# Plenty of Room at the Bottom: Nanotechnology as Solution to an Old Issue in Enhanced Oil Recovery
## 4 Nanocatalysts
In this study, aqueous metal salts were used along with a steam stimulation process, showing that produced oil had improved physical characteristics. The studies carried out on the topic were focused mainly on the particles used as nanocatalysts, and a minor part dealt with the technologies used to increase the temperature in order to trigger the upgrading processes. The materials reported in the literature are: VO\({}^{2+}\)[142], Ni [36; 37; 143; 144; 145; 146], Fe [142; 143; 147], W [36; 37; 144; 148], Mo [36; 37; 144], Cu [143; 147], Zr [148], Co [147], Cr [147], Pd [147], C [149], SiO\({}_{2}\)[150], SiO\({}_{2}\)/nanoFe [151], K\({}_{3}\)PMo\({}_{12}\)O\({}_{40}\)[152], and nanoclas (montmorillonite (MMT), modified with a quaternary ammonium salt) [153]. As in every mass transport phenomenon, two important aspects must also be considered: the stabilization and transportation of the nanocatalysts [143]. It is crucial that the nanoparticles move at the oil-water interface for the upgrading to take place. Furthermore, it is desirable to keep the nanoparticles in the reservoir after the catalysis process, causing negligible damage to the permeability of the porous media. These improved properties caused an increase in the recovery efficiency in laboratory flooding experiments [36; 37]. The influence of the nanoparticles was appreciated in experiments under different injection conditions: the recovery of vacuum gas oil (VGO--a product of vacuum distillation columns) without nanocatalysts; the recovery of diluted VGO, again in absence of nanoparticles; and the recovery in the presence of trimetallic nanocatalysts in emulsion with VGO. The results evidenced the nanocatalysts' effectiveness for thermal EOR purposes compared with the first two cases (Figure 32). This influence was also demonstrated using nanoclays on asphaltene deposition in a vapor extraction process (VAPEX) [153]. The results showed a high content of precipitated asphaltenes in the nanoclay matrix, implying that asphaltenes were adsorbed by the nanoclays (Figure 33). However, there is an inherent problem in the whole process, and this is how to transport the nanoclays down to the porous media. There are some restrictions in the carrier fluid, since water is not suitable due to the clay swelling. Figure 32: Recovery performance of hot vacuum gas oil (VGO) in the presence of trimetallic ultra-dispersed nanocatalysts at 320 and 340 \({}^{\circ}\)C. Figure reproduced from Ref. [36]. A different method to be used as carriers for the catalytic metals involves the use of amphiphilic nanoparticles into the water injection, which can also act as emulsion stabilizers (Figure 34) [147]. These particles take part in in-situ upgrading reactions (i.e., oxidation and hydrogenation), and are also able to modify the rock formation's wettability. Regarding the heating techniques employed, several authors have proposed microwaves or electrical devices in order to set up the temperature for the cracking process [137; 145; 149]. The effect  
Figure 34: **(top)** Schematic description of different nanohybrids being used as emulsion stabilizers and support of metal clusters; and **(bottom)** optical microscopy images of water/decalin emulsions stabilized by these nanohybrids. Figure reproduced from Ref. [147]. Figure 33: Asphaltene adsorption by Na\({}^{+}\) montmorillonite (MMT) nanoclays. Figure adapted from Ref. [153]. of different micron-sized powders on heavy oil viscosity without steam treatment using alternative heating methods (i.e., electrical or microwave techniques) was discussed. A greater viscosity reduction ratio, shorter reaction times, lower required temperature, and longer viscosity regression time [152] could be achieved (Figure 35). Overall, though this process proved to be efficient in laboratory-scale experiments, there is still research to do in terms of how to make it applicable to real field production, stimulating an entire portion of an oilfield with electromagnetic waves.