Abstract
This paper evaluates nanoparticle utilization to mitigate the injectivity loss due to pore-throat blockage near the wellbore. We develop a theory to explain how nanoparticles control particulates migration in the formation, and thus improve injectivity. Nanoparticles are pre-coated on the rock grains in 1-D porous medium prior to the injection of newly fine particles during low salinity water flooding. We hypothesize that the positive contribution of nanoparticles is related to the increased maximum retention capacity of the host rock by reduction of the surface potential between rock grains and suspended particulates. We develop semi-analytic MOC (method of characreristic) solutions for two different reference scenarios, in view of the difference between the initial attached fines concentration and the initial maximum retention concentration of fines without nanoparticle effects.
The effluent history plots are compared with the experimental data to verify the proposed theory. In addition, suspended, attached, and strained particle concentration profiles are calculated to evaluate the particle transport in a one-dimensional model. Our solution suggests two weak-form discontinuity fronts moving along the porous medium: suspended particle and attached particle fronts. The solution explains how effectively nanoparticles can prevent the decreased permeability through fixation of mobile particles. Permeability impairment and an associated increase in injection pressure (assuming a constant injection rate) are studied via mitigation index (MI) and injection index (J).
Through quantitative comparison of effluent concentration history and permeability decline, we validate the accuracy of the predictions. In practice, this paper provides analytical approach to evaluate performance of nanoparticles pre-treatment to sustain injection rate during low salinity water flooding.
