Simulation of reservoir permeability decline due to invasion of large particles

Particles can deposit in reservoir rocks and cause severe damage to their permeabilities. The mechanisms of permeability decline are attributed to adsorption, size exclusion and gravity settling of particles in porous media. Previous test results reveal that high particle concentration, low fluid velocity, large particle size lead to more damage. Traditional models are empirical correlations heavily dependent on core test data. In this paper, a network model incorporating the damaging mechanisms is used to study capture of large (non-Brownian) particles in porous media and resultant permeability damage. The model employs certain assumptions to imitate the characteristics of real porous media. The proposed procedure applies force analysis to obtain particle invasion depth, and determines damaging mechanisms by pore size to particle size ratio. The model assumes that for a particle much smaller than the pore where it is captured, surface deposition is the mechanism for permeability decline. For particle size comparable to pore size, pore throat plugging and bridging are the causes of permeability damage. The method is validated with test data and reasonably good results are obtained. The new model provides more insights into the deposition process and does not rely on core flooding data.