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Multi-Scale Lattice Boltzmann Simulation of Carbonate Rock Dissolution in Acidizing Process

Mahmoudi, Sadegh | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55541 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ayatollahi, Shahabodin; Jamshidi, Saeed; Raoof, Amir
  7. Abstract:
  8. During the Acidizing process in oil and gas reservoirs, the injected acid reacts with the rock grains, changes the rock pore structure and affects the flow conditions. Due to the presence of a large concentration gradient at the vicinity of the rock grains and the continuous changes in rock-fluid interfaces of the porous medium, the continuum assumption has been remained debatable for the effective local mass transport and effective molecular diffusion coefficients and the porosity-permeability relation in the continuum scale modeling of this process. Therefore, the need for pore scale modelling is evident. The novelty of this study relies in adapting the grid refinement method on the reactive Lattice Boltzmann modeling of dissolving conditions that computes the effective mass transport and diffusion coefficients on the pore scale and changing porous media on representative dimensions. Quadtree grid refinement method is a multiscale mesh refiner that adjusts the grid resolution based on recursive subdivisions and is able to reduce the computational load while keeping the desired precision. The developed method was verified against several benchmark problems with different levels of complexity. The accuracy and the computational benefits of the developed scheme were discussed in detail by comparing the Quadtree model against fine-grid LBM and coarse-grid LBM simulations, and analytical solutions, considering their relative errors. The simulation results with one- and two-level refinements show that quadtree is about two to four times faster relative to the uniform fine grid model. The relative error for quadtree model is somewhat between fine-grid LBM and coarse-grid LBM and near the fine-grid model. The qualitative regeneration of the experimental results for wormhole dissolution pattern also demonstrates the model’s robustness. This study uses the constructed model to simulate reactive flows using different pore structures on the representative dimensions and discusses the different flow conditions using dimensionless numbers of Damkohler, Peclet and Sherwood to characterize the variation in porosity-permeability relation and the mass transport coefficients due to rock dissolution. The simulation results at different flow conditions that produce face dissolution, wormhole and ramified dissolution patterns, demonstrate similar trends among the changes in permeability by dissolution, the variation in porosity-permeability relation based on the deviation from the Kozeny-Carman relation and the variation in Sherwood number. So that a 6-fold increase in permeability in the ramified dissolution pattern occurs in a similar process with a 3-fold increase in RQI and a 2-fold increase in Sherwood's number. Also, permeability with respect to porosity, RQI compared to normalized porosity, and Sherwood's number change with time, show a power of 3. This power is 2 for the wormhole dissolution model and 1 for the surface dissolution model. Despite the increase of the dispersion coefficient with the increase of the Peclet number from 10 to 100 in the surface, wormhole and ramified dissolution patterns, the wormhole dissolution pattern produces a special type of behavior for the effective dispersion coefficient. So that the concentration change rate changes with the power of 3 with respect to the Laplacian of the concentration. This means a decreasing behavior of the dispersion coefficient during the progress of the wormhole. The simulation results for a large domain size two-scale medium that contains a fracture with porous walls, also approve this behavior of the effective dispersion coefficient
  9. Keywords:
  10. Lattice Boltzmann Method ; Reactive Flow ; Mass Transfer Coefficient ; Porosity-Permeability Variation ; Grid Refinement

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