# PhreeqcUsers Discussion Forum

## Beginners => PHREEQC Basics => Topic started by: webster66 on July 12, 2018, 12:21:00 AM

Title: H2S(g) input
Post by: webster66 on July 12, 2018, 12:21:00 AM
Hello all,

I am trying to speciate some wells and need help on how to input the H2S(g) concentration. The data that I am using measured H2S(g) in mg/L at STP but the wells are oil brines that can reach pressures and temperatures up to 500atm and 150C, respectively.

In case it helps, I also have sulfide and sulfate data along with the main chemical species measured in chemical analysis. As well as CO2(g) and CH4(g) concentrations in mg/L.

Title: Re: H2S(g) input
Post by: dlparkhurst on July 12, 2018, 12:50:07 AM
There are a couple options available for sulfide. (1) You can enter the total concentrations of sulfide aqueous species by entering S(-2) in the SOLUTION definition, or (2) you can specify the log10 partial pressure of H2S(g) that is in equilibrium with the SOLUTION as follows:

SOLUTION
S(-2) 1 H2S(g) 0.5

This definition specifies 10^0.5 atm partial pressure of H2S(g). The total S(-2) will be a function of the temperature of the solution, and if Peng Robinson is used (phreeqc.dat, Amm.dat), the pressure.

Similarly, you can specify C(-4) or partial pressure of CH4(g), and C(4) (Total Dissolved Inorganic Carbon) or partial pressure of CO2(g).

Other alternatives use REACTION, EQUILIBRIUM_PHASES, or GAS_PHASE, REACTION_TEMPERATURE, or REACTION_PRESSURE to reconstitute the downhole conditions.

This thread may be of interest:
http://phreeqcusers.org/index.php/topic,1018.msg2948.html#msg2948