Stochastic simulations and perturabtions of structural models including topological changes.

in: Proceedings of the 29th Gocad Meeting

Abstract

During the estimation of reservoir OHIP, structural uncertainties are often a major but neglected factor. Moreover, structural uncertainties relative to layer thickness and faults play a key role in subsurface flow, wether faults are sealing barriers or drains. In particular, a change in the connection between faults may drastically alter fluid flow predictions. Whereas most structural uncertainty modeling techniques only allow for geometrical changes, keeping the topology fixed, we propose a new workflow for creating realistic stochastic structural models. For this, we suggest combining an implicit representation of geological surfaces which provides new perspectives for handling topological changes with a stochastic binary tree to represent the spatial regions of the structural model. In this paper, we present early implementation steps of this workflow, focusing on fault zones in the case of poor quality seismic data. We propose to build a 3D envelope around fault zones, then to compute the Medial Axis Transform of this 3D surface. We obtain a skeleton around which faults are simulated. In the case of branching faults, a segmentation of the skeleton allows to create different faults from one or several segments. The created faults can then be considered as a single network cutting the whole model in several fault blocks. One can describe their relations to each other as a binary tree, as in Constructive Solid Geometry. Each node of the tree is a fault, separating the space in two fault blocks. Changes in this binary tree modify the fault relations and therefore the topology of the model. Once the topology has been simulated with this method, one can generate various geometrical realizations and perturb those under input structural constraints.

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BibTeX Reference

@INPROCEEDINGS{Cherpeau2009a,
    author = { Cherpeau, Nicolas and Caumon, Guillaume and Levy, Bruno },
     title = { Stochastic simulations and perturabtions of structural models including topological changes. },
 booktitle = { Proceedings of the 29th Gocad Meeting },
      year = { 2009 },
  abstract = { During the estimation of reservoir OHIP, structural uncertainties are often a major but neglected factor. Moreover, structural uncertainties relative to layer thickness and faults play a key role in subsurface flow, wether faults are sealing barriers or drains. In particular, a change in the connection between faults may drastically alter fluid flow predictions. Whereas most structural uncertainty modeling techniques only allow for geometrical changes, keeping the topology fixed, we propose a new workflow for creating realistic stochastic structural models. For this, we suggest combining an implicit representation of geological surfaces which provides new perspectives for handling topological changes with a stochastic binary tree to represent the spatial regions of the structural model. In this paper, we present early implementation steps of this workflow, focusing on fault zones in the case of poor quality seismic data. We propose to build a 3D envelope around fault zones, then to compute the Medial Axis Transform of this 3D surface. We obtain a skeleton around which faults are simulated. In the case of branching faults, a segmentation of the skeleton allows to create different faults from one or several segments. The created faults can then be considered as a single network cutting the whole model in several fault blocks. One can describe their relations to each other as a binary tree, as in Constructive Solid Geometry. Each node of the tree is a fault, separating the space in two fault blocks. Changes in this binary tree modify the fault relations and therefore the topology of the model. Once the topology has been simulated with this method, one can generate various geometrical realizations and perturb those under input structural constraints. }
}