| Title | Gas Equilibria Controlling H2s in Different Philippine Geothermal Fields |
|---|---|
| Authors | Farell Siega, Noel Salonga and Franco D'Amore |
| Year | 2000 |
| Conference | World Geothermal Congress |
| Keywords | gas equilibria, steam fraction, reservoir temperature, Philippine fields |
| Abstract | The reservoir temperature and mass steam fraction ìyî can be evaluated through the simultaneous use of two gas equilibria reactions. This approach has been applied in selected Philippine geothermal field with the objective of finding suitable gas equilibria reaction, which would best characterize each field. The previous work on gas equilibria deals with the use of Fischer-Tropsch-pyrite/magnetite (FT-HSH1) reactions. In this study, the correlation of Fischer-Tropsch with pyrite-hematite (FT-HSH2) and pyrite-pyrrhotite (FTHSH3) reactions was considered which generated two additional grid diagrams. As in FT-HSH1, the variation in calculated reservoir parameters with time and the distribution of data points within the grid indicates reservoir processes such as steam addition and dilution by cooler fluids like reinjection fluid and meteoric water. The evaluation indicates that FT-HSH2 gave good correlation in mature hydrothermal system such as Tongonan, Mahanagdong and Palinpinon. It generally reflects the reservoir condition in these fields. All three gas equilibria methods, however are not applicable in highly degassed system such as Mt. Apo. Likewise, it gave inconsistent trends in mature system where acid-SO4 fluids are present such as in Mahanagdong-B, Bacon-Manito and Labo. In magmatic systems such as Pinatubo, Biliran and Alto Peak, the developed gas equilibria methods were able to delineate the characteristics of fluids in these areas. Acidic wells with significant magmatic contribution indicated relatively high reservoir temperature but lower steam fraction. Those wells with neutral-pH fluids but high gas content generally showed high steam fraction but lower temperature. |