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

摘要

Two types of fluids are encountered in the Onikobe geothermal reservoir, one is neutral and the other is acidic (pH=3). It is hypothesized that acidic fluid might be upwelling along a fault zone and that an impermeable barrier might be present between the acidic and neutral fluid zones. We carried out reactive geothermal transport simulations using TOUGHREACT (Xu and Pruess, 1998 and 2001) to test such a conceptual model. One-dimensional models were used to study the geochemical behavior due to mixing of the two fluids. Mn-rich smectite precipitates near the mixing front and is likely to form an impermeable barrier between regions with acidic and neutral fluids.