Surface electromagnetic (EM) methods were tested prior to CO2 injection at the PTRC Aquistore site at Estevan, Saskatchewan to determine their applicability to carbon sequestration monitoring. Magnetotelluric surveys in 2013, 2014 and 2015 resulted in successful definition of the pre-injection response and electrical resistivity model for the Williston Basin at Aquistore. These datasets define spatially uniform MT responses with a high level of repeatability. Controlled-source EM (CSEM) studies using a horizontal electric dipole transmitter have also been implemented at Aquistore. Preliminary analyses demonstrate that the CSEM experiment is well-designed, with measurable signal levels at all sites and a configuration that maximizes sensitivity to the sequestration reservoir. However, theoretical sensitivity modeling indicates that extremely large volumes of injected CO2 are required to produce measurable anomalies in the CSEM response. Greater sensitivity of both magnetotellurics and CSEM to the resistivity of shallower strata suggests these methodologies have superior application in leakage monitoring. / February 2017

I address the problem of finding a background model for the estimation of resistivities in the earth from controlled-source electromagnetic (CSEM) data by using seismic data and well logs as constraints. Estimation of resistivities is normally done by trial-and-error, in a process called “inversion”, by finding a model of the earth whose responses match the data to within an acceptable error; what comes out of the inversion is what is put into the model by the geophysicist: it does not come out of the data directly. The premise underlying this thesis is that an earth model can be found that satisfies not only the CSEM data but also the seismic data and any well logs. I present a methodology to determine background resistivities from seismic velocities using rock physics, structural constraints, and depth trends. The physical parameters of the seismic wave equation are different from those in the electromagnetic diffusion equation, so there is no direct link between the governing equations. I therefore use a Bayesian framework to incorporate not only the errors in the data and our limited knowledge of the rock parameters, but also the uncertainty of our chosen and calibrated velocity-to-resistivity transform. To test the methodology I use a well log from the North Sea Harding South oil and gas field to calibrate the transform, and apply it to seismic velocities of the nearby Harding Central oil and gas field. I also use short-offset CSEM inversions to estimate the electric anisotropy and to improve the shallow part of the resistivity model, where there is no well control. Three-dimensional modelling of this resistivity model predicts the acquired CSEM data within the estimated uncertainty. This methodology makes it possible to estimate background resistivities from seismic velocities, well logs, and other available geophysical and geological data. Subsequent CSEM surveys can then focus on finding resistive anomalies relative to this background model; these are, potentially, hydrocarbon-bearing formations.

