Changing the wettability in a mature reservoir can often result in renewed production and improved ultimate recovery rates. Welcome to an interview with Geoffrey Thyne, who talks to us today about wettability.
What is your name and your background?
Geoffrey Thyne. I am a geologist and geochemist who started my career working for Arco Oil and Gas back in 1979. I have taught at California State University Bakersfield and then Colorado School of Mines, worked at Enhanced Oil Recovery Institute in Wyoming until starting this company with my partners.
An Interview with Geoffery Thyne from E-Sal
What has been your research focus over the years?
I started in CO2-EOR, then moved into stable isotopes which lead to diagenesis and reservoir quality prediction. I got started in wettability about 10 years ago on a small project concerning low salinity water flooding and was sucked down the rabbit hole of how salinity and wettability interact.
What is wettability?
Wettability is the property of a surface to prefer one liquid phase over another. In our case we are talking about oil and water adhering to rock surfaces in a petroleum reservoir. The most practical aspect of wettability is relative permeability because wettability controls relative permeability, the shape and position of the curves, which control recovery. For example, in water-wet rocks, water flows more easily than oil. Wettability can change during a reservoir’s lifetime as new fluids are introduced, or pressure and temperature change.
What is wettability alteration? what is the purpose? how does it work?
Wettability alteration is the idea that you can change/improve the wettability in your reservoir to produce more oil.
In engineering terms, you want to shift your wettability to neutral wettability, which is the condition where oil and water move equally well. That is neither water-wet or oil-wet.
For many reservoirs, wettability can be shifted by changing the salinity. So, you want to test your reservoir to determine what the current wettability is, see if your oil-brine-rock wettability is sensitive to salinity and what salinity gives you the best results.
Please describe cases in which it has worked very well.
Best known example is Ekofisk field, offshore North Sea. Ekofisk is a giant chalk field under waterflood. The initial pilot waterflood was conducted with reservoir brine and projected recovery at EUR was 30-35%. After switching the injected water to seawater, and lowering salinity, the current projected EUR is 50%. That is an extra 600 million barrels. We have tested this case in the lab and found the experiments agree with the field case. In fact, the operators could further lower salinity to increase recovery even more.
What are your plans for the future?
Get more operators to work with us and continue to refine the process. We don’t know everything about how this works and feedback from the field is essential to move forward. While we will continue to improve the lab tests, keep trying to better understand how the process works, and are developing software to predict field wettability and how to improve it, field results are the best teacher.
Some examples are: SPE 129692, SPE 142690 and SPE 147410.