Three-Dimensional Modelling of Sant Corneli Anticline (Spain) Using a Hybrid-Geometric/geomechanical Approach

Three dimensional modeling and restoration of folded and faulted strata has traditionally utilized a variety of geometric and mechanical techniques, often in combination. Geometric techniques are computationally inexpensive, but lack the full stress solution and may be limited to plane strain. In contrast, mechanical techniques produce stress solutions implicitly, but are computationally expensive and may not efficiently model dynamic processes or large strains. We present a new mass-spring technique for structural restoration that is computationally inexpensive, accounts for heterogeneous displacement, models dynamic processes, and is based on physical laws of displacement. Geologic surfaces and volumes are represented by elements with finite mass connected by springs, and the point dynamics equations for each mass are integrated over the surface or volume for a given time step. Dynamic processes and large deformations are implicit in the model formulation and the model mimics natural processes by minimizing strain. The stress/strain for any element or mass can be computed based on motions of adjacent masses.

The Sant Corneli anticline is a plunging thrust-related anticline in the Spanish Pyrenees. This fractured reservoir analogue is cored by fractured carbonates capped by marl units that are subsequently overlain by a sequence of syn-tectonic sediments. The syn-tectonic strata record many aspects of fold kinematics that are unconstrained in most fault-cored folds, such as limb rotation and lateral fold propagation. Incremental restoration of the anticline demonstrates the capability of the mass-spring technique for unfolding surfaces and volumes while simultaneously restoring displacement on faults. Stresses predicted by mechanical restorations and forward models are compared to the observed sequence of fracturing, which provides an important validation of the restoration algorithms and our ability to predict sub-seismic fault and fracture orientations.