APPLICATION OF HYBRID ALUMINA/SILICA NANOFLUIDS FOR EOR IN CARBONATE RESERVOIRS

Abstract

Nanoparticles are gaining their attraction in EOR(Enhanced Oil Recovery) with technology development and the slump in oil prices. Nanoparticles are particles whose size is between 1 and 100 nm. Adding nanoparticles into injection fluid during the EOR process may activate many mechanisms such as wettability alteration, IFT(interfacial tension) reduction, mobility control, log-jamming effect, change in the disjoining pressure, etc. The researchers believe that the wettability alteration is the most acceptable one among all these mechanisms. Nanoparticles have many unique characteristics, such as a high surface-volume ratio, significant possibility to modify their surface, suitability and stability in harsh reservoir conditions and being environmentally friendly. The oil recovery in carbonate reservoirs is less than 40%, mainly because of the wettability effect. Due to nanoparticles ' unique characteristics and active mechanisms in the EOR process, it is very promising to implement nanofluid flooding to produce more oil from carbonate reservoirs. Silica (SiO2) nanoparticles have been largely testified in improving oil recovery before. The effect of aluminum(Al2O3) nanoparticles on EOR is also being investigated recently. However, there is little research on the hybrid(Al2O3/SiO2) nanoparticles for EOR. The combination effect of silica nanoparticles and alumina nanoparticles on EOR will be studied in this research to compare the performance of the hybrid nanoparticles with silica nanoparticles. Firstly, zeta potential and zeta size measurements were conducted to test the stability of SiO2 nanofluid, Al2O3 nanofluid and the hybrid(Al2O3/SiO2) nanofluid. Then the contact angle was measured to analyze the nanofluid effect on rock/oil/brine systems to determine the optimum nanofluid concentration for further core flooding experiments and to testify to the wettability alteration mechanism in the EOR process. Finally, a core flooding experiment was conducted to study the performance of the optimal silica and hybrid nanofluid in enhancing oil recovery. The stability results showed that SiO2 nanofluid could stay stable for at least 3 days without adding a stabilizer while Al2O3 nanofluid cannot remain stable even for 10 minutes after homogenization. However, with the help of the stabilizer SDBS(sodium dodecylbenzenesulfonate), Al2O3 nanofluid can stay stable for 2 hours (the base fluid for dissolving nanoparticles is distilled water in all cases). From the results of contact angle measurements, considering the volume of nanoparticles used, we can get that the optimal SiO2 nanofluid's concentration is 0.1wt.%,the optimal Al2O3 nanofluid's concentration is 0.05wt.%, and the optimal hybrid nanofluid is 0.05wt.%Al2O3/0.1wt.%SiO2. The wettability alteration result indicated that none of these nanofluids altered oil-wet pellets to water-wet conditions. The optimal hybrid nanofluid works worse than the optimal SiO2 nanofluid on wettability alteration in carbonate reservoirs at 80℃ with 10 degrees difference. During the core flooding experiment, the injection rates were set at 0.5cc/m,2cc/m,5cc/m and 7 cc/m to simulate the real injection rate in the oilfield and counteract the capillary end effect. At 80℃, the CSW (Caspian Seawater) displaced 41.8% of the original oil in the core and the optimal silica nanofluid improved recovery to 45.9%, while the optimal hybrid nanofluid enhanced oil recovery to 73.1%.