Fines stabilization by Ca ions and Its effect on LSW injection

Abstract

Fines mobilization during the injection of low-salinity water yields a decrease in well injectivity and productivity but may cause an increase in the reservoir sweep efficiency during oilfield waterflooding. We investigate the stability of clay fines under the combined alteration of Na and Ca concentrations. Consequent injections of Ca and Na solutions in natural and engineered cores intercalated by deionized water (DIW) injections have been performed. Fines migration has not been observed during DIW injection after preflush by CaCl₂ solution; further consequent injection of NaCl and DIW yields a significant fines mobilization and permeability decline. The tests demonstrate a strong hysteretic behavior of mutual adsorption–desorption of Ca and Na cations on the reservoir clays and rock. The same phenomena have been observed in the presence of residual oil, where fines migration has been accompanied by incremental oil production.