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1. Custom Type-Curve Generation for Pressure Transient Analysis of Elongated Linear Flow Systems Génération de courbes caractéristiques de réponse en pression pour des systèmes linéaires longs

Author

Wagner P. B., Economides M. J., and Ehlig-Economides C.

Subjects
Chemical technology, TP1-1185, Energy industries. Energy policy. Fuel trade, HD9502-9502.5
Abstract

When the drainage area of a flowing well is long and narrow, the pressure transient behavior of the well often cannot be analyzed by conventional means. Well tests which appear to exhibit linear flow behavior for extended periods, beyond the length of time which could be attributed to flow to a fracture, have been observed for both geothermal wells and for oil and gas wells. In geothermal formations and in some of the deep low-permeability gas fields the elongated reservoir shape results from long parallel faults which appear to bound the formations. Typically such wells are also penetrating natural fractures. In other reservoirs the elongated drainage shape is due to the river delta or alluvial environment in which the reservoir sands were originally deposited. Using a recently developed scheme for custom type curve generation for a wide variety of flow geometries, the particular behavior of the well producing from an elongated linear flow system is presented in detail. Cases examined include fractured wells of variable fracture length in varions positions within the flow channel and also of variable length. The effects of partial penetration are also demonstrated. This paper illustrates the use of custom type curves in computer-aided type-curve matching. With the help of relatively inexpensive computer graphics, custom type curves are displayed which exactly represent whatever is known about a particular drainage geometry, including such variables as formation thickness and areal extent, fracture length, partial penetration, and well location. Familles of curves can be generated and displayed along with the data to help determine unknown features of the reservoir geometry. An important contribution included in this work was the development of a set of orthogonal dimensionless parameters which facilitate the generation of familles of type curves which vary one reservoir shape parameter with implied effects on other parameters. The dimensionless solutions for any reservoir geometry are then readily developed for use in computer-aided type curve matching. Lorsque la zone de drainage d'un puits de production est longue et étroite, les méthodes classiques d'analyse du comportement des changements de pression ne peuvent être utilisées. De tels comportements, se prolongeant après la période pouvant être attribuée à une fracture, ont été observés pour des puits produisant de l'huile, du gaz et même pour certains puits géothermiques. La géométrie allongée, que l'on rencontre parfois dans certaines formations géothermiques et poches de gaz à grande profondeur et de faible perméabilité, peut être expliquée par des réseaux de fractures parallèles qui limitent la formation. Naturellement, les puits forés dans de telles formations peuvent traverser des fractures naturelles. Pour d'autres réservoirs, la forme allongée peut être causée par la géométrie de l'environnement dépositionnel deltaïque. Utilisant une méthode récemment développée permettant de produire des courbes caractéristiques de changement de pression pour une grande variété de géométries, le comportement particulier des puits drainant des formations allongées est présenté en détail. Les cas suivants ont été analysés : fissuration avec modification de la longueur de la fracture et diverses positions du puits dans la formation avec pénétration partielle de différentes longueurs. Les courbes sont construites directement sur le terminal. Elles prennent en compte exactement ce qui est connu de la géométrie du réservoir, de l'épaisseur, la forme, la longueur de la fissure, de la longueur de la zone perforée et de la position du puits. Des familles de courbes peuvent être générées et affichées, puis comparées aux données pour déterminer les paramètres inconnus de la géométrie du réservoir. Une contribution importante, présentée dans cet article, est le développement d'un système de paramètres orthogonaux sans dimensions qui facilite la génération des courbes caractéristiques. Les courbes caractéristiques de pression, correspondant à des géométries spécifiques à l'utilisateur, peuvent être superposées aux données de pressions en vue de déterminer les paramètres inconnus du réservoir (type curve matching).

Published
2006
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2. Multiple value systems for adaptive decision-making

Author

Economides, M. W.

Subjects
616.8
Abstract

Values, rewards, uncertainty and risk play a central role in economic and psychological theories of decision-making. Over the past decade, numerous experiments have used neuroimaging techniques to uncover the neural realization of such decision variables while individuals engage in a range of tasks. These have led to a consensus that economic choice involves interplay between multiple systems that enjoy both cooperative and competitive relations. In this thesis, I utilize functional magnetic resonance imaging (fMRI) and computational formalizations of choice to explore how these different brain systems interact to support adaptive decision-making. In Chapters 4 and 5, I present data from a task in which the inclusion of a dynamic environment required subjects to sometimes approach an option they would normally avoid, or avoid an option they would normally approach. This allowed me to uncover brain systems that track time-varying components of the environment, or immediate reward information, as well as the mechanisms by which these components are integrated. I found that adaptive control in this context involves downstream integration, via functional coupling, of distinct decision components that are computed in separate, often widespread, networks. Yet, choice variables represented in the striatum may in some cases be resistant to modulation, contributing to maladaptive behaviour. In Chapter 6, I investigate whether task training alters the way in which these different value systems manifest in choice; or more broadly, whether value computations in the brain adapt as humans become more proficient at internalizing models of the world. To address this, I trained subjects on a value-guided decision-making task for 3 consecutive days. The data are suggestive of a shift in the implementation of value-guided planning with training, from a more cumbersome, resource-dependant mechanism, to a more efficient and robust process that remains resistant to attentional load.

