Geological constraints on surface-based models through development of Rapid Reservoir Modelling

Surface-based geological modelling (SBM) represents all geological heterogeneity that impacts the spatial distribution of petrophysical properties using surfaces. To create surface-based models, rules are required to govern how surfaces interact such that resulting models are geologically sound. Previous studies used implicit rules or assumptions, often with the requirement that surfaces are created in stratigraphic or hierarchical order. A comprehensive set of explicit and universal rules to govern the interaction of stratigraphic surfaces has yet to be formalised. In this thesis, seven operators are presented that define how stratigraphic surfaces interact for geological modelling such that universal geological rules are obeyed. The operators can be applied through any SBM technique and are independent of geological process, scale and setting. The operators are demonstrated using three hand-drafted examples of siliciclastic and carbonate strata, at centimetre to kilometre scales, using outcrop, seismic and conceptual input data. These universal stratigraphic operators are then implemented in 3D in the sketch-based interface and modelling (SBIM) research prototype software Rapid Reservoir Modelling (RRM). Three case studies are presented using examples of siliciclastic and carbonate strata from different depositional environments, at multiple scales, using seismic, outcrop, and well log data to constrain and guide the sketches. The case studies demonstrate the operators and three different techniques for moving from 2D sketch to 3D model, revealing the flexibility and broad applicability of the operators for SBIM of stratigraphy. Lastly, the stratigraphic operators are leveraged in RRM to create structural models. Test cases are a conjugate fault model and a physical model of a salt-influenced passive margin. Gaps in the applicability of stratigraphic operators for ‘sketch-what-you-see’ structural modelling and diagenesis are identified and future updates to RRM are recommended. RRM is the first SBIM software that allows rapid prototyping of geological reservoir models and represents a step-change for the field.Open Acces

Unfolding the hippocampus: An intrinsic coordinate system for subfield segmentations and quantitative mapping

The hippocampus, like the neocortex, has a morphological structure that is complex and variable in its folding pattern, especially in the hippocampal head. The current study presents a computational method to unfold hippocampal grey matter, with a particular focus on the hippocampal head where complexity is highest due to medial curving of the structure and the variable presence of digitations. This unfolding was performed on segmentations from high-resolution, T2-weighted 7T MRI data from 12 healthy participants and one surgical patient with epilepsy whose resected hippocampal tissue was used for histological validation. We traced a critical image feature composed of the hippocampal sulcus and stratum radiatum lacunosum-moleculare, (SRLM) in these images, then employed user-guided semi-automated techniques to detect and subsequently unfold the surrounding hippocampal grey matter. This unfolding was performed by solving Laplace\u27s equation in three dimensions of interest (long-axis, proximal-distal, and laminar). The resulting ‘unfolded coordinate space’ provides an intuitive way of mapping the hippocampal subfields in 2D space (long-axis and proximal-distal), such that similar borders can be applied in the head, body, and tail of the hippocampus independently of variability in folding. This unfolded coordinate space was employed to map intracortical myelin and thickness in relation to subfield borders, which revealed intracortical myelin differences that closely follow the subfield borders used here. Examination of a histological resected tissue sample from a patient with epilepsy reveals that our unfolded coordinate system has biological validity, and that subfield segmentations applied in this space are able to capture features not seen in manual tracing protocols

A framework for geometric modeling and structural analysis of composite laminates

