Nanofluid pre-treatment, an effective strategy to improve the performance of low-salinity waterflooding

Low-salinity water (LSW) has been confirmed as a promising improved oil recovery technique. Implementing this technique, in some cases, induces fines migration and has posed great challenges on well injectivity. The aim of this work is to establish a mathematical foundation and explain the improved performance (both EOR and well injectivity) through nanofluid pre-treatment in single-layered and multi-layered heterogeneous reservoirs. We modify the fractional flow function while considering for fines straining effects in one-dimensional radial system, where fines migration varies with distance from the injection well owing to different drag forces. The interplay among nanoparticles, fines, and rocks is described through the maximum retention concentration of fine particles that depend upon both fluid quality and velocity. Our modification of the classical Buckley-Leverett theory leads to the characteristic curves along which water saturation varies. As low-salinity waterflooding continues, the induced fines migration delays the breakthrough of injected water, and bring uniform control of injected fluid entering each layer. On the other hand, fines migration may lead to the issue of well injectivity decline. Nanofluid pre-treatment can significantly mitigate fines migration near wellbore while it may occur far from the injection well. We discuss cases with different nanofluid treatment schemes prior to low-salinity waterflooding by comparing water-saturation profile, water-cut history plot, injection pressure, and oil recovery. A good agreement is obtained between semi-analytical solution and finite-difference simulation. It was observed that although nanofluid treatment slightly accelerate breakthrough of the injected water, it can help maintain long-term well injectivity and sweep efficiency. In practice, our work provides valuable insight to design of nanofluid utilization and improve efficiency of low-salinity waterflooding.