The Influence of Lateral and Vertical Heterogeneities on Stress Orientations: Insights and Applications Using Numerical Modelling

Jose Dirkzwager
University of Karlsruhe, Karlsruhe, Germany

Data from the World Stress Map Project indicate that changes in basin- and reservoir-scale stress orientation result from a combination of far-field loading (e.g. ridge-push, rotating plates), basin geometry (e.g. deltaic sequence), geological structures (e.g. fractures, diapirs), and rheological contrasts (e.g. shale vs. sand). Examples of this include the fanning geometry of the stress field in north-western Europe, generated as a result of Alpine convergence and plate tectonic reorganisations in the northern Atlantic region interacting with the pre-existing structural framework; the NE-SW oriented stress field of the Coso Range-Indian Wells Valley region, generated by a reorganization of major tectonic blocks and topography driven mass redistribution loads, and reservoirs in Brunei indicating varying break out orientations associated with location within the prograding delta. High data densities from well control near the reservoir and knowledge of the surrounding tectonic framework, generally provides information on the type of deformation. However, unexpected gradual or abrupt changes in the stress regime may be encountered when crossing fractures and/or stratigraphic interfaces and farther away from the reservoir. This is where numerical modelling provides an excellent mean to study these changes in stress orientations and magnitudes, since it is a relatively fast method that once calibrated at a few points and/or transects, produces reliable results throughout a 3D volume. The importance of knowing where these changes in stress field orientation occur will be demonstrated by presenting the results of the contemporary stress field in a producing reservoir with actual well control in the southern North Sea using 3D numerical modelling.