• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 133
  • 31
  • 26
  • 3
  • 3
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 241
  • 241
  • 65
  • 54
  • 49
  • 38
  • 31
  • 30
  • 30
  • 29
  • 28
  • 25
  • 24
  • 21
  • 18
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

Partitioning Biological and Anthropogenic Methane Sources

Down, Adrian January 2014 (has links)
<p>Methane is an important greenhouse gas, and an ideal target for greenhouse gas emissions reductions. Unlike carbon dioxide, methane has a relatively short atmospheric lifetime, so reductions in methane emissions could have large and immediate impacts on anthropogenic radiative forcing. A more detailed understanding of the global methane budget could help guide effective emissions reductions efforts.</p><p>Humans have greatly altered the methane budget. Anthropogenic methane sources are approximately equal in flux to natural sources, and the current atmospheric methane concentration is ~2.5 times pre-industrial levels. The advent of hydraulic fracturing and resulting increase in unconventional natural gas extraction have introduced new uncertainties in the methane budget. At the same time, the next few decades could be a crucial period for controlling greenhouse gas emissions to avoid irreversible and catastrophic changes in global climate. Natural gas could provide lower-carbon fossil energy, but the climate benefits of this fuel source are highly dependent on the associated methane emissions. In this context of increasing uncertainty and growing necessity, quantifying the impact of natural gas extraction and use on the methane budget is an essential step in making informed decisions about energy.</p><p>In the work presented here, I track methane in the environment to address several areas of uncertainty in our present understanding of the methane budget. I apply the tools of methane analysis in a variety of environments, from rural groundwater supplies to an urban atmosphere, and at a range of scales, from individual point sources to regional flux. I first show that carbon isotopes of methane and co-occurrence of ethane are useful techniques for differentiating a range of methane sources. In so doing, I also show that leaks from natural gas infrastructure are a major source of methane in my study area, Boston, MA. I then build on this work by applying the same methane carbon isotope and ethane signatures to partition methane flux for the Boston metro region. I find that 88% of the methane enhancement in the atmosphere above Boston is due to pipeline natural gas. </p><p>In the final portion of this thesis and the two appendices, I move from the distribution side of the natural gas production chain to extraction, specifically addressing the potential impacts from hydraulic fracturing in my home state of North Carolina. I combine the methane source identification techniques of the previous sections with additional geochemical analyses to document the pre-drilling water quality in the Deep River Triassic Basin, an area which could be drilled for natural gas in the future. This data set is unique in that North Carolina has no pre-existing commercial oil and gas extraction, unlike other states where unconventional gas extraction is currently taking place. This research is, to my knowledge, the first to examine the hydrogeology of the Deep River Basin, in addition to providing an important background data set that could be used to track changes in water quality accompanying hydraulic fracturing in the region in the future.</p> / Dissertation
72

The Environmental, Social, and Economic Impacts of Hydraulic Fracturing, Horizontal Drilling, and Acidization in California

Whalen, Christina 01 January 2014 (has links)
The oil extraction mechanisms of hydraulic fracturing, horizontal drilling, and acidization have recently spread throughout the state of California. This thesis explores and assesses whether federal and state legislation should approve of fracking operations in California after studying its effects on human health, the environment, and the economy. This thesis assesses the impacts of fracking; analyzes the role of current legislation and regulation; compares California fracking to fracking in other states and countries; and provides recommendations for future action.
73

A fully implicit stochastic model for hydraulic fracturing based on the discontinuous deformation analysis

Morgan, William Edmund 12 January 2015 (has links)
In recent years, hydraulic fracturing has led to a dramatic increase in the worldwide production of natural gas. In a typical hydraulic fracturing treatment, millions of gallons of water, sand and chemicals are injected into a reservoir to generate fractures in the reservoir that serve as pathways for fluid flow. Recent research has shown that both the effectiveness of fracturing treatments and the productivity of fractured reservoirs can be heavily influenced by the presence of pre-existing natural fracture networks. This work presents a fully implicit hydro-mechanical algorithm for modeling hydraulic fracturing in complex fracture networks using the two-dimensional discontinuous deformation analysis (DDA). Building upon previous studies coupling the DDA to fracture network flow, this work emphasizes various improvements made to stabilize the existing algorithms and facilitate their convergence. Additional emphasis is placed on validation of the model and on extending the model to the stochastic characterization of hydraulic fracturing in naturally fractured systems. To validate the coupled algorithm, the model was tested against two analytical solutions for hydraulic fracturing, one for the growth of a fixed-length fracture subject to constant fluid pressure, and the other for the growth of a viscosity-storage dominated fracture subject to a constant rate of fluid injection. Additionally, the model was used to reproduce the results of a hydraulic fracturing experiment performed using high-viscosity fracturing fluid in a homogeneous medium. Very good agreement was displayed in all cases, suggesting that the algorithm is suitable for simulating hydraulic fracturing in homogeneous media. Next, this work explores the relationship between the maximum tensile stress and Mohr-Coulomb fracture criteria used in the DDA and the critical stress intensity factor criteria from linear elastic fracture mechanics (LEFM). The relationship between the criteria is derived, and the ability of the model to capture the relationship is examined for both Mode I and Mode II fracturing. The model was then used to simulate the LEFM solution for a toughness-storage dominated bi-wing hydraulic fracture. Good agreement was found between the numerical and theoretical results, suggesting that the simpler maximum tensile stress criteria can serve as an acceptable substitute for the more rigorous LEFM criteria in studies of hydraulic fracturing. Finally, this work presents a method for modeling hydraulic fracturing in reservoirs characterized by pre-existing fracture networks. The ability of the algorithm to correctly model the interaction mechanism of intersecting fractures is demonstrated through comparison with experimental results, and the method is extended to the stochastic analysis of hydraulic fracturing in probabilistically characterized reservoirs. Ultimately, the method is applied to a case study of hydraulic fracturing in the Marcellus Shale, and the sensitivity of fracture propagation to variations in rock and fluid parameters is analyzed.
74

