| Abstract |
Geothermal energy in the Netherlands has been growing rapidly over the last decade. Several low-enthalpy geothermal projects have already been developed for greenhouse heating and the number of issued licenses promises an even faster growth in the future. Hot water is extracted from clastic aquifers of around 2000 mdepth which have been explored for oil and gas production in the past. Geothermal development in the Netherlands benefits from extensive knowledge of the Dutch subsurface, public availability of data and models of the subsurface and an excellent match between heat demand of greenhouses and subsurface potential. This puts the Netherlands in a rather unique position in the world, allowing very rapid growth of geothermal.TNO facilitates in geothermal development through putting subsurface information and models in a geothermal context (www.thermogis.nl) and applied research for successful placement and design of geothermal doublets and in ensuring good doublet operations. Dutch geothermal projects have been confronted with a whole range of issues which needed and still need to be resolved. These include worse than expected injectivity,assessment of land subsidence, the scope for reducing injection temperature for enhanced performance, prediction and mitigation of mineral scaling and dealing with oil and (CO2 containing)gas co-production.We have initiated research projects in close cooperation with project- developers. This provided an unique opportunity to study in detail data of the major geothermal projects, providing us with case studies for the different target reservoirs in the Netherlands. Here we present the (intermediate) results of our studies. Someresults are listed as follows:• For injectivity we concluded that many of the encountered problems most likely were related to near-well damage to the wells.• Lowering the temperature appears to enhance injectivity in many cases. This may be explained by thermomechanical effects which are not included in standard flow models, and this will be subject to future study.• Another geomechanical effect is land subsidence due to reservoir cooling. We found it may be measurable for some geothermal systems – but generally not significant.• A geochemical assessment of a degassing loop for geothermal water has been performed, to assess the sensitivity for scaling. With dissolved CO2 present in the reservoir, the scaling potential is highest due to degassing – if CO2 is kept in solution this risk is largely reduced. The predicted amount of scaling is sensitiveto the location-specific chemistry and distinct differences exist for the different studied reservoir types.. A study on the predicted location of precipitation (in the installation and reservoir) as governed by flowand precipitation rates. Further work also includes the effect of corrosion related redoxreactions and incorporation of radioactive isotopes in scales. |