Imaging Fines Migration Induced by Salinity Changes

Abstract

This project aims at confirming positive LS-EOR (low salinity enhanced oil recovery) effects with fluorescent microscopy, an unprecedented approach. The fluorescent microscopy employed in this project used a confocal microscope and total internal reflection fluorescence (TIRF); these allowed the acquisition of 3D images using a non-destructive procedure.
For the first part of the project, confocal microscopy was utilised to test the average fluorescent intensity and the scope of 8 different types of clay minerals. Comparing fluorescent features of high and low defect kaolinite, also 3 types of LDH Mg/Al and another 3 types of LDH Mg/Fe were included in this study. Moreover, SEM was applied to analyse the structure of clay minerals, and XRD was applied to determine the impurities within the clay samples. The sample which determined that clay minerals fluoresce on a consistent basis were aged with formation brine and either polar crude oil or non-polar crude oil, these aged clay samples were utilised for the second part of the project, which was aimed at observing any movement of clay by lowering the salinity. AFM and TIRF were employed for the latter section. Based upon the attained results, the following is notable: firstly, that the presence of iron in clay minerals diminishes the fluorescent intensity, also high defect clay minerals do not exhibit a steady fluorescence intensity. Secondly, testing with SEM and XRD revealed that KGa-1b might be the only clay sample that has the potential of autofluorescence, since the percentage of fluoresced pixels was more than the percentage of impure minerals that would fluoresce at the applied wavelength. Finally, AFM and TIRF confirmed LS-EOR effects even without the presence of polar components in the system, especially after fourfold dilution from the initial ionic concentration caused the clay minerals to move more vigorously; significant clay swelling at the salinity level was also witnessed. In summary, the novel approach of TIRF is deemed well suited in terms of its technique for the study of fines migration. Four-fold dilution of high salinity brine initiated clay swelling and dispersion, still salinity higher than generally accepted as the LS-EOR optimal salinity level was given. It can be interpreted that fines dispersion and migration could be initiated at a higher salinity, while the emulsion phase form and the oil molecule surface release may require a much lower ionic concentration in order to enable residual oil recovery. LS-EOR effects observed under the TIRF and AFM, arising due to the weaker electrostatic forces developed by lowering the system's salinity hence, the generally accepted importance of polar oil components for LS-EOR effects does not hold in these experiments. Positive LS- EOR effects revealed by TIRF, AFM, and FFM consequently concluded that electrical double layer expansion would be the most dominant attribution for LS-EOR.