NUMERICAL SIMULATION OF BASIN GEOMETRY INFLUENCE ON THE RESULTING STRESS PATH

It is well understood that the heterogeneous distribution of elastic rock properties in layered sedimentary strata has significant influence on the resulting horizontal stress magnitudes. If no direct stress measurements are available horizontal stress magnitudes in tectonically relaxed sedimentary basins are often assumed based on either the uniaxial strain model, the linear poro-elastic model, or the frictional equilibrium model. The uniaxial strain model and the linear poro-elastic model are based on assumptions of a static elastic medium of horizontal layers subjected to constant horizontal strain. Recent studies have shown that the validity of these assumptions is highly questionable. In addition, numerical modeling approaches for stress magnitude prediction commonly assume a rectangular geometry of a sedimentary basin with vertical model boundaries (for ease of application of boundary conditions). More realistic basin geometries accounting for sloped walls and an uneven bottom surface are not considered.

This study investigates the influence of sedimentary basin geometry on the resulting stress profiles. 2D plane strain finite element analysis is used to provide conceptual models of common basin geometries (such as intracratonic basins, rift basins, half graben basins, passive margin basins, forearc basins, etc). The models investigate basin size, depth, layer tilt, and material property heterogeneity on the resulting horizontal stress magnitudes. The model results indicate that the uniaxial strain model and the linear poro-elastic model are only applicable in large basins at locations far from the basin boundaries. For all other cases significant variations for the prediction of horizontal stress magnitudes occur, and therefore stress predictions based on elastic property measurements (as used for the uniaxial strain model and the linear poro-elastic model) are not recommended.