**4.1 Fossil energy and enhanced oil recovery (EOR)**

#### *4.1.1 Tertiary oil recovery*

Improved oil recovery (IOR) or enhanced oil recovery (EOR) are two terms used loosely to describe the improvement of oil recovery after both the primary and the secondary stages of oil production become economically unattractive or technically not feasible. In principle, IOR is the general term to designate any implemented means after secondary process that increases considerably the amount of oil recovered. On the hand, EOR defines a specific technique (or a combination of techniques) implemented to decrease the residual oil.

**139**

prevail [47].

[62–64].

tion of gases [67, 68].

*4.1.2 EOR mechanisms in respect of MO-NPs*

*4.1.2.1 Wettability and IFT alteration*

formation salinity (**Figure 7**).

mobility ratio.

*Nanocomposite and Nanofluids: Towards a Sustainable Carbon Capture, Utilization, and Storage*

EOR methods are grouped into thermal and non-thermal methods. Thermal methods are the most advanced techniques among EOR methods and are best suited for heavy oils and tar sand formations. In these methods, the heat is supplied to the reservoir in form of steam or fire, which favors the vaporization of stranded oil. The major drawbacks associated to thermal-EOR pertain to the geometry and the petro-

Non-thermal methods encompass techniques that reduce the interfacial tension (IFT) between the stranded oil and resident fluids and the viscosity of the oil. Among the most prominent methods, gas-EOR stands out because of it offers the possibility to sequester greenhouse gases. During a gas-EOR, the injected gas dissolves into the oil after a first (or multiple) contact leading to a foamy oil, whose viscosity is lower than that of the original oil [55]. Often, gas-EOR is challenged, in

If the slug is a surfactant [59], a polymer [60], or even a micellar solution [61], the oil is produced by reduction of IFT or wettability. Major problems associated to surfactant-EOR are the loss of chemical, phase partitioning and trapping, and the slug by passing. Unlike chemical-EOR, microemulsion-EOR relies on the reduction of the mobility ratio. Microemulsions, kinetically more stable than emulsions, are potentially viable because of the ultra-low IFT and their high interfacial area

Microbial-EOR uses the potential of microbes to yield either bio-surfactant, slimes (polymers), biomass and/or gases such as CH4, CO2, N2 and H2 as well as solvents and certain organic acids [65, 66]. Oil recovery mechanisms in microbial-EOR are like those of the classic chemical methods. This includes IFT reduction, emulsification, wettability alteration, improved mobility ratio, selective plugging, viscosity reduction, oil swelling and increased reservoir pressure due to the forma-

Nano-EOR has been reported to be the next generation of EOR, which is evidenced by the wealth in literature covering the topic [69–75]. Therefrom, it appears that the mechanisms of oil production using MO-NPs are (1) wettability and the IFT alteration, (2) advanced drag reduction, and (3) the decrease of the

Wettability is the preferential tendency of one fluid to wet (or to spread) onto a surface [76]. To produce more oil, the wettability of the oil-water-rock system should be shifted from oil-wet to a water-wet or strongly water wet condition. MO-NPs can adsorb onto the rock surface and form a nanotexture, which contributes to wettability alteration [77]. However, these mechanisms are affected by the

At a low salt concentration, the activity coefficient of the salt increases in a manner that the salt molecules sit within the oil phase. With the presence of salt at the interface, the excess surface concentration turns positive from which results a low contact angle (**Figure 7a**) and higher IFT (**Figure 7b)**. An oil production scenario in which the salt concentration is large, the salting-out effect seems to

MO-NPs are depleted at the interface and transferred back to oil phase. This breaks the oil-water interface adsorption, hence a high contact angle. The same behavior could be extended when two immiscible liquids (oil and water) meet each

*DOI: http://dx.doi.org/10.5772/intechopen.95838*

physical properties of the candidate formation [54].

part by, the deposition of heavy fractions [56–58].

## *Nanocomposite and Nanofluids: Towards a Sustainable Carbon Capture, Utilization, and Storage DOI: http://dx.doi.org/10.5772/intechopen.95838*

EOR methods are grouped into thermal and non-thermal methods. Thermal methods are the most advanced techniques among EOR methods and are best suited for heavy oils and tar sand formations. In these methods, the heat is supplied to the reservoir in form of steam or fire, which favors the vaporization of stranded oil. The major drawbacks associated to thermal-EOR pertain to the geometry and the petrophysical properties of the candidate formation [54].

Non-thermal methods encompass techniques that reduce the interfacial tension (IFT) between the stranded oil and resident fluids and the viscosity of the oil. Among the most prominent methods, gas-EOR stands out because of it offers the possibility to sequester greenhouse gases. During a gas-EOR, the injected gas dissolves into the oil after a first (or multiple) contact leading to a foamy oil, whose viscosity is lower than that of the original oil [55]. Often, gas-EOR is challenged, in part by, the deposition of heavy fractions [56–58].

If the slug is a surfactant [59], a polymer [60], or even a micellar solution [61], the oil is produced by reduction of IFT or wettability. Major problems associated to surfactant-EOR are the loss of chemical, phase partitioning and trapping, and the slug by passing. Unlike chemical-EOR, microemulsion-EOR relies on the reduction of the mobility ratio. Microemulsions, kinetically more stable than emulsions, are potentially viable because of the ultra-low IFT and their high interfacial area [62–64].

Microbial-EOR uses the potential of microbes to yield either bio-surfactant, slimes (polymers), biomass and/or gases such as CH4, CO2, N2 and H2 as well as solvents and certain organic acids [65, 66]. Oil recovery mechanisms in microbial-EOR are like those of the classic chemical methods. This includes IFT reduction, emulsification, wettability alteration, improved mobility ratio, selective plugging, viscosity reduction, oil swelling and increased reservoir pressure due to the formation of gases [67, 68].

Nano-EOR has been reported to be the next generation of EOR, which is evidenced by the wealth in literature covering the topic [69–75]. Therefrom, it appears that the mechanisms of oil production using MO-NPs are (1) wettability and the IFT alteration, (2) advanced drag reduction, and (3) the decrease of the mobility ratio.
