Building a Comprehensive Geomechanical Model for Chalk Compaction. Phase 1: Model Calibration from Plug to Reservoir Scale

The exploitation of chalk reservoir entails reservoir compaction and seafloor subsidence that can jeopardise the economic viability of a field. Despite the apparent monotonous aspect of chalk in the Danish North Sea, numerous geomechanical models were successfully applied to different fields to forecast rock deformation. The present study aims at building a geomechanical simulation approach capable of predicting compaction and seafloor subsidence in various reservoirs. Laboratory, well log and production data and in situ compaction measurements from different fields are reviewed to build a robust database used for model calibration. A strain-rate dependent constitutive model is implemented into Comsol Multiphysics and tested from core to reservoir scale. The results indicate differences in the elasto-plastic behaviour of Maastrichtian and Danian chalk. The back-analysis of uniaxial compaction tests shows that the hardening effect varies between rock types and a more pronounced effect is observed in Maastrichtian chalk. Model calibration for the rate-dependent deformation uses in situ compaction measurements collected in a producing reservoir over a seven year-long period. The results indicate that the rate-dependent behaviour of chalk is function of porosity and differs slightly between Danian and Maastrichtian chalk. Model calibration represents a key step to quantify chalk properties, which will be then used as input data to simulate compaction in different chalks fields.