DoubletCalc1D is a software tool developed by TNO. Using a simple subsurface model and well design, it calculates the amount of water that can be produced with a pump of a certain power. DoubletCalc1D underlies the ThermoGIS calculation model, which is described in the Calculation model section. The DoubletCalc1D software and manual can be downloaded from www.NLOG.nl/en/tools.

In the input screen (figure 5), the aquifer properties (depth, thickness, permeability, net-to-gross ratio and temperature), the pump and doublet properties (return temperature, pump efficiency, pump pressure) and the simplified well design are specified. Next, the software calculates the flow rate this doublet could produce, the geothermal power given the specified return temperature and the COP (Coefficient of Performance) given the pump efficiency (figure 6).

DoubletCalc1D not only asks the user to enter the expected value of the aquifer properties, but also to estimate the minimum and maximum values. This introduces the uncertainty of the parameter estimate in the calculation. In particular, the permeability uncertainty is important. A triangular distribution is generated for all properties. A large number (>1000) of calculations is then executed, during which a value is drawn for each property from the triangular distribution. This allows the construction of a probability distribution curve of the geothermal power (figure 7). In the example shown, the expected power is 8.34 MWth. The likelihood that the power is at least 6.43 MWth is 90%, and the likelihood that the power is at most 11.22 MWth is 10%.