Velocity profile in confined elliptic fractures

Pack, Stephen Ronald, January 1900 (has links)
Thesis (M.S.)--West Virginia University, 1998. / Title from document title page. "December 1998." Document formatted into pages; contains x, 78 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 57-58).
75

A toolbox of intelligent solutions for hydraulic fracturing models

Popa, Sergiu Andrei, January 1900 (has links)
Thesis (M.S.)--West Virginia University, 1998. / "December 1998." Document formatted into pages; contains ix, 119 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 84-85).
76

Automatic hydraulic fracturing design for low permeability reservoirs using artificial intelligence

Popa, Sergui Andrei, January 1900 (has links)
Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xiii, 303 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 235-238).
77

Fracturing Illinois: Fields of Political Contention in Hydraulic Fracturing Regulatory Policy

Buday, Amanda T. 01 August 2016 (has links)
This dissertation examines the interactions between social movement organizations and a variety of state and municipal targets of movement activity during the construction of the Illinois Hydraulic Fracturing Regulatory Act (HFRA). Hydraulic fracturing is a controversial method of oil and gas extraction which created an unusual amount of public interest and participation in policy construction. This dissertation provides an overview of the political environment in Illinois during the legislative negotiations for the HFRA, outlining the playing field of political negotiations, and the relative positioning of social movement actors competing for influence in that field. Additionally, I examine the causes and consequences of conflict between coalition partners opposed to fracking, focusing on the impact of differential resources, expertise, and institutional legitimacy. Using data from interviews with organization leaders from industry and environmental coalitions, key informants from government bureaus, and participant observation at public meetings, my research contributes to the political process literature by elaborating the heterogeneity of the state’s interests in political challenges and revealing cleavages within social movement coalitions.
78

Three Essays on the Economics of Hydraulic Fracturing

Asif Ehsan, Syed Mortuza 10 August 2016 (has links)
Hydraulic fracturing has been increasingly used in the USA to economically extract natural gas and oil from newly discovered shale plays. Despite new, more severe, and long term impacts of hydraulic fracturing compared to conventional drilling, regulatory practices are mostly implemented by states that regulate with older regulations that were were written before the widespread use of hydraulic fracturing. This dissertation presents three essays on the economics of hydraulic fracturing. A standard renewable lease in hydraulic fracturing runs for a five-year primary term. The first essay examines the effect of initial contract length on extraction behavior and social costs. It finds that the rate of extraction decreases over time for both, the social planner and the private extractor. In addition, the social planner has a more stable extraction path compared to the private extractor. Holding other things equal, if the social planner seeks to induce a private extractor to leave a higher in situ stock un-extracted, then the optimal contract duration is longer. Simulations illustrate the magnitude of social costs inherent in hydraulic fracturing and non-optimal fixed contract lengths. The second essay investigates the impact of the significantly increased bonding requirements for horizontal wells introduced in West Virginia in December, 2011, on the probability of violation committed by those wells. Results suggest that the increased bonding requirement has reduced the probability of violation by 2.6 to 3.2 percentage points. Moreover, it slightly reduces the number of violations done by horizontal wells. Finally, the third essay explores several aspects of Act-13, introduced on February 14, 2012, by Pennsylvania. This act imposes new fees that are assessed annually for fifteen years, on all unconventional gas wells in Pennsylvania. This chapter explores the impacts of Act-13 on the likelihood of an unconventional well's shut-down, rate of extraction, and probability of violation. Results suggest that wells incurring this increased fee schedule have a significantly higher likelihood (more than three times) of shut-down. Also, Act-13 have reduced the extraction rate, and the probability of violation committed by unconventional wells in Pennsylvania. / Ph. D.
79

Methylotrophic Methanogenesis in Hydraulically Fractured Shales

Marcus, Daniel N., Marcus 22 November 2016 (has links)
No description available.
80

Expertise Revisited: Reflecting on the Intersection of Science and Democracy in the Case of Fracking

Ahmadi, Mahdi 12 1900 (has links)
This dissertation aims to explain the conditions under which expertise can undermine democratic decision making. I argue that the root of the conflict between expertise and democracy lies in what I call insufficiently “representative” expertise – that is forms of scientific research that are not relevant to the policy questions at hand and that fail to make visible their hidden values dimensions. I claim that the scholarly literature on the problem of expertise fails to recognize and address the issue correctly, because it does not open the black box of scientific methodologies. I maintain that only by making sense of the methodological choices of experts in the context of policy making can we determine the relevance of research and reveal the hidden socio-political values and consequences. Using the case of natural gas fracking, I demonstrate how expert contributions – even though epistemically sound – can muddle democratic policy processes. I present four case studies from controversies about fracking to show how to contextualize scientific methodologies in the pertinent political process. I argue that the common problem across all case studies is the failure of expertise to sufficiently represent stakeholders’ problems and concerns. In this context, “representation” has three criteria: (1) the operational research questions on which the qualified experts work are relevant to stakeholders’ problems and concerns; (2) the non-epistemic values and consequences of epistemic choices of experts are compatible with social and political values and priorities; and (3) hidden values attached to facts are fully transparent and openly debated. In the conclusion, I propose a normative version of this representation theory that can be used to evaluate the appropriateness of expertise for democratic policy making. Instead of the value-free science ideal, I propose a new ideal to legitimately allow non-epistemic values in scientific reasoning without compromising the soundness of research.

Page generated in 0.0932 seconds