Integrated hydro-mechanical and seismic modelling of the valhall reservoir - Predicting subsidence, AVOA and microseismic

In this paper, we describe a workflow that integrates geomechanical, fluid-flow and seismic modelling that can be used to predict the stress distribution and evolution as well as various seismic attributes before and during production. Poroelastoplastic constitutive model is used to incorporate matrix failure during simulation, allowing strain hardening and weakening to develop within the model. This is especially important for modelling reservoir stress path and stress path asymmetry. The material model also enables the prediction of when and where failure occurs in the model, allowing us to model the likely microseismic response of a reservoir. Specifically, the finite element code ELFEN is coupled to the production simulation code VIP. The workflow is applied to the data-rich Valhall reservoir, North Sea to model seafloor subsidence. Furthermore, the output from the hydro-mechanical simulation is linked with a stress-dependent rock physics model to predict seismic attributes, allowing for an additional assessment of hydro-mechanical simulation via comparison and calibration with observed seismic. The results of the subsidence predictions compare well with field observations. For instance, the AVOA response calculated from the output of the hydro-mechanical simulation modelling closely resembles that measured from field seismic data, despite the limited calibration of the rock physics model to the Valhall reservoir rocks.