Generating variable shapes of salt geobodies from seismic images

in: The 19th Annual Conference of the International Association for Mathematical Geosciences, International Association for Mathematical Geosciences

Abstract

Modeling 3D salt geobodies from subsurface data usually requires lots of time and expertise. The difficulties encountered stem from the assumptions underlying geomodeling techniques. These techniques are designed for almost vertical single-valued surfaces, and generally minimize the surface curvature and the layer width variations. These assumptions are not verified for salt envelopes, which are thus often manually modeled with a deterministic expert-driven approach. We present in this paper an implicit methodology to generate automatically several possible models of salt top surfaces with varying geometries and topologies. As seismic imaging of salt is prone to velocity uncertainty and Fresnel zone effects, we take as input a seismic image that we segment into three regions: salt, sediments and uncertain, using seismic attributes. The uncertain region is assumed to contain the salt boundary and all the further computations will focus within this zone. We generate a monotonic scalar field ranging from zero at the contact with salt to one at the contact with sediments. This scalar field can be seen as the cumulated probability for any point of being outside the salt boundary, i.e., to be sediments. We then generate a random scalar field, also bounded between zero and one, that we use to threshold the first field. The salt boundary is implicitly defined by the zero isovalue of the difference of the two fields, and can be further extracted using marching cubes. We illustrate the method on a 3D synthetic data set and discuss the geometrical and topological implications of the choice of the random field parameters.

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    BibTeX Reference

    @INPROCEEDINGS{,
        author = { Clausolles, Nicolas and Collon, Pauline and Caumon, Guillaume },
         title = { Generating variable shapes of salt geobodies from seismic images },
         month = { "sep" },
     booktitle = { The 19th Annual Conference of the International Association for Mathematical Geosciences },
          year = { 2018 },
    organization = { International Association for Mathematical Geosciences },
          isbn = { 978-80-270-4612-6 },
      abstract = { Modeling 3D salt geobodies from subsurface data usually requires lots of time and expertise.  The difficulties encountered stem from the assumptions underlying geomodeling techniques. These techniques are designed for almost vertical single-valued surfaces, and generally minimize the surface curvature and the layer width variations. These assumptions are not verified for salt envelopes, which are thus often manually modeled with a deterministic expert-driven approach. We present in this paper an implicit methodology to generate automatically several possible models of salt top surfaces with varying geometries and topologies. As seismic imaging of salt is prone to velocity uncertainty and Fresnel zone effects, we take as input a seismic image that we segment into three regions: salt, sediments and uncertain, using seismic attributes. The uncertain region is assumed to contain the salt boundary and all the further computations will focus within this zone. We generate a monotonic scalar field ranging from zero at the contact with salt to one at the contact with sediments. This scalar field can be seen as the cumulated probability for any point of being outside the salt boundary, i.e., to be sediments. We then generate a random scalar field, also bounded between zero and one, that we use to threshold the first field. The salt boundary is implicitly defined by the zero isovalue of the difference of the two fields, and can be further extracted using marching cubes. We illustrate the method on a 3D synthetic data set and discuss the geometrical and topological implications of the choice of the random field parameters. }
    }