The subgrain microstructure was interpreted and quantified using the petrographic workstation at Shell Research Rijswijk. Then, using laboratory calibrations, we used the average subgrain diameter of each sample to calculate the in-situ differential stress and strain rate in the salt during the past few thousand years. This in turn was be translated into a velocity field using the model of the flow field expected in the salt. The geological model predicts a general squeeze flow, with only a minor horizontal movement of the top salt interface. As a best approximation, we used a horizontal Poiseulle flow model to calculate the expected horizontal displacement of the casing after 15 years.
Results show that the displacements are minor.
A sensitivity analysis indicates that significantly larger deformations are unlikely, and that the associated strains in the casing will remain elastic. Results of the present study can be further substantiated by refining the geological model using palinspastic reconstruction, and further quantifying the strain rate versus depth profile in additional samples taken in a future well. In order to gain quantitative insight into salt tectonic processes, and to model such processes either numerically or using physical analogue techniques, appropriate data on the flow properties of rocksalt and the underlying deformation mechanisms are needed. Depending on water content, these processes may be accompanied by fluid-assisted dynamic recrystallization. Various creep laws are available which adequately describe the observed behaviour.