Higher-order compositional simulation of asphaltene damage and removal in the wellbore by the CPA-EOS

Abstract

Simulation of asphaltene damage around the wellbore is important in relation to well productivity. Existing numerical approaches rely on the surface adsorption of asphaltene on the rock using a Langmuir isotherm. We demonstrate that asphaltene accumulation around the wellbore can be modeled as an asphaltene-rich liquid phase without the need to include surface adsorption explicitly. The relative permeability concept accounts for surface adsorption as well as pore-plugging. Our approach is fully verified with recent experimental data. This work is based on the fact that below the asphaltene onset pressure, an asphaltene-rich phase is formed with much higher viscosity than the oil phase from which it evolves. We perform phase behavior calculations using the cubic-plus association equation of sate (CPA-EOS). Flow and species transfer between the phases are simulated based on the higher-order method with high accuracy and low numerical dispersion. The algorithm includes full 3D unstructured gridding to model well damage and frequency and extent of asphaltenes removal in field scale applications. An example with a fracture crossing the producing well is included to examine deposition in the fracture and the matrix.