저류층 조건에서 분산안정성을 갖는 실리카 나노유체의 점성도 특성 연구 = Viscosity Characteristics of Silica Nanofluid with Dispersion Stability under Reservoir Conditions

국문 초록 (Abstract)

전 세계적으로 나노유체(nanofluid)에 대한 연구가 활발히 수행되고 있으나, 나노유체의 점성도와 같은 유변학적연구가 부족한 실정이다. 본 연구에서는 나노입자의 표면을 개질한 해수 기반의 실리카 나노유체를 합성한 후 분산안정성 평가를 수행하고, 점성도 측정을 위한 적정 전단속도(shear rate) 구간을 도출하였다. 고온·고염(100℃, 200,000 ppm)의 저류층 조건에서 실리카 0.01 ~ 7.0 wt% 나노유체의 분산안정성 평가 결과, 나노입자의 농도가 0.5 wt% 이상 첨가될 경우 나노입자의 직경은 모두 100 nm 이하로 측정되어 분산안정성을 확인하였다. 전단속도 1 ~ 100 s-1 조건에서 점성도 측정 결과, 모든 온도에서 나노입자 농도가 높아짐에 따라 점성도는 증가하였으며, 나노유체는70.89 ~ 100 s-1 전단속도 범위에서 난류를 발생시켜 점성도 측정값에 신뢰가 떨어지는 구간이 발생하였다. 따라서모든 나노입자 농도에서 전단속도 구간을 초기 불안정한 구간을 제외한 35.63 ~ 70.89 s-1 미만으로 설정 시 적절한점성도 값을 도출할 수 있을 것으로 판단된다. 석유회수증진공법 및 이산화탄소 지중저장 분야에서 신뢰성 있는주입성 연구를 수행하기 위해 본 연구에서 제시한 적정 전단속도 구간에서 나노유체의 점성도를 측정하길 권장한다.

다국어 초록 (Multilingual Abstract)

Globally, the research of nanofluids is actively ongoing, but there is a lack of research in rheo- logical properties such as the viscosity of nanofluids. In this study, seawater-based silica nanofluids using sur- face-modified nanoparticles were synthesized and dispersion stability test was performed. Also, a appropriate range of shear rate was derived to measure the viscosity. Dispersion stability test of silica nanofluids with 0.01 ~ 7.0 wt% under reservoir conditions with high-temperature and high-salinity (100°C, 200,000 ppm) showed that the size of nanoparticles was measured below 100 nm when nanoparticle concentrations were above 0.5 wt%. The viscosity measurements at shear rate from 1 to 100 s-1 revealed that viscosity of nanofluids increased as the concentration of nanoparticles increased at all temperature conditions. Furthermore, turbulence was gen- erated which made viscosity values unreliable at the shear rate range of 70.89 to 100 s-1 for nanofluids.
Therefore, it is concluded that appropriate viscosity values can be derived at the range of shear rate from 35.63 to below 70.89 s-1, excluding the initial unstable range, for all concentrations of nanoparticles. It is recom- mended to measure the viscosity of nanofluids in the proper range of shear rate presented in this study to per- form reliable injectivity studies for enhanced oil recovery and carbon capture and storage.

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