The technical model performs a DoubletCalc1D calculation on all XY locations (grid cells) of all aquifers to obtain the technical geothermal potential.
The input for the DoubletCalc1D calculation consists of a combination of maps, constant values and optimised values (see this table). The depth and thickness maps are described in the Aquifers section. The net-to-gross and permeability maps are described in the Properties section.
- The temperature is extracted from the 3D temperature model at mid reservoir depth. The salinity of the brine is linearly depending on depth.
- 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), 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.
- The internal casing diameter between the reservoir and the surface level is 8.5". The reservoir section also has an 8.5" diameter, and is assumed to be open hole.
- 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 [MWthermal], the flow rate [m³/hr] and the production temperature [°C].
Using the uncertainty in thickness and permeability, a probability distribution curve is mad of the transmissivity (thickness × permeabilitity). From this curve, the P90, P50 and P10 values of the transmissivity are determined. The technical calculation is then performed at each XY location and each aquifer for each of the P-values. This results per aquifer in P90-, P50- en P10-maps of flow rate and geothermal power.