Geothermal potential of the Tubbergen Formation in the Twente region of east Netherlands

Abstract

Here we report the potential geothermal prospectivity of clean sandstones in the Tubbergen Formation (Late Carboniferous) of the Twente area (eastern Netherlands). We were motivated by the prevailing paradigm that in The Netherlands geothermal power can only be harvested economically through large, expensive installations producing high-volumes from high-quality aquifers located between ca 1500 and 2500 m. No such aquifers are present in Twente. Our study shows that heat production is economically feasible from the Tubbergen Formation sandstones by producing smaller volumes from smaller, highly efficient installations that can be developed at considerably lower cost. Our reinterpretation of publicly available seismic and well data shows that potentially suitable sandstones occur over the whole area with thicknesses of up to 50 m, porosities reaching 20% and permeabilities reaching 300 mD. The Tubbergen Formation is ca 400-700 m thick in the study area and contains ca 60% sandstone. The top reservoir reaches ca 1500 m depth in the SW and the base reaches some 4300 m in the NE of the study area. The temperature is expected to range between 60-140 °C depending on depth. The Carboniferous is densely faulted with a block size of ca 3x4 km, each block being a potential target for geothermal development. To determine the economic feasibility, we performed an economic screening for a hypothetical location north of the city of Enschede and backed this up by reservoir simulations. The geologic risks of the Tubbergen Formation are: lack of permeability, reservoir thickness, and lateral extent of reservoirs. In our judgment the chance of economic success for this site is 50% or more. Upside potential is present in numerous fault blocks in the study area, and in adjacent areas where suitable sandstones with similar porosity and permeability at greater depth and higher temperatures are expected.