Grid-free surface-based modelling using NURBS surfaces : surface construction and workflow NURBS surfaces extruded from cross sections

Carl Jacquemyn and Yulia Melnikova and Pablo Salinas and Margaret Rood and Gary J. Hampson and D Jackson. ( 2017 )
in: 2017 Ring Meeting, ASGA

Abstract

Building spatially realistic representations of geological heterogeneity in reservoir models is a challenging task that is limited by the inflexibility of predefined pillar or cornerpoint grids. Rock types with diverse petrophysical characteristics are ‘averaged' within grid cells of arbitrary size and shape, and the continuity and connectivity of baffles, barriers or high- permeability zones is often lost. Because the same areal grid resolution is needed everywhere in the model, large features are over-resolved and small features are under-resolved or omitted. Moreover, common structural configurations including intersecting faults or overhanging horizons cannot be represented on pillar grids, and inclined surfaces need to be stair-stepped. We present a surface-based modelling workflow using 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. All heterogeneity of interest (structural, stratigraphic, sedimentologic, diagenetic) is modelled by its bounding surfaces, independent of any grid. Smooth surfaces are modelled using a parametric NURBS description. These surfaces are efficient to generate and manipulate, and allow fast creation of multiple realizations of geometrically realistic reservoir models that contain detail at appropriate scales. Surfaces are explicitly constructed by (1) extruding a cross section along a trajectory, or (2) using geostatistical models. Both approaches seamlessly integrate with commonly available information such as geological descriptions from cross sections and map views in outcrop or seismic data, or sill, range and anisotropy of variogram models. Model assembly consists of applying operations that define the interactions between surfaces (joining, terminating, stacking), in order to generate ‘watertight' volumes. Metadata are provided with each surface, and holds geological meaning (e.g. facies assignment) and the interaction relationships with other surfaces. Metadata supply all information needed for automated model construction. We demonstrate this NURBS surface-based approach using a coastal-plain and overlying wave-dominated shoreface succession, analogous to an upper Brent Group reservoir, North Sea (e.g. SPE10 benchmark reservoir model). Introduction

Download / Links

BibTeX Reference

@INPROCEEDINGS{Jacquemyn2017,
    author = { Jacquemyn, Carl and Melnikova, Yulia and Salinas, Pablo and Rood, Margaret and Hampson, Gary J. and Jackson, D },
     title = { Grid-free surface-based modelling using NURBS surfaces : surface construction and workflow NURBS surfaces extruded from cross sections },
 booktitle = { 2017 Ring Meeting },
      year = { 2017 },
 publisher = { ASGA },
  abstract = { Building spatially realistic representations of geological heterogeneity in reservoir models is a challenging task that is limited by the inflexibility of predefined pillar or cornerpoint grids. Rock types with diverse petrophysical characteristics are ‘averaged' within grid cells of arbitrary size and shape, and the continuity and connectivity of baffles, barriers or high- permeability zones is often lost. Because the same areal grid resolution is needed everywhere in the model, large features are over-resolved and small features are under-resolved or omitted. Moreover, common structural configurations including intersecting faults or overhanging horizons cannot be represented on pillar grids, and inclined surfaces need to be stair-stepped. We present a surface-based modelling workflow using 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. All heterogeneity of interest (structural, stratigraphic, sedimentologic, diagenetic) is modelled by its bounding surfaces, independent of any grid. Smooth surfaces are modelled using a parametric NURBS description. These surfaces are efficient to generate and manipulate, and allow fast creation of multiple realizations of geometrically realistic reservoir models that contain detail at appropriate scales. Surfaces are explicitly constructed by (1) extruding a cross section along a trajectory, or (2) using geostatistical models. Both approaches seamlessly integrate with commonly available information such as geological descriptions from cross sections and map views in outcrop or seismic data, or sill, range and anisotropy of variogram models. Model assembly consists of applying operations that define the interactions between surfaces (joining, terminating, stacking), in order to generate ‘watertight' volumes. Metadata are provided with each surface, and holds geological meaning (e.g. facies assignment) and the interaction relationships with other surfaces. Metadata supply all information needed for automated model construction. We demonstrate this NURBS surface-based approach using a coastal-plain and overlying wave-dominated shoreface succession, analogous to an upper Brent Group reservoir, North Sea (e.g. SPE10 benchmark reservoir model). Introduction }
}