A workflow for building and calibrating 3-D geomechanical models &ndash a case study for a gas reservoir in the North German Basin

摘要

The optimal use of conventional and unconventional hydrocarbon reservoirsdepends, amongst other things, on the local tectonic stress field. For example,wellbore stability, orientation of hydraulically induced fractures and –especially in fractured reservoirs – permeability anisotropies arecontrolled by the present-day in situ stresses. Faults and lithologicalchanges can lead to stress perturbations and produce local stresses that cansignificantly deviate from the regional stress field. Geomechanicalreservoir models aim for a robust, ideally "pre-drilling" prediction ofthe local variations in stress magnitude and orientation. This requires anumerical modelling approach that is capable to incorporate the specificgeometry and mechanical properties of the subsurface reservoir. The workflowpresented in this paper can be used to build 3-D geomechanical models basedon the finite element (FE) method and ranging from field-scale models tosmaller, detailed submodels of individual fault blocks. The approach issuccessfully applied to an intensively faulted gas reservoir in the NorthGerman Basin. The in situ stresses predicted by the geomechanical FE modelwere calibrated against stress data actually observed, e.g. boreholebreakouts and extended leak-off tests. Such a validated model can provideinsights into the stress perturbations in the inter-well space and undrilledparts of the reservoir. In addition, the tendency of the existing faultnetwork to slip or dilate in the present-day stress regime can be addressed.