Did you know that the North Sea is full of half-eaten apples?
Not literally of course, but I compare it with half-eaten apples because today we can only extract around 50 % of the oil on average. In other words, half of the oil is still remaining in the North Sea petroleum reservoirs. Discovering new fields is difficult, and drilling new wells is expensive. Would it not be a lot better if we could just extract as much oil as possible from existing fields?
Figure 1 – This is what the petroleum reservoirs in the North Sea looks like – a whole bunch of half-eaten apple. Photo courtesy Exhibition A.
The reason why it is not currently possible to extract 100% of the oil is that a petroleum reservoir consists of many small pores and cavities where the injection fluid cannot reach. There can also be a lot of oil that sticks to the rock grains (Figure 2) and therefore cannot be produced. If you think about adding up the surface area of all of these rock grains in the reservoir, the volume of immobile oil can be very large. One of my goals as a reservoir engineer is to find a way to “peel” off that oil and push it towards the production well.
Figure 2 – Illustration of how the oil is stuck in the reservoir. Figure from ntnutechzone.no
In this research, we return to the nature. To bring the analogy even further – apples hang on trees. If you break a tree down to its tiniest fragments, you find cellulose. Cellulose is the main component of plant (tree) cell walls, and by utilizing it in the nanoscale (nanocellulose), they have a potential as an oil recovery technique. Specifically, I am working with a research team to develop nanocellulose particles that will help produce more oil when they are injected into the petroleum reservoirs.
Figure 3 – From tree to cellulose. Photo by Per Olav Johnsen, PFI.
Figure 4 – Nanocellulose are tiny fibrils of cellulose that are in the nanoscale range. SEM-image by Per Olav Johnsen, PFI.
The nanocellulose particles are non-toxic, biodegradable and sustainable. The goal is to inject the particles together with seawater into the reservoir. A petroleum reservoir consists of micron sized pores, and it is therefore important that the injected particles are smaller than this, i.e. that they are in the nanoscale range (see Figure 5). The nanoscale means that the nanocellulose particles have widths between 1 nanometer (nm) to 100 nm. To put that into perspective, a fingernail grows 1 nanometer per second.
Figure 5 – Comparison of macro, micro and nanoscale.
One characteristic of nanocellulose is that it makes water thicker. You can think of it as transforming the water to toothpaste or syrup (even though the difference is not as extreme in reality). The thicker water will move more slowly through the reservoir and be able to sweep more of the reservoir. If we are able to push out only 1 % more oil (in other words, eat more of the apple), it will have a huge economic impact for the Norwegian society.
Norway is a wealthy country to live in because of the oil. However, many people think that oil does not relate to them or that it is only used to fuel cars. That is not true. Petroleum is necessary for many products including cosmetics, cleaning products, plastic, clothing (synthetic fiber) and roads (asphalt) just to name a few. Since the oil is so present in our everyday life, it is important to be able to extract as much oil as possible from the reservoirs, and to be able to do it in an environmental-friendly way.
Would you take two bites of an apple and afterwards just throw it away? I doubt it. I am a person who likes to eat the whole apple, so I want to make a change regarding all those half-eaten apples in the North Sea.
The injection of nanocellulose as a new enhanced oil recovery (EOR) method is part of a project called Green High Performance Systems for Enhanced Oil Recovery (GreenEOR). This project is funded by the Norwegian Research Council and initiated and led by the Paper and Fibre Research Institute (PFI) in Norway. The experimental work is performed at PFI and the Department of Petroleum Engineering and Applied Geophysics at NTNU.
This blog entry was written byPhD Candidate Reidun Cecilie Grønfur Aadland
Department of Petroleum Engineering and Applied Geophysics