This dissertation presents a formulation of the Continuous Sensitivity Equation Method (CSEM) applied to the Computational Fluid Dynamics (CFD) simulation of thermoacoustic instability problems. The proposed sensitivity analysis approach only requires a single run of the CFD simulation. Moreover, the sensitivities of field variables, pressure, velocity and temperature to boundary-condition parameters are directly obtained from the solution to sensitivity equations. Thermoacoustic instability is predicted by the Rayleigh criterion. The sensitivity of the Rayleigh index is computed utilizing the sensitivities of field variables. The application of the CSEM to thermoacoustic instability problems is demonstrated by two classic examples. The first example explores the effects of the heated wall temperature on the one-dimensional thermoacoustic convection. The sensitivity of the Rayleigh index, which is the indicator of thermoacoustic instabilities, is computed by the sensitivity of field variables. As the heat wall temperature increases, the sensitivity of the Rayleigh index decreases. The evolution from positive to negative sensitivity values suggests the transition from a destabilizing trend to stabilizing trend of the thermoacoustic system. Thermoacoustic instabilities in a self-excited Rijke tube are investigated following the relatively simple thermoacoustic convection problem. The complexity of simulating the Rijke tube increases in both dimensions and mechanisms which incorporate the species transport process and chemical reactions. As a representative model of the large lean premixed combustor, Rijke tube has been extensively studied. Quantitative sensitivity analysis sets the present work apart from previous research on the prediction and control of thermoacoustic instabilities. The effects of two boundary-condition parameters, i.e. the inlet mass flow rate and the equivalence ratio, are tested respectively. Small variations in both parameters predict a rapid change in sensitivities of field variables in the early stage of the total time length of 1.2s. The sensitivity of the Rayleigh index "blows up" at a specific time point of the early stage. In addition, variations in the inlet mass flow rate and the equivalence ratio lead to opposite effects on the sensitivity of the Rayleigh index. There exist some common findings on the application of the CSEM. For both thermoacoustic problems, the sensitivities of field variables and the Rayleigh index exhibit oscillatory nature, confirming that thermoacoustic instability is an overall effect of the coupling process between fluctuations of pressure and heat release rate. All the sensitivities of the Rayleigh index show rapid changes and "blow up" in the early stage. Although the numerical errors could influence the fidelity of computational results, it is believed that the rapid changes reflect the susceptibility to thermoacoustic instabilities in the studied systems. It should also be noted that the sensitivities are obtained for small variations in influential parameters. Therefore, the resulting sensitivities do not predict the occurrence of thermoacoustic instabilities under a condition that is far from the reference state determined by either CFD simulation results (employed in this dissertation) or experimental data. The sensitivity solver developed for the present research has the feature of flexibility. Additional mechanisms and more complicated instability criteria could be easily incorporated into the solver. Moreover, the sensitivity equations formulated in this dissertation are derived from the full set of nonlinear governing equations. Therefore, it is possible to extend the use of the sensitivity solver to other CFD problems. The developed sensitivity solver needs to be optimized to gain better performance, which is considered to be the primary future work of this research. / Ph. D.

The towed streamer controlled source electromagnetic (CSEM) system collects data faster than the conventional static node-based CSEM system. However, the towed streamer CSEM is typically much noisier than the conventional static node-based CSEM. Identifying and quantifying various sources of noise is important for the development of future robust electromagnetic streamer system. This is the problem I address in this thesis. I achieve this in three parts. First, I examine the idea that the towed streamer suffers from noise induced by its motion through the Earth’s magnetic field according to Faraday’s law of induction. I derive expressions for the motionally-induced noise for the cases of a horizontal streamer parallel to the acquisition vessel’s path and a curved streamer caused by a constant cross-current. These expressions demonstrate that the motionally-induced noise is sensitive to the magnitude of the feather angle at the head and at the tail of the streamer, and to the vertical and lateral motion of the streamer. The key finding is that no motionally-induced noise is generated when the streamer is horizontal and moving in a constant magnetic field. By contrast, when the streamer shape is curved because of cross-currents, motionally-induced noise is generated if the velocity of the streamer varies over time. Second, I analyse and compare the noise recorded using the first generation of towed streamer with the noise recorded using a static ocean bottom cable (OBC) CSEM. I find out that within the frequency range of interest, 0.01–1 Hz the towed streamer noise is 20 dB greater (factor of 10) than the noise recorded with the OBC CSEM. I show also that the motion of the telluric cable between the pair of electrodes in the towed streamer is responsible for this difference in amplitude between the two systems. In the frequency ranges, 0.03–0.1 Hz and 0.03–0.2 Hz, the motionally-induced noise is shown to be uncorrelated across all channels. However, within the frequency band 0.1–0.3 Hz, the motionally-induced noise correlation gradually increases and becomes well correlated at about 0.2 Hz. This correlated noise could be caused by ocean swell from surface waves, water flowing around the streamer or cross-currents. Finally, to identify and quantify the contribution of several distinct sources of noise, and to describe the mechanisms generating each source of noise, I co-designed a prototype towed streamer CSEM. I carried out an experiment with the prototype streamer suspended 1 m below the water surface in the controlled environment of the Edinburgh wave tank located in King’s building campus (the University of Edinburgh). I then subjected the streamer to flow running at velocities of 0–1ms−1 along its length and to waves propagating in the same direction, at 45°, and perpendicular relative to the streamer direction.

