Browsing by Author "Riviere, Beatrice M"

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    Discontinuous Galerkin and Finite Difference Methods for the Acoustic Equations with Smooth Coefficients
    (2015-04-20) Bencomo, Mario Javier; Symes, William W.; Warburton, Timothy C; Riviere, Beatrice M
    This thesis analyzes the computational efficiency of two types of numerical methods: finite difference (FD) and discontinuous Galerkin (DG) methods, in the context of 2D acoustic equations in pressure-velocity form with smooth coefficients. The acoustic equations model propagation of sound waves in elastic fluids, and are of particular interest to the field of seismic imaging. The ubiquity of smooth trends in real data, and thus in the acoustic coefficients, validates the importance of this novel study. Previous work, from the discontinuous coefficient case of a two-layered media, demonstrates the efficiency of DG over FD methods but does not provide insight for the smooth coefficient case. Floating point operation (FLOPs) counts are compared, relative to a prescribed accuracy, for standard 2-2 and 2-4 staggered grid FD methods, and a myriad of standard DG implementations. This comparison is done in a serial framework, where FD code is implemented in C while DG code is written in Matlab. Results show FD methods considerably outperform DG methods in FLOP count. More interestingly, implementations of quadrature based DG with mesh refinement (for lower velocity zones) yield the best results in the case of highly variable media, relative to other DG methods.
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    The characterization and visualization of multi-phase systems using microfluidic devices
    (2015-03-10) Conn, Charles Andrew; Biswal, Sibani L; Hirasaki, George J; Wong, Michael S; Riviere, Beatrice M
    The stability and dynamics of multi-phase systems are still not fully understood, especially in systems of confinement such as microchannel networks and porous media. In particular, systems of liquids and gases that form foam are important in a number of applications including enhanced oil recovery (EOR). This research seeks to better understand the mechanisms of multi-phase fluid interaction responsible for the displacement of oil. The answers to these questions give insight into the design of efficient EOR recovery strategies, and provides a platform on which researchers can perform studies on pore-level phenomena. Our experiments use poly(dimethylsiloxane) (PDMS) devices which can be made using inexpensive materials without hazardous chemicals and can be designed and fabricated in just a few hours to save time, money, and effort. The unique contribution of this thesis is the development of a general “reservoir-on-a-chip” research platform that facilitates study of multi-phase systems relevant to energy-industry applications. Experiments with a fractured porous media micromodel quantified pressure drop and remaining oil saturation for different recovery strategies. It demonstrated foam flooding’s superior performance compared to waterflooding, gas flooding, and water-alternating-gas flooding by increasing flow resistance in the fracture and high-permeability zones and directing fluids into the low-permeability zone. Mechanisms of phase-separation were observed which suggest it is inappropriate to treat foam as a homogeneous phase. Experiments with foam in a 2-D porous matrix investigated mechanisms of foam generation, destruction, and transport and related foam texture (bubble size) to pressure drop and apparent viscosity. MATLAB code written for this thesis automated quantification of over 120,000 bubbles to generate plots of bubble size distributions for alpha olefin sulfonate (AOS 14-16) at different foam quality (gas fraction) conditions. The experimental devices and analytical software tools developed in this work open the door for future experiments to screen and compare surfactant formulations. One may readily envision developing libraries of surfactant data from micromodel experiments which can then be data-mined to discover relationships between surfactant structure, performance, and environmental conditions.