Within the Netherlands, 24 geothermal systems have been realized of which 18 added to production of 3.7 PJ of heat in 2018. The main application domain is horticulture. The ambition of the Dutch government is to increase the production of geothermal energy in the Netherlands to 15 PJ in 2030, subsequently 110 PJ in 2050 and to expand the application domain to district heating and industry. Kramers et al. (2012) published an article on the direct heat resource assessment stating that the recoverable heat amounts to just over 63000 PJ, assuming a reinjection temperature of 35 °C. This resource estimate combines all direct heat projects regardless of their maturity. A state-of-the-art resource assessment can support the Dutch government policy to realize its ambition by classifying the resources based on project maturity, including reference to the obstructing issues in the maturation of projects such as technical, financing, licensing and/or social and environmental complexities. In January 2019, 78 exploration licenses are active or have been applied for. At least one geothermal project is defined in each of these licenses, at different levels of advancement. Outside the existing licenses and licenses applied for, The Netherlands provides ample space for geothermal development by geothermal projects, yet in a conceptual stage. At the moment, there are no tools or practical methodology to integrate all the available information in a coherent and automated manner. Furthermore, a method to quantify the geothermal energy resources of projects ‘not yet realized’ using the United Nations Framework Classification (UNFC) resource classification system, would help policymakers to decide upon the most appropriate measures to relieve the obstruction issues to reach the 2030-2050 geothermal ambitions. In this study, we show the results of a resource assessment and classification system for geothermal energy while incorporating environmental and social issues in the classification, as required by the UNFC-2009. As basis for this resource assessment, we use the webtool ThermoGIS. ThermoGIS which uses information on the Dutch subsurface derived from the regional mapping by the Geological Survey and which is updated by incorporating newly gained insights and data, provides a comprehensive overview of the geothermal potential for a selected set of aquifers. The resource estimate, including the uncertainty range related to these figures, at the status date 1-1-2019 of the Dutch geothermal “project portfolio” is classified using UNFC, resulting in a set of resource figures per resource class according to project maturity: commercial, potentially commercial, non-commercial and exploration projects. Furthermore, some additional development options are introduced like installing heat pumps on relevant projects and stimulation on projects with poor productivity to increase the resource potential. Next level analysis envisages that future projects are given an attractivity attribute reflecting, amongst others, proximity to areas of favourable heat demand, proximity to heat network, which will guide the order of the exploration drilling sequence. An estimate on the geothermal portfolio maturation speed will then reflect on the minimum number of wells to be drilled to reach the geothermal ambition. @en

We implement a Coulomb rate-and-state approach to explore the nonlinear relation between stressing rate and seismicity rate in the Groningen gas field. Coulomb stress rates are calculated, taking into account the 3-D structural complexity of the field and including the poroelastic effect of the differential compaction due to fault offsets. The spatiotemporal evolution of the Groningen seismicity must be attributed to a combination of both (i) spatial variability in the induced stressing rate history and (ii) spatial heterogeneities in the rate-and-state model parameters. Focusing on two subareas of the Groningen field where the observed event rates are very contrasted even though the modeled seismicity rates are of similar magnitudes, we show that the rate-and-state model parameters are spatially heterogeneous. For these two subareas, the very low background seismicity rate of the Groningen gas field can explain the long delay in the seismicity response relative to the onset of reservoir depletion. The characteristic periods of stress perturbations, due to gas production fluctuations, are much shorter than the inferred intrinsic time delay of the earthquake nucleation process. In this regime the modeled seismicity rate is in phase with the stress changes. However, since the start of production and for two subareas of our analysis, the Groningen fault system is unsteady and it is gradually becoming more sensitive to the stressing rate.@en