Fluid extraction from geological formations for purposes of subsurface utilization leads to a pore pressure drop in reservoirs and potentially to compaction and seismicity. The geomechanical behaviour, and thus production-related compaction, of siliciclastic reservoirs is governed by the composition of reservoir sandstones, which includes porosity, grain size distribution, and detrital and authigenic mineralogy. One siliciclastic reservoir which is undergoing compaction related to fluid extraction is the Rotliegend of the Groningen gas field. In this research, we investigate potential approaches to upscale the sandstone composition from the micro-scale (thin sections, plugs) to the well and reservoir scale. Input data to the upscaling models will include 3D geometries based on existing data (e.g., seismic data, well logs, sedimentological core descriptions, and petrographic data).
Based on the extensive reports provided by the operator of the Groningen gas field, among the petrographic properties, the presence of authigenic clays tends to affect the geomechanical behaviour the most. In particular, we are defining the fractions of the clay-coating minerals (illite, kaolinite, etc.) and their effect on the inelastic deformation of reservoir sandstone as well as paying close attention to the presence of chlorite as its distribution corresponds to the areas associated with increased subsidence and seismicity.
We employed short-wave infrared spectroscopy, a non-destructive and time-efficient technique, to obtain mineralogy logs for the Upper Rotliegend Group. We aim to validate the current results, obtained from four selected wells representing contrasting areas of the Groningen gas field, against a comprehensive petrographic dataset, including X-ray diffraction, thin section descriptions, and modal point count analysis. Furthermore, the obtained results will be examined in conjunction with petrophysical data such as Gamma-ray, density, and neutron porosity logs as well as seismic data to establish the observed mineralogical trends. Ultimately, our results will serve as a foundation for selecting samples and designing geomechanical experiments to test the proposed hypotheses.
In parallel, we are selecting the upscaling and modelling techniques to develop a detailed model of the Dutch subsurface that matches well the existing heterogeneous structures. The resulting 3D reservoir composition model of the Groningen gas field will be combined with the results of the deformation experiments to link reservoir composition to geomechanical behaviour. This will enable an updated, more realistic, 3D geomechanical model of the Groningen gas field that can be utilised by other researchers to better predict future compaction and subsidence.
