Low salinity water (LSW) has been confirmed as an efficient improved oil recovery technique. Accompanying this technique, however, induced fines migration by chemical environments of low salinity has posed great challenges to well injectivity and productivity. It has been shown that nanoparticles can effectively enhance attractive forces between fine particles and grain surfaces through changing the surface zeta potentials of fine particles, and significantly mitigating formation damage caused by fine particles and clogging pore-throats. In practice, this paper not only provides an analytical model to confirm the feasibility of nanoparticle application to reduce fines migration, but also presents improvement analysis of LSW flooding performance with nanoparticles application.
The paper introduces an axisymmetric flow model and Method of Characteristic (MOC) to study the effects of nanofluid-slug preflush to improve the displacement performance of low salinity injections. The interplay among nanoparticles, fines, and rocks is described by a physical-chemical reaction model. The maximum retention concentration of fine particles is derived in two-phase flow. A new formulation for fraction flow function considering fines migration in water-phase is introduced. The semi-analytical solutions of low salinity water flooding without/with fines migration and nanofluid pre-treatment are derived and verified by numerical simulations.
The results indicate that: 1) as the low salinity water saturation increases, the detachment of fines attached on rock grains exaggerates. The majority of fines detachment and pressure loss occur in the region near the well; 2) the induced fines migration by low salinity water can delay the time of water breakthrough, and extend the duration of no-water production. However, fines migration can also lead to decline of well injectivity; 3) at the early life of water flooding (before water breakthrough), the recovery factor of conventional water flooding is larger than that of low salinity water flooding. At the late life (after breakthrough), the recovery factor of low salinity water flooding exceeds that of conventional water flooding; 4) nanofluid pre-treatment prior to the injection of low salinity water accelerate the breakthrough of injected water, and decrease the injection pressure drop to improve well injectivity. In this paper, the optimal nanofluid treatment range is 0.1, which takes advantages of low salinity water to enhance oil recovery, and prevent decline of well injectivity as well.