Laminated fiber-reinforced polymer (FRP) composites show considerable promise in structural applications due to their good combination of low weight and high strength. However, the manufacturing costs of laminated composites is significantly higher than their metallic counterparts. As a consequence, estimating the residual life of composites becomes critical, and can enable reusability in applications that demand lower mechanical strength requirements. One of the major factors affecting the residual life of the laminated composites is the defects introduced during manufacturing or in service. A common way of determining defects in the composite laminates is using non-destructive evaluation (NDE) techniques. In this study, a framework for modeling and structural analysis of composite laminates is presented. The framework follows the laminate manufacturing process and incorporates structural elements, such as stiffeners, as well as defects, such as delaminations, determined using NDE techniques. Each layer composing the laminate is modeled separately and combined to generate the final laminate. The layer combination process is called bonding and involves computation of boundary conditions for the constitutional model being selected for the analysis. Then, the final laminate model and the computed boundary conditions are used during the structural analysis. The initial framework used commercial off-the-shelf (COTS) software, i.e. 3D ACIS Modeler for 3-dimensional modeling and SIMULIA Abaqus for structural analysis via finite element modeling. The framework was then extended to use the NURBS library, NURBS-Python, and the isogeometric analysis library, gIGA, which were developed as a part of this study and released as free and open-source software on GitHub. Using NURBS for modeling and isogeometric analysis for structural analysis provide several advantages, such as directly operating on the exact geometry, and therefore; achieving better estimations on interlaminar and intralaminar stresses and strains, which has significant importance in determining the residual life of the composite laminates

Doctor of Philosophy

dissertationIt is imperative to obtain a complete network graph of at least one representative retina if we are to fully understand vertebrate vision. Synaptic connectomics endeavors to construct such graphs. Though previously prevented by hardware and software limitations, the creation of customized viewing and analysis software, affordable data storage, and advances in electron imaging platform control now permit connectome assembly and analysis. The optimal strategy for building complete connectomes utilizes automated transmission electron imaging with 2 nm or better resolution, molecular tags for cell identification, open access data volumes for navigation, and annotation with open source tools to build three-dimensional cell libraries, complete network diagrams, and connectivity databases. In a few years, the first retinal connectome analyses reveal that many well-studied cells participate in much richer networks than expected. Collectively, these results impel a refactoring of the inner plexiform layer, while providing proof of concept for connectomics as a game-changing approach for a new era of scientific discovery

Developing a hierarchical Digital Core Analysis workflow for petro-physical characterisation of cross-laminated reservoir rocks at pore scales

The study presented in this thesis addresses a critical shortfall of Digital Core Analysis (DCA) in the petro-physical characterisation of natural rock samples that exhibit complex and spatially non-separable multi-scale arrangements of mineral grains of variable sizes and chemical compositions. Since those multi-scale arrangements define non-stationary (heterogeneous) grain-pore distributions, they must be characterised on sufficiently large sample volumes for sample reconstruction at pore and grain scales, to simulate the fluid flow processes for predicting petro-physical properties. Such characterisations can only be done in a multi-stage manner at multi-scales and multi-locations on a sample, due to the mutual constraints of the imaging field of view and resolution. Typical multi-scale approaches fuse images from various sources based on shared features (e.g. disproportionately large grains) as cross-scale references, but have limited application when the shared features are less obvious (non-separable) across multi-scale images. For common cross-lamination in sandstone rocks that exhibit hierarchical structures controlling grain-pore distribution and are demarcated by physical features such as inter/intra-lamina (set) bounding surfaces, a multi-scale DCA workflow would be ideally suited for the petro-physical characterisation but would be challenging to apply when the visibility of cross-scale shared features (bounding surfaces) is weak. This work argues that the workflow needs to have the following elements: 1) a multiscale spatial sampling/characterisation procedure; 2) a way to maintain correct cross-scale spatial correlation among individual sampled datasets through shared features, as reference to the same sample, and 3) a stochastic reconstruction procedure that honours the multiscale structures identified in 1) and correlated in 2), and reconstructs the poregrain-scale non-stationarity they expressed across the correlated datasets. The work presented in this thesis focuses on cross-lamination in sandstone rocks to identify challenges arising to multi-scale characterisation and to develop a suitable hierarchical DCA workflow. For this purpose, an outcrop tight Aeolian cross-laminated sandstone sample of 6x6x6 cm3 that includes representative hierarchical structures was chosen. The key achievements are: 1) a suitable imaging-based exploratory and recursive sampling and characterisation procedure to maximise correlation between datasets. Analysis on the resultant multi-scale datasets showed that sharp and gradual grain compositions change between adjacent laminasets (inter-laminaset) and laminae (intra-laminaset), respectively, to form thin but finite-thickness bounding surfaces, which are ideally suited as shared physical features. However, challenges are identified including a) the inter-laminaset bounding surfaces are obscured by “artefacts” and cannot be enhanced by existing techniques and b) intra-laminaset bounding surfaces are hard to be even observed because of gradual composition variation. 2) To identify the two types of bounding surfaces as shared features to help registration, two new techniques were developed by exploring geological knowledge on structural morphology and mineral compositions, respectively, and were shown to be able to successfully identify and extract shared inter- and intra-laminaset bounding surfaces. 3) For a pair of realisations of sampled inter- and intra-laminaset bounding surfaces and estimated grain-pore distribution information, a non-stationary index map of grain texture (size and orientation) on the whole sample domain can be constructed to define the mean of affinity transformations for stochastically populating stationary (homogeneous) grain and pore structures by a reconstruction method which is implemented based on Multiple Points Statistics (MPS). One reconstructed pore-grain model was obtained in this work and contains 11900x11900x11900 voxels at a voxel resolution of 4 µm. This model was verified to capture key pore-grain variations associated with the characterised lamination structures