Published
2015

6. Natural gas and LNG trade--a global perspective: new dynamics within the gas industry will accelerate its ability to eclipse oil as the premier fuel of the world economy

Author

Mokhatab, S., Economides, M. J., and Wood, D.

Subjects
Natural gas -- Prices and rates -- Supply and demand, Gas industry -- Industry forecasts -- Capacity, Liquefied natural gas -- Supply and demand -- Prices and rates, Energy industry -- Industry forecasts -- Capacity, Business, Petroleum, energy and mining industries, Company pricing policy, Capacity, Prices and rates, Supply and demand, Industry forecasts
Abstract

Oil prices have been very volatile on the upside. However, oil prices are nothing compared to the natural gas (NG) price roller coaster. Why is NG now selling for about [...]

Published
2006

7. Fast Sequences of Non-spatial State Representations in Humans

Author

Kurth-Nelson, Z., Economides, M., Dolan, R., and Dayan, P.

Subjects
Adult, Male, Adolescent, Neuroscience(all), Brain, Magnetoencephalography, Article, Young Adult, Task Performance and Analysis, Visual Perception, Humans, Learning, Female, Visual Cortex
Abstract

Summary Fast internally generated sequences of neural representations are suggested to support learning and online planning. However, these sequences have only been studied in the context of spatial tasks and never in humans. Here, we recorded magnetoencephalography (MEG) while human subjects performed a novel non-spatial reasoning task. The task required selecting paths through a set of six visual objects. We trained pattern classifiers on the MEG activity elicited by direct presentation of the visual objects alone and tested these classifiers on activity recorded during periods when no object was presented. During these object-free periods, the brain spontaneously visited representations of approximately four objects in fast sequences lasting on the order of 120 ms. These sequences followed backward trajectories along the permissible paths in the task. Thus, spontaneous fast sequential representation of states can be measured non-invasively in humans, and these sequences may be a fundamental feature of neural computation across tasks., Highlights • Task requires navigating between objects whose neural representations can be decoded • After task has been learned, spontaneous MEG activity encodes reverse paths • These spontaneous sequences are up to four states long • Sequences might be cognate with rodent hippocampal “replay”, The rat hippocampus spontaneously imagines past and future locations in rapid sequences (sometimes called “replay”), which link multiple locations into coherent neural representations. Kurth-Nelson et al. find similar sequences in humans, in a non-spatial task, suggesting they are a ubiquitous mechanism.

Published
2016

8. Mixed mold pulmonary infections in haematological cancer patients in a tertiary care cancer centre

Author

Magira, E.E. Jiang, Y. Economides, M. Tarrand, J. Kontoyiannis, D.P.

Abstract

There is a paucity of data regarding mixed mold pulmonary infections (MMPIs) in patients with haematological malignancies with or without haematopoietic stem cell transplantation (HSCT). We retrospectively studied 27 such patients (2005-2015) and compared them to patients with invasive pulmonary aspergillosis (IPA) caused by Aspergillus fumigatus. Factors associated with the diagnosis of MMPIs were significant corticosteroid use [20 (74%) vs 6 (22%), P

Published
2018

10. Model-Based Reasoning in Humans Becomes Automatic with Training

Author

Economides, M., Kurth-Nelson, Z., Lübbert, A., Guitart-Masip, M., and Dolan, R.

Subjects
Adult, Male, Adolescent, Decision Making, Computational Biology, Models, Biological, Young Adult, lcsh:Biology (General), Reward, Task Performance and Analysis, Humans, Female, lcsh:QH301-705.5, Reinforcement, Psychology, Algorithms, Research Article
Abstract

Model-based and model-free reinforcement learning (RL) have been suggested as algorithmic realizations of goal-directed and habitual action strategies. Model-based RL is more flexible than model-free but requires sophisticated calculations using a learnt model of the world. This has led model-based RL to be identified with slow, deliberative processing, and model-free RL with fast, automatic processing. In support of this distinction, it has recently been shown that model-based reasoning is impaired by placing subjects under cognitive load—a hallmark of non-automaticity. Here, using the same task, we show that cognitive load does not impair model-based reasoning if subjects receive prior training on the task. This finding is replicated across two studies and a variety of analysis methods. Thus, task familiarity permits use of model-based reasoning in parallel with other cognitive demands. The ability to deploy model-based reasoning in an automatic, parallelizable fashion has widespread theoretical implications, particularly for the learning and execution of complex behaviors. It also suggests a range of important failure modes in psychiatric disorders., Author Summary Automaticity develops with task familiarity. One possible explanation is that automaticity arises when performance of the task becomes habitual, or model-free. Here we asked whether goal-directed, or model-based, reasoning could also become automatic, or resistant to distraction. We used a well-characterized task that differentiates model-based from model-free action. We replicate previous findings that distraction strongly impairs model-based reasoning in task-naive subjects. However, in subjects with prior exposure to the task, distraction does not impair model-based reasoning. This suggests that humans can deploy sophisticated and flexible reasoning more extensively than previously thought.

Published
2015

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