Numerical Simulation for the Effect of Mud Cake Time-Dependent Properties on Wellbore Stability

Mud cake quality is the key to evaluating the plugging capacity of workover fluid and plays an important role in wellbore stability and reservoir protection. A hydraulic mechanical coupling model was established to investigate the mechanism of mud cake dynamic characteristics while considering the influence of annular flow field, filtrate invasion and particle deposition theory in combination with the dynamic plugging effect of mud cake. The influences of filtration time, particle size distribution, solid fraction, workover fluid viscosity and formation lithologic characteristics on mud cake dynamic properties, pore pressure, collapse pressure and fracture pressure were investigated. The results show that improving mud cake sealing performance is conducive to broadening the safe mud weight window. A small mean particle size is conducive to improving the coalescence stability of the particles, which can form a dense mud cake. A large standard deviation can improve the dispersion of particle size distribution and enhance the matching efficiency between particle size and pore throat. An increase in solid fraction mud cake is beneficial to building up a thin and dense plugging zone. Workover fluid viscosity has no significant influence on collapse pressure and fracture pressure. The formation permeability has the most significant impact on fracture pressure, which proves the good adaptability of wellbore strengthening technology in high permeability formation. The definition of time-dependent mud cake was developed.A hydro-mechanical wellbore stability risk prediction model was developed.The suggestions for the optimization of drilling fluid were provided.