Abstract
Building geometrically realistic representations of geological heterogeneity in reservoir models is a challenging task that is limited by the inflexibility of pre-defined pillar or cornerpoint grids. The surface-based modelling workflow uses grid-free surfaces that allows efficient creation of geological models without the limitations of pre-defined grids. Surface-based reservoir modelling uses a boundary representation approach in which all heterogeneity of interest (structural, stratigraphic, sedimentological, diagenetic) is modelled by its bounding surfaces, independent of any grid. Volumes bounded by these surfaces are internally homogeneous and, thus, no additional facies or petrophysical modelling is performed within these geological domains and no grid or mesh discretisation is needed during modelling. Any heterogeneity to be modelled within such volumes is incorporated by adding surfaces. Surfaces and curves are modelled using a parametric non-uniform rational B-splines (NURBS) description. These surfaces are efficient to generate and manipulate, and allow fast creation of multiple realisations of geometrically realistic reservoir models. Multiple levels of surface hierarchy are introduced to allow modelling of all features of interest at the required level of detail; surfaces at one hierarchical level are constructed so as to truncate or conform to surfaces of a higher hierarchical level. This procedure requires the joining, terminating and stacking of surfaces to ensure that models contain “watertight” surface-bounded volumes. NURBS curves are used to represent well trajectories accurately, including multi-laterals or side-tracks. Once all surfaces and wells have been generated, they are combined into a reservoir model that takes into account geological relationships between surfaces and preserves realistic geometries.
Highlights
Surface-based reservoir modelling and simulation is an approach to modelling subsurface reservoirs in which reservoir heterogeneity that impacts fluid flow is represented explicitly by their bounding surfaces (Caumon et al 2009; Deveugle et al 2011; Graham et al 2015a, b; Hassanpour et al 2013; Jackson et al 2009, 2013, 2015; Massart et al 2016a, b; Pyrcz et al 2005; Sech et al 2009; Zhang et al 2009)
The inputs for surface-based modelling are the bounding surfaces that define structural features, sediment bodies, facies and/or lithology distributions, and other types of geological heterogeneity. This is very different from conventional approaches in which geostatistical or object-based methods are used to distribute properties over pre-defined grid cells, and from hybrid surfaceand grid-based approaches in which some scales of heterogeneity are represented by surfaces that are discretised on a cornerpoint grid on which further facies or petrophysical modelling is performed (Hassanpour et al 2013; Pyrcz et al 2005, 2009; Ruiu et al 2016; Zhang et al 2009)
A non-uniform rational B-splines (NURBS)-surface-based modelling approach allows all geological heterogeneity of interest and wells of any trajectory to be represented without reference to a pre-defined grid
Summary
Surface-based reservoir modelling and simulation is an approach to modelling subsurface reservoirs (water, geothermal, petroleum) in which reservoir heterogeneity that impacts fluid flow is represented explicitly by their bounding surfaces (Caumon et al 2009; Deveugle et al 2011; Graham et al 2015a, b; Hassanpour et al 2013; Jackson et al 2009, 2013, 2015; Massart et al 2016a, b; Pyrcz et al 2005; Sech et al 2009; Zhang et al 2009). The grid refinement provides local geometrical accuracy (i.e. small grid cells) at the expense of computational efficiency (i.e. a large number of grid cells). Pyrcz et al (2005) and Zhang et al (2009)
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