Svenska översättningar av Brief Electricity and Magnetism Assessment (BEMA) och Conceptual Survey of Electricity and Magnetism (CSEM) har gjorts. BEMA och CSEM är forskningsbaserade flervalsprov som testar konceptuell förståelse inom elektromagnetism och kan vara utgångspunkt för en fysikundervisning med fokus på konceptuell förståelse på flera nivåer av utbildning. Originalfigurer har använts med en figur modifierad för att förtydliga positionen av en partikel (CSEM uppgift 15). För att motivera översättningarna har det argumenterats för en konceptuell fysikundervisning i kontrast mot en traditionell. Detta gjordes utifrån Skolverket, en rapport ifrån Skolinspektionen och ett flertal publikationer inom Physics Education Research (PER). Speciellt har det argumenterats för en konceptuell fysikundervisning inom elektromagnetism genom att en översikt av de konceptuella utmaningar som området ofta innebär för elever har presenterats. Vid tillfällen har det också givits riktlinjer för hur utbildare kan gå tillväga för att bemöta dessa utmaningar. Utifrån aspekterna svårighetsindex, träffsäkerhet och reliabilitet inom Classic test Theory (CTT) kan BEMA och CSEM anses vara likvärdiga. Den som vill använda BEMA eller CSEM bör därför främst, och kanske också enbart, kolla på vilket av testerna som innehållsmässigt bäst stämmer överens med den aktuella kursen. BEMA och CSEM är innehållsmässigt väldigt lika och har flera uppgifter gemensamma, samtidigt som det finns skillnader, till exempel testar BEMA förståelse för elektriska kretsar medan CSEM inte gör det. Antar vi att BEMA och CSEM är likvärdiga utvärderingsverktyg, och eftersom båda består av ungefär lika många (31 och 32) uppgifter samt enbart flervalsfrågor, kan de användas som för- och eftertest inom samma grupp eller parallellt om två grupper ska testas inom samma kurs. Uppgifter om elektriska kretsar kan då behöva uteslutas ifrån BEMA för en bättre innehållsmässig överensstämmelse mellan proven. CTT är beroende av testgrupp, och eftersom de CTT resultaten som presenteras är baserade på amerikanska collegestudenter kan det vara lämpligt att som utbildare undersöka om BEMA och CSEM även är likvärdiga inom den kontext som de ska användas. / Swedish translations of Brief Electricity and Magnetism Assessment (BEMA) and Conceptual Survey of Electricity and Magnetism (CSEM) have been made. BEMA and CSEM are research-based multiple choice tests on conceptual understanding of electromagnetic concepts. They can be used as a starting point for physics teaching with emphasis on conceptual understanding at several levels of education. Figures are from the original tests with one figure modified in order to clarify the position of a particle (CSEM question 15). In order to motivate the translations I make a case for a conceptual approach to physics teaching in contrast to a traditional. This was based on the Swedish National Agency for Education, a publication from the Swedish School Inspectorate and several publications within Physics Education Research (PER). I Specifically make a case for a conceptual approach to physics teaching within electricity and magnetism with an overview of common student difficulties. Occasionally guidelines for how educators can deal with these challenges are given. Based on the aspects difficulty, discrimination and reliability within Classic test Theory (CTT) BEMA and CSEM can be considered equivalent. Those who wish to use BEMA or CSEM should therefore mainly, and perhaps only, decide which test to use based on which test that best matches the course in terms of covered content. Contentwise BEMA and CSEM are very similar and have many questions in common. However, there are differences between them. For example, BEMA tests understanding regarding electric circuits while CSEM does not. If we assume that BEMA and CSEM are equal in quality and combine this with the fact that they are made out of almost the same amount of questions (31 and 32) that are only multiple choice, BEMA and CSEM can potentially be used as pre- and post-tests within the same group or in paralell if two groups are to be tested within the same course. In order to match the two tests in terms of content, electric circuit questions could be omitted from BEMA. CTT results depend on the tested group, and since the CTT results that are presented is based on American college students, further investigation is needed to ensure that they are equivalent also in the Swedish context.