Reliability and life prediction of ceramic composite structures at elevated temperatures

Methods are highlighted that ascertain the structural reliability of components fabricated of composites with ceramic matrices reinforced with ceramic fibers or whiskers and subject to quasi-static load conditions at elevated temperatures. Each method focuses on a particular composite microstructure: whisker-toughened ceramics, laminated ceramic matrix composites, and fabric reinforced ceramic matrix composites. In addition, since elevated service temperatures usually involve time-dependent effects, a section dealing with reliability degradation as a function of load history has been included. A recurring theme throughout this chapter is that even though component failure is controlled by a sequence of many microfailure events, failure of ceramic composites will be modeled using macrovariables

Improved characterisation and modelling of heterolithic tidal sandstone reservoirs

Tidal heterolithic sandstone reservoirs comprise millimetre- to centimetre-scale intercalations of mudstone and sandstone. Their effective flow properties are poorly predicted by data that do not sample a representative elementary volume (REV), or models that fail to capture the complex 3D architecture of sandstone and mudstone layers. The aim of this dissertation is to develop improved predictions of effective single and multiphase permeabilities in heterolithic tidal sandstones. A surface-based modelling approach has been developed, which honours the geometry of geologic heterogeneity surfaces, integrating easily measurable outcrop derived dataset as input parameters. The workflow uses template surfaces to represent heterogeneities classified by geometry rather than length-scale. The surface-based methodology has been applied to generate generic, 3D mini-models of trough and planar cross-bedded tidal sandstones with differing proportions of sandstone and mudstone. The models closely capture the bedform architectures observed at outcrop and are suitable for flow simulation. Quantitative geometrical input data to construct the models was extracted from an outcrop analogue which records deposition in a tide-dominated deltaic and estuarine setting. The model results demonstrate that effective single-phase permeability of tidal crossbedded sandstones varies with sample volume. A REV of 1 m3 was identified, confirming that the model volume of 9 m3 (> REV) yields representative values. The impact on effective permeability of seven geometric parameters controlling the density of mudstone drapes was determined: mudstone drape coverage, foreset thickness, toeset dip angle, dune climb angle, foreset to toeset ratio, style of cross-bedding (trough or tabular), size of the mudstone drape patches. The impact of seven geometric parameters on effective permeability was determined. Effective permeability decreases as the mudstone fraction increases, and is highly anisotropic. Each parameter investigated can significantly impact on effective permeability, depending upon the flow direction and sandstone fraction, causing considerable spread of the values. During oil/water flow, relative permeabilities are not affected by mudstone drapes, but the irreducible oil saturation varies depending on flow direction and mudstone content. The workflow presented here can be used with subsurface data, supplemented by outcrop analog observations, to generate effective single and multi-phase permeability values to be derived for use in larger-scale reservoir models.Open Acces

Neural Representations of Visual Motion Processing in the Human Brain Using Laminar Imaging at 9.4 Tesla

