Injecting nanofluids (NFs) has been proven to be a potential method to enhance oil recovery. Stranded oil is produced by wettability alteration where nanoparticles form a wedge film on pore wall surfaces, which is thought to shrink the pore space of the reservoir. Furthermore, ensuring the stability of the injected NF during the application is a major challenge. A low permeability reservoir and salinity of water make the response of NF injection to the formation damage more difficult. This article, therefore, studied the formation damage induced by the injection of alumina nanofluids (Al-NFs) in a relatively low permeability (7.1 mD) sandstone core. The salinity of the postflush water was also considered to mitigate the destructive impact. Al-NF was formulated by dispersing alumina nanoparticles (Al-NPs) in an aqueous solution of sodium dodecylbenzene sulfonate (SDBS) at its critical micelle concentration (CMC, 0.1 wt %). The formation damage, inherent to Al-NF injection, was evaluated by core-flooding tests. The assays consisted of the injection of 1 PV Al-NF (0.05 wt %) at the trail of which postflush at different salinities was flooded. The study found that the salinity of the postflush has an effect on the formation damage and oil recovery factor (RF). A chase water with a salinity concentration of 3 wt % sodium chloride (NaCl) produced an RF of 8.7% compared to a base case of water-flooding with a pressure drop of up to 13 MPa across the core (70 mm in length). These results pertained to the deposition of Al-NPs at the injection end. However, lowering the postflush salinity to 1 wt % NaCl mitigated the formation damage as evidenced by the decrease in pressure (35%) and an increase in RF to 17.2%.

Reduction of interfacial tension (IFT) between residual crude oil and formation fluids in oil reservoirs is the key to enhanced oil recovery (EOR) by surfactant flooding. However, adsorption of injected surfactant on minerals in the oil-bearing rock matrix reduces the effectiveness of this method. The present study investigated the effects of surfactant adsorption and desorption in the rock matrix on the oil recovery ratio achieved by surfactant-EOR. Sodium dodecylbenzene sulfonate (SDBS), a common surfactant in EOR, was used with Berea sandstone samples (rock particles and cores) as adsorbent. Adsorption of SDBS in the samples increased with concentration, and the static saturated amount was 0.9 mg-SDBS/g-rock for 1.0 wt% SDBS-water solution. If brine (1.0 wt% salinity) was injected after saturated adsorption of SDBS in the core, 83 % of adsorbed SDBS was desorbed into the brine (the reversibility effect). To clarify the reversibility effect in oil reservoirs, field scale numerical simulations were conducted for a typical 5 spot model (area: 180 m 180 m, thickness: 60 m) using core-flooding data reported previously. By introducing the reversibility model into the simulations on of surfactant flooding injection of slugs of 0.1 PV and 0.3 PV into the initial reservoir, oil recovery factor showed differences of 2.3 % and 2.9 % compared to without the model, respectively. Injection of the surfactant solution after water-flooding caused a difference of only 0.4 %

Low Salinity Water (LSW) incorporates in surfactant Enhanced Oil Recovery (EOR) as a pre-flush is a common practice aiming to reduce the formation salinity, which affects surfactant adsorption. However, in a field implementation, the adsorption of surfactant is unavoidable, so creating a scheme that detaches the trapped surfactant is equally essential. In this study, LSW was a candidate to enhance the desorption of surfactant. LSW solely formulated from NaCl (1 wt.%), Sodium Dodecylbenzene Sulfonate (SDBS) was chosen as the primary surfactant at its critical micelle concentration (CMC, 0.1 wt.%). It found that injecting LSW as post-flush achieved up to 71.7% of SDBS desorption that lower interfacial tension against oil (31.06° API) to 1.3 mN/m hence bring the total Recovery Factor (RF) to 56.1%. It was 4.9% higher than when LSW injecting as pre-flush and 5.2% greater than conventional surfactant flooding (without LSW). Chemical analysis unveiled salinity reduction induces Na+ ion adsorption substitution onto pore surface resulting in an increment in surfactant desorption. The study was further conducted in a numerical simulation upon history matched with core-flood data reported previously. By introducing LSW in post-flush after SDBS injection, up to 5.6% RF increased in comparison to other schemes. The proposed scheme resolved the problems of adsorbed surfactant after EOR, and further improve the economic viability of surfactant EOR.