MODELING OF GEOCHEMICAL INTERACTIONS BETWEEN ACIDIC AND NEUTRALFLUIDS IN THE ONIKOBE GEOTHERMAL RESERVOIR, JAPAN

摘要

Two types of fluids are encountered in the Onikobegeothermal reservoir, one is neutral and the other isacidic (pH=3). It is hypothesized that acidic fluidmight be upwelling along a fault zone and that animpermeable barrier might be present between theacidic and neutral fluid zones. We carried outreactive geothermal transport simulations usingTOUGHREACT (Xu and Pruess, 1998 and 2001) totest such a conceptual model. One-dimensionalmodels were used to study the geochemical behaviordue to mixing of the two fluids. Mn-rich smectiteprecipitates near the mixing front and is likely toform an impermeable barrier between regions withacidic and neutral fluids.