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Multiphase flow in porous media with phase transitions: from CO₂ sequestration to gas hydrate systems

Fu, Xiaojing (2017) Multiphase flow in porous media with phase transitions: from CO₂ sequestration to gas hydrate systems. PhD thesis, Massachusetts Institute of Technology.

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Ongoing efforts to mitigate climate change include the understanding of natural and engineered processes that can impact the global carbon budget and the fate of greenhouse gases (GHG). Among engineered systems, one promising tool to reduce atmospheric emissions of anthropogenic carbon dioxide (CO₂) is geologic sequestration of CO₂, which entails the injection of CO₂ into deep geologic formations, like saline aquifers, for long-term storage. Among natural contributors, methane hydrates, an ice-like substance commonly found in seafloor sediments and permafrost, hold large amounts of the world's mobile carbon and are subject to an increased risk of dissociation due to rising temperatures. The dissociation of methane hydrates releases methane gas-a more potent GHG than CO₂-and potentially contributes to a positive feedback in terms of climatic change. In this Thesis, we explore fundamental mechanisms controlling the physics of geologic CO₂ sequestration and natural gas hydrate systems, with an emphasis on the interplay between multiphase flow-the simultaneous motion of several fluid phases and phase transitions-the creation or destruction of fluid or solid phases due to thermodynamically driven reactions. We first study the fate of CO₂ in saline aquifers in the presence of CO₂-brine-carbonate geochemical reactions. We use high-resolution simulations to examine the interplay between the density-driven convective mixing and the rock dissolution reactions. We find that dissolution of carbonate rock initiates in regions of locally high mixing, but that the geochemical reaction shuts down significantly earlier than shutdown of convective mixing. This early shutdown reflects the important role that chemical speciation plays in this hydrodynamics-reaction coupled process. We then study hydrodynamic and thermodynamic processes pertaining to a gas hydrate system under changing temperature and pressure conditions. The framework for our analysis is that of phase-field modeling of binary mixtures far from equilibrium, and show that: (1) the interplay between phase separation and hydrodynamic instability can arrest the Ostwald ripening process characteristic of nonflowing mixtures; (2) partial miscibility exerts a powerful control on the degree of viscous fingering in a gas-liquid system, whereby fluid dissolution hinders fingering while fluid exsolution enhances fingering. We employ this theoretical phase-field modeling approach to explain observations of bubble expansion coupled with gas dissolution and hydrate formation in controlled laboratory experiments. Unraveling this coupling informs our understanding of the fate of hydrate-crusted methane bubbles in the ocean water column and the migration of gas pockets in hydrate-bearing sediments.

Item Type:Thesis (PhD)
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Fu, Xiaojing0000-0001-7120-704X
Additional Information:© 2017 Massachusetts Institute of Technology. Submitted to the Department of Civil and Environmental Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil and Environmental Engineering. Thesis Supervisor: Ruben Juanes. Title: Associate Professor, Civil and Environmental Engineering. I would like to express my deepest gratitude to my research advisor, Ruben Juanes, for your insightful teaching, patience, kindness, friendship and for always giving me the courage and resources to explore new ideas; To my dearest collaborator, mentor and friend, Luis Cueto-Felgueroso, I am deeply grateful for your generosity, kindness, insights, patience and friendship; To my committee member Carolyn Ruppel, I am truly grateful for your time, advice and encouragement, and for showing me the fascinating world of gas hydrates; To my committee chair Charlie Harvey, for always being a great source of intellectual discussion and inspiration; To former and current members of the Juanes research group, thank you for creating so many great memories and for your friendship. I will miss the Thai/Indian take out and pizza lunches at the group meetings, the ping pong tournaments and dinner preparation at group retreats, and the Friday beers; I am very lucky to have really wonderful friends from the Parsons laboratory, the Pierce laboratory and the rock climbing community; thank you for keeping my head above the water all these years; To my parents Ming Fu and Li Wan, I want to thank you for all that you have provided for me. To my dad, who teaches me to be brave and curious, and to my mom, who teaches me to love and appreciate mathematics and life, thank you for giving me the freedom to explore the world far away from you and home; Last but not least, to my partner Ryan Lewis, thank you for your love, encouragement, patience and companion, and for damping all the turbulence and creating rays of sunshine in my life. I am so blessed to have you by my side.
Subject Keywords:Civil and Environmental Engineering
Record Number:CaltechAUTHORS:20200903-141148620
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105247
Deposited By: Tony Diaz
Deposited On:08 Sep 2020 18:29
Last Modified:08 Sep 2020 18:29

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