Investigation of Modified Silica Nanoparticles' Efficiency in Enhancing Oil Recovery - An Experimental Study

Abstract

As it has become difficult to discover new hydrocarbon resources, the focus has shifted towards innovative enhanced oil recovery (EOR) technologies that extract more oil out of producing reservoirs. The addition of modified silica nanoparticles (NPs) to the injected water shows promise as a cost-effective EOR technique. Compared to other additives, nanoparticles have the advantage of a large activated surface area, surface customization and are an easily producible base material.

Several experimental methods were used to analyze the effectiveness of how modified silica nanoparticles can improve oil recovery. The main objectives were to determine the recovery factor from the nanoflooding phase by conducting coreflooding experiments, and understand the significant EOR mechanisms that occur during transportation of nanoparticles in a porous medium. In addition, the wetting forces in an oil/nanofluid/solid system were analyzed by performing contact angle measurements, and the interfacial interactions were studied through emulsion tests.

Coreflooding experiments were carried out at ambient conditions using Berea Sandstone cores for both nanofluid-decane and nanofluid-crude oil systems. Three different sizes of nano-structured silica particles were dispersed in synthetic North Sea water (NSW) at 0.05 wt.%. The nanoparticles were named according to their aggregated particle diameters of 72 nm (NS-S), 112 nm (NS-M) and 128 nm (NS-L), where S, M and L denote small, medium and large, respectively. The resulting nanofluids were implemented as a tertiary recovery technique, after water injection. Waterflooding with NSW was conducted after the nanoflooding stage to determine the retention strength of the nanoparticles in the system.

The main conclusions were that nanofluids produced incremental oil for all the seven displacement tests. The recovery mechanism was believed to be of a chemical nature, as the smallest nanoparticle (NS-S) performed slightly better as an EOR agent. However, the dominating EOR mechanism was likely the in-situ creation of unstable oil-in-water emulsions. Lastly, wettability alteration and interfacial tension reduction were considered to have a small impact on mobilization of residual oil.

The effluent and influent analysis of fluid compositions and core properties showed that NPs slowly retained in the system. However, the retention was found reversible, as nanoparticles were not observed in the effluent crude oil.

Coreflooding results have shown that application of nanoparticles provide an approach to transcend the current EOR technology. In the nanoparticle-based EOR research, no reservoir simulator has been developed. It was proposed in this thesis that nano-EOR could be implemented to a reservoir simulator, by modifying brine model options such as low salinity and surfactant flood.