I run a reservoir simulation using ECLIPSE for the case of CO2 injection in a carbonate reef reservoir. Gas production starts in 2014, and CO2 injection starts in 2019, ends in 2029. From our simulation, it is proved that CO2 flooding increases the gas cumulative production for up to 50 years. What I ended up with, is the profile of water cut over production time, which seems like in the Figure I attach. As you can see, it shows a "wild" fluctuation for year after 2040, which I don't understand and can't explain.
From this result, I would like to open a discussion about whether the "wild" fluctuation is caused by what is called, "numerical instability". If so, what factors that causes this fluctuation? And, is the result of this water cut result can be accepted?
I appreciate for your replies. Thank you :)
I think there might be a problem with your initial conditions in the model since they start at 0. You could vary the initial conditions and see if that helps to something small (ie. 0.001) or start the model at a higher value and see if that changes things)
I would suspect that there is some instability in the operations, likely from unclear parameters when integrating and extrapolating the models beyond the dataset. You could apply some regression model to smooth the line out or change the step size. There are alot of different methods for dealing with this, specifically in signal processing. I suggest reworking the model to see if you can try and minimize this first before applying some other method.
Munqith, if you have production breaks the water/gas segregation will cause fluctuations. You have similar early on 2018 also. LGR around the wells may mitigate some of these effects. If you have hysteresis option turned on, some of these fluctuations maybe due to the relperm change between imbibition and drainage cycle.
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