Effect of Salt Composition on Clay Release in Berea Sandstones

Summary The effect of salt composition of fluid injected into clay-bearing Berea sandstones on the water-sensitivity phenomenon has been studied. Experiments were carried out with solutions of sodium and/or calcium ions, which are the ions commonly found in the formation. Freshwater flooding of sandstones previously exposed to sodium salt solutions results in the release of clay particles and a drastic reduction in permeability. The permeability reduction is lessened, however, when calcium ions are also present in the salt solution. Formation damage is virtually eliminated when the solution composition is adjusted to give calcium surface coverages greater than a critical value of 75 %. The effect of the fluid composition on the damage process is explained by the double-layer interactions between the surface of the clay particles and the pore walls.