The In-situ Stress Field in the Netherlands: Regional Trends, Local Deviations and an Analysis of the Stressregimes in the Northeast of the Netherlands (2017)

Deze MSc scriptie is geschreven door oud-stagiair Eelco Mechelse.

Knowledge of the state of stress is of significant importance to have a thorough understanding of subsurface geomechanics. The World Stress Map (WSM) is the main source of present-day stress data in Western Europe and indicates a regional NW-SE maximum horizontal stress (SH) trend for the Netherlands. However, for more local studies the WSM lacks the required resolution. Therefore, the first objective of this research is to expand the Dutch Stress Map (DSM) database in which SH orientations are collected. As such, a better understanding can be obtained of the horizontal stress field with depth and the SH orientations that deviate from the regional trend. In addition, this research aims to characterize the insitu stress regimes with depth in the Groningen field, using different one-dimensional stress models.

This research first highlights the importance of the stress state and indicates which in-situ stress information is currently lacking in the Netherlands. Moreover, it is shown how stress-induced borehole features serve as basis for the determination of horizontal stress directions. The datasets used to expand the DSM database are presented, after which an extensive analysis is performed on the collected SH orientations. Subsequently, the stress magnitudes are quantified by studying the sensitivity of the in-situ stress regime to different 1D stress models. Moreover, the workflow is described for developing a 3D geomechanical model, which can serve as basis for future studies.

The research shows that the DSM database is expanded with 86 new boreholes across the Dutch on- and offshore regions. The analysis of the database indicates a dominant NW-SE SH orientation, both spatially and with depth. In most stratigraphic groups, the SH direction falls within the range of 315° ±22.5°, although a larger degree of variation is observed in the post-salt stratigraphies. On a local scale, two case studies show that SH orientations, which deviate from the regional NW-SE trend, can be related to the presence of a salt structure and a normal fault. The 1D in-situ stress models all indicate a normal faulting stress regime at reservoir depth (Rotliegend) and deeper. In the interval between the reservoir and Earth’s surface, no unambiguous stress regime is identified as the regime is more sensitive to the different boundary conditions applied.