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Unlike water, which moves through an oil-saturated environment in the form of separate streams, nanofluid displaces oil uniformly, and this increases the oil recovery factor.

A significant part of all proven world oil reserves are located in so-called terrigenous (sandy) reservoirs. This means that the oil-bearing fluid must be extracted from the porous rocks, consisting of sand particles with a grain size of 0.01 to 10 mm. Voids between grains of sand look like an extensive network of microchannels with characteristic sizes from 1 to 1000 micrometers through which a special mixture of oil, gas and water moves.

Scientists reported that for the development of such fields the waterflooding method is often used: oil is displaced from the porous environment by water or surface-active agents (surfactants). It should be noted that the efficiency of oil extraction by existing methods in all oil-producing countries is considered unsatisfactory. Average oil recovery from reservoirs ranges from 25 % to 40 %. To increase this indicator, oil-producing corporations use thermal steam stimulation, in-situ combustion, and hot water displacement of oil. Air is pumped into the reservoir, exposed to carbon dioxide, nitrogen, flue gases. But these methods, including the displacement of oil by water surfactant solutions or polymer solutions, do not fully solve the problem. In recent years, there have appeared works devoted to the effect of nanosuspensions on the coefficient of oil recovery from the reservoir. And the developments of researchers from Siberia prove that the addition of nanoparticles can significantly increase the "oil recovery" of porous rocks.

“For simulating we used the experimentally measured values of interfacial tension and interfacial angle at the oil - rock - nanofluid line. Water suspension with silicon oxide nanoparticles with an average size of 5 nanometers was used as nanofluid. The concentration of nanoparticles varied from 0 to 1 wt. %. As a result of simulating, it was shown that the addition of nanoparticles to the displacing fluid significantly increases the oil recovery factor. For example, nanosuspension with 1 wt. % SiO2 with a size of 5 nanometers increases this coefficient more than twice as compared to water. This happens solely by improving the wetting of rocks,” said Vladimir Zhigarev, co–author of the research, senior lecturer at the Department of Drilling Oil and Gas Wells at the School of Oil and Gas, SibFU, researcher at the Laboratory of Physical and Chemical Technologies for the Development of Hard-to-Recover Hydrocarbon Reserves.

Experts noted that in the case of clear water, the displacement fluid moves through the oil-saturated formation in the form of separate streams. Such streams of water break through to the exit from the computational domain quite quickly, and after this "breakthrough" the spread of water over the volume of the porous environment actually stops. At the same time, most of the volume of the porous environment still remains filled with oil, and further washing of such rock does not bring results. The process of displacing oil by nanofluid proceeds in a completely different way. The movement of nanofluid at high concentrations of nanoparticles occurs not in separate streams, but more uniformly throughout the volume of the computational domain, and if water breaks through to the outlet from the computational domain in about a second from the start of waterflooding, then nanofluid with a particle concentration of 1 wt. % makes this dash in about 1.8 seconds.

“As a result of the use of nanofluids, a much larger volume of porous rock is embraced by its displacement movement, therefore, more oil is washed out of the rock. This study confirms the prospects of using nanoparticles for the development of already discovered deposits and design of new ones,” the researcher continued.