This paper presents new laboratory data quantifying the catalytic effects of two common nonhydrocarbon contaminants (i.e., CO2 and N2) on the liquid water vaporization process as well as the water vapor content for natural gases at high-pressure, high-temperature (HP/HT) reservoir conditions. We conducted laboratory studies to measure the isothermal, equilibrium water vapor content for seven dry gas mixtures at pressures from 500 to 20,000 psia and temperatures of 300°F and 400°F. Gas mixtures evaluated in our study contained up to 20 mol% of either CO2 or N2 each. Principle results of our laboratory study demonstrate the following phase behavior:
temperature has a significant impact on the water vaporization process and the quantity of water vapor dissolved in a natural gas with no nonhydrocarbon contaminants. Increasing the temperature from 300°F to 400°F increases the equilibrium water vapor content by more than 70% above that for the gas at 300°F;
the presence of CO2 in the gas phase also enhances the solubility of water vapor in a natural gas. Increasing the CO2 content from 5 mol% to 20 mol% increases the maximum water vapor content by 20% to 40%, respectively, above that measured for the same gas with no CO2 These increases were observed at both 300°F and 400°F;
the presence of CO2 in the gas phase combined with higher temperatures further augments water vapor solubility in a natural gas. For example, the equilibrium water vapor content for the gas with 20 mol% CO2 at 400°F increased by 80% above that measured for the same gas at 300°F;
the presence of N2 in the gas phase suppresses the water vaporization process and reduces the quantity of water vapor dissolved in the gas. At 300°F, 5 mol% N2 reduces the water vapor content from 10% to 20% of that for the same gas with no N2. Further increases in N2 content reduce the water vapor content below that for the same gas with no N2;
the enhanced water vapor solubility at higher temperatures counters the suppressive effects of N2 in the gas phase. Increasing the N2 content at 400°F increases the maximum water vapor content from 5% (20 mol% N2) to 10% (5 mol% N2) above that measured for the same gas with no N2.