AAPG Annual Convention and Exhibition

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Basin Geomechanics for Exploration – Examples and Modeling Approaches


Basin geomechanics applies the principles of geomechanics at the basin scale and is used in exploration in order to determine how stress field variations impact petroleum systems, top and fault seal integrity, as well as pore pressure and reservoir quality variations. Examples of problems addressed by basin geomechanics are traps in compressional settings that experience increased lateral stress thereby impacting residual HC column and fluid phase, enlarged HC columns and drilling windows in HPHT settings due to pressure coupling effects, preferred HC charge directions along natural fractures caused by stress anisotropy, vertical stress variations due to changing stress field in space and time, fault reactivation during or after time of charging etc. In order to address such problems, a dynamic approach of the basin-wide stress field is needed, in contrast to reservoir geomechanics problems where a static description is usually sufficient. Current basin modeling capabilities employ 1D methods based on the Terzaghi principle of vertical effective stress using a visco-plastic rheology. It is clear that such a vertical load-based approach cannot represent large deviatoric stress variations and in turn many of the above-mentioned problems cannot be addressed. Applying reservoir modeling capacities is not appropriate either since they don't address the dynamics of basin-scale deformations coupled with thermal and flow fields. New coupled approaches are being developed to overcome these limitations. We will show with some examples what is at stakes and some tentative solutions to the coupling problem, both how a general geomechanics code can be applied to basin-scale problems and how a basin-modeling code can be coupled with general stress calculations. We will also show with an example from the North Sea that the amount of necessary coupling is a function of the geological history and not of the present-day stress situation.