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Simulation and Experimental Study of Permeability Reduction in Porous Media Due to Mud Filtrate Invasion Under Dynamic Conditions

Movahedi, Hamed | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55416 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Jamshidi, Saeed
  7. Abstract:
  8. The reduction of the effective permeability of the reservoir rock in the production area due to various factors is called formation damage. Formation damage is always one of the topics discussed in petroleum engineering. Among the primary and important cases that lead to damage to the formation are the filtration of drilling mud into the production area and the deposition of colloidal particles inside the porous rock during the drilling operation. The length of the productive zone in contact with the drilling fluid usually reaches several hundred feet in Iranian formations. In this study, the aim is to more accurately estimate the amount of permeability reduction caused by the penetration of drilling mud filtrates. The drilling fluid flow inside the well is usually a two-phase flow including fluid-particle. At first, the hydrodynamics of the multiphase flow inside the well was simulated using Computational Fluid Dynamics (CFD) and Eulerian-Eulerian model. Laminar and turbulent flows in the annular space of the drilling string and the well wall were considered, and the turbulence model was developed along with appropriate coefficients for particle-fluid multiphase flow (slurry flow). Multiphase flow was considered for different particle diameters and concentrations. The simulation of flow in annular space was validated using available experimental data for laminar and turbulent flow modes. Realizable and standard k-ε turbulence models were used to predict turbulence in this study. After that, the amount of wall shear stress was simulated for different states and this value was used to estimate the erosion rate of the mud cake surface formed on the well wall. Filtration modeling includes the growth rate model of the mud cake formed on the wall and the penetration of the mud strainer into the porous medium of the well wall. The rate of mud cake formation on the well wall is completely dependent on the shear stress applied by the fluid on the wall. Also, the penetration depth and penetration concentration of particles into the porous medium is also dependent on the mud cake thickness and the pressure difference between the well and the formation. The erodibility of drilling mud cake and its thickness under different flow conditions, solution ionic strength and filtration flux rate were modeled by dynamic filtration device. Finally, the amount of damage to the formation caused by the permeation of the strainer into the porous medium was determined by injection tests and simulations using filtration theory and dispersion-transmission model. Considering the deposition and erosion of colloid particles inside the cavities, the amount of colloid deposition inside the porous medium was estimated under different conditions of flow speed, ionic strength and particle concentration. The results showed that the hydrodynamics of the flow in the annular space in the turbulent flow state, by the turbulence model can be realized in each phase with new corrected coefficients (C2=4.2, C3=1.3, CT=0.0131, σk=1, σ=1.2σε) a more accurate prediction. from the pressure drop along the annular tube. The results also showed that a sigmoid function with reasonable accuracy (R2>0.962) can describe the sediment thickness patterns with wall shear stress. Furthermore, as the shear stress increased from 0 to 2 Pa, the average cake thickness for the saline bentonite base fluid decreased by 80%. The results also showed that the concentration of clay particles in the filtrate reached 350 ppm in the thickness of the cake below one millimeter, and it reached over 1000 ppm for the surface without cake. The results were also well matched to the diffusion-dispersion model along with the terms of sedimentation and sedimentation rate. Based on this, the amount of solid material deposition in the porous medium was correctly described. Also, the results showed that the pressure drop inside the porous medium can be well modeled by sedimentation equations
  9. Keywords:
  10. Formation Damage ; Slurries ; Drilling Mud Flow Rate ; Sedimentation ; Sedimentation Coefficient ; Flow Hydrodynamics ; Dynamic Filtration

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