In Situ Heavy Crude Oil Upgrading via Catalytic Aquathermolysis with a Nickel-Based Catalyst Deposited Over a Rock Matrix

In situ upgrading of heavy crude oil (10.0 °API) was carried out via catalytic aquathermolysis using a nickel-based catalyst impregnated onto a limestone rock matrix at 300 °C and 300 psi for 72 h. The catalyst was effectively retained within the rock matrix and self-activated under reaction conditions, leading to the formation of catalytically active crystalline phases, such as nickel phosphate ([Ni₃(PO₄)₂]) and nickel sulfide (NiS), as confirmed by X-ray diffraction and X-ray fluorescence analyses. Unlike previous catalytic aquathermolysis reports that mainly describe soluble or transient catalytic species, this study demonstrates for the first time the in situ generation and stabilization of these active nickel phases within a carbonate matrix, providing long-term catalytic activity under reservoir-relevant conditions. Importantly, the limestone matrix facilitated catalyst retention and promoted the in situ generation of active nickel phases, thereby creating synergistic sites that markedly enhanced the efficiency of the catalytic aquathermolysis process. Compared to the pristine heavy crude oil, the upgraded oil exhibited improved properties by reducing the viscosity by 44%, increasing API gravity by 4 units, and enhancing the gasoline and diesel fractions by 54 and 44%, respectively, primarily at the expense of the residue content, which decreased from 66.4 to 45.5%. GC-simulated distillation analysis of the upgraded oil revealed a notable reduction in molecular weight, attributed to the catalytic upgrading process through hydrocracking reactions of heavy hydrocarbons. Gas chromatography of the evolved gases revealed the presence of hydrogen, methane, and hydrogen sulfide, serving as indirect evidence of the catalytic aquathermolysis process. These light compounds were generated through the thermal and catalytic cleavage of C-S and C-C bonds in heavy crude oil molecules, with reaction rates enhanced by the presence of the catalyst. The fed water molecules participated in hydrogen transfer, hydrocracking, and desulfurization reactions. It was also deduced that the interaction between the catalyst and the limestone matrix provided additional active sites, ultimately eliminating the need for external hydrogen sources. These findings demonstrate the potential of in situ catalytic aquathermolysis as a transformative technology for upgrading heavy crude oil, enhancing both its recovery and quality, and paving the way for field-scale applications.