Application of Integrated Multicomponent Geothermometry at the Chachimbiro Thermal Area, a Difficult Geothermal Prospection Case

摘要

Multicomponent geothermometry coupled with numerical optimization is applied to thermal springs of Chachimbiro, Ecuador, to gain insights on the geothermal potential of the area, and to possibly reconstruct the composition of the deep geothermal fluid. Major sources of uncertainty in the chemical prospection of the area arise from the absence of zones of upflow and boiling, which suggests that the Na-Cl thermal end-member is likely affected by mixing with Ca-HCO_3 shallow groundwater and, possibly, by degassing before discharging at the surface. Data from a previous study were used to group and select waters for application of the method. Due to the lack of detailed information on local reservoir mineralogy, different mineral assemblages and equilibration constraints have been applied to estimate thermo-chemical conditions at depth. Numerical optimization with single and multiple waters indicate deep equilibrium temperatures around 260°C, somewhat more than previous estimates (230±5°C) by classical methods. The reconstructed deep water compositions are sensitive to the optimization procedure and choice of mineral assemblage, however the range of estimated temperatures is comparatively less sensitive to these modeling constraints. The variability of results reflects the intrinsic sensitivity of the method to the mineral assemblage selected as representative of the deep reservoir, which is typically poorly known in newly prospected geothermal areas.