Abstract: This invention relates to a method of treating wells completed in subterranean formations containing unconsolidated sand particles, so as to form a permeable barrier which permits relatively free flow of liquids including petroleum therethrough while restraining the flow of sand particles into the wellbore. The method comprises formulating a treating fluid containing a compound which undergoes acid catalyzed polymerization, preferably an oligomer or furfuryl alcohol, and an anhydride of a strong acid such as phosphorous tribromide mixed in a suitable diluent such as methyl isobutyl ketone. The composition is injected into the formation. The anhydride reacts with trace amounts of water forming an acid which catalyzes the polymer. Polymerization produces more water to react with additional anhydride.