Functionalised nanoparticles for enhanced oil recovery: emulsification and demulsification

Abstract

This thesis describes the synthesis and development of functionalised nanoparticles (NPs), which should form stable dispersion and act as efficient emulsifiers for subsurface oil and gas applications. These NPs have to be stable and function as emulsifiers at an elevated temperature and high salinity, aiming to increase oil recovery. Particle stabilised emulsions are very stable against phase separation. However, in order to recover the oil produced from a well, these emulsions have to be broken. Therefore a new demulsification technique was developed. All these findings are crucial for using NPs in every aspect of the oil extraction process, for instance as nanosensors, contrast agents or additives in drilling and injection fluids.

In order to produce functional NPs, the surface of silica NPs was modified by grafting five different polymers via different methods in order to synthesise stable, aqueous dispersions of functionalised nanoparticles at reservoir condition. Four key criteria were identified from the experiments to produce NPs; Oligo 2-dimethylamino-ethyl-methacrylate grafted silica NPs (ODMEAMA-SiO2) were synthesised accordingly. ODMEAM-SiO2 had a hydrodynamic diameter of 65 nm and were stable in brine, up to 1.7 M American Petroleum Institute (API) brine at 65°C; these NPs also acted as efficient emulsifiers under the same condition, forming stable decane-in-brine emulsions with 75 vol% of decane; the droplet size of emulsions decreased with increasing molarities of NaCl and/or CaCl2 salts. The viscosity of particle stabilised (Pickering) emulsion behaved as a visco-elastic gel and can be lowered efficiently by additional water dilution to 1 Pa∙s .

The transport of various NPs through a high permeability water and oil saturated Bentheimer and Berea sandstone was studied by passing up to 500 Pore volume (PV) NPs dispersions through them. Seven different NPs were qualitatively compared with a surfactant polyoxyethylene nonylphenyl ether (ENP), with respect to the retention of NPs and enhanced oil recovery (EOR). The retention of NPs was 3.5 folds lower than ENP surfactant in high permeability core. The addition of 1 wt% ODMEAMA-SiO2 in water did improve the enhanced oil recovery (EOR) that is after initial water flood by 8.5 % from the high permeability core. For the lower permeability core, polystyrene NPs were found to emulsify oil in-situ by producing an emulsion, which allowed recovering extra 27.5% oil.

A new demulsification approach was demonstrated. Hydrophobic silanised sand was used to pack filtration columns (SPC) and a particle stabilised oil-in-water (o/w) emulsion passed through. The effectiveness of hydrophobic SPC to break down o/w emulsion was subsequently studied by two different sand sizes and compared to traditional thermal, gravitational treatment. Demulsification was not observed by increasing the temperature to 65°C or centrifugation at 7500 rpm. Phase separation can be achieved by exploiting the difference in freezing points of internal and external phase of emulsions, or using the hydrophobic surface of SPC as wetting and coalescing medium. However, freezing which was time consuming and energy intensive, was not practical for large scale application. The SPC approach is efficient, fast, simple, flexible to use, with highest recovery of oil as 88 % and NPs as 93%.