In this study we present a techno-economic models for deep geothermal projects using best practices for asset evaluation from the Oil&Gas industry, taking into account natural uncertainties and decision trees to evaluate sensitivities and different scenarios (cf. Floris and Peersmann, 2002). In this approach Fast model calculations for the techno-economic evaluation are used to calculate the performance of the geothermal systems, investigating sensitivities of the performance due to both natural uncertainties beyond control (e.g. flow characteristics, subsurface temperatures), engineering options (bore layout and surface facilities options) and economic uncertainties (e.g. electricity price, tax regimes).
We developed the methodology first for the re-use of deep boreholes drilled by oil and gas industry for a Deep Borehole Heat Exchanger (DBHE). A DBHE is based on the principle of a fluid migrating through a coaxial pipe in the subsurface, heated gradually by migrating downwards in the outer pipe, whereas the inner pipe acts as the return path for the heated fluid. The energy performance of the DBHE is proportional to the temperature difference between injected and produced water multiplied by the injection rate (m3/h). Kohl et al, 2002 have presented a full numerical performance analysis of such systems. In our decision support approach we use fast models for the temperature evolution of the water in the well based on fast analytical solutions of Kujawa and Nowak (2000a, 2000b). This allows to calculate in a matter of seconds the performance and its sensitivity to uncertainties and the effect of various engineering options.
For doublet systems in deep (enhanced) geothermal systems we use analytical methodologies developed for the Soultz project (Heindiger et al., 2006). Preliminary results indicate that the performance of the system is primary sensitive to subsurface temperature, flow rates which can be sustained in the fractured rock, and the fracture area involved in the fluid flow.