Fines migration is known as one of the mechanisms of permeability alteration during water disposal or artificial aquifer recharge processes (McDowell-Boyer et al). However, there is limited direct evidence of fines migration during water flow. This paper presents conclusive evidence for the fines migration and resultant permeability damage using 3D micro-CT imaging assisted experiments.
A single phase flooding experiment was performed on a Berea sandstone core plug in multiple steps. Firstly, a micro-CT image of the dry core plug was taken before flooding. Then the core plug was saturated with 4% NaCl brine, followed by the injection of deionised water. The pressure drop across the core plug was monitored during the injection of 4% NaCl brine and deionised water, and produced water samples are analysed for particle concentration and type by combining particle counting methods and SEM-EDS analysis. After the flooding experiment the core plug was reimaged and the second micro-CT image registered to the first to quantify the fines migration. Laboratory measurements show an order of magnitude drop in permeability during deionised water injection, which was associated with large concentration of produced fines in the produced water samples. SEM-EDS analysis of the core plug and fines shows that clay particles were mobilized during deionised water injection, some of which blocked the pores and others were produced. Navier-Stokes equation was solved on the 3D images to compute absolute permeability. The computed permeability on the micro-CT image before the experiment matches with the experimentally measured initial permeability. The computed permeability on the image after the experiment shows a permeability drop by a factor or 2.5 due to fines straining near the core outlet.
The proposed experimental approach can be used in designing key parameters like injection rates, well location and well completion for water disposal or aquifer recharge processes.