Publications
67 results found
Jacquemyn C, Jackson MD, Hampson GJ, 2019, Surface-based reservoir modelling: Automatic assembly for multiple stochastic realizations
© 81st EAGE Conference and Exhibition 2019. All rights reserved. Surface-based reservoir modelling for hydrocarbon or geothermal reservoirs is a modelling approach that represents subsurface heterogeneity by surfaces. All heterogeneity of interest is modelled only by its bounding surfaces, free from a predefined grid. This overcomes grid-related limitations of conventional modelling approaches such as stair-stepping, loss of connectivity or continuity and resolution limitations to capture small features that are essential to flow. Creating surface-based models relies on generating 100's of surfaces of different geometries, scales and relationships, all representing a boundary between volumes with different properties. We show how adding metadata to every surface enables automatic assembly of all these individual surfaces into a surface-based reservoir model. Metadata signifies why a surface exists and includes what properties are on either side of a surface, which volume it intersects and the level of detail it represents. Multiple model realisations can now be built automatically from stochastically generated bounding surfaces.
Jacquemyn C, Jackson MD, Hampson GJ, 2019, Surface-based reservoir modelling: Automatic assembly for multiple stochastic realizations
Surface-based reservoir modelling for hydrocarbon or geothermal reservoirs is a modelling approach that represents subsurface heterogeneity by surfaces. All heterogeneity of interest is modelled only by its bounding surfaces, free from a predefined grid. This overcomes grid-related limitations of conventional modelling approaches such as stair-stepping, loss of connectivity or continuity and resolution limitations to capture small features that are essential to flow. Creating surface-based models relies on generating 100's of surfaces of different geometries, scales and relationships, all representing a boundary between volumes with different properties. We show how adding metadata to every surface enables automatic assembly of all these individual surfaces into a surface-based reservoir model. Metadata signifies why a surface exists and includes what properties are on either side of a surface, which volume it intersects and the level of detail it represents. Multiple model realisations can now be built automatically from stochastically generated bounding surfaces.
Jacquemyn C, Jackson MD, Hampson GJ, 2019, Surface-based geological reservoir modelling using grid-free NURBS curves and surfaces, Mathematical Geosciences, Vol: 51, Pages: 1-28, ISSN: 1874-8953
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. 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 discretization 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 NURBS (non-uniform rational B-splines) description. These surfaces are efficient to generate and manipulate, and allow fast creation of multiple realizations 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 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.
Salinas P, Jacquemyn C, Kampitsis A, et al., 2019, A parallel load-balancing reservoir simulator with dynamic mesh optimisation
The use of dynamic mesh optimization (DMO) for multiphase flow in porous have been proposed recently showing a very good potential to reduce the computational cost by placing the resolution where and when necessary. Nonetheless, further work needs to be done to prove its usability in very large domains where parallel computing with distributed memory, i.e. using MPI libraries, may be necessary. Here, we describe the methodology used to parallelize a multiphase porous media flow simulator in combination with DMO as well as study of its performance. Due to the peculiarities and complexities of the typical porous media simulations due to its high aspect ratios, we have included a fail-safe for parallel simulations with DMO that enhance the robustness and stability of the methods used to parallelize DMO in other fields (Navier-Stokes flows). The results show that DMO for parallel computing in multiphase porous media flows can perform very well, showing good scaling behaviour.
Salinas P, Jacquemyn C, Kampitsis A, et al., 2019, A parallel load-balancing reservoir simulator with dynamic mesh optimisation
Copyright 2019, Society of Petroleum Engineers. The use of dynamic mesh optimization (DMO) for multiphase flow in porous have been proposed recently showing a very good potential to reduce the computational cost by placing the resolution where and when necessary. Nonetheless, further work needs to be done to prove its usability in very large domains where parallel computing with distributed memory, i.e. using MPI libraries, may be necessary. Here, we describe the methodology used to parallelize a multiphase porous media flow simulator in combination with DMO as well as study of its performance. Due to the peculiarities and complexities of the typical porous media simulations due to its high aspect ratios, we have included a fail-safe for parallel simulations with DMO that enhance the robustness and stability of the methods used to parallelize DMO in other fields (Navier-Stokes flows). The results show that DMO for parallel computing in multiphase porous media flows can perform very well, showing good scaling behaviour.
