Investigation of Nanoparticles in Enhanced Oil Recovery 

Most of the global oil production is achieved by water flooding (secondary oil recovery). However, in order to increase oil recovery factor, it is important to lower oil water interfacial tension to make oil and water to be more miscible; it is also important to alter rock wettability in natural or oil-wet reservoir conditions to make oil more detachable from rock surface. Conventionally, these are achieved by enhanced oil recovery technologies, e.g., thermal flooding and chemical flooding. However, these technologies are limited by their high energy consumption, high cost, undesirable stability in high salinity, and high environmental damage.

In this research, novel materials of carbon-based nanoparticles (carbon quantum dots, CQDs) and a set of nanocomposites (hybrids of titanium dioxide and carbon-based nanoparticles) were developed and tested in EOR. The investigated materials were discovered to increase oil recovery through different mechanisms including not only IFT reduction and wettability alteration, but also temporary log-jamming (applicable when using CQDs in EOR).

All materials investigated in this project were ready synthesised using a novel continuous hydrothermal flow synthesis system. CHFS provides a consistent, rapid, continuous production process by using supercritical water and a flow system. The reaction can be controlled by altering reaction pressure, temperature, reactants’ concentration, and flow rate.

CQDs studied in this research was functionalised by p-sulfonic acid calix[4]arene and the particle size was controlled to an extremely small level of 1.76 nm + 0.36 nm. This small size provides CQDs the ability to pass though ultra-tight porous media in rocks, and potentially cause temporary log-jamming to increase oil sweeping efficiency.

To select the best nanocomposite, a set of TiO2-carbonaceous nanocomposites consisting of TiO2, carbon quantum dots (synthesised from two different carbon resources – citric acid or glucose), and reduced graphene oxide, were screened. The screening methodologies included different characterisations methods such as of zeta potential, IFT, and wettability measurement. From these studies was concluded that TiO2-graphene nanocomposite exhibited the most promising properties for EOR.

In summary, both CQDs and TiO2-graphene nanocomposite could significantly increase oil recovery efficiency in EOR. A maximum of 17 ± 0.2% additional oil was recovered in core flooding using low CQDs concentration of 0.01 wt% in high salinity condition of 90000 ppm brine; and a relatively high incremental oil recovery factor of approx. 62% was achieved by TiO2-graphene nanocomposite in core flooding. A number of mechanisms have been investigated to understand the effect of nanoparticles in oil recovery. It was found that temporary log-jamming appears to be the main mechanism for CQDs in EOR, as pressure increases were associated with additional oil production. Whereas for TiO2-graphene nanocomposite, interfacial tension reduction and wettability alteration are the main mechanisms that explain the experimental results.