Balanced Restoration of Geological Volumes with Relaxed Meshing Constraints
Balanced restoration aims at unfolding and unfaulting complex deformed structures by iteratively removing deformations caused by successive tectonic events, to retrieve the depositional state of the model. Restoration then helps understanding a geodynamic scenario, reduce structural uncertainties by testing the consistency of the structural model, and, given a correct mechanical behavior law, evaluate retro-deformation.
An elastic finite element model can be used to solve restoration problems, by setting displacement boundary conditions on the top horizon, supposedly flat at the deposition time step; fixing some pin zones (typically, it can be a pin point, a pin line or/and a pin wall); and defining contacts between the fault foot wall and hanging wall. This method is generally applied on a tetrahedral mesh conformable to both faults and horizons, for it provides accurate representations even in complex structural settings. However, conforming to stratigraphic surfaces, including erosive and onlaping surfaces, drastically increases the number of mesh elements, and possibly reduces mesh quality, causing issues during finite element computations. One consequence is that mesh limitations are the main bottleneck to apply finite-element-based restoration to actual settings. To face this problem, we propose to represent horizons as a property of the tetrahedral model, and to transfer the associated boundary conditions onto the neighboring nodes of the mesh, using an “implicit” approach. New boundary conditions are defined to this new type of horizons, and a hyper-elastic rheology is set to emulate the absence of the restored layers. The proposed method provides results comparable to those of the explicit technique, at much lesser effort. Also, the implicit method provides a convenient way to handle unconformities in restoration, both for eroded surfaces, and on baselap layer geometries.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009