Permeability decrease in sandstone reservoirs by fluid injection Hydrodynamic and chemical effects

Formation damage induced by a chemical effect resulting from non-compatibility between the injected fluid and the reservoir has been studied extensively and is well documented. However, formation damage induced by a hydrodynamic effect of flow, and the combined effects when the salinity and flow rate are varied simultaneously, have been studied less. This paper describes results from a set of core flood experiments carried out with a variety of filtered NaCl solutions subjected to increased flow rates to investigate the mechanisms of formation damage induced by the release and capture of in situ particles. Regarding the release mechanisms, the results confirm the existence of a critical flow rate above which the permeability decreases as a consequence of the hydrodynamic release of particles. This critical flow rate is found to be higher than those observed in the literature, and is observed to increase with the fluid salinity as predicted by the electric double-layer theory. The higher the salinity of the fluid, the higher is the critical flow rate and the less is the permeability decrease. Regarding the capture mechanisms, filtering or size exclusion appears to be the principal cause of permeability decrease at high injection flow rates. The hydrodynamic effect can reduce the permeability by more than 50%, but is less severe than the chemical effect. (C) 1998 Elsevier Science B.V. All rights reserved.