DoubletCalc is a programme for calculating the indicative power of a geothermal doublet. It can generate the probability graphs required to be submitted with the application for the SDE+ and/or the Guarantee Scheme for Geothermal Energy. The latest version is DoubletCalc v1.4.3.

DoubletCalc v1.4.3

Compared to v1.4, this version has extra functionality relating to output. The output screen shows more results and the information in the "base case details" export has been expanded.

DoubletCalc v1.4.3 software (version 17 December 2014, including java 7 runtime). 
DoubletCalc v1.4.3 manual (TNO 2014 R11396, 1 October 2014).
DoubletCalc v1.4.3 source code (Java/JavaFX).

Older versions

DoubletCalc v1.4 software (version 25 February 2014) and manual.
DoubletCalc v1.3 software (version 30 November 2009).

DoubletCalc v1.5.0-beta

Currently DoubletCalc v1.5 is in development. This beta version is available for testing purposes. Bugs and/or unexpected behaviour can be submitted through the NLOG contact page.

DoubletCalc v1.5.0-beta software (version 17 May 2021, including java 8 runtime).

The most important changes in v1.5 compared to v1.4.3 are:

  • Upgrade to Java 8 and JavaFX 2 libraries.
  • Additional input fields for transmissivity and thermal rock properties.
  • Optionally use pressure, temperature & salinity dependent viscosity correlation of Kestin, 1981.
  • The distribution (min - median - max) of permeability or transmissivity can be executed in the logarithmic domain.
  • First-order estimate given of doublet lifetime.
  • Output results in excel format. 


DoubletCalc 2D v1.0 (DC2D) is a software tool developed by TNO. Using this software it is possible to calculate the temperature and pressure around two or more geothermal wells, in two dimensions (2D) and over the course of time. The software has been developed to bridge the gap between simple 1D simulation tools such as TNO's DoubletCalc v1.43 (DC1D, Mijnlieff et al. 2014), and advanced 2D and 3D reservoir simulators such as Eclipse.

Manual DoubletCalc 2D V1.0 (DC2D) (pdf)


To support the search for suitable locations for geothermal energy, TNO has developed a free geothermal information system: ThermoGIS™ (see This system gives everyone access to a preliminary rough estimate of the geothermal potential of a certain location and to a wealth of information on geothermal energy in the Netherlands.

Salinity calculations

TNO has developed an Excel spreadsheet for calculating the salinity of formation water in ppm NaCl equivalents. When the composition of the water is input, it gives the salinity value. This can be used when determining the input values for DoubletCalc. The finishing touches are currently being made to the spreadsheet. The file will be made freely available when the QC has been completed.

Calculating the skin value of horizontal wells

DoubletCalc cannot be used to calculate the geothermal power if the design of the geothermal project assumes horizontal wells. Instead, an indication of the geothermal capacity can be obtained by using analytical methods such as those published in the public domain to calculate the improvement in productivity resulting from a horizontal production trajectory. TNO has implemented these methods in an Excel spreadsheet, in order to capture the productivity improvement in a skin value. An alternative way of determining the flow and hence the geothermal capacity when using a horizontal well is to use a reservoir simulator.

Manual for equivalent skin horizontal well (pdf)
Equivalent skin horizontal well (xls)

Spreadsheet to determine indicative injection pressure space 

The Geomech_V2.xlsx spreadsheet and its accompanying manual TNO manual for GeoMech can be used to ascertain the relationship between the injection pressure applied in the injection well and the various gradients:
State Supervision of Mines maximum injection pressure gradient

  • Lithostatic pressure gradient
  • Hydrostatic pressure gradient
  • Minimal horizontal tension gradient (Shmin)
  • Minimal horizontal tension gradient, taking account of the thermal effects of injection water on the rock (Shmin thermal)


For more information, see memorandum.

Conversiontool for injection pressure in geothermal wells

During the geothermal energy production process cooled formation water is injected back into the reservoir by applying additional injection pressure. The injection pressure downhole, at reservoir depth, is not measured during the production period. This overpressure is an important factor for seal integrity. The injection pressure is measured at the tubing head. The conversion from injection pressure at reservoir depth to injection pressure at the tubing head depends a.o. on injection temperature and flow rate. This conversion tool calculates the injection pressure limit at the tubing head, for variable operational settings, corresponding to the maximum allowed injection pressure at reservoir depth. 
At the request of State Supervision on Mines (SodM), TNO-AGE developed this conversion tool (also published on the website of SodM). SodM adds this tool to the Toezichtsarrangement Geothermie (TAG) and requests geothermal operators to use this tool for the yearly report. In this yearly report operators show that the applied injection pressure at the well head, which is measured during the year, did not exceed the maximum allowed injection pressure at reservoir depth. To conclude, this tool is only meant for conversion of injection pressure, not to define the maximum allowable injection pressure.


Determination outline production licence

This tool is used to determine the outline of a production licence using the French method.

Bepaling begrenzing winningsvergunning - Franse methode