| Title | Tongonan Geothermal Reservoir Liquid Saturation Evolution Using Gas Geochemistry |
|---|---|
| Authors | Alvin Remoroza |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | Gas Geochemistry, FT-HSH, H2/Ar, CO/Ar |
| Abstract | Understanding temporal changes in Tongonan reservoir liquid saturations using geochemical techniques allows us to optimize and forecast energy extraction and reservoir performance. Tongonan has been operating for more than 40 years, originally produced two-phase fluids at the wellhead from a liquid-dominated reservoir, boiled due to production-related pressure decline and began to produce excess steam eventually some wells produced 100% steam. Downhole and surface measurements of pressure, temperature and enthalpy were used to validate the y-grid gas geothermometry analysis. Temporal changes in the reservoir steam fractions showed periods of extensive reservoir boiling from the start of production up to 2005 (increase from3.08% to 5.3%) and brine reinjection returns in 2015 (decrease to 2.65%). Time series analysis of the y-grid gas geothermometer found a good correlation between reservoir steam fraction and production enthalpy. The less than 15% reservoir steam fraction is too low to be interpreted as dry-out and superheat at the reservoir conditions. Correlation with field events highlighted significant periods of steam fraction decrease and temperature increase which coincided with extensive drilling activities. Drilling water added to the reservoir may have collapsed steam zones and decreased the reservoir steam fraction, while increased extraction from the newly drilled wells induced hot deep fluid upflow. In another period, an earthquake that occurred beneath the resource may have caused some change in deep hydrology and recharge. |