Green high performance systems for Enhanced Oil Recovery

In order to meet the growing energy needs in today's society, an increase in petroleum recovery from existing reservoirs is desirable. Overall, only a third of the petroleum present in known reservoirs is recovered with established technologies (primary-recovery methods using natural reservoir forces, and secondary-recovery methods by water/gas flooding). In order to increase the recovery, so-called tertiary-recovery methods are required, also referred to as enhanced oil recovery or EOR. The objective of the GreenEOR project is to contribute to enhanced oil recovery in a sustainable manner, by developing a novel series of green fluids for chemical EOR applications based on nanocellulose, alone or in combination with other EOR components. Nanocellulose is a collective term for nanoscaled particles produced from wood, a sustainable and green resource. Nanocelluloses have a promising potential as green flooding additives due to several properties as e.g. excellent viscosifying and shear thinning properties, hydrophilic nature, excellent possibilities for chemical modification and robustness compared to dissolved polymers. The potential of nanocelluloses as EOR additives have been explored in the GreenEOR project, both as pure nanocellulose-suspensions, as well as nanocellulose in combination with other components. In the project it has been a close cooperation between different research areas comprising nanocelluloses, surface interactions, rheology and core flooding. The temperature in oil wells can be high (>100 °C), and the retention time long; days for drilling fluids and months for EOR fluids. Hence, it is important to assess the temperature stability over time of nanocellulose dispersions to clarify their suitability as rheology modifiers of water-based fluids at such harsh conditions. Dispersions of different types of nanocellulose have been subjected to heat aging. The results showed that the best types were stable after heating to 140 °C for three days. The effect of additives was studied, and format salts increased the temperature stability of the dispersions, while there was no effect of using phosphate buffer. Interactions between nanocellulose dispersions and two different core types have been studied. The purpose was to reveal how nanocellulose dispersions flow through oil reservoirs and if and how this can influence oil extraction. Two different types of nanocellulose were dispersed in brine and injected into sandpacks and Berea sandstone cores, respectively. The experimental parameters that were varied in addition to type of nanocellulose included sand grain size, salinity and flow rate. It was shown that the flow of nanocelluloses was influenced by these parameters and that nanocellulose can cause reduced permeability. Positive conditions for the flow was small nanocellulose particles, low salinity, high initial permeability of the core / sandpack and high flow rate. A substantial viscosity increase of nanocellulose dispersions upon heat aging at temperatures above 90 °C has previously been shown. This change in material properties at very low concentrations in water has been proposed as an active mechanism for EOR, as highly viscous fluids will be forced into new areas of the formation and more oil will be recovered. To investigate this in more detail, a high-temperature (120 °C) core flood experiment was carried out. This was done after another EOR method had been applied, so called low salinity flooding. Total oil recovery still increased somewhat after the nanocellulose flooding. A negative effect was that the permeability was reduced significantly during the trial. Studies using more environmentally friendly surfactants combined with nanocellulose have been performed. The nanocellulose was combined with anionic sulfonate surfactants in order to decrease interfacial tension (IFT) between oil and water. In combination, the increase of water viscosity and decrease of IFT should result in higher ultimate oil recovery than if only conventional water flooding was applied. Interactions between the nanocellulose and the surfactants have been investigated through adsorption studies, rheology and IFT measurements. A synergy effect between CNF and surfactants upon viscosity of injection water, simultaneous with substantial decrease in IFT, was observed. The results suggest that an EOR system consisting of CNF and sulfonate surfactants is very promising. Many flooding trials using different types of nanocelluloses have been done in the project. The best results gave an oil recovery of 89 %. This is very high. In all trials we have observed reduction in permeability in varying degree. This was caused by some nanocellulose particles or aggregates that were to big to flow through the cores. If this problem is solved, nanocelluloses may have a large potential in connection with EOR.

Commercial production of nanocellulose is now established or under way, with Norway as one of the leading nations both scientifically and industrially, and products containing nanocellulose are entering the market. Industrial production and utilization of nanocellulose is still in its initial phase, with large potential for new innovations. In oil field industry there is a need for greener and more biobased alternatives for oil field applications. Therefore, use of nanocelluloses to improve the oil recovery in a sustainable manner is advantageous for both research areas. The knowledge base gained in GreenEOR is an excellent basis for the continuation of research on utilizing nanocellulose in this novel application. In todays' society, a transition into a more biobased economy is in focus. With more research on the use of nanocelluloses in EOR, it is envisioned that this will contribute to establishment of industrial activities and increased employment in the biobased sector.

The vision of the GreenEOR project is to contribute to enhanced oil recovery in a sustainable manner, by developing a novel series of green fluids for chemical EOR applications based on nanocellulose, alone or in combination with other EOR components. Nanocellulose is a group of nanoscaled particles produced from wood, and is thus an abundant and green resource. The material is still on the research stage, but industrial production has started and is expected to grow as application areas are established. Nanocellulose has a promising potential as a green flooding additive (excellent viscosifying and shear thinning properties, hydrophilic particles, excellent possibilities for chemical modification, particle character instead of dissolved polymers), and this potential will be explored in the GreenEOR project. In order to succeed, the nanocellulose particles (cellulose nanofibrils and cellulose nanocrystals) must be designed to have adequate dimensions and surface chemistry. Nanocellulose may alone give increased oil recovery, by increasing viscosity and/or changing flow pattern. Synergistic effects on EOR can be obtained by combining nanocellulose with other additives. The project will examine and evaluate anticipated critical issues for use of nanocellulose in EOR, such as flooding capability, synergistic rheological modulation, pore bridging and resistance to microbial degradation. The project will explore both pure nanocellulose-suspensions, as well as nanocellulose in combination with other components. The development will depend on close cooperation between different research areas comprising nanocellulose, surface interaction, rheology and core flooding. Leading specialists within all these fields are represented in the GreenEOR project.