Technical model

The technical model performs a DoubletCalc1D calculation on all XY locations (grid cells) of all aquifers to obtain the technical geothermal potential.

The technical input for the DoubletCalc1D calculation in ThermoGIS consists of a combination of maps of the geometry and rock properties, constant values, and optimized values (see this table).

• The temperature is extracted from the 3D temperature model.
• The salinity of the water is assumed to be depth-dependent according to: salinity [ppm] = 70,000 / 1,500 × depth [m]. Salinity affects, among other things, the density and viscosity of the produced water and therefore the required pumping power.
• The distance between the two wells at aquifer level is optimized per aquifer and per XY location. A large distance increases the resistance the water experiences when moving to a well. A small distance causes early thermal breakthrough in the production well. The maximum allowed cooling of the production water after 50 years is set to 10% of the difference between the initial aquifer temperature and the return temperature. The well distance is iteratively minimized, while at the same time the maximum cooling is not exceeded.
• Next, the pump pressure is optimized. A higher pump pressure results in a higher flow rate and therefore a higher geothermal power. On the other hand, a higher pump pressure increases the costs of operating the pump and possibly results in a higher cost per unit energy. Furthermore, the pump pressure is limited by the pump specifications (set to 300 bar in ThermoGIS), and the protocol ‘Definition maximum injection pressure for geothermal production’ (in Dutch). Within these constraints, the pump pressure is optimized towards a minimum cost per unit energy (see the Economic Model for the calculation of the production costs).
• The 'well trajectory curvature factor' is used to calculate the along-hole well depth of both wells from the vertical depth and the well distance. This is calculated as: along-hole length = curvature factor × √((vertical depth)² + (½ × well distance)²). In practice, this factor ranges between 1.0 and 1.13.
• The internal casing diameter between the reservoir and the surface level is 8.5". The reservoir section is completed as open hole with the same diameter.
• The well penetration angle in the reservoir is assumed to be 45° (deviation from vertical). In order to simulate this deviation in the flow calculation, a negative skin is assumed, which has a value of -1 for a 45° angle.

The most important results of the technical analysis are maps for each aquifer and stack depicting the geothermal power [MW_thermal], the flow rate [m³/hr] and the production temperature [°C].