The influence of fault slip, compaction variability and lithological layering on surface deformation above the Groningen gas field

Considerable surface subsidence (>30 cm) has occurred since the start of gas production from the Groningen gas field. Seismic activity started in 1986 and is now known to be concentrated on reservoir cutting faults. The subsidence has mostly been caused by pressure depletion leading to reservoir compaction. However, the spatial and temporal distribution of reservoir compaction is incompletely known because other processes likely also contribute to the surface deformation pattern.

Our study is part of the collaborative DeepNL/Subsidence project. Its aim is to identify the subsurface drivers of subsidence above the Groningen gas field and to forecast future subsidence, by assimilating geodetic time series into geophysical models of both the shallow soils and the deeper overburden and reservoir. Since data assimilation can be computationally intensive, our eventual aim is to design geophysical models with the minimum complexity that is needed to reproduce the observed surface deformation. Therefore, in the present study, we explore which sub-soil characteristics may possibly have a resolvable expression in the geodetic time series.

We use analytical and finite element models with simplified representations of the subsurface geometry. We estimate surface displacements associated with slip on reservoir faults of different dimensions, and with spatial variability of reservoir compaction. In addition, we explore the influence of the mechanical rock property profile of the reservoir and overburden, including the inelastic behaviour of the reservoir sandstone (Pijnenburg et al., 2018, 2019).