Salinas P, Jacquemyn C, Kampitsis A, et al., 2019, A parallel load-balancing reservoir simulator with dynamic mesh optimisation
Copyright 2019, Society of Petroleum Engineers. The use of dynamic mesh optimization (DMO) for multiphase flow in porous have been proposed recently showing a very good potential to reduce the computational cost by placing the resolution where and when necessary. Nonetheless, further work needs to be done to prove its usability in very large domains where parallel computing with distributed memory, i.e. using MPI libraries, may be necessary. Here, we describe the methodology used to parallelize a multiphase porous media flow simulator in combination with DMO as well as study of its performance. Due to the peculiarities and complexities of the typical porous media simulations due to its high aspect ratios, we have included a fail-safe for parallel simulations with DMO that enhance the robustness and stability of the methods used to parallelize DMO in other fields (Navier-Stokes flows). The results show that DMO for parallel computing in multiphase porous media flows can perform very well, showing good scaling behaviour.
Salinas P, Jacquemyn C, Kampitsis A, et al., 2019, A parallel load-balancing reservoir simulator with dynamic mesh optimisation
Copyright 2019, Society of Petroleum Engineers. The use of dynamic mesh optimization (DMO) for multiphase flow in porous have been proposed recently showing a very good potential to reduce the computational cost by placing the resolution where and when necessary. Nonetheless, further work needs to be done to prove its usability in very large domains where parallel computing with distributed memory, i.e. using MPI libraries, may be necessary. Here, we describe the methodology used to parallelize a multiphase porous media flow simulator in combination with DMO as well as study of its performance. Due to the peculiarities and complexities of the typical porous media simulations due to its high aspect ratios, we have included a fail-safe for parallel simulations with DMO that enhance the robustness and stability of the methods used to parallelize DMO in other fields (Navier-Stokes flows). The results show that DMO for parallel computing in multiphase porous media flows can perform very well, showing good scaling behaviour.
Onyenanu GI, Jacquemyn CEMM, Graham GH, et al., 2018, Geometry, distribution and fill of erosional scours in a heterolithic, distal lower shoreface sandstone reservoir analogue: Grassy Member, Blackhawk Formation, Book Cliffs, Utah, USA, Sedimentology, Vol: 65, Pages: 1731-1760, ISSN: 0037-0746
Many shoreface sandstone reservoirs host significant hydrocarbon volumes within distal intervals of interbedded sandstones and mudstones. Hydrocarbon production from these reservoir intervals depends on the abundance and proportion of sandstone beds that are connected by erosional scours, and on the lateral extent and continuity of interbedded mudstones. Cliff‐face exposures of the Campanian ‘G2’ parasequence, Grassy Member, Blackhawk Formation in the Book Cliffs of east‐central Utah, USA, allow detailed characterization of 128 erosional scours within such interbedded sandstones and mudstones in a volume of 148 m length, 94 m width and 15 m height. The erosional scours have depths of up to 1·1 m, apparent widths of up to 15·1 m and steep sides (up to 35°) that strike approximately perpendicular (N099 ± 36°) to the local north–south palaeoshoreline trend. The scours have limited lateral continuity along strike and down dip, and a relatively narrow range of apparent aspect ratio (apparent width/depth), implying that their three‐dimensional geometry is similar to non‐channelized pot casts. There is no systematic variation in scour dimensions, but ‘scour density’ is greater in amalgamated (conjoined) sandstone beds over 0·5 m thick, and increases upward within vertical successions of upward‐thickening conjoined sandstone beds. There is no apparent organization of the overall lateral distribution of scours, although localized clustering implies that some scours were re‐occupied during multiple erosional events. Scour occurrence is also associated with locally increased amplitude and laminaset thickness of hummocky cross‐stratification in sandstone beds. The geometry, distribution and infill character of the scours imply that they were formed by storm‐generated currents coincident with riverine sediment influx (‘storm floods’). The erosional scours increase the vertical and lateral connectivity
