Bromate Oxidation of Ammonium Salts: In Situ Acid Formation for Reservoir Stimulation

A redox chemistry approach has been employed to synthesize an assortment of acids in the subterranean environment for the purpose of enhancing productivity from hydrocarbon-bearing rock formations. Experimental studies revealed that bromate selectively oxidizes a series of ammonium salts NH₄X where X = F^-, Cl^-, Br^-, SO₄^2-, and CF₃CO₂^- to produce 5-17 wt % HX. Importantly, the in situ method allows strategic placement of the acid in the zone of interest where the fluid is heated, and the reaction is triggered. Ammonium counteranions are shown to influence the kinetics of the bromate-ammonium reaction, and the conditions are tailored to promote oxidation of ammonium at reservoir temperatures. The reaction is observed to be acid-catalyzed, where the formation of bromous acid (HBrO₂) is involved in the rate-limiting step. As a result, an induction period that scales with the p K_a of the acid being formed is followed by rapid formation of the reaction products.