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# T2Well constant fluid properties and EOS1 relationship?

Hi,

I am currently modelling a wellbore with constant density, thermal conductivity and specific heat capacity thermophysical properties at surface temperature 40 degrees like so:

Wella    2  1665.e00    1.0000  0.1E-07   85.0E-6   0.1E-07   0.6255    4204.0
0.0e-10
1           0.00       .00        1.      1.00
8

Wellb    2  1665.e00    1.0000   0.1e-07  0.00E-11   0.1e-07    0.6255   4204.0
0.0e-10
1           0.00       .00        1.      1.00
8
Wellc    2  1665.e00    1.0000   0.1e-07  85.0E-06   0.1e-07    0.6255   4204.0
0.0e-10
1           0.00       .00        1.      1.00
8

I am also using EOS1 for TOUGH2, with default parameter choices 1, 2, 2, 6 set in MULTI. The fluid is pure water for single phase flow at a constant mass flow rate of 162 kg/s pumped down to 7 km and rises up to surface through wellc.

I wanted to ask how the density, thermal conductivity and specific heat variables of the wellbore fluid is related to the EOS I am using? I can see in the T2Well manual that the drift flux model is calculated using a density mixture (is this the density I have set 1665 kg/m^3?). Under EOS1 in the TOUGH2 manual it also states that for each iteration the water properties are calculated as a function of temperature and pressure but that this is dependent on the phase of the fluid.

Will I have to adjust the constant wellbore properties to consider depths at 6 km? (wellb) or will that affect the thermodynamic equations if I am assuming constant pumping?

Kind regards,

Hannah Doran

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• Dear Hanna,

the parameters listed under ROCKS block are related to wellbore discretization elements, not to the fluid flowing within the wellbore. Fluid properties are computed according to the thermodynamic conditions and EOS module used, in your case EOS1.

Thus, fluid properties will be computed properly by T2Well-EOS1 for the local thermodynamic conditions evolving in time along the wellbore during the simulation.

On the other hand, look carefully to T2Well user's guide to understand which is the meaning of the ROCKS parameters you highlighted in yellow color, when applied to wellbore elements.

Regards,

Alfredo

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The manual states all parameters in ROCKS are the same as how TOUGH2 defines them apart from the first permeability value PER(1), thermal conductivity (negative value for semi-analytical thermal exchange between well and surrounding formation via conductive flow) and a capillary function (= 8). I have changed density, thermal conductivity and specific heat capacity to suit the water properties of EOS1.

Thanks again,

Hannah

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• Dear Hanna,

fluid properties will be computed according to local conditions by the EOS (EOS1 in your case) in all grid elements, either belonging to reservoir or wellbore.

Under ROCKS you assign the rock properties, not fluid properties. Thus, for T2Well runs and for domains assigned to wellbore elements, the values chosen should not make a lot of difference (unless used for other purposes, as PER1). You may try running the same problem with different rock properties for the same wellbore elements and comparing the results.

Regards,

Alfredo

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• Alfredo Battistelli Thank you so much!

I wanted to ask another question if that's okay. Can I set a time dependent surface backpressure as opposed to having 1 fixed pressure in PARAM? For instance, if there is a way to add a managed pressure operation where for a certain time step and temperature the pressure is added onto the initial pressure? Is there a way to do this via a table?

Kind regards,

Hannah

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• Dear Hannah,

if I understood properly your question, you would like to have a variable P boundary, with P varying in time according to some constraint specific of your simulated problem.

As far as I know in TOUGH2 (you posted the question under the TOUGH2 forum) , there is no built-in option in the simulator able to do that.

Constant P boundaries are obtained in TOUGH2 by using elements with an infinite volume. This will fix P, T and phases composition. In principle you might inject/extract fluid or heat to change the P or the T (or both) of an infinite volume element, providing the injection/ectraction rates are computed to reproduce the desired changes. Karsten Pruess already showed how to evaluate the extraction/reinjection rates in order to reproduce a given P or T history.

You might have a look to a document written for Petrasim's users of TOUGH2 implementing Karsten's approach at:

For iTOUGH2, you should have a look to the Stefan's report about enhancements of TOUGH2 supported by iTOUGH2 (see chapter 6):

Regards,

Alfredo

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• Hi Alfredo,

Apologies in the delay to my reply. Thank you so much for your comments! I now have a better understanding on the ROCK properties dependent on the EOS after doing the recommended tests. I have already set a constant P boundary of infinite volume, but yes the issue described above is for a function to be added to alter the pressure with time.

My plan is to transfer this code over into TOUGH3 (changing flow rate REGFX into a GENER of flow rate) so I will look to that manual to see if these pressure boundaries can be applied. If not, the constant pressure will have to remain.

Kind regards,

Hannah

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• Thanks for your.

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