Forward and Backward modelling : the Simple Shear hypothesis

Cyril Galéra and Chakib Bennis and Isabelle Moretti and Jean-Laurent Mallet. ( 1999 )
in: $19^th$ Gocad Meeting Proceedings

Abstract

ln order to define the prospects to be drilled, structural geologists have to take into account ail available data to approach the true 3D geometry of an area. Usually these data consist of seismic images (2D and/or 3D), wells and surface data. Olten the study has two steps: first to build coherent markers (horizons and faults) based on the most reliable data and then to restore them. The interest of restoration is to test the existence of an acceptable deformation path from a realistic initial geometry to the current one. In 2D as in 3D, the main hypothesis is that of mass conservation which can be specified by length and/or surface deformation depending on the deformation mode of the mate rial (Dahlstrom, 1969). Various deformation modes have been documented that can be correlated to the competence of the material: flexural slip for highly competent layers, simple shear for recent poorly compacted sediment and flow for ductil layers such as shaly decollement level and salt (Moretti & Larrère, 1989). Rigid rotation also exists in extensive crustal domain (tilted block and domino style area). In extensive domain, like those along margins, where early tilting of the base ment is followed by fast sedimentation, growth faults and rollovers are created by simple shear deformation which affects the sediments. To help structuralists in such a context, we developed a new set of tools to build geologically coherent 3D block diagram based on the simple shear criteria and then applied this criteria to model the deformation (Galera et al. 1999). A first presented tool allows us to entirely construct a listric fault given the initial geometry of a horizon, the final one and the fault segment between the two positions. Another one enables us to construct the final (resp. initial) horizon knowing the listric fault, the throw and the initial (resp. final) horizon. The third one is a modeling of a rollover evolution versus time while sedimentation and fault displacement are coeval.

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    BibTeX Reference

    @INPROCEEDINGS{Galera1999a,
        author = { Galéra, Cyril and Bennis, Chakib and Moretti, Isabelle and Mallet, Jean-Laurent },
         title = { Forward and Backward modelling : the Simple Shear hypothesis },
     booktitle = { $19^th$ Gocad Meeting Proceedings },
          year = { 1999 },
      abstract = { ln order to define the prospects to be drilled, structural geologists have to take
    into account ail available data to approach the true 3D geometry of an area. Usually
    these data consist of seismic images (2D and/or 3D), wells and surface data. Olten
    the study has two steps: first to build coherent markers (horizons and faults) based on
    the most reliable data and then to restore them. The interest of restoration is to test
    the existence of an acceptable deformation path from a realistic initial geometry to the
    current one. In 2D as in 3D, the main hypothesis is that of mass conservation which
    can be specified by length and/or surface deformation depending on the deformation
    mode of the mate rial (Dahlstrom, 1969). Various deformation modes have been
    documented that can be correlated to the competence of the material: flexural slip for
    highly competent layers, simple shear for recent poorly compacted sediment and flow
    for ductil layers such as shaly decollement level and salt (Moretti & Larrère, 1989).
    Rigid rotation also exists in extensive crustal domain (tilted block and domino style
    area). In extensive domain, like those along margins, where early tilting of the
    base ment is followed by fast sedimentation, growth faults and rollovers are created by
    simple shear deformation which affects the sediments.
    To help structuralists in such a context, we developed a new set of tools to build
    geologically coherent 3D block diagram based on the simple shear criteria and then
    applied this criteria to model the deformation (Galera et al. 1999). A first presented
    tool allows us to entirely construct a listric fault given the initial geometry of a horizon,
    the final one and the fault segment between the two positions. Another one enables us
    to construct the final (resp. initial) horizon knowing the listric fault, the throw and the
    initial (resp. final) horizon. The third one is a modeling of a rollover evolution versus
    time while sedimentation and fault displacement are coeval. }
    }