Abstract
Smart water flooding (SWF) has become an enhanced oil recovery (EOR) technique in field applications, as it provides better microscopic displacement efficiency in a relatively economic and environmentally friendly manner compared to other EOR techniques. The ionic composition, the key parameter that affects SWF performance in carbonates, has been extensively investigated to understand the EOR mechanism. The most widely accepted mechanism is that the ion exchange between injected brine and reservoir rock causes wettability alteration towards more water wet, leading to an improvement in oil recovery. Nevertheless, a consistent understanding and explanation of the geochemistry of how specific ions affect EOR performance has yet to emerge.
In this study, hybrid smart brine formulations were developed by spiking seawater with specific amounts of phosphate and hexametaphosphate (HMP) and their potential to increase oil recovery from carbonate core plugs were asseessed. Interfacial tension (IFT) measurements were performed for various smart brines with crude oil. In addition, brine compatibility analysis was conducted to study the potential of salt precipitation due to interactions between injected water and formation water, and the ability of the smart brines to create emulsions was assessed. A series of core flooding experiments was conducted to evaluate the ability of smart brines to increase oil recovery. Amott-Harvey/USBM wettability analysis was conducted to select smart brines and study their effect on wettability. Zeta potential measurements were conducted to capture the possible electric double-layer expansion.
It was concluded that excessive spiking with HMP led to precipitation and the optimal concentration was determined. Moreover, wettability analysis indicated that HMP is a stronger wettability modifying agent than phosphate, while phosphate performed better in reducing the IFT than HMP. Core flooding experiments demonstrated that creating a hybrid smart brine containing both phosphate and HMP has combined advantages. In addition, none of the studied smart brines generated an emulsion. Zeta potential measurements showed that flooded samples exhibited less negative values than aged samples, indicating the release of trapped oil. This study demonstrates the potential of increasing oil recovery from carbonate core plugs and can help to understand the impact of phosphate and HMP on EOR performance.
