## Abstract

The partial pressures of CO_{2}, H_{2}S and H_{2} in geothermal reservoir waters are fixed by temperature-dependent mineral equilibria. The dissolved gases have a significant effect at which depth the rising hot waters start to boil, if their temperature exceeds 250°C and, particularly, when it exceeds 300°C. The following functions describe the temperature dependence of P_{CO2 }, P_{H2S} and P_{H2 }, respectively: log P_{CO2 } = -2.81 - 5012.7T^{-1} - 0.00919T + 6.464 log Tlog P_{H2S(s)} = -18.75 - 24738.9T^{-1} - 0.10133T + 43.170 log Tlog P_{H2S(d)} = -2.76 - 5758.2T^{-1} - 0.00850T + 6.359 log Tlog P_{H2(s)} = -10.14 - 17763.1T^{-1} - 0.04084T + 23.368 log Tlog P_{H2(d)} = 9.85 + 7290.3T^{-1} + 0.07202T - 22.651 log T. where P is partial pressure (in bars abs.); and T is temperature (in kelvins). Two functions are given for each of H_{2}S and H_{2}. One set (indicated by subscript d) is valid for all waters < 200°C and waters in the range 200-300°C if chloride concentrations are < 500 ppm. The other set (indicated by subscript s) is valid for all waters > 300°C and waters in the range 200-300°C if containing > 500 ppm Cl^{-}. It is considered that the temperature functions are valid for waters in basaltic to acidic volcanic rocks and also for some waters, at least, in sedimentary rocks. The following function describes crudely total gas pressure plus P_{H2O} in geothermal systems: log P_{total} = 0.00543 - 621.4T^{-1}.

Original language | English |
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Pages (from-to) | 319-328 |

Number of pages | 10 |

Journal | Chemical Geology |

Volume | 49 |

Issue number | 1-3 |

DOIs | |

Publication status | Published - 10 Jun 1985 |