Use of gravimetry in detailed geophysical prospection of potential geothermal energy exploitation sites: Case studies in the Czech Republic
Methodological aspects of gravity data processing and interpretation for assessing the possibility of exploiting geothermal energy for electricity production are presented. Gravimetry is one of the most economical and most effective geophysical methods for exploration of deep geologic structures. Unfortunately the gravity inversion ambiguity problem introduces the necessity of constraining gravity models by other independent data. The procedures interpreting 2D gravity models constrained by the results of an integration of other suitable geophysical methods are described in three case studies in the Czech Republic. Gravity, reflection and refraction seismics, magnetometry, resistivity, and vertical electric sounding data were collected along profiles at each locality. Two-dimensional gravity models based on complete Bouguer anomalies were constructed taking into account the results of processing and interpretation of other geophysical data. Relevant factors influencing the potential for geothermal energy exploitation were evaluated from the interpreted geophysical models. Promising zones suitable for future exploration were established at each locality. The most important structures for locating geothermal production and injection drills are deep tectonic fault zones which can freely support fluid flow. The presented examples show that the gravity anomalies caused by fracture zones can be significant enough to unambiguously interpret and evaluate their importance in terms of hydrological permeability. In addition, the presented case histories demonstrate that two-dimensional geophysical surveys can effectively be used to reduce exploration costs in geothermal projects.