A fluid-inclusion investigation of the tongonan geothermal field, philippines

Abstract

At least 660 fluid-inclusion homogenization temperature (Th) and 44 freezing temperature (Tm) measurements, mainly on anhydrite crystals sampled to 2.5 km depth from 28 wells, record thermal and chemical changes in the Tongonan geothermal field. Interpretations of the Th (175–368°C range). Tm (-0.3 to -12.7°C range) and crushing stage observations indicate that early trapped fluids contained up to ≈2 mol% CO 2 (now measured at <0.4 mol%). reservoir temperatures have decreased by ≈20°C overall (−88 to + 145° C range) compared with minimum Th temperatures, but the reservoir salinity has remained constant at ≈1.7 weight% NaCl equivalent (or 10,000 ppm Cl). In present boiling zones, NaCl dominates the contribution to Tm, and salinity here has increased to 6 weight% NaCl equivalent.