Investigation of Interface Phenomena in Low Salinity/Smart Waterflooding by Applying Molecular Dynamics Simulation

Badizad, Mohammad Hassan | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53848 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ayatollahi, Shahab; Ghazanfari, Mohammad Hossein; Koleini, Mhammad Mehdi
  7. Abstract:
  8. Low salinity/smart waterflooding is simple to apply and a promising enhanced oil recovery method in which ion-tuned saltwater is injected into subsurface oil reservoirs. Many aspects of this operation, in particular those pertaining to nano-scale, are not yet fully understood. The present dissertation is an attempt to shed light on the microscopic properties and behavior of rock/brine/oil interfaces throughout low salinity/smart waterflooding. Several simulations were carried out for oil/brine and calcite/brine categories each containing various ions and hydrocarbons compounds. The surface contribution of non-functional oil compounds (aromatics and aliphatics) near brine medium was scrutinized in the presence or absence of asphaltene molecules. an electrical double layer (EDL) is established at the hydrocarbon/brine contact region. The intensity and charge sign of each layer depends on the identity of cations and anions in the solution. Aliphatic and aromatic compounds behave differently at the interface where the latter showed a greater tendency for approaching the aqueous phase in order to establish weak hydrogen bonds with water molecules. Asphaltene molecules could potentially change the ions behavior and consequently, interfacial properties by aggregating at the oil/brine contact area and forming a coherent molecular network. Asphaltenes and ions drive the interfacial tension of the water/oil system through the kinetic energy and virial terms of the pressure tensor, respectively. We realized the importance of wetting water mono-layers in regulating access of ions (particularly, divalent ones) to the calcite/brine interface. Sodium cations act as adsorption sites for anions, notably charged organic compounds, over a calcite substrate. An increasing amount of sodium content intensifies the surface adsorption of carboxylate compounds onto a calcite surface. Besides, sodium adsorption leads to a positively charged layer over the calcite substrates which believed to be a potential source for the positively charged surface potential of carbonates. Calcium and magnesium cations are capable to coordinate the carboxylates and thus facilitating the desorption of polar compounds from the calcite surface. Sulfates tend to adhere onto surface residing sodium cations, thus diminishing overall surface charge as well as inhibiting adsorption of carboxylate molecules. Our research showed the direct attachment of carboxylic compounds on a calcite surface via interacting with carbonate groups. Sodium cations compete with carboxylic molecules for occupying carbonate groups and as a result, diminish the surface adsorption of those compounds. Molecular simulations showed the role of sulfate anions paired to the surface sodiums for adsorbing carboxylic acids. Simulation of an imbibing NaCl solution within a calcite slit revealed the impact of temperature on the displacement velocity, flow regimes, and even the localization of ions and water molecules at the calcite/water interface
  9. Keywords:
  10. Interfaces ; Calcite ; Ion ; Brine ; Molecular Dynamic Simulation ; Low Salinity Water Flooding ; Low Salinity/Smart Waterflooding

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