In-situ catalytic upgrading of heavy oil using oil-soluble transition metal-based catalysts

[Display omitted] •Oil-soluble metal-based (Fe, Co, Ni) catalysts for catalyzing aquathermolysis.•Metal-based complexes, oxide, sulfide were in-situ formed and play a catalytic role.•These catalysts show good catalytic effects at 300 °C for heavy oil upgrading.•Reduced viscosity, decreased resin and asphaltene, removed sulfur and nitrogen.•Nickel-based catalyst shows the highest catalytic activity. In this study, oil-soluble transition metal-based catalysts (Fe, Co, Ni) are proposed for catalyzing aquathermolysis reactions in steam injection process for heavy oil production to achieve in-situ upgrading of heavy oil. Their catalytic performance and possible mechanism were investigated by autoclave experiments together with a comprehensive analysis of the change in physical and chemical properties of the upgraded oil using SARA analysis, viscosity measurement, GC, GC–MS, FTIR, and 13C NMR, etc. Simultaneously, the in-situ transformation of these catalysts was also analyzed by TG-FTIR, XRD, and Mössbauer spectra, etc. to better under the possible catalytic mechanism. The results showed that the in-situ transformation of these oil soluble catalysts occurred during the thermal treatment process at 250 °C and 300 °C, and their metal-based complexes, oxide, sulfide, and sometime pure metal were in-situ generated and played a catalytic role for aquathermolysis reactions. These catalysts showed a good catalytic performance at 300 °C for heavy oil upgrading in reducing viscosity, increasing saturates content (especially low molecule weight alkanes), decreasing resins and asphaltenes content, removing sulfur and nitrogen, and decreasing polyaromatics content, etc. by inhibiting the condensation and recombination reactions and promoting thermal decomposition reactions of heavy components (resin, asphaltene, and polycyclic aromatics, long chain alkanes, etc.) and hydrogenation reaction. Nickle gives the best catalytic performance. The low cost and easy access together with its high catalytic activity make its wide application a great potential in catalyzing aquathermolysis reaction in steam injection process for in-situ upgrading and heavy oil recovery.