Jacquemyn C, Rood M, Melnikova Y, et al., 2018, My Geology Is Too Complex for My Grid: Grid-Free Surface-Based Geological Modelling, EAGE annual conference and exhibition
Salinas P, Jacquemyn C, Heaney C, et al., 2018, Simulation of enhanced geothermal systems using dynamic unstructured mesh optimisation, EAGE annual conference and exhibition
Jacquemyn C, Jackson MD, Hampson GJ, et al., 2018, Geometry, spatial arrangement and origin of carbonate grain‐dominated, scour‐fill and event‐bed deposits: Late Jurassic Jubaila Formation and Arab‐D Member, Saudi Arabia, Sedimentology, Vol: 65, Pages: 1043-1066, ISSN: 0037-0746
<jats:title>Abstract</jats:title><jats:p>Outcrop analogues of the Late Jurassic lower Arab‐D reservoir zone in Saudi Arabia expose a succession of fining‐upward cycles deposited on a distal middle‐ramp to outer‐ramp setting. These cycles are interrupted by erosional scours that incise up to 1·8 m into underlying deposits and are infilled with intraclasts up to boulder size (1 m diameter). Scours of similar size and infill are not commonly observed on low‐angle carbonate ramps. Outcrops have been used to characterize and quantify facies‐body geometries and spatial relationships. The coarse grain size of scour‐fills indicates scouring and boulder transport by debris or hyperconcentrated density flows strengthened by offshore‐directed currents. Longitudinal and lateral flow transformation is invoked to produce the ‘pit and wing’ geometry of the scours. Scour pits and wings erode up to 1·8 m and 0·7 m deep, respectively, and are on average 50 m wide between wing tips. The flat bases of the scours and their lack of consistent aspect ratio indicate that erosion depth was limited by the presence of cemented firmgrounds in underlying cycles. Scours define slightly sinuous channels that are consistently oriented north–south, sub‐parallel to the inferred regional depositional strike of the ramp, suggesting that local palaeobathymetry was more complex than commonly assumed. Weak lateral clustering of some scours indicates that they were underfilled and reoccupied by later scour incision and infill. Rudstone scour‐fills required reworking of material from inner ramp by high‐energy, offshore‐directed flows, associated with storm action and the hydraulic gradient produced by coastal storm setup, to generate erosion and sustain transport of clasts that are generally associated with steeper slopes. Quantitative analysis indicates that these coarse‐grained units have limited potential for correlation b
Jackson C, Magee C, Jacquemyn C, 2018, Rift-related magmatism influences petroleum systems development in the NE Irish Rockall Basin, offshore Ireland
Salinas P, Lei Q, Jacquemyn C, et al., 2018, DYNAMIC UNSTRUCTURED MESH ADAPTIVITY FOR IMPROVEDSIMULATION OF GEOTHERMAL WATER EXTRACTION INRESERVOIR-SCALE MODELS, 3rd Thermal and Fluids Engineering Conference
Jacquemyn C, Rood MP, Melnikova Y, et al., 2018, My geology is too complex for my grid: Grid-free surface-based geological modelling
© 2018 Society of Petroleum Engineers. All rights reserved. Building spatially realistic representations of heterogeneity in reservoir models is a challenging task that is limited by predefined pillar or cornerpoint grids. Diverse rock types are ‘averaged’ within grid cells of arbitrary size and shape; continuity of baffles, barriers or high-permeability streaks is often lost; large features are over-resolved and small features are under-resolved or omitted. We present a surface-based modelling workflow using grid-free surfaces that allows creation of geological models without the limitations of predefined grids. Surface-based modelling uses a boundary-representation approach, modelling all heterogeneity of interest by its bounding surfaces, independent of any grid. Surfaces are modelled using a NURBS description. These surfaces are efficient, and allow fast creation of multiple realizations of geometrically realistic reservoir models. Surfaces are constructed by (1) extruding a cross section along a plan-view trajectory, or (2) using geostatistical models. Surface metadata is created to allow automatic assembly of these individual surfaces into full reservoir models. We demonstrate this surface-based approach using common elements such as facies belts, clinoforms, channels and concretions, which are combined into reservoir models that preserve realistic geometries. This is applied to a coastal-plain and overlying shoreface succession, analogous to an upper Brent Group reservoir, North Sea (e.g. SPE10-model).
