Changes in Water Chemistry from Interaction with CO2 for Storage

[MariaG]

Good Day Everybody,

Hope everyone is keeping safe.

Could someone help with the following problem: in the context of injecting CO2 into a formation for permanent CO2 storage (referred to as carbon capture and storage, CCS), what is the best routine to determine the changes in formation water chemistry (composition and pH) when exposed to the CO2 stream at a specific reservoir temperature-pressure, gas production rate (e.g. 140 Bcf) and % CO2 in the produced gas (e.g. CO2 10%)?

Thanking you in advance,

Maria

[dlparkhurst]

PHREEQC has been applied to CO2 injection for gas storage and oil recovery. I think you could find some investigations in the literature. A quick search also found some postings in this forum.

Here is a simple example that makes a formation brine in equilibrium with halite and calcite with a log10(PCO2) of -2 and 100 atm total pressure, and increases the log10(PCO2) to 1 (10 atm), maintaining equilibrium with calcite. Pitzer.dat is used for the database because of the high ionic strength.

Code: [Select]

SOLUTION
-pressure 100
EQUILIBRIUM_PHASES 1
Halite 0 10
CO2(g) -2 10
Calcite 0 10
SAVE solution 1
END
USE solution 1
EQUILIBRIUM_PHASES 1
CO2(g) 1 10
Calcite 0 10
END


[MariaG]

Thank you for the response.
In order to evaluate all the changes to the water composition and pH due to the introduction of CO2, shall the calcite equilibrium be removed from the simulation?

Many thanks.

[dlparkhurst]

Yes, if you just want the solubility of CO2, then remove Calcite equilibrium.