SCIENTISTS at Swansea University, UK have developed a novel, ‘green’ surfactant which improves oil recovery by 72%. The surfactant is quick and simple to synthesise and could provide a cheaper, greener alternative to common EOR surfactants.
Enhanced oil recovery (EOR) is a process used to increase the amount of oil that can be recovered from a reservoir. There are several different methods of EOR. One method is chemical injection, which involves injecting a mixture of water and chemicals into an oil well. Surfactants can be used to improve oil recovery by reducing the surface tension of oil, making it less “clingy” and easier to push out, and increase the wettability of porous rocks, allowing water to penetrate more easily.
The researchers at Swansea developed a single chain, hydrocarbon-based surfactant that is stable in the “harsh” conditions of EOR and is able to improve oil recovery by 72% in both low and high brine solutions. According to literature, other surfactants, such as sodium dodecylsulfate (SDS), only improve oil recovery by 45%, alone.
According to Shirin Alexander, the effectiveness of the developed surfactant is due to its ability to reduce the surface and interfacial tension of oil/water “remarkably” compared to other single chain surfactants. Alexander is a Fellow in the College of Engineering at Swansea and a lead researcher. She also credited the surfactant’s “effective wettability alteration and capability to maintain the aggregation structure under extreme heat and salinity”.
In high concentration, surfactants form aggregates (micelles) in which the hydrophobic portions of the molecules form a core that is capable of interacting with (solubilising) oil. According to Alexander, for many surfactants, harsh conditions such as heat and salts can disrupt the aggregation structure. However, the new surfactant showed “very good stability in these harsh well conditions.”
Typically, surfactants that contain fluorocarbon or siloxane chains are more effective than linear chain hydrocarbons at reducing surface tension. However, fluorocarbon surfactants are environmentally hazardous, and siloxanes may be hydrolytically unstable. “The surfactant developed by the team is hydrocarbon-based, which has the potential to be a ‘green’ replacement,” said Alexander.
In addition, the effectiveness of the developed surfactant for EOR means additives, such as polymers, are not required. Polymers can be used in conjunction with surfactants for EOR. They increase the viscosity of the injected water, which improves the water/oil mobility ratio and can increase oil recovery. However, the increase in viscosity can also make the injected water more difficult to reuse, meaning that the mixture of polymers and surfactants has to be disposed of.
“Since polymers do not easily decompose and surfactants themselves can be poisonous to wildlife, this can have potentially harmful and long-lasting environmental impacts,” said Alexander.
The novel surfactant presents a class of potentially important material which could be used in various EOR scenarios, such as low salinity and smart water. And despite the effectiveness of the surfactant alone, it could also be used in alkaline-surfactant-polymer and nanoparticle-surfactant flooding.
Andrew Barron, Professor in the College of Engineering at Swansea, said: “Despite the desire to shift to renewable energy, the global demand for oil is not abating, and we must find ways to enhance recovery of resources using methods with low environmental impact. So-called green hydrocarbon technology is one of the focus areas of ESRI [the Energy Safety Research Institute at Swansea University], along with CCUS and alternative sustainable energy sources, for a multifaceted approach to lowering emissions and the environmental impact of energy and resource production”.
Energy & Fuels: http://doi.org/c5hx
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