0

# EOS7 - Specifying initial conditions

Hi all,

I want to specify this initial condition using EOS7:

• Reservoir temperature: 240 degC
• Chloride concentration: 600 ppm weight = 0.06%-wt
• CO2 concentration: 0.5%-wt
• Steam fraction: 0.1

I know that EOS7 in a strict sense handles NaCl brine and air, but in the TOUGH2 user's manual it is stated that (Sec. 6.6, pg. 40):

"(In EOS7) The brine is modeled as NaCl solution, while the non-condensible gas is air, although the treatment could be adapted, with minor modifications, to other brines and gases."

For 2 phase conditions the primary variables are (gas phase pressure, brine mass fraction, gas saturation+10, temperature). My questions are:

1. How do I specify an air mass fraction that represents a 0.5%-wt of CO2?  Is it by using an air mass fraction that has the same partial pressure as 0.5%-wt of CO2, adding this partial pressure to Psat(T=240 degC of pure water) and setting this sum as the gas phase pressure (PV1)?

2. For the chloride, EOS7 default brine has 24.98%-wt NaCl, so I guess to get 0.06%-wt I need to specify a brine mass fraction of 0.06/24.98 = 0.0024, right?

Manuel

5replies Oldest first
• Oldest first
• Popular
• Manuel Rivera
• Geothermal reservoir engineer at Mercury NZ Ltd.
• Manuel_Rivera
• 3 yrs ago
• Reported - view

And by the way, I have decided to use EOS7 instead of EWASG because I don't want to simulate changes in porosity and permeability due to salt deposition.

Like
• Dear Manuel,

I suggest you look into using ECO2N V2 (see attached).   -Curt

Like
• Manuel Rivera
• Geothermal reservoir engineer at Mercury NZ Ltd.
• Manuel_Rivera
• 2 yrs ago
• Reported - view

Thank you Curt Oldenburg , I will take a look at it.

Like
• Dear Manuel,

I think EWASG was definetely a better choice than EOS7 for your probleam, dealing with a mixture of water, NaCl and CO2.

To simulate CO2 with EOS7 you should actually modify the coding of NCG thermophysical properties in EOS7 including that of CO2 to replace those used for air. Which is not strightforward.

If solid salt precipitation occurs, the 'active' porosity (or the porosity available for fluid phases) will be reduced in EWASG. But you can avoid the effects on permeability by setting IE(11)=0

IE(11) = 1: *** ALLOWS CHOICE OF DEPENDENCE OF PERMEABILITY ON ACTIVE FLOW POROSITY.
= 0: PERMEABILITY DOES NOT VARY WITH FLOW POROSITY.

By the way: your initial salinity was very low, just 600 ppm. In order to reach halite saturation you should have an almost complete boiling of initial brine, which is not so easy to occur during a simulation.

Regards,

Alfredo

Like
• Manuel Rivera
• Geothermal reservoir engineer at Mercury NZ Ltd.
• Manuel_Rivera
• 2 yrs ago
• Reported - view

Alfredo Battistelli Thanks, yes it is the proper choice. I decided to use EWASG instead.

Like
Like Follow
• 2 yrs agoLast active
• 5Replies
• 164Views
• 3 Following