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  • Writer's picturePatrizio Raffa

Thinking back to (almost) 10 years of research in enhanced oil recovery (EOR)

Although of the 8 PhD projects that I’m currently supervising, only one is about EOR (a second will start next year), if you ask anyone in my department what is my research about, the answer will be most of the time: EOR.

I don’t like much this label, not only because it does not represent all my research interests, but also because I’m not really married to this research, for reasons that you will better understand by reading this; nonetheless, I earned it because I have been involved in this research since I joined the Product Technology group in Groningen, as a postdoc, in 2011.

Why EOR?

EOR research is driven mainly by one factor: the need to keep up with the increasing demand of energy, chemicals, and materials, as fossil resources decrease. Needless to say, the main push comes from oil companies and their entourage (i.e., chemical companies that produce polymers or surfactants for EOR). But of course, its relevance goes beyond that, as our current society cannot exists without fossil fuels.

Sure, research in green, renewable, sustainable, bio-based alternatives to fossil fuels, is nowadays very active, and every day it makes important progresses. However, when we look at the worldwide energy consumption data, it is clear that the day when we will completely replace fossil fuels is still far to come: more than 75% of the total energy still comes from oil, gas and coal, and the total consumption of these resources still increases every year.

Additionally, today we consume renewable sources at higher rate than they regenerate, making them already insufficient. To testify that, Earth overshoot day comes currently in August, and it’s earlier every year (in 2020 the trend is opposite, but it is clearly a temporary effect due to the COVID outbreak).

Polymer science is also looking closely at recycling and end-of-life fate of plastics, rubber, and composite materials, trying to achieve closed-loop economy and carbon neutrality as much as possible. This research has received less focus than biobased polymers, as recently pointed out by an interesting review. This is also not enough.

From all this, it is clear that parallel to the mentioned research, we still need to get our hands dirty with research in oil recovery methods. In other words, despite not being “trendy”, research in EOR “it’s a dirty job, but somebody’s gotta do it”. As said before, the push comes mostly from oil companies, as governments and public research funds are much more dedicated to renewables. And this is probably right, as we should not forget that fossil fuels are the major responsible of anthropogenic carbon dioxide emissions, and lookind ahead we absolutely need to abandon them as source of energy. I can imagine that, if we will become very efficient with recycling, it will be still ok using them to produce polymers, but we are getting in a very speculative territory here.

Also, as a side note, you will find many engineers involved in such a research, but not as many chemists or polymer scientists, or at least this is my impression so far, and it may be limited to Europe. My personal opinion is that this is why we still use pretty much the same polymers for EOR that we used back in the 70s. But maybe it is just because they work, and they are damn cheap!

What is my EOR research about?

As I wrote above, I came to Groningen in 2011 to work on a 2-years postdoc project on EOR, under the supervision of Prof. Francesco Picchioni. He had got a grant with the Dutch Polymer Institute (DPI), financed by Shell and SNF, to develop polymeric surfactants for this application. He had a simple but interesting research question: polymer flooding and surfactant flooding are among the most used EOR methods, alone or in combination. So, what happens if we put their function in a single molecule, in other word, in a polymeric surfactant? The answer to this question is tricky, as the polymers and surfactants have completely different recovery mechanisms, but I will not go too much in the details. If you are interested you can read several reviews on the subject.

So, I worked on this project for those 2 years, that later became 3. Then the project was concluded, but I stayed here in Groningen with another postdoctoral contract. During that time, I did many other things, but still some leftover EOR work continued, in the form of co-supervising students with Francesco.

And still today, I continue this research on my own, mostly within another DPI project, this time as a PI and supervisor of a PhD student, Alex. From next year, again with Francesco, I will be supervising a CSC scholarship PhD.

Intermezzo: my view on EOR research and applied research in general

It is worth noticing that of all the papers that I have published so far in my “EOR” research (about 10 research articles), only the one just published (5 years after I finished the experiments!), contains an actual testing of my polymers for the real application. This is because my main interest in this research has been since the beginning a thorough investigation of the synthesis and physico-chemical characteristics of these kind of polymers, and how these will depend on the polymer structure.

