USE OF FINITE ELEMENT FORWARD MODELING IN ANALYZING GEOLOGIC STRUCTURES

Mechanical forward modeling of geologic structures is a significant advance over geometric techniques (i.e., fault-related folding in it’s many guises) in terms of understanding the way that rocks deform. This is particularly important if one wishes to be predictive about small-scale deformation within permeable or impermeable beds. Geometric (or so-called kinematic) techniques for analyzing structures, particularly shear fault bend folding and tri-shear, have an advantage in being tunable to closely match a specific, observed structure. A disadvantage lies in that they treat all rock types in the same way. The area of a section is fixed during analysis. These techniques cannot be applied in 3D. Finally, these models are not predictive. Best-fit parameters on one cross-section model do not necessarily pertain to adjacent sections. Finite element-based mechanical models can incorporate a complete range of rock behaviors and the stresses and thermal regimes in which they are deformed. They are also amenable to 3D problems. An application of these techniques to basement-cored uplifts from the Bighorn Basin in Wyoming demonstrates they predict realistic geometries and replicate the thinning and thickening of the individual units as seen in the field. The main drawbacks of these methods are the time and computational resources it requires to run realistic models, and the inability to tune the models to explicitly match a specific geometry. Finite element models provide an excellent improvement over geometric techniques for analyzing structures, while not completely replacing their utility for quick-look analysis of the general elements of a structure.