Visual study of TiO2 nanofluid stabilization methods on inhibition of asphaltene precipitation in porous media

Abstract

In situ recovery involves injection of lixiviant into an ore formation to extract a target metal. Applicability of in situ recovery is confined to deposits where adequate permeability exists. A key challenge is establishing uniform contact between the fluid and the formation in fractured environments, particularly if fractures become blocked by gypsum and other precipitates during leaching, which restricts solution flow. The degree of contact between the lixiviant and the ore is most often the critical rate-limiting factor. Prevention of asphaltene precipitation in reservoir rocks has been shown to resolve such issues in petroleum production. This research explores the potential effect of titanium dioxide (TiO2) nanoparticles in destabilizing asphaltene deposition in porous media in the presence of heptol, with a view to extend the understanding gained in this study to an in situ recovery environment. The effect of TiO2 nanofluid on incremental oil recovery was investigated using three different nanofluid stabilization methods: stabilization by ultrasound; alkaline solution addition to the nanofluid; and the application of ultraviolet radiation. The results show that the ultrasonic system is not suitable for TiO2 nanoparticle stabilization in the fluid. Alkaline addition stabilizes TiO2 nanoparticles but decrease acidic sites on the surface of the nanoparticles, which leads to lower asphaltene adsorption on TiO2 nanoparticles and a lower nanoparticle surface charge, and results in nanoparticle flocculation and instability. Ultraviolet radiation was found to be the best method for stabilizing TiO2 nanoparticles. Asphaltene adsorption did not occur at concentrations below 3000 ppm TiO2 and thus, the recovery increase using these concentrations was attributed to an increased viscosity of the injected fluid and a reduction of its interfacial tension with the host oil.