Technology Update: Electrokinetic Deposition of Asphaltenes Studied Under Dynamic Conditions

Abstract

Technology Update Asphaltenes represent the heaviest fraction of crude oil, which are known to precipitate when the crude is added to aliphatic solvents such as n-pentane or n-heptane and yet remain soluble in light aromatic solvents such as benzene or toluene (Gawrys et al. 2006; Borton et al. 2010). They are characterized by highly complex structures that contain multiple aromatic rings and have a large hetero-atom content (e.g., nitrogen, oxygen, and sulfur) and metal content (e.g., vanadium and nickel) (Yarranton 2000; Hashmi and Firoozabadi 2012). Asphaltenes tend to self-associate on a molecular level, depending on the composition, temperature, and pressure of the system. Precipitation of the particles out of solution results in flocculation, where they begin to deposit on hydrophobic surfaces such as metal pipes and surface equipment used for the production and transportation of crude oils (Khvostichenko and Andersen 2009). These tendencies result in reduced flow or complete blockage of producing wells and surface equipment, including pumps, pipelines, and separators. Currently, the only methods of treatment are through the use of chemical dispersants and inhibitors, which increase the stability of asphaltenes to prevent deposition. Once asphaltene deposition has occurred, running a “pig” through the pipeline is often the method used to scrape the solids that accumulated on the walls of the pipe. It is known that asphaltene molecules can be polarized, gaining an electric charge by introducing an electrostatic field (Hashmi and Firoozabadi 2012; Khvostichenko and Andersen 2009; Khvostichenko and Andersen 2010; Hosseini et al. 2016). The polarity of the asphaltene particles is directly related to its hetero-atom content, with a higher hetero-atom content giving increased levels of polarity and a higher rate of aggregation (Hosseini et al. 2016). Experimental Device Our ultimate goal is to build a device (Fig. 1a) that would remove asphaltenes from crude oil near the point of production, using electrokinetics. Thus, a scaled-down device (Fig. 1b) was fabricated and tested using a model oil to prove the concept and study some of the parameters that would influence the design of a larger-scale device.