| Abstract |
From September 2014 through March 2015 six ‘Heat Needle’ probes were deployed around the Cuitzeo Lake geothermal zone in central Mexico, to assess their functionality and outcomes in geothermal exploration. The trial was part of Project 23 of the Mexican Center for Geothermal Energy Innovation (CeMIE-Geo): Testing probes for measuring shallow heat flow in geothermal zones. The Cuitzeo Lake is located within the Mexican Volcanic Belt and presents several geothermal manifestations in its surroundings, being the zones of Araró and San AgustÃn del MaÃz two of the most attractive. The six Heat Needles were placed in these two zones, even though there are another two zones of interest. They proved relatively simple to deploy and retrieve. Only one Heat Needle suffered minor damage during an attempted deployment in stony ground. That Heat Needle was replaced with another, and all six were subsequently recovered in re-usable condition. Heat Needles at two sites were apparently tampered with before the end of the trial, cutting short their recording period. Also, two out of seven sensors in one Heat Needle failed to record for any of the trial period for an unknown reason. Each Heat Needle precisely recorded thermal gradient in the top 1.10 m of soil at 15-minute intervals for the duration of the trial, and made a single measurement of the thermal conductivity profile of the soil. Combining the thermal gradient records with the thermal conductivity measurements provided an estimate of surface heat flow through time at each site. Superficial heat flow values ranged from 3.5 to 17.5 W/m2, which is up to two magnitude-orders higher than the average continental value, suggesting preliminary discharge values between 7.5 and 12.5 MWth for square kilometer. The conclusion is that these high values were strongly affected by the temperature of the huge shallow thermal aquifers identified in the subsoil of both areas. That is, the high values of heat flow estimated with the probes, after filtering the diurnal, seasonal and meteorological contributions, reflect the local heat discharge due to the shallow and/or sub-surface aquifers, which seem to be indicative of a deeper hydrothermal geothermal reservoir. This, in turn, tends to confirm the high geothermal potential of the Cuitzeo Lake zone, as interpreted by other geological, geophysical and geochemical surveys conducted there. |