Do nanoplate surfactants hold the key?

Potentially game-changing research which seeks to unlock the potential of nanotechnology to help maximise production from oil wells and extend the life of mature fields is under way in the US under an ITF-funded laboratory-based particle research project. Launched earlier this year by a Texas A&M University chemical engineering department research team, the two-year project aims to determine the effectiveness of nanoplate surfactants for enhanced oil recovery. Professor Zhendong Cheng and Anthony Onukwu fill in the details.

As fields reach maturity existing reserves need increased support to get oil out of the ground and although production rates have improved in recent years, 60-70% of oil remains untapped using today’s methods and technology. There is still considerable scope for further advances and effective use of innovative solutions during the enhanced oil recovery (EOR) process has the potential to allow oil companies to elicit up to 80% of the remaining reserve.

Chemical EOR’s current contribution to worldwide production is limited but there is considerable interest in its capabilities from energy companies around the world. Consequently, the topic was included in ITF’s 2010 call for proposals on EOR technology.

As a result of ITF’s call, a two-year laboratory-based particle research project is underway in the US which aims to determine the effectiveness of nanoplate surfactants for EOR. The project, now approaching its half-way point, is being undertaken by a team of researchers from the Department of Chemical Engineering at Texas A&M University with funding from ITF members Chevron, Dong Energy and Wintershall.

Prof Zhendong Cheng’s expertise lies in the area of complex fluids and soft condensed matter physics. He joined Texas A&M University as an assistant professor in the Artie McFerrin Department of Chemical Engineering in August 2004 becoming associate professor in 2010. Prof Cheng secured his BS and MS degrees, respectively, in China’s University of Science & Technology Modern Physics Department in 1990 and Beijing’s Institute of High Energy Physics in 1993. He obtained his PhD degree from the Princeton University Physics Department in 1999 and was a postdoctoral fellow of ExxonMobil Research & Engineering and Harvard University (with Prof Dave Weitz).

The use of surfactants in chemical EOR to release trapped oil by lowering interfacial tension has been a topic for research and development work in the past, but it is now possible that nanoplate surfactants could offer advanced properties in comparison to those that have previously been studied.

The 2-D schematic representation of the fabrication of surface and edge-modified amphiphilic nano-sheets. The initial step consists of grafting a coupling agent over the surface and the edges of a-ZrP. Subsequently, the exfoliation of the crystals is carried out to obtain the surface and edge-modified nanosheets from their outer and inner layers, respectively.

The researchers are looking at the synthesis of what are known as Janus nanoparticles – named because they offer two strikingly different faces from a single layer of inorganic atoms. One side is drawn to water – hydrophilic – and the other is repelled by it – hydrophobic. The team is working to develop a synthetic route to functionalise both faces so it can be used as a surfactant in the EOR process.

Anthony Onukwu served as a petroleum engineer and a project engineer in UK and West Africa before joining ITF as a senior technology analyst. He has bachelor and master degrees respectively in material engineering and petroleum engineering and nine years’ oil & gas industry experience, focusing on reservoir management, production optimization, well completion and subsea production systems. Currently SPE Aberdeen Section chairman for 2012/13, Onukwu is the ITF focal person for enhanced oil recovery.

The hydrophilic and hydrophobic properties of Janus particles will be tested to demonstrate their potential use as nano-surfactants. The value of nanoplate surfactants, similar to conventional surfactant, is to lower the interfacial tension of trapped oil to mobilise it. Once oil is mobilised, any emulsions which have formed will tend to merge into a continuous oil phase, resulting in banked oil which can then be extracted and produced.

The a-zirconium phosphate crystals. (a) SEM micrograph. (b) Zoomed view of a particular crystal showing cracks along the lamellar layers. (c) Idealized structures of the alpha phase of zirconium phosphate (a-ZrP).

The researchers are also investigating the benefits of an anisotropic, geometric shape which could bring special advantages for surface activity. The large lateral surface area offers strong absorption energy to the oil-water interface, while the ultra-thin nature of the nanoplates offers extraordinary stability to the liquid film between two emulsions, which prevents coalescence, since the maximum sustainable capillary pressure is inversely proportional to the particle thickness.

Characterization of stable emulsions stabilized by a-ZrP-ODI nano-sheets and unstable emulsions using non-modified a-ZrP nanosheets. Representative (a) optical micrograph and (b) confocal laser scanning micrograph of o/w emulsions using a-ZrP-ODI as surface active agents. (c) Observation of o/w emulsions stabilized by non-modified a-ZrP monolayers. The emulsion coalesced and quickly creamed. (d) Optical micrographs of the o/w emulsion right after emulsification and (e) after 24 days, which indicate that non-modified a-ZrP nanosheets are not good emulsifiers due to the observed coalescence. (f) Creaming of o/w emulsions stabilized by a-ZrP-ODI nanosheets. The emulsion presents less creaming compared to (c) due to the lesser degree of coalescence. (g) Micrograph showing the oil-in-water droplets after emulsification. (h) o/w emulsion micrograph from the top and (i) from the middle after 24 days, where no coalescence was observed.

The prize for achieving this can be significant and it is estimated that for every additional one percent of recovery efficiency, about four billion barrels of oil would ultimately be produced. As a result, innovative EOR technologies which can improve traditional methods of production while offering increased oil recovery and the potential to make abandoned fields economically viable again are particularly attractive to operators.

The research team is also looking into ways the nanoplates can be tailored to the specific needs of individual reservoirs while remaining environmentally friendly, suitable for high temperature and high salinity use, and cost effective. There has also been recent interest in their potential for a number of applications including more effective drug delivery, and solar cell development. OE