Abstract: The disclosed invention is a method for improving the permeability of an underground hydrocarbon reservoir containing clay particles or other silaceous fines where damage has occurred or may occur. The method requires the injection into the hydrocarbon reservoir of an aqueous treating solution having a pH greater than about 12 and comprising about 2% to about 25% by weight of an alkali metal hydroxide. The invention also includes the injection of an aqueous buffer solution into the reservoir before, and optionally, after the injection of the treating solution. The before and after buffer solutions should have a pH greater than about 12 and comprise about 0.5% to about 5% by weight of alkali metal hydroxide and about 0.5% to about 5% by weight of alkali metal salt. The high pH aqueous buffer solutions maintain reaction products in solution, minimizing precipitation within the formation from the treating solution.