Dear colleagues, dear sponsors,

  Welcome to the 2011 Nancy Gocad Meeting to attend another harvest or research advances in geomodeling. This year’s topics cover a wide spectrum, from geological interpretation and characterization to reservoir gridding and history matching. Two principles underlie the research done at the Gocad Research Group: bring in more geological and physical concepts in geomodeling workflows, and propose ways to sample the related uncertainty.

  The presentations of Florent Lallier illustrate this philosophy on the difficult problem of automated well correlation. The general correlation algorithm proposed by Florent uses elementary correlation rules between well sections or interfaces to compute likely correlations. Florent declines these rules in several contexts: carbonate buildups, carbonate ramps, magnetostratigraphic data in clastic rocks. Along these lines, Charline Julio also proposes methods to exploit first order information extracted from seismic data to constrain lateral trends in the computation of correlation costs.

  In structural modeling, classical workflows have undergone tremendous advances recently thanks to the advent of implicit surfaces, which makes model building faster and more robust than classical surface-based modeling. As shown by Nicolas Cherpeau, these improvements open new perspectives for assessing structural uncertainty not only about stratigraphy but also about fault networks. It is now possible to simulate stochastic faults conditionally to sparse data and make both their geometry and topology variable. The sampled structural uncertainty can then be reduced by assimilating ancillary data types such as reservoir production curves. In this inverse process, topological and geometrics changes are treated by a novel way to parameterize and perturb the stochastic structural model. In the presence of 3D seismic data, Nicolas’ work could be extended by incrementally inserting faults in a structural model until seismic reflectors are correctly matched. Doing this raises two main challenges.

  First, one needs appropriate meshing methods to represent discontinuities in the domain of study, even in complex cases where surfaces are tangential. To tackle this longstanding problem,  Jeanne Pellerin  proposes a 3D surface remeshing method based on Centroidal Voronoi Tessellations that clears the path for controlled simplifications and easier conformable mesh generation. To manage thin features and low angle contacts a minimum set of points is inserted  unlike classical Delaunay insertion strategies which tend to dramatically increase the number of mesh elements.

  Second, there is a need for more forward-like methods able to quickly deform numerical rock volumes in order to match subsurface data. As a first step towards that goal, Gautier Laurent has started revisiting a deformation method originally designed in computer graphics. From some boundary conditions, Gautier computes a 3D deformation field using a discrete network of rigid elements; although still at an early stage, this approach is very promising for controlling the amount of ductile deformation in geological layers, especially the neighborhood of fault zones. The vector-field based deformation method presented by Antoine Bouziat could be used for the same purpose, or simply to deform / update geological models interactively.

  At a smaller scale, Francois Bonneau introduces a discrete fracture network simulation method able to honor connectivity data between wells. The direct integration of such information, together with geomechanically realistic fracture propagation rules, is a major step forward in history matching of fractured reservoirs. Moreover, the application of the method to the Soultz geothermal reservoir opens interesting perspectives in the integration of microseismicity data in DFN modeling. In the case of fold-related curvatures in thin geomechanically layered strata, this method can also benefit from the theoretical work of Jean-Jacques Royer relating stretching and bending energies to surface Gaussian and mean curvatures. Object-based simulation is also used in the karst modeling approach by Pauline Collon-Drouaillet and Gaetan Bardy. In their papers, they describe new way to appropriately generate branchwork karsts while honoring input data.

  The ultimate goal of geomodels is often to simulate physical processes in the subsurface. Because these processes often involve tensor fields, Charlotte Botter proposes new ways to visualize such fields using dynamic elliptical particles computed and displayed through the GPU. When it comes to flow simulation, discretization is often a challenge because heterogeneities do not necessarily meet the requirements of simple discretization schemes. Three works are presented this year to tackle this challenge. Jean-Jacques Royer proposes a formulation of the flow equations directly in depositional space. This theory sets the bases to directly run streamline simulation in chronostratigraphic space, thereby removing the need for explicit reservoir gridding. The two other papers precisely look into ways to generate reservoir grids in present-day physical space. Jérémy Ruiu proposes a set of algorithms to truncate corner-point grids by structural models, which clears the path for a fault block-wise reservoir gridding strategy. Romain Merland proposes strategies to make unstructured polyhedral grids conformable to structural frameworks. These methods, based on a global minimization, are compatible with the gridding approaches investigated by Deborah Siffert, who shows experimentally that coarse reservoir gridding based on fine-scale vorticity field is a method of choice in adaptive reservoir gridding.

 As each year, I am also extremely pleased to welcome presentations from other members of the Gocad Consortium. These presentations reveal the diversity and dynamism of research performed by our community, covering geomodeling case studies, GIS, geostatistics and image analysis, 3D restoration, geophysical inversion and gridding. I would like to thank all the authors of this volume for the quality of their papers and for sharing their work during the 31^st Gocad Meeting.

 I wish you a great and memorable conference!