Modeling of fluid filtration and near-wellbore damage along a horizontal well

A method was developed to simulate drilling fluid invasion of a two-phase system (water-based mud in an oil-bearing formation) and to subsequently evaluate the damage along a horizontal well. The proposed model includes fluid invasion, filter cake buildup, and relative permeability components. Filter cake and mud filtration models were developed based on a mass balance equation of cake deposition and erosion and Darcy's equation. A convection-dispersion equation was solved numerically to characterize filtrate invasion. Exposure time, permeability anisotropy, and various formation properties are considered as factors causing non-uniform fluid invasion in horizontal wells. The results of the simulation provide the distribution of fluid filtrate and indicate the maximum invasion depths and the degree of fluid invasion around the wellbore. Coupling these results with relative permeability curves allows the assessment of the distribution of effective permeabilities. The effective permeability distribution and the depth of invasion are the keys to estimating the damage caused by fluid invasion. Damage radius and skin factor predicted by the model are in agreement with published results. Overall, this method provides improvement of fluid filtrate characterization and estimation of damage along a horizontal well.