Integration of Structural Analyses with Numerical Modeling: Analysis of Stress and Strain Evolution to Aid Reservoir Exploration and Development

Kevin J. Smart¹, David A. Ferrill¹, Goodluck I. Ofoegbu¹, Darrell W. Sims¹, Nathan M. Franklin¹, and Alan P. Morris^2
1 CNWRA, Southwest Research Institute, San Antonio, TX
² University of Texas San Antonio, San Antonio, TX

A fundamental gap exists in the oil and gas industry between exploration, and subsequent drilling and production activities. Geologic and geophysical data utilized in exploration typically yield geometric and kinematic information rather than the stress and rock properties desired by reservoir and production engineers. Numerical geomechanical modeling can bridge the gap by coupling physically realistic and mechanically rigorous analyses that yield testable predictions. A three-dimensional structural model based on seismic and well data can serve as a template for construction of a geomechanical model coupled with realistic rock properties. These mechanically reasonable forward models can validate kinematic restorations, and track complete stress and strain histories throughout the structure. We present an analysis of the stress/strain evolution during regional-scale inversion. A generalized example was developed that is compatible with structures in the North Sea where early regional extension was followed by a period of regional contraction. The models correctly predict the development of hanging wall roll-over and crestal graben formation during extension. During subsequent structural inversion the model predicts a transition from extensional to contractional strain in the crestal region and progressive widening of the zone of contraction. The stress history is intriguing in that the evolution at a particular location is strongly influenced by geometry (e.g., proximity to a fault) along with the cumulative effects of all preceding load increments. The conventional wisdom that differential stress increases with depth may be inappropriate in some areas, and prediction of stress magnitudes and orientations based on simple assumptions and final geometries can be misleading. Numerical modeling of complex structures can be used to develop more realistic stress histories that can feed reservoir engineering analyses.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005