Even as the world aims to go green with regard to energy sources, crude oil is still the most commonly used source of energy, accounting for 33 % of the world’s energy consumption.
Most of the oilfields around the world have matured, and finding new oilfields is proving to be difficult. But even after primary and secondary recovery, two-thirds of the crude oil remains trapped in the reservoir. Thus there is a need to extract the maximum amount of oil from these reservoirs.
Low-salinity waterflooding is one oil recovery technique that has gained significant attention from researchers because of its constructive, affordable, and environmentally friendly nature.
This technique can be enhanced by combining it with a surfactant. Surfactants are chemical compounds that decrease the interfacial tension between two mediums, such as liquid-liquid, liquid-gas, or liquid-solid.
Low-salinity water with surfactant leads to better oil recovery. However, surfactants can degrade under harsh reservoir conditions and get lost in the reservoir due to their retention, precipitation, and adsorption on the surface of the reservoir rock.
Nanoparticles can help resolve this issue. Nanoparticles are extremely small particles, undetectable to the human eye, in the size range of nanometres, or one billionth of a meter.
Nanoparticles prevent surfactant adsorption on the reservoir rock surface, thereby preventing surfactant loss and making it available for oil recovery.
Although low-salinity water-surfactant-nanoparticles result in higher oil recovery compared to just low-salinity water or surfactant alone, researchers would like to understand this phenomenon better. Thus the microscopic-level interactions need to be visualized.
Microfluidic devices can help to visualize these phenomena. Microfluidics help to manipulate a small amount of fluids at nanoscales and even smaller sizes. They find use in various industries, such as pharmaceuticals, microelectronics, biotechnology, and in the oil industry.
Microfluidic devices are a cost-effective alternative to selecting a treatment before they are used in the oilfield. Even so, core flooding experiments require the use of micro-computed tomography, clinical computed tomography, positron emission tomography, and magnetic resonance imaging for visualization which are all expensive and bulky and cannot be used in the field. Thus, lab-on-a-chip devices are a good alternative.
Although there is a lot of literature on microfluidics and enhanced oil recovery (EOR), very few papers talk about the use of oppositely charged nanoparticles (positive) and anionic surfactant in low-salinity seawater used for crude oil recovery from porous media.
In this study, the authors of which include Mr. Ganesh Kumar from the Department of Ocean Engineering, Prof. Ethayaraja Mani, and Prof. Jitendra S. Sangwai from the Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai, India, have utilized positively charged nanoparticles, Ludox CL colloidal silica nanoparticle, and anionic surfactant, aerosol-OT (AOT) in low salinity seawater conditions, which represents a novel approach to the microfluidic enhanced oil recovery.
Four nanofluids, NF0, NF1, NF2, NF3, and NF4, were prepared at different surfactant and nanoparticle concentrations. The interfacial tension (IFT), wettability, and oil displacement were studied.
The following were the concentrations used for the four nanofluids:
- NF0: 0 wt % nanoparticles + 150 ppm AOT
- NF1: 0.5 wt % nanoparticles + 112.5 ppm AOT
- NF2: 1 wt % nanoparticles + 75 ppm AOT
- NF3: 1.5 wt % nanoparticles + 37.5 ppm AOT
- NF4: 2 wt % nanoparticles + 0 ppm AOT
Base fluid used: Low-salinity seawater (5000 ppm)
Nanoparticles used: Ludox CL silica nanoparticles
AOT: Dioctyl sodium sulfosuccinate surfactant or aerosol-OT.
ppm: Parts per million
Of the four nanofluids, NF3 nanofluid showed a significant reduction in interfacial tension of 49.3 % compared to only crude oil-seawater system. NF3 also had the highest oil displacement efficiency (88.85 % of the original oil-in-place). NF3 nanofluid had better stability, significant reduction in interfacial tension, wettability alteration from oil-wet to water-wet, and was highly effective in oil displacement, which is helpful for enhanced oil recovery applications. This study could help lead to the development of an efficient and cost-effective injection fluid for enhanced oil recovery operations.
Dr. Himanshu Sharma, Assistant Professor from the Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, India, appreciated and acknowledged the importance of this study with the following comments: “Investigation of fluid flow through porous media using microfluidic devices is a powerful technique to understand underlying mechanisms. In this study, Prof. Sangwai and his team performed a microfluidic investigation of oil displacement using nanofluids; a promising and emerging technique to increase oil recovery. Their study showed various mechanisms responsible for increasing oil recovery including emulsification and wettability alteration. In particular, a thin layer of nanofluid was observed between grains and oil which, in my opinion, is an excellent observation and the likely mechanism of wettability alteration when using nanofluids. Overall, it is an excellent study and provides insights into various mechanisms at play when nanofluids are used for oil recovery.”
Article by Akshay Anantharaman
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