Photovoltaic Thermal/Hybrid collectors are an emerging technology that combines PV and solar thermal collectors by producing heat and electricity simultaneously. In this paper, thermal and electrical performance of PV/T collectors are analyzed and presented for the climate of RAK, UAE. Thermal performance evaluation is done following the collector output model presented in European standard EN 12975-2 and electrical performance evaluation is done by analyzing the effect of water circulation on the performance of PV/T collectors. Additionally, a PV/T system is designed for residential use in UAE and simulated using simulation software Polysun. Power output and requirements of the system along with its financial analysis is presented. Alternative solar energy systems to PV/T system are analyzed in terms of power output, specific requirements and financial analyses. Finally, a study is made to reveal the impact of incentives towards sustainable energy systems on the economic feasibility of PV/T systems for residential use in UAE. / <p>The project is done in cooperation with CSEM-uae under local supervision of Mr. Manoj Kumar Pokhrel.</p>

La présentation porte sur les deux principaux domaines de recherche dans lequel je me suis investi, depuis 2003, au BRGM, celui du développement de la prospection par Résonance Magnétique Protonique (RMP), et l'utilisation des méthodes Electro-Magnétique à Source Contrôlée (CSEM). Une brève introduction rappellera le principe de la mesure RMP. La première partie, présentera les travaux réalisés pour raffiner les modèles utilisés, pour prendre en compte la variation du signal liée aux conditions de mesures (champ géomagnétique, topographie) et à l'environnement géologique (zone non-saturée dans la craie, forte conductivité sur le bord de la mer Morte). Afin d'appréhender la nature 2D/3D des objets étudiés, j'ai développé un modèle 3D de la réponse RMP et mis au point une approche permettant d'évaluer la position et le volume de cavités remplies d'eau (imagerie d'un conduit karstique près de Rocamadour et cartographie de la dissolution d'une couche de sel générant des effondrements « sinkholes »). Enfin j'ai développé un programme d'inversion qui permet de réaliser une tomographie en 2D/3D de la teneur en eau et des temps de relaxation (illustrée dans le cas d'un aquifère sédimentaire interrompu par un système de failles). La deuxième partie concernera la mesure de la résistivité électrique par de grands dispositifs appliquée à l'imagerie d'aquifères complexes (biseaux salés et milieu volcanique) et la mise au point d'un dispositif CSEM dédié au suivi temporel de la résistivité dans un aquifère. L'originalité réside dans l'utilisation du tubage métallique des forages pour injecter le courant électrique en profondeur et permettant par la mesure en surface du champ électrique et magnétique, de mesurer les variations de résistivité au sein d'un réservoir profond. Ces travaux ont été réalisés dans le cadre du suivi de l'injection de CO2 (résistant) dans des réservoirs salins. La performance du dispositif sera illustrée par une étude numérique et sa mise en œuvre sur le site pilote de Ketzin en Allemagne. Je conclurai cet exposé par un aperçu des orientations vers lesquelles je propose de faire porter l'effort de recherche dans ces deux domaines, aujourd'hui en pleine évolution.