Salinas P, Jacquemyn C, Heaney C, et al., 2018, Simulation of enhanced geothermal systems using dynamic unstructured mesh optimisation
© 2018 Society of Petroleum Engineers. All rights reserved. Recently, a novel method for heat extraction from geothermal reservoirs has been proposed, it is named radiator enhance geothermal system (RAD-EGS). In this method, the heat is extracted by placing two horizontal wells separated vertically, and injecting the cold water in the deepest one. Modelling a geothermal reservoir with wells can be very challenging as the scales to be considered can span several orders of magnitude. Around the wells (metres scale) it is well known that there is a high-pressure drawdown, while the dimensions of the reservoir are typically of many kilometres. Modelling across these scales using a fixed mesh can be computationally very expensive. Here, an unstructured dynamic mesh optimisation method is used to dynamically optimise the mesh to the fields of interest such as temperature and/or pressure to ensure that a certain precision across the domain is obtained. This methodology places the resolution where and when necessary, reducing the number of elements to ensure a certain accuracy when compared to an equivalent fixed mesh. Wells are represented using a 1D line which is represented by a line vector, whose position is not modified when adapting the mesh.
Salinas P, Jacquemyn C, Heaney C, et al., 2018, Simulation of enhanced geothermal systems using dynamic unstructured mesh optimisation
Recently, a novel method for heat extraction from geothermal reservoirs has been proposed, it is named radiator enhance geothermal system (RAD-EGS). In this method, the heat is extracted by placing two horizontal wells separated vertically, and injecting the cold water in the deepest one. Modelling a geothermal reservoir with wells can be very challenging as the scales to be considered can span several orders of magnitude. Around the wells (metres scale) it is well known that there is a high-pressure drawdown, while the dimensions of the reservoir are typically of many kilometres. Modelling across these scales using a fixed mesh can be computationally very expensive. Here, an unstructured dynamic mesh optimisation method is used to dynamically optimise the mesh to the fields of interest such as temperature and/or pressure to ensure that a certain precision across the domain is obtained. This methodology places the resolution where and when necessary, reducing the number of elements to ensure a certain accuracy when compared to an equivalent fixed mesh. Wells are represented using a 1D line which is represented by a line vector, whose position is not modified when adapting the mesh.
Salinas P, Lei Q, Jacquemyn C, et al., 2018, Dynamic unstructured mesh adaptivity for improved simulation of geothermal water extraction in reservoir-scale models, Pages: 1245-1248
A novel method to simulate near-wellbore flow in geothermal reservoirs by using dynamic unstructured mesh optimisation and the Double Control Volume Finite Element method (DCVFEM) is presented. The mesh resolution is dynamically adapted to a field of interest, allowing to focus the mesh resolution only when and where it is required. Geology is represented by bounded surfaces whose petrophysical properties are constant within each of this surfaces. We demonstrate that the method has wide application in reservoir-scale models of geothermal fields, and regional models of groundwater resources.
Jacquemyn C, Rood MP, Melnikova Y, et al., 2018, My geology is too complex for my grid: Grid-free surface-based geological modelling
Building spatially realistic representations of heterogeneity in reservoir models is a challenging task that is limited by predefined pillar or cornerpoint grids. Diverse rock types are ‘averaged’ within grid cells of arbitrary size and shape; continuity of baffles, barriers or high-permeability streaks is often lost; large features are over-resolved and small features are under-resolved or omitted. We present a surface-based modelling workflow using grid-free surfaces that allows creation of geological models without the limitations of predefined grids. Surface-based modelling uses a boundary-representation approach, modelling all heterogeneity of interest by its bounding surfaces, independent of any grid. Surfaces are modelled using a NURBS description. These surfaces are efficient, and allow fast creation of multiple realizations of geometrically realistic reservoir models. Surfaces are constructed by (1) extruding a cross section along a plan-view trajectory, or (2) using geostatistical models. Surface metadata is created to allow automatic assembly of these individual surfaces into full reservoir models. We demonstrate this surface-based approach using common elements such as facies belts, clinoforms, channels and concretions, which are combined into reservoir models that preserve realistic geometries. This is applied to a coastal-plain and overlying shoreface succession, analogous to an upper Brent Group reservoir, North Sea (e.g. SPE10-model).
