Trends of Fluid Enthalpy based on Solute Geothermometers as Indicator of Reservoir Processes in Tongonan Geothermal Field, Leyte, Philippines

Abstract

The trends of enthalpy based on ph-vsical measurement and solute geothermometer of T(SiO3 and T(Xa-K-Ca) are used as indicator of near-well reservoir processes in Tongonan production wells that have been utilized since 1983. The application of this method on selected wells shows promising results since identijed reservoir processes based on enthalpy trends are consistent with that observedj-om other chemical parameters such as CI trends.

The identijed reservoir processes include the follouing: (I) no boiling or mixing indicated by E-meas = E-nkc = E-silica and exhibited by production wells located near the outflow region in Malitbog sector such as ne11 501, uhich is characterized by liquid-dominated discharge with stable fluid chemistry; (2) localized pressure drawdown indicated by E-meas > E-nkc > E-silica and observed in production uells 1 OZp 106, I I OD and 401 located near the upflow region in Upper Mahiao sector; (3) reinjection fluid mixing indicated bv E-nkc E-meas = E-silica and observed in production wells 105D and 212 located near the reinjection sink of Tongonan-1; (4) reservoir-wide drawdown indicated by E-meas > Enkc = E-silica and exhibited by production wells located in Sambaloran sector such as well 212; and (5) mixing of cooler meteoric water indicated b.v E-nkc > E-silica E-meas and observed in wells 508, 102 and 106.