After obtaining the exploration licence, the licence holder will work towards the drilling phase. To get a good understanding of the subsurface in the study area and to map the geological uncertainties, a detailed geological study has to be carried out. The outcome of this investigation has effect on the possible doublet configuration(s) and the associated geothermal power.

Before a well can be drilled, an environmental licence must be obtained in addition to the exploration licence. The environmental licence is not covered by the Mining Act. In addition, a work program for the construction of a borehole must be submitted to the State Supervision of Mines (SSM). See also Chapter 8 in the Mining Regulations.

When the involved authorities have approved the drilling plans, first an exploration well will be drilled to test the presence and quality of the target reservoir. This can be done, among other things, by log measurements in the borehole, sampling cores of the target reservoir and/or a well test. If these data show that the geothermal energy can be exploited economically, the successive well(s) will be drilled to complete the geothermal system.

Detailed Geological Study

Prior to drilling it is important to map the subsurface in as much detail as possible in order to reduce uncertainties and to select the best subsurface target location for the potential geothermal system.

The mapping of the subsurface is done using seismic and borehole data. To determine the properties of the target reservoir the best possible way, a petrophysical analysis is performed. Based on these studies, the most optimal well configuration can be determined relative to the surface location. On this basis an expected geothermal power can be determined. 

The findings of the detailed geological study can be used to apply for the SDE+ and RNES incentive schemes. The report of the detailed geological study for an SDE + and / or RNES application must meet the reporting requirements drawn up by TNO-AGE. On behalf of RVO, TNO-AGE does the geotechnical evaluation of the application for an SDE+ or RNES.

Preparations drilling phase

When the subsurface is mapped and the reservoir properties are determined it is also possible to get a view of possible dangers and associated risks of exploration and exploitation of the subsurface. These dangers and risks need to be addressed in the work program for the construction of the borehole, and at a later stage in the production plan.

Completion drilling phase

Irrespective of the result of the well(s), the operator is obliged to supply all data / measurements that fall under the Mining Act to the Dutch government. TNO collects and manages these data on behalf of the government. For more information, see the page on data supply.