Optimization Assisted Asphaltene Deposition Modeling in Porous Media During a Natural Depletion Scheme

Abstract

Changes in thermodynamic properties such as pressure, temperature, and composition may result in asphaltene precipitation and deposition in porous media. In addition, asphaltene deposition can cause wettability alteration, permeability reduction, and ultimately a decrease in the productivity of a reservoir. Natural depletion is one of the most common processes of asphaltene deposition in which pressure changes destabilize the dissolved asphaltene in the oil and settle them onto the rock surface. In this work, natural depletion experiments in consolidated core samples were performed under simulated reservoir conditions to obtain reliable data and analyze the asphaltene deposition mechanisms. A mass balance equation, momentum equation, asphaltene deposition, and permeability reduction models were applied to model the process of permeability changes as a result of asphaltene deposition. MATLAB programming language was used to calculate the numerical form of the above equations iteratively. A genetic algorithm technique was employed as the optimization tool for history matching and determination of model parameters. Modeling and optimization results showed an accurate match with measured data. Optimization confirmed that all major deposition processes (surface deposition, entrainment, and pore throat plugging) were effective in permeability changes. Calculation of precipitated asphaltene saturation by the introduced equation provides information on the volume fraction of porous media that was evaded by the precipitated asphaltene particles.