Realising the Full Potential of Oil Fields: A Novel Microemulsion System for Highly Efficient Enhanced Oil Recovery

Crude oil is a limited resource—a refrain we have heard repeatedly over the past three decades. One of the ways to maximise our natural oil resources is enhanced oil recovery (EOR). EOR techniques can help recover 30–60% oil from a given reservoir, whereas traditional primary and secondary recovery techniques can obtain only 20–40%.

In EOR, a fluid (such as carbon dioxide or a fluid mixture) is injected into the reservoir to pull out residual oil that could not be captured through primary and secondary recovery. Microemulsions are highly promising injection fluid candidates for chemical EOR due to their high efficiency in extracting residual oil from reservoirs. But microemulsions are not stable under high temperature and pressure, making them degrade or deform inside reservoirs.

Now, a team of researchers—led by Dr. Nilanjan Pal of the Indian Institute of Petroleum and Energy (IIPE) and Prof. Ajay Mandal of the Indian Institute of Technology (Indian School of Mines), Dhanbad—has developed a novel, highly stable microemulsion system for sustainable, cost-effective, and highly efficient EOR. Their work has been published in Energy & Fuels.

A microemulsion is typically made by mixing oil, water, surfactant, and occasionally, a co-surfactant. In a microemulsion, the droplets of the dispersed phase range between 1 to 100nm in diameter, giving them different properties from macro- emulsions. The surfactant helps in the formation of micelles, which are spherical structures formed by molecules with a hydrophilic (water-soluble) tail and a hydrophobic (water-insoluble) head. The heads come together to form a hydrophobic core, and the hydrophobic tails radiate outwards like a child’s drawing of the sun. Micelles are critical to reduce surface tension in liquid mixtures, which then improves their flow properties

In this paper, the researchers created a microemulsion using an olefin sulfonate surfactant (ENORDET) and cost-effective silica nanoparticles. “Normally, the application of microemulsions in the field comes with certain challenges, such as 2 with rheology (flow behaviour), fluid handling, and stability of the microemulsion under the saline/salty conditions in the reservoir,” explains Dr. Pal. “ENORDET is a novel surfactant with unique molecular properties; thus, we investigated if it would be favourable for application in EOR.”

For their research, the team investigated two microemulsions—one with only ENORDET and one with ENORDET and cost-effective silica nanoparticles. First, they prepared the microemulsions using a high-energy technique. The formation of microemulsion after mixing was confirmed by analysing the turbidity of the mixture. The researchers also characterised the microemulsions using dynamic light scattering studies as well as zeta potential (a type of electric potential) studies. One of the important ways to understand the suitability of a microemulsion for EOR is through its Winsor behaviour. Oil and water do not mix; thus, they form two distinct phases—an aqueous (water) phase and an oil phase. A Winsor I microemulsion is an oil-in-water microemulsion that occurs in the aqueous (water) phase. Conversely, a Winsor II system is a water-in-oil microemulsion in the oil phase. However, in a Winsor III system, the surfactant forms a microemulsion between the oil and aqueous phases. “For EOR, Winsor III is the ideal state because it can achieve ultralow interfacial tension,” says Dr. Pal. “Ultralow interfacial tension enhances the wettability of the stone in oil reservoirs, effectively ‘washing out’ more oil. It also improves capillary behaviour, reducing drag force and making it easier for the fluid to flow.”

The researchers found that the microemulsion initially showed Winsor I behaviour, which then transitioned to Winsor III phase and then Winsor II with increasing salt concentration. They also used pendant and sessile drop analyses methods, to better understand the surface forces on the microemulsion. In pendant drop analysis, the droplet is suspended from a needle, whereas in sessile analysis the droplet is placed on a flat surface. The pendant drop analysis revealed that the interfacial tension at the oil-microemulsion interface was significantly low compared to plain water as an injection fluid. Sessile analysis indicated a transition from oil-saturated rock to water- wet state with time, which is useful for EOR.

They also investigated the flooding behaviour of the microemulsion in a sandstone core model, a common model used in petrophysical engineering to investigate how certain factors affect the oil recovery process. “The core-flood studies revealed around 20% recovery and 29% recovery of original in place oil for the ENORDET and ENORDET–silica nanoparticle microemulsions after secondary water flooding was completed, indicating its effectiveness for EOR,” explains Dr. Pal. This means that if 40% of the total oil in the reservoir was recovered after the secondary recovery process, then the ENORDET microemulsion could improve that number up to 52% and the ENORDET–silica nanoparticle emulsion could improve that to 57.4%. This research, overall, provides strong evidence that an ENORDET- and silica- nanoparticle-stabilised microemulsion has great potential for EOR. The findings of 3 this study lay the foundation for the use of this novel microemulsion system in EOR. Future research in this direction could focus on scaling the process up for practical implementations in the field.

“Petroleum is a precious and limited resource,” concludes Dr. Pal, “We hope that our research can provide a means to increase recovery from our oil fields, extend their productive life, and make sure that we can safely and sustainably make the most of our natural resources.”

Congratulations to the research team on their excellent work!