Investigating Asphaltene Deposition in Hydrocarbon/Water Systems

Abstract Asphaltenes are one of the most challenging flow assurance problems encountered during production in the oil and gas industry. Despite ongoing debate about the best laboratory methods to assess asphaltene control chemical efficacy, it is common practice to use dry oil to eliminate the impact of water on tests. This is because the effects of water, particularly of varying salinities, are not well understood or studied. In this work, we investigate asphaltene deposition generated using crude oil blends with different water cuts and salinities. Brine was added to the crude oil blends either as zero-TDS deionized water or varying total dissolved solids (TDS) sodium chloride (NaCl) brines that closely simulate the average salinity in the Gulf of Mexico (GoM). A deposition-based testing methodology (the micro-reactor) was used to collect the asphaltene deposits generated from the oils. Design of Experiment (DOE) was employed to guide the deposition-based experiments and analyze the results. The weight percent of asphaltene deposited from lab tests was used as a response to three factors: test duration, stirring speed, and the percentage of asphaltene destabilization reagents. The correlation of asphaltene deposits with these three factors indicated heptane percentage consistently influences asphaltene deposition. The presence of water introduces additional complexities, particularly with the interaction of time and water cut. Further tests of asphaltene precipitate obtained using heptane and deposits obtained from a micro-reactor with deionized (DI) water and different saline solutions show that salinity affects both the deposit mass and particle size. Molecular analysis with Infrared (IR) and SEM/EDX (scanning electron microscopy/energy dispersive x-ray) analysis confirmed the existence of sulfur in the asphaltene deposits and showed that with high salinity brine, there are fewer hydrogen bonds in the deposit. These findings enhance our understanding of asphaltene deposition in the presence of water/salinity and will facilitate the continued development of effective asphaltene control chemicals moving forward.