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Dynamic Simulation of Wettability Alteration Induced by Low-Salinity-Effect: Study of Phenomena within Thin Water Film

Pourakaberian, Arash | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53864 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Mahani, Hassan; Joekar Niasar, Vahid
  7. Abstract:
  8. Recent experimental studies have demonstrated that the lowering of brine could alter the wettability of the oil-brine-rock systems from an oil-wetting state toward a more water-wetting state. This so-called “Low-salinity effect” (LSE) is one of the main effects of the enhanced oil recovery technology based on low-salinity waterflooding. “Double layer expansion” (DLE) in the thin brine film is proposed as the principal mechanism of this phenomenon. Nonetheless, the role of the electrical behavior of the oil/brine and rock/brine interfaces on the kinetics and dynamics of this process is not well understood. Moreover, since most of the previous works have either dealt with a thin film at equilibrium condition with infinite length or neglected the film phenomena, we investigate both the dynamics of pressure evolution in the film and the time-scale of LSE using moving boundary simulation.In this regard, the film phenomena are studied by finite element-based computational fluid dynamics (CDF) using Firedrake. Simulations are carried out in two conditions of rigid boundary and moving boundary. The coupled physics of electro-diffusion and hydrodynamics in a charged thin water film is studied by solving the Poisson-Nernst-Planck and the Navier-Stokes equations. Moreover, the non-equilibrium disjoining pressure and effective ionic diffusion rate are determined under different electrical boundary conditions (BCs), film lengths, film thicknesses, and salinity gradients. In addition, the impact of surface roughness and surface complexation reactions on the oil and rock surfaces in the above-mentioned phenomena are investigated. Finally, the simulation of the wettability alteration and the displacement of the oil/brine interface (moving boundary) is conducted utilizing Arbitrary-Lagrangian-Eulerian (ALE) method and the velocity field.Numerical results show that electro-diffusion in the thin film is non-Fickian and up to 25-fold slower than Fickian diffusion according to the electrical behavior of interfaces. Moreover, Maxwell stress is the dominant source of EDL force build-up in the vicinity of pore (bulk) fluid. This force can then trigger wettability alteration. Boundary conditions that lead to the strengthening of the electric field (such as constant charge) are most favorable in terms of observing LSE.Furthermore, film thickness affects mainly the EDL force rather than the rate of ionic transport. On the contrary, film length has a significant effect on the time-scale of diffusion. Our results also show the effect of ionic strength gradient on diffusion time is relatively minor (up to 2-fold of Fickian diffusion).Investigation of the effect of two roughness parameters (amplitude and frequency) on EDL pressure and diffusion time showed that the impact of frequency is stronger on the pressure field. Moreover, there is a significant relationship between the Wenzel roughness parameter and the diffusion time; the larger this parameter, the smaller the effective diffusion coefficient. The different roughness geometries can promote wettability alteration of surface to more water-wet or more oil-wet in comparison with the smooth surface.It is found that the reduction of the concentration of divalent cations within the film strengthens the disjoining pressure, indicating the synergistic effect of the electrostatic bridging mechanism and the double layer expansion mechanism. Hence the ion type and their reactions at the interfaces are determining factors.The moving boundary simulations confirm the results of the transient electrostatic disjoining pressure evolution obtained in a rigid boundary system. Contrary to common belief, reduction of brine salinity does not always lead to wettability alteration toward a more water-wetting state or expansion of the double layer. Three factors affect the time-scale of oil/brine interface displacement and wettability alteration: 1) the amount of ions transported from the film to the pore-fluid, 2) ionic diffusion time, and 3) the magnitude of the electrostatic disjoining pressure in the thin film
  9. Keywords:
  10. Thin Films ; Low Salinity Water Flooding ; Wettability Alteration ; Effective Diffusivity ; Oil-Brine-Rock System ; Poisson-Nernst-Planck Equation ; Dynamic Disjoining Pressure ; Moving Boundary Simulation ; Rock Surface Roughness

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