Marion G. Reed

Water sensitivity of sandstones containing swelling and non-swelling clays

Abstract The study presented here focuses on the phenomenon of water sensitivity of sandstones containing swelling and nons-welling clays. This paper describes results of an ongoing investigation on the mechanisms of permeability reduction in sandstones containing swelling and non-swelling clays. These studies show that the critical salt concentrations of sodium chloride and potassium chloride needed to prevent loss of permeability in sandstones containing swelling clay (Stevens sandstone) are considerably higher than the corresponding values for Berea sandstone. A critical salt concentration of calcium chloride is shown to exist for these sandstones. As opposed to Berea sandstone, pH control may not be sufficient to eliminate loss of permeability in swelling clay sandstones. The results show that crystalline swelling of smectites/mixed layer clays induces significant permeability reduction in the swelling clay sandstones considered in this paper.

Effect of salt composition on clay release in Berea sandstones

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.

Volumetric treatment efficiencies of some commercial clay stabilizers

This paper reports on volumetric treatment efficiencies of three commercially available clay-stabilizer treatments that were evaluated in the laboratory. Rock volume treated per unit chemical volume varied up to three-fold between stabilizers and depended on sandstone mineral properties. The results are valuable for designing clay-stabilizer treatments and maximizing stabilizer cost-effectiveness.