Wong, Michael S2021-04-132022-05-012021-052021-04-12May 2021Xu, Yan. "Understanding Heavy Oil Viscosity Reduction Chemistry Using Metal-Ligand Compounds." (2021) Diss., Rice University. <a href="https://hdl.handle.net/1911/110276">https://hdl.handle.net/1911/110276</a>.https://hdl.handle.net/1911/110276Heavy oil is an abundant energy resource, but its recovery remains challenging primarily due to its high viscosity. Thermally enhanced oil recovery in the presence of metal-ligand compounds (MLCs) has been studied as a promising method for in situ viscosity reduction and oil quality upgrading. However, the interactions between MLCs and crude oil components at the molecular level are poorly understood, and the mechanistic details for viscosity reduction are unclear. This work studies the post-reaction viscosity and compositional changes of a real heavy oil upon thermal treatment with model MLCs. The iron para-toluenesulfonate (or iron tosylate, FT), was studied extensively as a MLC. Peace River oil viscosity and compositional changes after the thermal+FT treatment were compared with the thermal-only treatment at a wide treatment temperature range (80 – 295 °C). The results show that the thermal+FT treatment lowered oil viscosity by up to -20% more than thermal-only treatment at high temperatures. FT reduced oil viscosity by decomposing to release one ligand to form 4-methylbenzenethiol that interfered with asphaltene intermolecular interactions, and by catalytically reacting with the asphaltene to decrease its overall content in oil. FT also increased the oil viscosity at low temperatures (80-220 °C) due to iron MLC associating with the asphaltene clusters. Palladium(II) acetylacetonate ("PdA") was used as a model MLC to study the heavy oil viscosity change effects at low temperatures. The treated Peace River oil viscosity and compositional changes were studied in a wide temperature range (80- 300 °C). The result shows that PdA reduced heavy oil viscosity as low as 80 °C (reduced by 35% at 130 °C). Like FT, PdA also released ligand to form acetylacetone to disaggregated the asphaltene clusters, which lowers oil viscosity. Interestingly, PdA formed Pd metal at high temperatures, which hydrogenated the resin sulfonate groups, lowered resin contents, and thus lowered oil viscosity. Also, in the 80-130 °C range, the asphaltene fraction increased due to PdA intercalating into the asphaltene clusters, countering the acetylacetone effects. While PdA reduces oil viscosity at mild temperatures, the non-noble metals MLCs are more attractive for large-scale application. The combination of molybdenum dioxide bis(acetylacetonate) ("MoA") and alkali MLC sodium acetylacetonate ("NaA") reduced oil viscosity by -25% at 130 °C. This viscosity drop was greater compared to the effect of only MoA (-15 %) and only NaA (-5%), indicating that the combination of MoA and NaA has a surprising synergistic effect. The result shows that the viscosity reduction is surmised to arise from three effects: NaA-promotion of MoA ligand release, a lowering of resins contents, and the disruption of acid-base interactions between asphaltene clusters. All the MLCs reactions are performed in a non-stirred batch reactor and heated to as high as 300 °C. A simple dimensional analysis of the heat and mass transfer process was used to verify that the reaction system is well mixed. The results suggested that conduction was the main heat transfer method inside our non-stirring batch reactor, and convection was not important. Mass transfer of "MLCs" might occur mainly through molecular diffusion at time scales sufficient for the well-mixed condition. Overall, this work provides a selection rationale for appropriate metals and ligands towards a long-term vision of site-specific downhole heavy oil recovery.application/pdfengCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.Heavy oilViscosity reductionThesis2021-04-13