Decoding kerogen oxidation

J Hur and L Mai and S Singh and KL Hull and MJA Qomi and YN Abousleiman, CHEMICAL ENGINEERING JOURNAL, 520, 165562 (2025).

DOI: 10.1016/j.cej.2025.165562

Oxidative hydraulic fracturing fluid additives play a crucial role in increasing kerogen porosity and permeability within hydrocarbon-rich source rocks, leading to improved energy resource recovery in the unconventional reservoirs. Despite recent advances and successful field applications, the thermodynamics, kinetics, and mechanistic picture of source shale kerogen oxidation at the nano-and micro-scales remain poorly understood. Here, we combine in operando and post mortem experiments with first principle and reactive molecular simulations on mature and immature isolated kerogen samples reacting with sodium oxyhalide additives in brine. The early stage oxidation of kerogen, examined post mortem, reveals extensive microcracking that significantly increases the accessible surface area. This oxidation also leaves distinct signatures in both the experimental and computational C-O and C-H FTIR bands. From a thermodynamic perspective, we demonstrate that oxidation generates energetically unstable moieties and drives the reaction forward by producing excess entropy. We also find that immature kerogen degrades more rapidly than mature kerogen, with the hydrogen-to- carbon ratio identified as the key factor in determining the oxidation rate. Reactive MD simulations suggest that oxidation involves ring- opening and C-C bond breakage, with reaction rates matching those observed in in operando FTIR measurements. The experimental activation energy for the reaction is close to that of oxyhalide self-diffusion, suggesting that kerogen oxidation may be governed by diffusion in chemically induced microcracks. These findings are crucial for optimizing fluid additive design and understanding oxidative reactions during hydraulic fracturing in unconventional reservoirs. They can improve fracture face permeability, enhance fluid flow and hydrocarbon recovery, and support permanent CO2 sequestration. Our ongoing research also explores how CO2 sorption varies with kerogen maturity, which is key to sequestration capacity and efficiency.

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