3-D Parameterization of the Geological Space: The GeoChron Model

Moyen, Remi, Jean-Laurent Mallet, Tobias Frank, École Nationale Supérieure de Géologie, INPL/CRPG, Nancy, France

Building a 3D-mesh covering the domain of study is one of the key points in reservoir modeling. This mesh must integrate data from various sources and nature (fault geometry, stratigraphic setting, property data, ...), and must allow for different uses (geostatistics, upscaling, flow simulation, ...).

The common pratice consists in building a “regular structured stratigraphic grid” formed of hexaedral cells whose indexes (i,j,k)can be considered as a sampling of a 3D parametric function (u,v,t). In this function, (u,v)corresponds to curvilinear “paleo-geographic” coor­dinates tangent to the horizons, and (t), viewed as an analog to the geological age of the ter­rains, is a sub-vertical curvilinear axis approximately orthogonal to the horizons.

However, the regular aspect of these grids induces geometric and modeling approxima­tions, especially in complex fault networks or folded environments. In this article, we pro­pose to use a new mathematical model, called GeoChron, which uses an unstructured tetraedral mesh and allows the parametric function to be computed whatever the complex­ity of the fault network and independantly of any structured stratigraphic grid, getting thus rid of most of the mentionned approximations.

The usual geostatistics algoritms relying on the structured nature of the grid, we then present a method allowing classical property modeling algorithms to be used on this unstruc­tured mesh. We also show that, unlike structured grids, this method is totally independant of the algorithms used for property modeling, and can thus be used in any framework.