Consistent boundary conditions in 3D mechanics-based restoration: validation on an extensional sandbox model and guidelines

Benjamin Chauvin and John H. Shaw and Guillaume Caumon and Andreas Plesch. ( 2016 )
in: 2016 RING Meeting, ASGA

Abstract

Geomechanical restoration methods are dependent on boundary conditions to ensure geological consistency of the restored model in terms of geometry and strain. Recent works have shown that classical restoration boundary conditions such as flattening a datum horizon may lead to inconsistent displacement and strain fields. This limits the methods ability to recover accurate paleo-geometries and predict areas prone to fracturing and other sub-seismic deformation. In some cases, the addition of lateral displacement constraints, equivalent to the opposite far-field tectonic shortening or extension, provides a more accurate restoration. However, such constraints may not be known. All these considerations motivate the quest for guidelines to choose appropriate boundary conditions. We restore a laboratory sandbox model with a basal silicone layer, characterized by structures analogous to those found in suprasalt extensional environments. The deformed geometry is interpreted from 3D tomography imaging, and a time-series of cross-section tomography images provides a benchmark to quantify restoration error. To restore a complex fault network, we implement novel contact conditions. These constraints tie branch lines between faults and ensure continuity between parts of a same fault cut and displaced by later faults. Moreover, we show that a shortening boundary condition is generally necessary to accurately restore the kinematic evolution of the model. This condition is likely to improve restorations in real geologic cases, in particular to capture internal deformation. We test different methods to assess the shortening: the sum of the fault heaves, a dilation analysis and the area-depth method. The latter may provide a lower bound and dilation analysis could be complementary. Finally, we propose guidelines to define optimal boundary conditions.

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BibTeX Reference

@INPROCEEDINGS{,
    author = { Chauvin, Benjamin and Shaw, John H. and Caumon, Guillaume and Plesch, Andreas },
     title = { Consistent boundary conditions in 3D mechanics-based restoration: validation on an extensional sandbox model and guidelines },
 booktitle = { 2016 RING Meeting },
      year = { 2016 },
 publisher = { ASGA },
  abstract = { Geomechanical restoration methods are dependent on boundary conditions to ensure geological consistency of the restored model in terms of geometry and strain. Recent works have shown that classical restoration boundary conditions such as flattening a datum horizon may lead to inconsistent displacement and strain fields. This limits the methods ability to recover accurate paleo-geometries and predict areas prone to fracturing and other sub-seismic deformation. In some cases, the addition of lateral displacement constraints, equivalent to the opposite far-field tectonic shortening or extension, provides a more accurate restoration. However, such constraints may not be known. All these considerations motivate the quest for guidelines to choose appropriate boundary conditions.

We restore a laboratory sandbox model with a basal silicone layer, characterized by structures analogous to those found in suprasalt extensional environments. The deformed geometry is interpreted from 3D tomography imaging, and a time-series of cross-section tomography images provides a benchmark to quantify restoration error.

To restore a complex fault network, we implement novel contact conditions. These constraints tie branch lines between faults and ensure continuity between parts of a same fault cut and displaced by later faults. Moreover, we show that a shortening boundary condition is generally necessary to accurately restore the kinematic evolution of the model. This condition is likely to improve restorations in real geologic cases, in particular to capture internal deformation. We test different methods to assess the shortening: the sum of the fault heaves, a dilation analysis and the area-depth method. The latter may provide a lower bound and dilation analysis could be complementary. Finally, we propose guidelines to define optimal boundary conditions. }
}