During natural behavior, much of the motion signal falling into our eyes is due to our own movements. Therefore, in order to correctly perceive motion in our environment, it is important to parse visual motion signals into those caused by self-motion such as eye- or head-movements and those caused by external motion. Neural mechanisms underlying this task, which are also required to allow for a stable perception of the world during pursuit eye movements, are not fully understood. Both, perceptual stability as well as perception of real-world (i.e. objective) motion are the product of integration between motion signals on the retina and efference copies of eye movements. The central aim of this thesis is to examine whether different levels of cortical depth or distinct columnar structures of visual motion regions are differentially involved in disentangling signals related to self-motion, objective, or object motion. Based on previous studies reporting segregated populations of voxels in high level visual areas such as V3A, V6, and MST responding predominantly to either retinal or extra- retinal (‘real’) motion, we speculated such voxels to reside within laminar or columnar functional units. We used ultra-high field (9.4T) fMRI along with an experimental paradigm that independently manipulated retinal and extra-retinal motion signals (smooth pursuit) while controlling for effects of eye-movements, to investigate whether processing of real world motion in human V5/MT, putative MST (pMST), and V1 is associated to differential laminar signal intensities. We also examined motion integration across cortical depths in human motion areas V3A and V6 that have strong objective motion responses. We found a unique, condition specific laminar profile in human area V6, showing reduced mid-layer responses for retinal motion only, suggestive of an inhibitory retinal contribution to motion integration in mid layers or alternatively an excitatory contribution in deep and superficial layers. We also found evidence indicating that in V5/MT and pMST, processing related to retinal, objective, and pursuit motion are either integrated or colocalized at the scale of our resolution. In contrast, in V1, independent functional processes seem to be driving the response to retinal and objective motion on the one hand, and to pursuit signals on the other. The lack of differential signals across depth in these regions suggests either that a columnar rather than laminar segregation governs these functions in these areas, or that the methods used were unable to detect differential neural laminar processing. Furthermore, the thesis provides a thorough analysis of the relevant technical modalities used for data acquisition and data analysis at ultra-high field in the context of laminar fMRI. Relying on our technical implementations we were able to conduct two high-resolution fMRI experiments that helped us to further investigate the laminar organization of self-induced and externally induced motion cues in human high-level visual areas and to form speculations about the site and the mechanisms of their integration

Quantifying Reservoir Heterogeneity Through Outcrop Characterization: 1. Architecture, Lithology, and Permeability Distribution of a Seaward-Stepping Fluvial-Deltaic Sequence, Ferron Sandstone (Cretaceous), Central Utah

The internal architecture of natural gas reservoirs fundamentally controls production efficiency and the volume of gas unrecovered at abandonment. To better understand reservoir complexity, we investigated relations between sandstone architecture and permeability structure of landward-stepping (wave-modified) Ferron deltaic sandstones exposed in central Utah. Deltaic sandstones extend 4 mi along sediment-transport direction in the landward-stepping Ferron genetic sequence GS 5. Most sand was deposited in transgressive, delta-front, and distributary-channel facies. Distributary channels constitute the principal reservoir facies because mean permeability in distributary-channel sandstones is approximately twice that of delta-front and transgressive sandstones, and because distributary-channel sandstones are well developed. Channel architecture, bounding-surface character, and permeability distribution change systematically from landward to seaward position in the system. Near the landward limit, mean permeability is 300 md, mud occurs as clasts along channel-flank bounding surfaces, and permeability systematically decreases upward. Near the seaward extent of the system, mean permeability is 750 md, mud is segregated into discrete strata-bounding sand bodies, and vertical permeability trends are uniformly high. Statistical analysis shows that lithofacies are the fundamental sandstone architectural units. Similar lithofacies have similar permeability character, regardless of position in the facies tract. Variable preservation of lithofacies controls permeability distribution throughout the channel system. Semivariogram analysis shows that vertical and horizontal permeability correlation distances correspond to distances between bounding surfaces and to sand-body dimensions. Diagenetic overprint is minor, owing to low burial temperatures.Bureau of Economic Geolog