Measurements of mineral-brine and oil-brine zeta potentials for improved understanding of controlled salinity water flooding.

It is well known that oil recovery from carbonate reservoirs can be increased by modifying the injected brine composition in a process 'controlled salinity water-flooding' (CSW). However, the mineral- to pore-scale processes responsible for improved oil recovery (IOR) during CSW remain ambiguous and there is no method to predict the optimum CSW composition for a given crude-oil-brine rock system. However, commonly across many of the previously suggested underlying mechanisms for CSW is that they should all lead to measurable changes in the zeta potential. The zeta potential is a measure of the electrical potential at mineral-brine and oil-brine interfaces and is a proxy for the electrostatic forces acting between these interfaces. Previous work has shown that for carbonate systems, dilution of the injection brine yields a more negative zeta potential at the mineral-brine interface, and that IOR is observed by CSW only when the oil-brine interface is interpreted to be negatively charged. Instances where the oil-brine interface was interpreted to be positively charged showed no IOR. It was further shown that IOR could be correlated with the change in zeta potential at the mineral- and oil- brine interfaces. This project aims to improve understanding of the mineral-brine zeta potential behaviour for a range of different sandstone minerals and also to improve understanding of the oil-brine zeta potential behaviour. Previous literature suggests that the oil-brine interface should always be negatively charged, however these measurements are made far from reservoir conditions. This work will aim to develop new methods to probe the zeta potential of the oil-brine interface using the streaming potential method.