A ReaxFF Potential for Modeling Organic Matter Degradation with Oxybromine Oxidants.

ABSTRACT

Oxidation of organic matter with oxybromine oxidants is ushering in a new era of enhanced hydrocarbon recovery. While these potent reagents are being tested in laboratory and field experiments, there is a pressing demand to delineate the molecular processes governing oxidation reactions at geological depth. Here, we parameterize a ReaxFF potential to model the oxidative decompositions of aliphatic and aromatic hydrocarbons in the presence of water-NaBr solutions that contain oxybromine (BrOn)- oxidizers. Our parameterization results in a reliable empirical bond-order potential that accurately calculates bond energies, exhibiting an RMSE of ∼1.18 eV, corresponding to 1.36 % average error. Reproducing bond dissociation and binding energies from Density Functional Theory (DFT), our parameterization proves transferable to aqueous environments. This H/C/O/Na/Br ReaxFF potential accurately reproduces the oxidation pathways of small hydrocarbons with oxybromine oxidizers. This force field captures proton and oxygen transfer, C-C bond tautomerization, and cleavage, leading to ring-opening and chain fragmentation. Molecular dynamic simulations demonstrate the oxidative degradation of aromatic and aliphatic kerogen-like moieties in bulk solutions. We envision that such reactive force fields will be useful to understand better the oxidation reactions of organic matter formed in geological reservoirs for enhanced shale gas recovery and improved carbon dioxide treatments.