A NUMERICAL SIMULATION OF H2O-CO2 HEATING IN A GEOTHERMAL RESERVOIR

Abstract

A computer program in Visual Basic 6.0 is written to calculate steam tables for pure water up to 800?C and 1400 bar. The steam tables are created as a DLL (Dynamic Link Library) object with properties: temperature, pressure, specific volume, enthalpy and entropy for liquid and vapor phases, and liquid-vapor state. The steam tables can be incorporated in any computer program on the Windows platform. Using the steam tables a program is written to simulate the heating of water and carbon dioxide in a geothermal reservoir with varying amount of water, carbon dioxide and alkalinity.
The minerals NaHCO3, Na2CO3 and NaOH may precipitate only in the extreme case while all the water is converting into vapor phase. It is not discussed here.

The pressure in the reaction vessel is, in general, first controlled by CO2, then by water vapor and in the last again by CO2, while all the water is converting to the liquid phase.

On extracting vapor from the reaction vessel, all the CO2 transfer to vapor phase except for highly alkaline fluid (i.e. degassing occurs first). On the other hand in case of extracting liquid, the amount of CO2 in the extracted fluid decreases in case of acidic fluid, whereas increases in case of alkaline fluid. Thus the variation of gaseous species concentration with time may provide useful information on the geothermal reservoir fluid characteristics.