Modelling the In Situ Stress Distribution in a Rotliegend Gas Reservoir

Optimal exploitation of conventional and unconventional hydrocarbon reservoirs requires detailed knowledge on the specific in situ stress field including all perturbations in stress magnitude and orientations due to faults and contrasts in rock mechanical properties. A geomechanical model comprising the detailed reservoir geometry and a mechanical stratigraphy is successfully built for a case study gas field in the North German Basin. The model is calibrated against well data and reveals in detail the local distribution of the in situ stresses. This validated model can now be used for stress predictions in the inter-well space and undrilled parts of the reservoir. In addition, the tendency of the existing fault network to slip or dilate in the present-day stress regime can be addressed. This is also possible for paleo-stress states, however, uncertainties especially regarding the paleo-stress field description and the paleo-properties of rocks and faults have to be kept in mind. The workflow outlined above can be used to build 3D geomechanical FE models for various types of reservoirs and ranging from field-scale models to smaller, highly detailed submodels of specific fault blocks.