Sensitivity of Subsidence Data in the Northeastern Netherlands to Geological Complexities

Abstract

Large parts of the Netherlands have
experienced subsidence due to anthropogenic soil deformation (peat
oxidation and clay shrinkage and swell) since the Middle Ages. As of the
start of gas production from the Groningen reservoir in 1968, the
northeastern Netherlands has seen additional subsidence (>30 cm)
originating from deep reservoir compaction. Due the land being situated
close to sea-level this poses a significant societal problem. Geodetic
surface observations (InSAR) contain components of both shallow and deep
subsidence. This study is part of a larger project on subsidence
forecasting, which aims to disentangle deep and shallow (soil) drivers
of subsidence by assimilating geodetic time series in geomechanical
models of the subsurface. This requires the models to be highly
efficient. In this study, we focus on modelling the deep subsurface
(reservoir and overburden). We perform a sensitivity analysis to
investigate the level of geometrical and mechanical complexity of the
reservoir and overburden that can be resolved from the data, to reach
optimal model efficiency.

We employ a semi-analytical mechanical
model for the Groningen subsurface using the PSGRN/PSCMP code by Wang et
al. (2006) of laterally uniform viscoelastic layers. We use the
Visvalingam–Whyatt algorithm to simplify the existing geological model
to versions with decreasing levels of complexity. The surface
deformation resulting from the different model versions are used in a
convergence test to define the required model complexity. We find that
we can achieve orders of magnitude improvement in model run time
efficiency, depending on the data uncertainty.

Wang, R., Lorenzo Martín, F., Roth, F.
(2006): PSGRN/PSCMP - a new code for calculating co- and post-seismic
deformation, geoid and gravity changes based on the
viscoelastic-gravitational dislocation theory. Computers and
Geosciences, 32, 4, 527-541.