A mechanism study of nanoparticles for enhanced oil recovery
Keywords: Energy Resources Engineering.

The application of nanotechnology in enhanced oil recovery (EOR) is emerging because nanoparticles have the potential to alter rock properties like wettability and fluid properties such as interfacial tension (IFT). In addition, a newly-proposed theory of the structural disjoining pressure (SDP) has become popular in the scientific community as well. However, a systematic literature review shows that ambiguity exists regarding which components in nanofluid play the role of changing wettability and interfacial tension (IFT). In addition, there are only a limited number of numerical and experimental studies to investigate the theory of the structural disjoining pressure (SDP), none of which can strictly confirm the theory. This motivates us to study these potential candidates of the mechanisms of nano-enhanced oil recovery (nano-EOR). We first conducted experiments using the contact angle goniometer to measure the contact angle and the interfacial tension (IFT) for various nanofluid compositions and the results showed that the addition of bare silica nanoparticles could reduce the contact angle. Specifically, a reduction in nanoparticle size and an increase in nanofluid concentration could further reduce the contact angle. However, bare nanoparticles did not change the interfacial tension (IFT). In order to investigate the theory of the structural disjoining pressure (SDP), we extended the model with a configuration that simulates the real case of the detachment of an oil droplet. The results showed that four conditions favor the spreading of the nanofluid on the substrate and the detachment of the oil droplet from the substrate to which it attached due to the structural disjoining pressure (SDP). These conditions include a high nanofluid concentration, a small nanoparticle size, a small contact angle of the nanofluid/oil/substrate system looking from the nanofluid phase, and a large oil droplet. Three imaging experiments were conducted using environmental scanning electron microscopy (ESEM) and dynamic fluid-film interferometry (DFI) to verify the theory of nanofluid spreading due to the structural disjoining pressure (SDP). ESEM imaging experiments showed the result of a single layer of nanoparticles but could not eliminate the effect of evaporation. Combining the ESEM images with the results from DFI in a liquid cell eliminated the evaporation effect and confirmed that nanoparticles are capable of spreading over the substrate in a thin film that is composed of one single layer of nanoparticles. Moreover, an experiment into the extension of the coffee ring effect showed the discovery of a new coffee ring pattern. Finally, we conducted a nanofluid flooding experiment using carbonate rocks. It was able to isolate the effect of the two confirmed mechanisms on the oil recovery rate at core-scale and tested the potential of nano-enhanced oil recovery (nano-EOR) at core-scale. We determined that an increase in oil recovery of 6% was due to the wettability alteration and another 6% increase in oil recovery was due to the mechanism of the structural disjoining pressure (SDP) for our low permeable carbonate core.