Deep groundwater and its potential effects on underground storage and geothermal heat extraction activities in the Netherlands

This study leverages data on deep (>500 m) groundwater from the Dutch subsurface to assess the potential impacts of (re)using depleted natural gas fields and aquifers for (large) scale underground storage (e.g., UHS, CO₂), and geothermal (heat) extraction/storage (GHE/S). To date, we have collected data from 700 deep groundwater samples obtained from 161 onshore and offshore wells. This data comes from the Dutch public geological archive (www.nlog.nl), which contains extensive and valuable information accumulated over six decades of oil, natural gas and geothermal exploration and production in the Netherlands. In addition to groundwater composition, we also gathered information on groundwater sampling and laboratory methodologies, rock properties, mineralogy and environmental conditions of underground reservoirs, and the composition of drilling fluids and unrecovered natural gas, among others. Our primary focus is to evaluate the quality of this data and determine its suitability for biogeochemical modelling. These findings are being integrated with laboratory experiments conducted on groundwater samples from operational oil/gas/geothermal wells in the Netherlands. This allows us to reproduce, quantify, and predict the effects of environmental changes that may occur in specific underground reservoirs due to current and planned underground production and storage projects. The results are particularly valuable for the growing number of performance screening studies on UHS, CCS, and geothermal projects, many of which may have yet to fully account for the impact of biogeochemical processes on their estimates of production/injection rates and/or storage capacities. Our findings also offer practical recommendations for optimal sampling and analysis practices for biogeochemical monitoring studies, which may differ from those typically employed by oil, gas, and geothermal companies. The ultimate goal of this study is to better characterize, quantify, and predict the potential short- and long-term impact and risks of microbial activity and geochemical reactions in the various geological formations targeted for underground activities in the Netherlands.