Simple Models for Permeability Impairment in Reservoir Rocks Caused by Asphaltene Deposition

Abstract

This study formulates two models for estimating permeability impairment caused by asphaltene deposition. The first model is based on a mass balance and is capable of predicting permeability reduction in either vertical or horizontal wells. The model accounts for both the effects of position in the reservoir and time. The second model is formulated on the basis of the capillary tube theory. It accounts for the rock pore-size distribution but does not account for the time dependence. Both models are formulated in integral form to allow for analytic solutions when symbolic formulation exists for the parameters affecting the deposition process. Both modeling approaches account implicitly for the effects of pressure, temperature, and fluid composition, by including the asphaltene radius distribution. Even though the mass-balance model is one-dimensional and is valid for only single-phase flow in porous media, it can be used to estimate the permeability reduction for both homogeneous and heterogeneous formations. The capillary tube model requires less input variables than the mass-balance model and does not depend on any tuning parameters. However, it is neither sensitive to the position in the reservoir nor to the well type penetrating the reservoir. These reasons make the capillary tube model useful only for a qualitative description and thus capable of only giving a first-order estimate of the permeability reduction caused by asphaltene deposition.