In sandstones, the EOR-effect by injecting low salinity water has been known since early 1990s, but no commonly accepted chemical understanding of the mechanism of the process has been obtained. We have worked on the topic since 2008, and we have proposed a chemical mechanism based on detailed chemical experiments and documentation.
As the low salinity water invades the porous medium, desorption of active ions, especially Ca2+, from the clay surface will increase the pH at the clay-water interface, which in turn causes desorption of organic material from the clay surface. Increased capillary forces will improve the microscopic sweep efficiency, and an oil bank is built up.
Using this knowledge of the chemical rock-fluid interactions we were able to predict the potential for low salinity effects in sandstone reservoirs.
As an example we explained why the Snorre single well pilot in the North Sea did not respond to the low salinity water injection. The formation contained a large amount of Plagioclase, that lead to an initially high pH in the formation which reduced the adsorption of organic material onto the clay. Initially low adsorption of organic material onto the reservoir rock decreases the EOR potential of low salinity water injection.
- Chemical verification of the EOR mechanism by using low saline/smart water in sandstone. A. RezaeiDoust, T. Puntervold, and T. Austad. (2011). Energy & Fuels, 25.
- Smart Water as Wettability Modifier in Carbonate and Sandstone: A Discussion of Similarities/Differences in the Chemical Mechanisms. A. RezaeiDoust, T. Puntervold, S. Strand, and T. Austad. (2009). Energy & Fuels, 23.
- Why such a small low salinity EOR - potential from the Snorre formation? A.J. Reinholdtsen, A. RezaeiDoust, S. Strand, and T. Austad. (2011). 16th European Symposium on Improved Oil Recovery. Cambridge, UK.
- A discussion of the low salinity EOR potential for a North Sea sandstone field. A. RezaeiDoust, T. Puntervold, and T. Austad. (2010). Paper SPE134459 presented at the SPE Annual Technical Conference and Exhibition. Florence, Italy.
- Chemical mechanism of low salinity water flooding in sandstone reservoirs. T. Austad, A. RezaeiDoust, and T. Puntervold. (2010). Paper SPE 129767 prepared for presentation at the 2010 SPE Improved Oil Recovery Symposium. Tulsa, Oklahoma, USA.