Evaluation of nano silica fluid recovery mechanisms for enhanced oil recovery

Abstract

This study aims to evaluate the oil recovery potential of hydrophilic silica nanofluids in sandstone reservoirs at varying salinities and concentrations. The impact of nanofluid as secondary and tertiary recovery mechanisms on recovery potential is also discussed, and recovery mechanisms are determined for all flooding parameter variations. The integrated study of parameters, recovery, and mechanism is to outline the impact of changes in fluid parameters on mechanisms and recovery for future clear understanding of the mechanisms at a specific set of nanofluid conditions. The study conducted at ambient conditions and flooding was carried out at 1000 psi overburden pressure. The nano flooding was carried out for 12 nano meter nanosilica with concentrations of 0.02 wt. %, 0.05 wt. %, 0.07 wt. % and 0.10 wt. % in salinity ranges from 20,000 to 40,000 ppm. Along with recovery potential, recovery mechanisms were also determined by contact angle evaluation, interfacial tension (IFT) measurements, porosity reduction evaluation, and pressure differential monitoring. In scenario 1, it was observed that the highest recovery at 20,000 ppm salinity was achieved with 0.05 wt. % of nanosilica which was approximately 11% of original oil in place (OOIP). The dominant mechanism was found to be wettability change to water wet condition (i.e., reduced to 46º) and interfacial reduction (i.e., reduced to 14.9 from 18.5 mN/m), whereas for higher concentrations mechanical mechanisms like mechanical entrapment along with pore jamming were also found to play the role. Whereas in scenario 2, where salinities were changed, the highest recoveries were recorded for 20,000 and 40,000 ppm (i.e., 11% and 11.2% of OOIP respectively). In the case of 20,000 ppm salinity, wettability change and IFT reduction played the dominant role but when salinity was increased to 30,000 ppm, due to instability of the solution the impact of wettability change and IFT reduction subsided hence recovery declined to 8.33% of OOIP. In the case of 40,000 ppm though nanofluids formed agglomerations and wettability change and IFT reduction were not dominant but mechanical entrapment enhanced the recoveries further. In the third scenario, it was outlined that at lower injection rate of 0.5 ml/min the recovery potential was lowered, as reduction in disjoining and mechanical mechanisms impact was observed. Application of nanofluids as tertiary recovery mechanism was found to be suitable as compared to secondary recovery in terms of recovery. Hence for optimum effect of nano flooding on oil recovery, the optimum design of nanofluid concentration, stability, injection rate, and mode of application have been identified. For the most effective nano flooding it should be ensured that major mechanisms like wettability change, interfacial reduction, and log jamming remain equally active. The study establishes that design of any nano flooding as tertiary recovery mechanism would be effective when a mechanistic study is carried out ensuring effectiveness of chemical and mechanical mechanisms which would result in incremental recovery.