suggest and confirm the interdependence between changes in salinity, cation exchange, and pH, leading to drastic permeability reductions. These results therefore provide new insight into the phenomenon of formation damage caused by water sensitivity or injection of incompatible brines. We also describe a unified approach to understanding these results and the findings of previous investigators. Predictions obtained from a physicochemical model based on ion exchange and colloidal chemistry agree well with experimental observations. The effect of different cations on formation damage also was investigated. This study can be extended to predict migration of bacteria and other particulates that cause formation damage.
