Energy Systems and Technologies for the Coming Century ...

Temperature and salinityTemperature and salinity of the reservoir water increase with depth. Basedon available data from a number of wells a general temperature-depthrelation is established, showing a general gradient of about 25–30°C per km,but local anomalies occur due to variations in thermal conductivity related tolithology variations (Balling et al., 1992). The salinity of the formation waterincreases almost lineary with depth reaching near-saturation at c. 3000 m,though the salinity gradient may be steeper near evaporates, e.g. theZechstein halites (Laier 1989).Exploration risks and decision toolPredictions of the quality and performance of subsurface reservoirs at depthsof 1-3 km are uncertain. The geological uncertainty reflects the complexity ofthe subsurface geology and the amount and validity of available data. Inareas with intense deformation due to faulting and folding of the geologicallayers, predictions are uncertain, whereas predictions are more reliable andrequire less data in areas with weak deformation and high continuity of thelayers. In order to evaluate the exploration risks consistently, GEUS iscurrently developing a systematic approach in which the primary factors suchas burial depth, lithological continuity, gross and net thickness, faults,porosity and permeability, temperature, and formation water chemistry areestimated. The investments for establishing a geothermal power plant arehigh and in order to reduce the risks GEUS has developed a stepwiseapproach where the available data at every decision point is evaluatedbefore further data acquisition and investments are initiated (Fig.6).Fig.6. Scheme showing data evaluation steps and decision gates.Risø International Energy Conference 2011 Proceedings Page 1359