| Abstract |
The local meteoric water line for the Bacon- Manito Geothermal Production Field may be represented by the equation: $H = 8*d80 + 13.4. Based on the analysis of the available data, most of the thermal waters within the msource were derived from rainwater. The isotopic signatures of the acid-sulfate springs indicate steam-heating and am affected mainly by evaporation. The lake waters were also affected by evaporation, except for Lake Naghaso which apparently has deep brine component and is affected by steam-heating. Similarly, the neutral-chloride springs have deep- fluid signatu=. The Bacman Geothermal Prrxlucton Field is comprised of a single geothennal system, which is centered within the Botong atea. The Osiao- Pangas (OP) wells tap the center of the resource and encounter fluids which are already products of boiling of the parent water. The parent water, which closely resembles OP-4D, has an isotopic composition of d80 = +2.0 % and 62H = -26.0 %. The fluids at the upflow are isotopically enriched (+4.0 %o) and becomes depleted (-3.9 560) as it outflows towards nodhnodhwest in the central Palayang Bayan and southwest in the Cawayan sector. The fluids along the outflow path are products of dilution between meteoric waters and the parent water. Wells situated at the margins, like CN-2RD and CN-3RD are tapping steam-condensate type of fluids. Although there are limited data, the outflow possibly extends towards the Manito area fadher nodh. After seven years of production, the most prominent processes occurring in the resewoir are boiling and dilution. Isotopic trends indicate that the central Palayang Bayan sector has been diluted with fluids coming from rhe western part. This fluid, termed as the Masakmt fluid, is isotopically depleted, slightly coolec less mineralized and has lower gas and boron contents. The effect of dilution is manifested by the depletion of l80 and 2H in the central wells. Although not clearly indicated by the isotope data, boiling could also be occurring in this part of the resewoir. Chemical tmnds, e.g. increasing discharge enthalpy and gas and chloride concentrations, show that boiling does occur in some wells. These mean that the dilution pmess masks the effect of boiling in the isotopic signatures of the fluids. The OP wells, on the other hand, are showing enrichment in the isotopic composifion. As pressures draw down, these wells experience boiling in the msewoir. |