Modelling the mechanical impact of CO2 injection into a carbonate reservoir of the Paris Basin
Résumé
CO2 injection into a depleted hydrocarbon field or a deep saline aquifer can induce a variety of more or less strongly coupled physical and chemical processes. In an oil field pore pressure variations due to hydrocarbon production and CO2 injection directly impact mechanical properties, through stress field changes in and around the reservoir. Such modifications can lead to reservoir or caprock failures, reservoir compaction or uplift and the reactivation of faults. These phenomena can influence the sealing efficiency of geological storage. To be able to correctly design CO2 storage, and to perform the associated risk assessment, an accurate prediction of reservoir and subsurface mechanical behaviour is needed. To assess geological hazards related to hydrocarbon extraction or to underground gas storage, we use integrated 3D geomechanical modelling. In this approach a reservoir simulator is used first to compute the whole pressure history during depletion and CO2 injection periods. The pressure computed by the multiphase fluid-flow description of the reservoir simulator is then used as an input parameter of a geomechanical simulator. This is a one-way coupling procedure, that does not account for feedback of mechanical deformation on pore pressure. The results of the geomechanical modelling are analysed in order to study the induced deformation and in-situ stress changes due successively to oil production and CO2 injection. The influence of both production and injection steps are illustrated by a numerical model built from a carbonate reservoir in the context of the Paris Basin. The modelling is performed in the framework of the project PICOREF, supported by the French National Agency of Research.