Asphaltene Near-well-bore Formation Damage Modeling

Abstract

When during oil production the thermodynamic conditions within the near-well-bore formation lie inside the asphaltene deposition envelope of the reservoir fluid, the flocculated asphaltenes cause formation damage. Mathematically, formation damage is a reduction in the hydrocarbon effective mobility, λ, λ=ko∕μo=kkro∕μo. Three possible mechanisms of asphaltene-induced formation damage have been discussed in the literature. Asphaltenes can reduce the hydrocarbon effective mobility by a) blocking pore throats thus reducing the rock permeability, k, b) adsorbing onto the rock and altering the formation wettability from water-wet to oil-wet thus diminishing the effective permeability to oil, ko, and c) increasing the reservoir fluid viscosity, μo, by nucleating water-in-oil emulsions. In the most frequently encountered case of asphaltene-induced formation damage where under-saturated oil is being produced without water, the most dominant damage mechanism is blockage of pore throats by asphaltene particles causing a reduction in rock permeability k. This paper presents a rather simple, yet realistic way of modeling asphaltene-induced near-well formation damage caused by blockage of pore throats by asphaltene particles. The model utilizes both macroscopic and microscopic concepts to represent the pore throat blockages. It also utilizes the Thermodynamic-Colloidal Model of Asphaltene, TCModelSM, an existing AsphWax asphaltene phase behavior model capable of simulating the asphaltene particle size distribution as a function of the thermodynamics of the system. The new asphaltene near-well formation damage model is applied in one case where it is used to track the degree of formation damage as a function of time and the effect it has on near-well-bore and well-bore hydraulics. Similarly the model can be used to study a priori the economics of developing a reservoir known to contain under-saturated asphaltenic oil.