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

Abstract

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 NH 4 X where X = F − , Cl − , Br − , SO 4 2− , and CF 3 CO 2 − 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 (HBrO 2 ) is involved in the rate-limiting step. As a result, an induction period that scales with the pK a of the acid being formed is followed by rapid formation of the reaction products.

Oxidative Kerogen Degradation: A Potential Approach to Hydraulic Fracturing in Unconventionals

“…The performance of the mixed system relative to sodium bromate alone was better because of the formation of acid. Our recent study into bromate chemistry demonstrates that it readily oxidizes ammonium cations . In turn, approximately one H + is liberated per ammonium as demonstrated through extensive stoichiometric titration studies.…”

“…Our recent study into bromate chemistry demonstrates that it readily oxidizes ammonium cations. 41 In turn, approximately one H + is liberated per ammonium as demonstrated through extensive stoichiometric titration studies. Ultimately, persulfate is also reduced to sulfate, and sulfuric acid is thereby generated.…”

“…Similarly, ammonium is also oxidized by bromate, though chlorate and iodate are ineffective under similar conditions. 41 The reactivity of bromate could be enhanced by acidic conditions. Additional degradation tests (Table 3) were performed in the presence of HCl and H 2 SO 4 and the percent degradation that occurred in a 3 h time frame doubled (47 wt %, Ker 6) and tripled (81 wt % Ker5), respectively, relative to 3 h with sodium bromate alone (26 wt %, Ker 3).…”

“…Chlorate, by contrast, was slightly effective, though repeated experiments demonstrated that it was much less so than bromate. Similarly, ammonium is also oxidized by bromate, though chlorate and iodate are ineffective under similar conditions …”

Novel Approach for Sandstone Acidizing Using in Situ-Generated Hydrofluoric Acid with the Aid of Thermochemicals

“…This oxidation reaction is an autocatalytic reaction that requires heat to initiate. Hull et al used sodium bromates (NaBrO 3 ) as a powerful oxidizer to react with ammonium fluoride and produce HF according to eq . This reaction requires heating the reaction medium up to 150 °C for 3 h in order to produce a transparent solution. …”