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The continuous demand for unconventional oil, such as heavy oil as an alternative energy supply, justifies the global oil reserves of as high as 1734 billion barrels in 2019.
However, the drawback of current conventional oil extraction methods, known as primary and secondary methods, is known to have a lower efficiency of around 5%-30% of the well’s potential. The primary oil recovery method extracts oil either via the natural rise of hydrocarbons to the earth’s surface or artificially lifting with pump jacks. Secondary oil recovery aims for about 30% by injecting gas or water that will displace oil from its resting place to the earth’s surface. To meet the demand for maximum oil recovery, the scientists explore a tertiary technique that involves altering the oil properties and enhancing their conductivity to the extraction process.
The recent lab-test demonstration from the University of Houston of an inexpensive and non-toxic nanofluid, made up of sodium, can efficiently recover 80% of high viscosity oil from reservoirs. This enormous improvement in the recovery percentage gives noble hopes of using nanofluids for the enhanced oil recovery system.
What is Nanofluid?
Nanofluids are the colloidal suspensions, made by mixing nanoparticles in another base fluid of lower viscosity. Some typically considered nanoparticles to prepare nanofluids are metals, oxides, carbon nanotubes with the choice of water, ethylene glycol, and oil as base fluids.
By achieving the stability of nanofluids by proper dispersion through ultrasonication, surfactant, and pH control, nanofluids' use in comparison to the conventional chemical injection brings additional functionality of magnetic, pH-responsive properties and material surface modification.
The University of Houston’s demonstration used sodium’s high reactivity with water and prepared sodium nanoparticles in silicone oil. This allowed sodium to disperse throughout the reservoir before coming into contact with water in the reservoir, after which the chemical reaction encouraged heat generation. The production of sodium hydroxide helped the oil to reduce its viscosity. Another by-product, hydrogen gas, was used for gas flooding.
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Properties of Heavy Oil
The widely used definition for heavy oils is based on the API scale, recommended by the American Petroleum Institute to be equal to or smaller than 20 degrees (Santos, Loh, Bannwart, & Trevisan, 2014).
Heavy oils have distinctive characteristics of high specific gravity, elevated viscosity, low H/C ratio (more than 15 carbon atoms in the chain), including high contents of asphaltene, resin, heavy metals, sulfur and nitrogen. The heavy oil consists of relatively small amounts of heteroatoms, but their presence brings in catalyst contamination and corrosion problems.
Efficient Recovery of Oil from Reservoirs
The enhanced oil recovery system extracts up to 60% oil using the most commonly adopted methods of the thermal recovery system (TRS), gas injection technique (GIT), and chemical injection (CI).
In a TRS, steam reduces the oil's viscosity through heating that encourages an easier flow of oil to the surface. The GIT injects natural gas, nitrogen, and carbon dioxide into the reservoir and improves oil displacement. A CI lowers surface tension and increases water-flooding efficiency freeing trapped oil in the reservoir.
In 2020, Onyemachi, Onwukwe, Duru, Chikwe and Uwaezuoke carried out an experiment to enhance the oil recovery using nanoparticles, such as magnesium oxide, silicon oxide, aluminum oxide and zinc oxide with Irvingia gabonensis in Nigeria. Their results demonstrated that adding Irvingia gabonensis into the nanofluids enhanced oil recovery in the range of 50.3% to 53.2%, with aluminum oxide nanoparticles performing the best. According to Cheraghian, Rostami and Afrand, nanofluids help the release of oil drops that are trapped in thin throats and microchannels of the reservoir rock, which leads to the absorption process, wettability alteration of reservoir rocks and changing of interfacial tension between reservoir fluids.
Prospect of Nanofluid in Heavy Oil Recovery System in Future
The large injection volume needed for nanofluids in the recovery system means the synthesis and production cost is still a significant issue. The nanofluids also have the challenge of being adaptable to different oil reserves, which possess different and unique properties. Although nanotechnology is a relatively new field in petroleum industries, its speedy advancement in a field test and pilot studies can confront all the boundaries and hold a stable solution in the oil and gas industries.
References and Further Reading
Ahmed, M. S. (2019). Nanofluid: New Fluids by Nanotechnology. In A. Shahzad, Thermophysical Properties of Complex Materials. doi:10.5772/intechopen.86784
BP. (2020). Oil. [Online] bp: https://www.bp.com/en/global/corporate/energy-economics/statistical-review-of-world-energy/oil.html#oil-reserves (Accessed on 4 October 2020).
Cheraghian, G., Rostami, S., & Afrand, M. (2020). Nanotechnology in Enhanced Oil Recovery. Processes. doi:10.3390/pr8091073
Office of Fossil Energy. (n.d.). Enhanced Oil Recovery. [Online] ENERGY.GOV: https://www.energy.gov/fe/science-innovation/oil-gas-research/enhanced-oil-recovery (Accessed on 04 October, 2020).
Onyemachi, J. C., Onwukwe, S. I., Duru, U. I., Chikwe, A. O., & Uwaezuoke, N. (2020). Enhancing oil recovery through nanofluids flooding with Irvingia gabonensis in the Niger Delta. Journal of Petroleum Exploration and Production Technology. doi:10.1007/s13202-020-00953-x
Peng, B., Zhang, L., Luo, J., Wang, P., Ding, B., Zeng, M., & Cheng, Z. (2017). A review of nanomaterials for nanofluid enhanced oil recovery. RSC advances, 7(51), 32246-32254. doi:10.1039/C7RA05592G
Petro Industry News. (2014). What is the Difference between Primary, Secondary & Enhanced Recovery for Oil Extraction? [Online] Petro Industry News: https://www.petro-online.com/news/fuel-for-thought/13/breaking-news/what-is-the-difference-between-primary-secondary-amp-enhanced-recovery-for-oil-extraction/31405 (Accessed on 4 October 2020).
Santos, R. G., Loh, W., Bannwart, A. C., & Trevisan, O. V. (2014). An Overview of Heavy Oil Properties and its Recovery and Transportation Methods. Brazilian Journal of Chemical Engineering, 31(03), 571 - 590. doi:10.1590/0104-6632.20140313s00001853
University of Houston. (2020). Inexpensive, non-toxic nanofluid could be a game-changer for oil recovery. [Online] Science News: https://www.sciencedaily.com/releases/2020/09/200910134000.htm (Accessed on 4 October 2020).