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# Pressure vs CO2 DG

Hi everyone,

I've asked my self a question that i can't find a plausible answer, i hope that you can help me with this.

It regards to CO2 injection at 15 ºC and 33 MPa on a reservoir [density=2300kg/s; por=0.2; per=129 mD, CWET=2.51W/(mW) and SPHT=1000 J/(kg/k)].

On pressure graph there is a pick before ir raises continuously, at the first months of injection.

The DG graph doesn't have the same pick, although it should be softer than the pressure one, because of the temperature fall.

Why both graphs doesn't show similar behaviour in the first times of injection?

Can anyone help me with?

Thank you so much for your help.

Luis

Best Regards,

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• Luis,

Before I attempt to answer your question, there are a few pieces of information I need to know:

1. Where exactly in the reservoir (i.e., distance from the well) are these plots based upon?
2. Are the number of symbols on your graphs indicative of the number of points used to generate the plots?  In other words, are you plotting more pressure values over the same time span than you are density points?
3. If you changed the y-axis scale on your density plot with, say, the minimum value being around 800 kg/m^3, do you see any evidence of early time fluctuations?

I don't pretend I'll know the answer to this after you check on these items, but it'll help me narrow things down a bit.

Thanks!

- Mikey

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• Hi Mickey,

Thank you very much!

1. These graphs are from the injection cell (the cell where the well is located), so i assume that there is no distance between the well and the reservoir, but i don't know if it is right or not...;

2. That's a good question...in fact i don't know why it did happen because my MCYPR is 16 steps to plot and print so it should be the same for both, i think;

3. I've done what you suggested and i din't see any time fluctuations..

Thank you very much,

Luis

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• Hi Mickey,

Thank you very much!

1. These graphs are from the injection cell (the cell where the well is located), so i assume that there is no distance between the well and the reservoir, but i don't know if it is right or not...;

2. That's a good question...in fact i don't know why it did happen because my MCYPR is 16 steps to plot and print so it should be the same for both, i think;

3. I've done what you suggested and i din't see any time fluctuations..

Thank you very much,

Luis

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• Luis,

Sorry about the delay.  I'm not entirely sure about why this isn't noted in gas density, but I would expect there to be early fluctuations in pressure due from having to overcome the capillary entry threshold.  Once the water surrounding the well is displaced by the injected CO2, you'll have a single-phase stream exiting the well, which will require a smaller pressure gradient to maintain the set flow rate.

You originally mentioned that you set your model to inject at a constant pressure (33 MPa), but is it possible it's set to inject at a constant rate instead?  If not, I don't see why your pressure plot wouldn't just be held constant at 33 MPa at the well.

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• Hi Mickey,

Thanks a lot for the explanation. In fact it is set for constant injection rate.

Thanks a lot,

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• Hi  luis ,

I have an input file where CWET for one of the rocks is negative, -2.15. I would like to ask you if you what this means. Also, the density for one of the rocks is 2600e3, while for the rest is only 2600. Does this have a meaning? Thank you in advanced!

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• Jose,

if you are using T2Well, it would probably mean that domain belongs to a wellbore section for which you want the calculation of wellbore heat exchange using the analytical formulation by Ramey.

A very high rock density is usually used to enforce a constant T. The same for the specific heat. Better to use the latter, as it should not alter the heat balance printed by sub BALLA.

Regards,

Alfredo

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