Asphaltenes, resins, and aromatic hydrocarbons are all molecular substances found in crude oil. Asphaltenes, in particular, tend to deposit in critical regions of the oil production process, such as at the wellbore and in transportation pipelines, interrupting flow and damaging infrastructure. At present, chemical dispersants are utilized to either disperse asphaltenes into minute agglomerates or to increase the stability of solubilized asphaltene, with the aim of preventing deposition. Unfortunately, these chemical dispersants tend to fail in the field, and sometimes even exacerbate existing deposition problems in the wellbores. To better resolve this flow assurance problem, a thorough comprehension of the mechanisms by which chemical dispersants modify asphaltene deposition behavior under dynamic flow conditions is required.
Rice University researchers led by Professor Sibani Lisa Biswal conducted an in depth study of asphaltene deposition kinetics. Through the use of microfluidic devices, they probed the influence of dispersants under dynamic flow conditions in porous media micromodels; these dispersants altered both the size of asphaltene aggregates and the intermolecular interactions between them, leading to differences in diffusion and shear removal during the deposition process. Researchers from The Petroleum Institute in United Arab Emirates and University of Huddersfield in the UK also contributed to the study. The work is currently published in the research journal, Energy Fuels.
“We can have better resolution in evaluating and screening chemical dispersants or inhibitors by using this microchip. This microsystem only takes milliliters of crude oil.” lead author, Yu-Jiun Lin said.
The team commenced the study by obtaining asphaltenes extracted from Canadian bitumen. A model oil was prepared by dissolving the extracted asphaltenes in toluene. The researchers then injected the model oil, along with a precipitant and various dispersants, into a microfluidic device constructed to mimic the porosity and permeability of the near-wellbore region. As the mixture flows through the micromodel and deposits on various surfaces, the deposition kinetics were visualized in real time at the pore scale. In this work, four commercially used alkylphenol chemical dispersants were tested.
The authors observed that the initial asphaltene deposition worsened in the presence of each of the tested dispersants, but the mechanism by which plugging and permeability reduction occurred would vary. Injection of chemical dispersants effectively reduced the size of asphaltene aggregates, resulting in higher initial deposition rates, but simultaneously altered intermolecular interaction energies, which could generate “softer aggregates” that were readily eroded in shear flow after deposition, thereby lowering the overall deposition rate.
This study has successfully shown that smaller asphaltene aggregates are better able to resist shear flows from the fluid and deposit heavily, while careful application of chemical dispersants can alter the convection-diffusion interactions and intermolecular interactions between aggregates to hinder deposition. In conclusion, this research demonstrates that the use of porous media microfluidic devices offers a unique platform to develop and design effective chemical dispersants for flow assurance problems.
Yu-Jiun Lin, Peng He, Mohammad Tavakkoli, Nevin Thunduvila Mathew, Yap Yit Fatt, John C. Chai, Afshin Goharzadeh, Francisco M. Vargas, and Sibani Lisa Biswal. Characterizing Asphaltene Deposition in the Presence of Chemical Dispersants in Porous Media Micromodels. Energy Fuels 2017, volume 31, pages 11660-11668.
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