Salinas P, Pavlidis D, Jacquemyn C, et al., 2017, Simulation of geothermal water extraction in heterogeneous reservoirs using dynamic unstructured mesh optimisation, AGU FALL
Zhang Z, Geiger S, Rood M, et al., 2017, A Tracing Algorithm for Flow Diagnostics on Fully Unstructured Grids With Multipoint Flux Approximation, SPE Journal, Vol: 22, Pages: 1946-1962, ISSN: 1930-0220
Flow diagnostics is a common way to rank and cluster ensembles of reservoir models depending on their approximate dynamic behavior before beginning full-physics reservoir simulation. Traditionally, they have been performed on corner-point grids inherent to geocellular models. The rapid-reservoir-modeling (RRM) concept aims at fast and intuitive prototyping of geologically realistic reservoir models. In RRM, complex reservoir heterogeneities are modeled as discrete volumes bounded by surfaces that are sketched in real time. The resulting reservoir models are discretized by use of fully unstructured tetrahedral meshes where the grid conforms to the reservoir geometry, hence preserving the original geological structures that have been modeled.This paper presents a computationally efficient work flow for flow diagnostics on fully unstructured grids. The control-volume finite-element method (CVFEM) is used to solve the elliptic pressure equation. The flux field is a multipoint flux approximation (MPFA). A new tracing algorithm is developed on a reduced monotone acyclic graph for the hyperbolic transport equations of time of flight (TOF) and tracer distributions. An optimal reordering technique is used to deal with each control volume locally such that the hyperbolic equations can be computed in an efficient node-by-node manner. This reordering algorithm scales linearly with the number of unknowns.The results of these computations allow us to estimate swept-reservoir volumes, injector/producer pairs, well-allocation factors, flow capacity, storage capacity, and dynamic Lorenz coefficients, which all help approximate the dynamic reservoir behavior. The total central-processing-unit (CPU) time, including grid generation and flow diagnostics, is typically a few seconds for meshes with O (100,000) unknowns. Such fast calculations provide, for the first time, real-time feedback in the dynamic reservoir behavior while models are prototyped.
Salinas P, Pavlidis D, Xie Z, et al., 2017, A robust control volume finite element method for high aspect ratio domains with dynamic mesh optimisation, American Physical Society Division of Fluid Dynamics meeting
Salinas P, Pavlidis D, Jacquemyn C, et al., 2017, A Robust Control Volume Finite Element Method for Highly Distorted meshes, SIAM Conference on Mathematical and Computational Issues in the Geosciences
Salinas P, Pavlidis D, Xie Z, et al., 2017, Improving the robustness of the control volume finite element method with application to multiphase porous media flow, International Journal for Numerical Methods in Fluids, Vol: 85, Pages: 235-246, ISSN: 1097-0363
Control volume finite element methods (CVFEMs) have been proposed to simulate flow in heterogeneous porous media because they are better able to capture complex geometries using unstructured meshes. However, producing good quality meshes in such models is nontrivial and may sometimes be impossible, especially when all or parts of the domains have very large aspect ratio. A novel CVFEM is proposed here that uses a control volume representation for pressure and yields significant improvements in the quality of the pressure matrix. The method is initially evaluated and then applied to a series of test cases using unstructured (triangular/tetrahedral) meshes, and numerical results are in good agreement with semianalytically obtained solutions. The convergence of the pressure matrix is then studied using complex, heterogeneous example problems. The results demonstrate that the new formulation yields a pressure matrix than can be solved efficiently even on highly distorted, tetrahedral meshes in models of heterogeneous porous media with large permeability contrasts. The new approach allows effective application of CVFEM in such models.
Jacquemyn C, Melnikova Y, Jackson MD, et al., 2017, Surface-based modelling of subsurface reservoirs using parametric NURBS surfaces
A new surface-based geological modelling approach is developed to generate bounding surfaces based on NURBS (non-uniform rational B-splines) to represent geological heterogeneity of interest without imposing it on a predefined grid. The surfaces represent a broad range of heterogeneity types across a range of length-scales, including structural heterogeneity such as folds, faults or fractures, stratigraphic heterogeneity associated with sediment bodies of various scales and geometries (e.g. clinoforms, channelized features or build-ups) and boundaries between different facies or lithologies. Reservoir modelling using parametric NURBS surfaces has many advantages over conventional grid-based reservoir modelling approaches. A surface-based modelling approach overcomes issues related to geometrical complexity (e.g. non-monotonic surfaces) and representing heterogeneity over a range of length scales. The NURBS representation of these surfaces provides a computationally efficient way to represent their complex geometry. With a limited number of control points, complex and geometrically realistic surfaces can be created, with high level of detail where needed. Because NURBS form smooth surfaces, no stairstepping effects are introduced. The strength of NURBS surfaces lies in representing geologically-realistic complex heterogeneity explicitly across multiple scales.
