For geothermal pourposes I am researching waters related to Cretaceous limestone-dolostomes and sandstones not too far of an inverse fault. The temperature at surface conditions is of 19 ºC (water for drill after 24 hours of pumping) that is quasi equal at the temperature estimated using the local geotherm, but I get a reservoir temperatura of 39 ºC using the silica-quart geothermomer. The Saturation index of quartz is oversaturated =0.35.
Thanks Mathias for your quick replay. I have used the Calcedony thermometer and I get a temperature lower than the surface temperature so I think it doesn't work properly. The same for the amorphous silica (I get negative values).The saturation index for both mineral phases are subsaturated and out equilibria. My doubt is if silica-quartz geothermometer is a good option to estimate the reservoir temperature or the sobresaturation indicates there is no quartz in the aquifer.
Best wishes
Javier
SiO2 Quartz and SiO2 Chalcedony are well known and mostly applicable geochemical thermometers for the evaluation of reservoir temperature of the geothermal system. SiO2 Quartz is applicable where reservoir temperature is exceeded 100 degree centigrade. However for less surface and reservoir temperature SiO2 Chacedony can be used. These geo chemical thermometers are based on some empirical relation ships which have been drawn on data based and by inversion. As prediction of reservoir temperature is a very sensitive job and on this results potential geothermal field can be predicted for any other advance study. In addition to Silica thermometer, activity- activity phase diagram study may confirm your accuracy. Find out at what temperature Quartz come under saturation. This will be close to your base temperature. For detailed study try to read:
Ellish and Mahon; Donald E white; Fournier and Truesdell.
Thanks Virendra for your answer and references. A doubt, you say that the Quartz-silica thermometer is applicable for temperatures higher than 100 Celsius degrees. In my case study the temperature of the reservoir is probably lower than 100 Celsius degree, should I use Quartz-silica thermometer or chalcedony-silica thermometer?. Another point, I have used activity-activity phase diagram and I get that kaolinite would be a phase in equilibrium with water, should I use Quartz-silica thermometer then?
Javier, In your case Quartz silica geothermometer may not work. Better you use SiO2 Chacedony thermometer. However Na-K -Ca geo thermometer can also be tried. You have correctly evaluated with good approach. Equilibrium of kaolinite with water may indicate < 100 degree centigrade as base temperature.
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