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H2S vs CO2.


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Hi Guys! 

 

Sorry for English. Friend (russian) of mine suggested me to use this platform for the chemical related question. Hopefully someone will understand and help me.

 

I'm working for oil and gas company and i'm going to drill an exploration well at the unknown area.

 

So, the situation is:

 

  • Well will be drilled down to 4250m TVD/MSL (true vertical depth/mean sea level). Offshore with 1700m of water depth. Thus only 2550m of formation (earth, ground) will be drilled. We will drill thru the claystone, salt and thru the CARBONATE reservoir. 900m of reservoir full of gas.
  • Top of reservoir at 3340m. Bottom at 4200m. Carbonate reservoir.
  • Reservoir is absolutely permeable porous formation. Full of dry gas. Dry gas means Methane. CH4. Concentration is not known. Some small part of C2, C3, C4 can exist, but not to much. Based on the offset data (wells around, to far, but still some information) and geological information (comparison, seismic data and so on) we predict gas with 0.24 s.g. (specific gravity/water) at the reservoir conditions. Note: we use specific gravity, but not density. Methane 0.55SG / air at standard conditions. Or water related if we speak about gas at reservoir conditions. It's simplify other (pressures) calculations on the later stage.
  • Reservoir conditions: 80 deg C, 444bar at 3340m and 464bar at 4200m. Gas 0.24sg/air.
  • Sour gas. Up to 200-500ppm of H2S confirmed by other offset wells in the region. The presence of CO2 is likely in case of H2S occurrence (usual sour gas association in carbonate reservoirs).
Question: 
Is there any way to predict CO2 concentration depending on H2S concentration (%, ppm)?
 
Thank you guys for any help and explanations!
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Hi Guys! 

 

Sorry for English. Friend (russian) of mine suggested me to use this platform for the chemical related question. Hopefully someone will understand and help me.

 

I'm working for oil and gas company and i'm going to drill an exploration well at the unknown area.

 

So, the situation is:

 

  • Well will be drilled down to 4250m TVD/MSL (true vertical depth/mean sea level). Offshore with 1700m of water depth. Thus only 2550m of formation (earth, ground) will be drilled. We will drill thru the claystone, salt and thru the CARBONATE reservoir. 900m of reservoir full of gas.
  • Top of reservoir at 3340m. Bottom at 4200m. Carbonate reservoir.
  • Reservoir is absolutely permeable porous formation. Full of dry gas. Dry gas means Methane. CH4. Concentration is not known. Some small part of C2, C3, C4 can exist, but not to much. Based on the offset data (wells around, to far, but still some information) and geological information (comparison, seismic data and so on) we predict gas with 0.24 s.g. (specific gravity/water) at the reservoir conditions. Note: we use specific gravity, but not density. Methane 0.55SG / air at standard conditions. Or water related if we speak about gas at reservoir conditions. It's simplify other (pressures) calculations on the later stage.
  • Reservoir conditions: 80 deg C, 444bar at 3340m and 464bar at 4200m. Gas 0.24sg/air.
  • Sour gas. Up to 200-500ppm of H2S confirmed by other offset wells in the region. The presence of CO2 is likely in case of H2S occurrence (usual sour gas association in carbonate reservoirs).
Question: 
Is there any way to predict CO2 concentration depending on H2S concentration (%, ppm)?
 
Thank you guys for any help and explanations!

 

 

Охренеть - вопрос. Компликейтед энд диффикулт - эт точно сказано! Что ви хотеть от chemists, там, где geologists должны мазу тянуть?

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There is no way to measure it...the well is not drilled yet. The idea is to predict CO2 concentration based on any logical hypotheses and data we have. Geologist won't help with that as it is purely chemical question. 

 

Perhaps i've provided excess of information. Let me try to simplify:

 

  1. There is a pure Methane with 500ppm of H2S
  2. Gas is trapped inside porous carbonates. CaCO3
  3. 80 deg C, 450bar, no light, time 70M years

Questions for chemists: 

  1. Does it react? CaCO3+H2S=CaS+HOH+CO2
  2. Any possibility to calculate CO2 (%,ppm,mol...anything) based on H2S?

Thanks

Ссылка на сообщение

There is no way to measure it...the well is not drilled yet. The idea is to predict CO2 concentration based on any logical hypotheses and data we have. Geologist won't help with that as it is purely chemical question. 

 

Perhaps i've provided excess of information. Let me try to simplify:

 

  1. There is a pure Methane with 500ppm of H2S
  2. Gas is trapped inside porous carbonates. CaCO3
  3. 80 deg C, 450bar, no light, time 70M years

Questions for chemists: 

  1. Does it react? CaCO3+H2S=CaS+HOH+CO2
  2. Any possibility to calculate CO2 (%,ppm,mol...anything) based on H2S?

Thanks

 

For a long time, the gas phase, the temperature is not high. For the calculation of the equilibrium constant, we can use standard thermodynamic parameters of substances.
 
ΔH(CaCO3) = -288.45 ΔS(CaCO3) = 22.2
ΔH(H2S) = -4.82 ΔS(H2S) = 49.15
ΔH(CaS) = -115.3 ΔS(CaS) = 13.5
ΔH(H2O) = -57.80 ΔS(H2O) = 45.11
ΔH(CO2) = -94.05 ΔS(CO2) = 51.06
 
ΔG = ΔH - T*ΔS = 26060 - T*38.31
T = 353 K
ΔG = 12.54 kcal/mol = 52.67 kJ/mol
 
ln(Kp) = -ΔG/RT = -17.89
Kp = 1.7*10^-8
Kp = P(CO2)^2/(P0(H2S) - P(CO2))
P0(H2S) = 500/1000000*450 = 0.225 bar = 22500 Pa
 
P(CO2)^2 + 1.7*10^-8*P(CO2) - 0.0003825 = 0

 

P(CO2) = 0.0195 Pa 

 

If I never made a mistake, the pressure CO2 is totally negligible.

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А можно в общих чертах? :)

 

 

Насколько я понял - метан, содержащий 500 ppm сероводорода находится в ловушке из пористого кальцита под давлением 450 бар при 80С.

Вопрос - скока там CO2 накопится при реакции сероводорода с кальцитом. 

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У метана критическая температура сжижения -82С вроде, значит там он не в сжиженном состоянии.

Чет какой-то странный подход. Сероводород рассматривается вроде как продукт выветривания гипса. 

И реакция эта:

 

 

Does it react? CaCO3+H2S=CaS+HOH+CO2

Какой то обратный процесс выветривания. Только там наверно гидросульфит какой-нить.

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У метана критическая температура сжижения -82С вроде, значит там он не в сжиженном состоянии.

Чет какой-то странный подход. Сероводород рассматривается вроде как продукт выветривания гипса. 

И реакция эта:

Какой то обратный процесс выветривания. Только там наверно гидросульфит какой-нить.

 

Про сжиженное состояние никто и не толкует. 450 атм при 80С. Давление, правда высокое изрядно. 

Откуда из гипса сероводород возьмётся? Только серобактерии какие-нить могут восстановить. 

Да и вопрос не об источнике сероводорода, а о вероятном составе газа.

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Вообще-то сероводородная кислота чуть слабее угольной, а CaCO3 гораздо менее растворим, чем H2S, т.е. никакой реакции не будет. Тем более там должны быть сухие условия, т.к. при появлении воды, тут же образуется Ca(HCO3)2, который наверняка устойчив при таком давлении CO2. 

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