Management of Geological and Drilling Risks of Geothermal Projects in the Netherlands

Abstract

In this paper a recommended workflow and methodology of geological and drilling risk management is shown and discussed with data of the Erica geothermal project in The Netherlands. Drilling boreholes for development of geothermal energy with depths of 2000 to 3500 m is a relatively new/recent activity in the Netherlands. Ten geothermal doublets have been drilled so far since 2007 in The Netherlands. Several drillings have been completed with lower geothermal flows than expected. Furthermore, unexpected dissolved gas contents up to 1.5 Nm3 gas per m3 water have been measured at one project while at another project oil is being coproduced. Also several sidetracks due to swelling clays, mud losses and lost-in-hole equipment have been required to reach the aquifer, and a few projects that have been realised are suffering from scaling and/or corrosion problems. These problems have been mitigated, but as a consequence due to these events the geothermal project costs have increased rather unexpectedly. For the detailed Erica geothermal design and budget planning a geological risk study was used to investigate and calculate the geological and drilling risks to establish the financial risk budget for the drilling. Geological risks are generally difficult to influence while drilling risks can be managed or influenced when proper and effective measures are taken. As a result of the local geological setting, several risks issues have been identified: permeability, depth top reservoir, temperature, overpressure, salinity, salt plugging, initial and residual gas, dissolved gas, H2S and shallow gas. The parameters that have impact on the calculation of geothermal power (Pt) are taken into account in the uncertainty analysis: permeability, depth and temperature of the reservoir. Other parameters that influence the project budget and can also have impact on the geothermal power are taken into account in the risk management.