Presence of cultural refuse has long posed a serious challenge to meaningful geological interpretation of near surface controlled–source electromagnetic data (CSEM). Cultural refuse, such as buried pipes, underground storage tanks, unexploded ordnance, is often highly conductive and magnetically permeable. Interpretation of the CSEM response in the presence of cultural noise requires an understanding of electromagnetic field diffusion and the effects of anomalous highly conductive and permeable structures embedded in geologic media. While many numerical techniques have been used to evaluate the response of three dimensional subsurface conductivity distributions, there is a lack of approaches for modeling the EM response incorporating variations in both subsurface conductivity σ and relative permeability μr. In this dissertation, I present a new three dimensional edge–based finite element (FE) algorithm capable of modeling the CSEM response of buried conductive and permeable targets. A coupled potential formulation for variable μ using the vector magnetic potential A and scalar electric potential V gives rise to an ungauged curl–curl equation. Using reluctivity (v=1/mu ), a new term in geophysical applications instead of traditional magnetic susceptibility, facilitates a separation of primary and secondary potentials. The resulting differential equation is solved using the finite element method (FEM) on a tetrahedral mesh with local refinement capabilities. The secondary A and V potentials are expressed in terms of the vector edge basis vectors and the scalar nodal basis functions respectively. The finite element matrix is solved using a Jacobi preconditioned QMR solver. Post processing steps to interpolate the vector potentials on the nodes of the mesh are described. The algorithm is validated against a number of analytic and multi dimensional numeric solutions. The code has been deployed to estimate the influence of magnetic permeability on the mutual coupling between multiple geological and cultural targets. Some limitations of the code with regards to speed and performance at high frequency, conductivity and permeability values have been noted. Directions for further improvement and expanding the range of applicability have been proposed.

While geophysical reservoir characterization has been an area of research for the last three decades, geophysical reservoir monitoring, time-lapse studies, have recently become an important geophysical application. Generally speaking, the main target is to detect, estimate, and discriminate the changes in subsurface rock properties due to production. This research develops various sensitivity and feasibility analyses to investigate the effects of production-induced time-lapse changes on geophysical measurements including seismic and controlled-source electromagnetic (CSEM) data. For doing so, a realistic reservoir model is numerically simulated based on a prograding near-shore sandstone reservoir. To account for the spatial distribution of petrophysical properties, an effective porosity model is first simulated by Gaussian geostatistics. Dispersed clay and dual water models are then efficiently combined with other well-known theoretical and experimental petrophysical correlations to consistently simulate reservoir model parameters. Next, the constructed reservoir model is subjected to numerical simulation of multi-phase fluid flow to replicate a waterflooding scenario of a black oil reservoir and to predict the spatial distributions of fluid pressure and saturation. A modified Archie’s equation for shaly sandstones is utilized to simulate rock resistivity. Finally, a geologically consistent stress-sensitive rock physics model, combined with the modified Gassmann theory for shaly sandstones, is utilized to simulate seismic elastic parameters. As a result, the comprehensive petro-electro-elastic model developed in this dissertation can be efficiently utilized in sensitivity and feasibility analyses of seismic/CSEM data with respect to petrophysical properties and, ultimately, applied to reservoir characterization and monitoring research. Using the resistivity models, a base and two monitor time-lapse CSEM surveys are simulated via accurate numerical algorithms. 2.5D CSEM modeling demonstrates that a detectable time-lapse signal after 5 years and a strong time-lapse signal after 10 years of waterflooding are attainable with the careful application of currently available CSEM technology. To simulate seismic waves, I employ different seismic modeling algorithms, one-dimensional (1D) acoustic and elastic ray tracing, 1D full elastic reflectivity, 2D split-step Fourier plane-wave (SFPW), and 2D stagger grid explicit finite difference (FD). My analyses demonstrate that acoustic modeling of an elastic medium is a good approximation up to ray parameter (p) equal to 0.2 sec/km. However, at p=0.3 sec/km, differences between elastic and acoustic wave propagation is the more dominant effect compared to internal multiples. Here, converted waves are also generated with significant amplitudes compared to primaries and internal multiples. I also show that time-lapse modeling of the reservoir using SFPW approach is very fast compared to FD, 100 times faster for my case here. It is capable of handling higher frequencies than FD. It provides an accurate image of the waterflooding process comparable to FD. Consequently, it is a powerful alternative for time-lapse seismic modeling. I conclude that both seismic and CSEM data have adequate but different sensitivities to changes in reservoir properties and therefore have the potential to quantitatively map production-induced time-lapse changes. / text

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