Hydrochemical Features of a Geothermal Test Well in a Volcanic Caldera, Mt. Pinatubo, Philippines

Abstract

Mt. Pinatubo is one of several recent-age volcanoes along
the west Luzon volcanic arc. A fumarole near the suminit
emits gases with magmatic characteristics. Several thermal
springs on the east and west flanks yield various fluid typos,
including neutral chloride and bicarbonate. Three wellbores
probed the Mt. Pinatubo caldera from elevations of +1230
through -1600 mRSL. Trajectories may be described i W
central, crossing a boundary wall from the inside, and skirting
a wall [probably] on the inside. Brine discharges indicate
severe evapo-concentration effects accompanied by other
phenomena. Severity of evapo-concentration indicates low
fluid mobility near the wellbores. Large variations for ratios of
component concentrations were observed, indicating negligible
natural circulation (mixing). Implications about fluid
movements and heat transfer processes are explored. Three
components of steam can be quantified and all are significant:
separate entry, adiabatic boiling, and boiling by rock heat.