11.7.1 Higher Order Grid Geometry and Properties

Recently, the reservoir modeling industry has seen increased integration between reservoir fluid flow and geomechanical calculations, and a corresponding increase in the use of finite element grids. RESQML provides a new vendor-neutral finite element grid description, which supports higher order grid geometry and properties. Higher order grid geometry may be attached to cell faces, cell edges, cells, or additional subnodes. This ability provides the geometric support for higher order finite element grids.

Subnode geometry is not sufficient to uniquely define the shapes or volumes of the resulting cells, as the latter depends on the method of interpolation between the nodes and subnodes, not just the nodal positions. A classification of the possible finite element shape interpolation schemes is not included in RESQML, although in some circumstances, an interpolation scheme may be inferred from the corresponding lower order grid description. This is in contrast to hinge nodes, where an explicit interpolation (triangulation) of the cell face is implied.

RESQML treats these geometries as additional information to an existing column-layer or unstructured geometry. This is an example of a deliberate strategy in which we start with a simple grid and then provide optional extensions. This provides guidance to a RESQML reader on how to ignore extensions that are not included within their internal data model, while still providing the possibility of some degree of data transfer. Instead of using flags to describe grid options, the extensions themselves are localized in specific data objects, and the RESQML reader may check for their existence and respond accordingly.