Combining multiple quantitative structural analysis techniques to create robust structural interpretations

Abstract

Carefully selected 2D transects contain an abundance of structural information that can constrain 3D analyses of petroleum systems. Realizing the full value of the information in a 2D transect requires combining multiple, independent structural analysis techniques using fully interactive tools. Our approach uses quantitative structural geologic software that instantaneously displays structural computations and analyses, eliminating time-intensive manual measurements and calculations. By quickly testing multiple hypotheses, we converged on an optimal solution that is consistent with available data. We have combined area-depth-strain (ADS) analysis, structural restoration, and forward modeling of a structural interpretation of a fault-propagation fold in the Niger Delta. These methods confirmed the original interpretation and furthermore quantified displacement, strain, detachment depth, and kinematic history. ADS analysis validated the interpreted detachment depth and revealed significant layer-parallel strain (LPS) that varied systematically with stratigraphic depth. The stratigraphic distribution of the LPS was diagnostic of structural style and, in this example, discriminated against fixed-axis and constant-thickness fault-propagation folding. A quantitative forward model incorporating backlimb shear and trishear fault-propagation folding accurately reproduced folding and faulting in the pregrowth section and folding in the growth section. The model-predicted strain distributions were consistent with those from ADS analysis. The highest local strains on the back limb of the structure were spatially coincident with two backthrusts, which accommodated these strains. Animations of a more complete model including the backthrusts revealed that the backthrusts formed sequentially as rock passed through the main fault bend.