For me the research in EOR was never about finding a new polymer for the application that would outperform the currently used ones. This should be at most the concern of the companies paying for the research, but as an academic I didn’t really care about that. Of course, in my research I tried to optimize the structure of our polymers to meet the requirements needed for the application (for example retaining viscosity in conditions of high salinity), but this interested me only as an answer to a scientific question (why and how the salinity influences the properties of the polymer in solution?). Sure, if the new polymers show promise in the application, that is welcome progress, but increasing knowledge and understanding the behavior of the polymers is what scientific research is (or at least should be) really about, even when it is applied.

As many of my projects are in collaborations with companies, and aimed at developing new industrial products, I have often seen this attitude: the goal is making a new product, better and cheaper than the existing ones, as quick as possible, beating the competitors, and possibly patent it. The scientific curiosity, trying to understand how things really works, comes after. Actually, I have seen this sometimes more in fellow academics, than in researchers working at the companies, which saddens me a little.

Back to my research

So, to go back to the main topic here, more than making a polymer that would work better than others, I wanted to understand what principles would make it work better. Also, this is very clear in EOR research, you can never find something that works better in absolute sense. Every reservoir is different from another (for type of rocks, heterogeneity, porosity, presence of fractures, temperature, composition of oil present, etc…) and what works best for one, may be the worst choice for another. In this research, what interested me the most, were the polymers themselves.

Polymeric surfactants, or as I prefer to call them now, amphiphilic polymers (because not always they are surfactant, but they always are amphiphilic…) are a very interesting class of macromolecules: they have useful properties, complex aggregation behavior, stimuli-responsiveness, and all is very dependent on which kind of structure they possess (for example a block structure, rather than a random distribution of monomers).

I am still today fascinated by them and interested in explore them, beyond their possible application in EOR, or any other field.

The initial outcome of my research is represented by two papers purely about structure-properties relationships: how the architecture (diblock, triblock and star block) and the polymer molecular weight and composition (specifically blocks length) would influence the rheological properties in water solution (the ones most relevant for EOR application). From a detailed rheological study, I was able to indirectly confirm that, regardless their molecular structure, block copolymers of polystyrene and polymethacrylic acid (as sodium salt) form stable spherical micellar aggregates, and their rheology is a direct consequence of this structures. Later on, we were also able to visualize these micelles by cryo-TEM, and their semi-ordered structure in a concentrated gel-like solution. In my opinion the beautiful images we got (you can find analogous ones in the gallery section of this website), didn’t get the attention they deserved (but I think this about all my work… who doesn’t?)

Another important observation was that these polymers are not surface active (that’s why we cannot call them surfactant). And I had also noticed that the viscosity was greatly (and negatively for EOR) affected by salinity and pH. Therefore, further subsequent work was dedicated to introduce monomers that would not be salt or pH sensitive, such as PEG-acrylate or glycerol mono methacrylate (check also this one), that can be obtained by hydrolysis of glycidyl methacrylate, a commercial and widely used compound. These, let’s call them “second generation” amphiphilic polymers for EOR, were also surface active, as they were supposed to be according to the initial plan.

On a side note, the pH and salinity responsiveness of these polymers, gave me the idea of using them as smart materials for sensing, and this is at the basis of a nice collaboration with Prof. Andrea Pucci, a dear friend working at the university of Pisa.

Anyway, few years into this research, a proof that my polymers could be used in the real EOR application was still lacking. It took some time to obtain core flood experiments, because large amounts of polymer are required and the experimental setup is rather challenging, for a group that is not specifically expert in that (let’s remember I’m an organic chemistry, turned into a polymer chemist). To make a long story short, some preliminary promising results are there. You can read all about it in my recently published work here. It was a difficult work to publish, it came back several times, rejected from 2 journals and with 4 rounds of revisions from the one that finally published it. I was also invited to submit a cover from the first one, but as the work was finally rejected in the second round of review, of course it was not published. Since I am quite proud of what I had made, I like to show it here below.

If you scroll through my publications, you will see some more work in EOR, done helping out some of Francesco’s students, or writing reviews and even a book with my colleague and dear friend, but most of all favorite drinking buddy, Eng. Dr. Pablo Druetta. And surely there is more to come, as we are just one year in Alex’s PhD, which is a follow up of the work described so far, and a CSC scholarship PhD on the use of some special nanoparticles for EOR, is about to start.

Looking at the future, I certainly want to continue research with amphiphilic polymers, but possibly moving towards other kind of applications, in particular smart materials for applications in robotics, electronics, and medicine (such as drug delivery systems), and of course always looking at the more fundamental aspects of synthesis and properties.

If you made it to this point, I wish to thank you very much for reading!

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