Zhang Z, Geiger S, Rood M, et al., 2017, Flow Diagnostics on Fully Unstructured Grids, Pages: 772-787
Flow-diagnostics are a common way to rank and cluster ensembles of reservoir models based on their approximate dynamic behaviour prior to commencing full-physics reservoir simulation. Traditionally, flow diagnostics are carried out on corner-point grids inherent to geocellular models. The novel "Rapid Reservoir Modelling" (RRM) concept enables fast and intuitive prototyping and updating of reservoir models. In RRM, complex reservoir heterogeneities are modelled as discrete volumes bounded by surfaces that can be modified using simple sketching operations in real time. The resulting reservoir models are discretized using fully unstructured 3D meshes where the grid conforms to the reservoir geometry. This paper presents a new and computationally efficient numerical scheme that enables flow diagnostic calculations on fully unstructured grids. Time-of-flight and steady-state tracer distributions are computed directly on the grid. The results of these computations allows us to estimate swept reservoir volumes, injector-producer pairs, well-allocation factors, flow capacity, storage capacity and dynamic Lorenz coefficients which all help approximate the dynamic reservoir behaviour. We use the Control Volume Finite Element Method (CVFEM) to solve the elliptic pressure equation. A scalable matrix solver (SAMG) is used to invert the linear system. A new edge-based CVFEM is developed to solve hyperbolic transport equations for time-of-flight and tracer distributions. An optimal reordering technique is employed to deal with each control volume locally such that the hyperbolic equations can be computed in an efficient node-by-node manner. This reordering algorithm scales linearly with the number of unknowns. The total CPU time, including grid generation and flow diagnostics, is typically below 3 seconds for grids with 50k unknowns. Such fast calculations provide, for the first time, real-time feedback on changes in the dynamic reservoir behaviour while the reservoir m
Jacquemyn C, Melnikova Y, Jackson MD, et al., 2017, Surface-based modelling of subsurface reservoirs using parametric NURBS surfaces
A new surface-based geological modelling approach is developed to generate bounding surfaces based on NURBS (non-uniform rational B-splines) to represent geological heterogeneity of interest without imposing it on a predefined grid. The surfaces represent a broad range of heterogeneity types across a range of length-scales, including structural heterogeneity such as folds, faults or fractures, stratigraphic heterogeneity associated with sediment bodies of various scales and geometries (e.g. clinoforms, channelized features or build-ups) and boundaries between different facies or lithologies. Reservoir modelling using parametric NURBS surfaces has many advantages over conventional grid-based reservoir modelling approaches. A surface-based modelling approach overcomes issues related to geometrical complexity (e.g. non-monotonic surfaces) and representing heterogeneity over a range of length scales. The NURBS representation of these surfaces provides a computationally efficient way to represent their complex geometry. With a limited number of control points, complex and geometrically realistic surfaces can be created, with high level of detail where needed. Because NURBS form smooth surfaces, no stairstepping effects are introduced. The strength of NURBS surfaces lies in representing geologically-realistic complex heterogeneity explicitly across multiple scales.
Melnikova Y, Jacquemyn C, Osman H, et al., 2016, Reservoir modelling using parametric surfaces and dynamically adaptive fully unstructured grids, ECMOR XV - 15th European Conference on the Mathematics of Oil Recovery, Publisher: EAGE Publications BV
Geologic heterogeneities play a key role in reservoir performance. Surface based geologic modeling (SBGM) offers an alternative approach to conventional grid-based methods and allows multi-scale geologic features to be captured throughout the modeling process. In SBGM, all geologic features that impact the distribution of material properties, such as porosity and permeability, are modeled as a set of volumes bounded by surfaces. Within these volumes, the material properties are constant. The surfaces have parametric, grid-free representation, which, in principle, allows for unlimited complexity, since no resolution is implied at the stage of modeling and features of any scale can be included. Surface based models are discretized only when required for numerical analysis. We report here a new automated and integrated workflow for creating and meshing stochastic, surface-based models. Surfaces are represented through non-uniform rational B-splines (NURBS). Multiple relations between surfaces are captured through geologic rules that are translated into Boolean operations (intersection, union, subtraction). Finally, models are discretized using fully unstructured tetrahedral meshes coupled with a geometry-adaptive sizing function that efficiently approximate complex geometries. We demonstrate the new workflow via examples of multiple erosional channelized geobodies, fault models and a fracture network. We also show finite element flow simulations of the resulting geologic models, using the Imperial College Finite Element Reservoir Simulator (IC-FERST) that features dynamic adaptive mesh optimization. Mesh adaptivity allows us to focus computational effort on the areas of interest, such as the location of water saturation front. The new approach has broad application in modeling subsurface flow.
Jacquemyn C, Wang X, Lei Q, 2016, Controls of bed thickness, fracture spacing and relative transmissibility on fluid flow and karstification in fractured layered carbonates, AAPG Carbonate Reservoirs
Melnikova Y, Jacquemyn C, Osman H, et al., 2016, Reservoir modelling using parametric surfaces and dynamically adaptive fully unstructured grids
Geologic heterogeneities play a key role in reservoir performance. Surface based geologic modeling (SBGM) offers an alternative approach to conventional grid-based methods and allows multi-scale geologic features to be captured throughout the modeling process. In SBGM, all geologic features that impact the distribution of material properties, such as porosity and permeability, are modeled as a set of volumes bounded by surfaces. Within these volumes, the material properties are constant. The surfaces have parametric, grid-free representation, which, in principle, allows for unlimited complexity, since no resolution is implied at the stage of modeling and features of any scale can be included. Surface based models are discretized only when required for numerical analysis. We report here a new automated and integrated workflow for creating and meshing stochastic, surfacebased models. Surfaces are represented through non-uniform rational B-splines (NURBS). Multiple relations between surfaces are captured through geologic rules that are translated into Boolean operations (intersection, union, subtraction). Finally, models are discretized using fully unstructured tetrahedral meshes coupled with a geometry-Adaptive sizing function that efficiently approximate complex geometries. We demonstrate the new workflow via examples of multiple erosional channelized geobodies, fault models and a fracture network. We also show finite element flow simulations of the resulting geologic models, using the Imperial College Finite Element Reservoir Simulator (IC-FERST) that features dynamic adaptive mesh optimization. Mesh adaptivity allows us to focus computational effort on the areas of interest, such as the location of water saturation front. The new approach has broad application in modeling subsurface flow.
Jacquemyn C, Melnikova Y, Jackson MD, et al., 2016, Geologic modelling using parametric NURBS surfaces
Most reservoir modelling/simulation workflows represent geological heterogeneity on a pillar-grid defined early in the modelling process. However, it is challenging to represent many common geological features using pillar grids: Examples include intersecting faults, recumbent folds, slumps, and non-monotonic injection structures such as salt diapirs. It is also challenging to represent multi-scale features, because the same number of pillars must be present in all layers so there is little flexibility to adjust the areal grid resolution. We present a surface-based geological modelling (SBGM) workflow that uses NURBS (Non-Uniform Rational B-Splines) surfaces to represent geological heterogeneities without reference to a pre-defined grid. The NURBS surfaces represent a broad range of heterogeneity types, including faults, fractures, stratigraphic surfaces across a range of length-scales, and boundaries between different facies or lithologies. The geological model is constructed using the NURBS surfaces and a mesh created only when required for flow simulation or other calculations. The mesh preserves the geometry of the modelled surfaces. NURBS surfaces are an efficient and flexible tool to model complex geometries and are common in many modelling and engineering disciplines; however, they are rarely used in reservoir modelling. Complex surfaces can be created using a small number of control points; modelling with NURBS surfaces is therefore computationally efficient. We report here a variety of new stochastic approaches to create geological NURBS surfaces, including (1) extrusion of spatially variable cross-sections, (2) parametric 3D geometry templates, and (3) perturbation of control points to yield similar results to some pixel-based geostatistical methods. Surface interactions, such as erosion, stacking or conforming, are enforced to ensure geological relationships are preserved and the boundary representation is watertight. We illustrate our NURBS SBGM approach
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