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Browsing by Author "Tang, Xu"

Now showing 1 - 3 of 3
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    Determining Coalbed Methane Production and Composition from Individual Stacked Coal Seams in a Multi-Zone Completed Gas Well
    Ripepi, Nino; Louk, Kyle; Amante, Joseph; Schlosser, Charlies; Tang, Xu; Gilliland, Ellen (MDPI, 2017-10-02)
    This work proposes a novel and cost-effective approach to determine coalbed methane (CBM) production and composition from individual coal seams in a multi-zone completed CBM well. The novel method uses water to cover individual coal seams in a low pressure CBM well followed by an Echometer fluid level survey to determine the water level. Corresponding gas flow measurements and natural gas chromatography analysis are used to determine gas production and composition from unique zones. A field test using this technology is conducted in Central Appalachia for a multi-zone CBM well containing 18 coal seams. Test results show that the shallow coal seams contribute the majority of the total CBM production in this multi-zone well, and the deeper coal seams contain more heavy hydrocarbons like ethane and propane.
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    Measurements, Modeling and Analysis of High Pressure Gas Sorption in Shale and Coal for Unconventional Gas Recovery and Carbon Sequestration
    Tang, Xu (Virginia Tech, 2017-01-10)
    In order to exploit unconventional gas and estimate carbon dioxide storage potential in shale formations and coal seams, two key questions need to be initially answered: 1) What is the total gas-in-place (GIP) in the subsurface reservoirs? 2) What is the exact ratio between bulk gas content and adsorbed gas content? Both questions require precise estimation of adsorbed phase capacity of gases (methane and carbon dioxide) and their adsorption behavior in shale and coal. This dissertation therefore analyzes adsorption isotherms, thermodynamics, and kinetics properties of methane and carbon dioxide in shale and coal based on experimental results to provide preliminary answers to both questions. It was found that the dual-site Langmuir model can describe both methane and carbon dioxide adsorption isotherms in shale and coal under high pressure and high temperature conditions (up to 27 MPa and 355.15K). This allows for accurate estimation of the true methane and carbon dioxide GIP content and the relative quantity of adsorbed phases of gases at in situ temperatures and pressures representative of deep shale formations and coal seams. The concept of a deep shale gas reservoir is then proposed to optimize shale gas development methodology based on the successful application of the model for methane adsorption in shale. Based on the dual-site Langmuir model, the isosteric heat of adsorption is calculated analytically by considering both the real gas behavior and the adsorbed phase under high pressure, both of which are ignored in the classic Clausius–Clapeyron approximation. It was also found that the isosteric heat of adsorption in Henry's pressure region is independent of temperature and can serve as a quantified index to evaluate the methane adsorption affinity on coal. In order to understand the dynamic response of gas adsorption in coal for carbon sequestration, both gas adsorption kinetics and pore structure of coal are investigated. The pseudo-second order model is applied to simulate the adsorption kinetics of carbon dioxide in coals under different pressures. Coal particle size effects on pore characterization of coal and carbon dioxide and nitrogen ad/desorption behavior in coal was also investigated.
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    Micrometer-scale Experimental Characterization of the Lower Huron Shale in the Central Appalachian Basin
    Tan, Xinyu; Gilliland, Ellen; Tang, Xu; Fan, Ming; Ripepi, Nino (American Geophysical Union, 2020)
    The mechanical properties of shale play an important role in hydraulic fracturing design. Although the popular nanoindentation method can be performed to evaluate some mechanical characteristics of organic matter, it is still difficult to fully characterize mechanical properties of organic components of shale due to their small scale which is usually on the order of micrometers or even nanometers. As a novel material characterization tool, Atomic Force Microscopy (AFM) has shown great potential to characterize surface properties and pore structures at micrometer- and nanometer-scale and has been applied to investigate the elastic properties of organic components in shale by multiple researchers. Raman and FTIR can detect chemical bands by utilizing molecular vibration information. Because Raman and FTIR measurements are non-destructive, high sensitivity, and short in duration, they have been used extensively to study maturation processes of organic components in coal and shale samples. To some extent, these two methods can be considered as complementary to each other, and more comprehensive understanding about maturation processes of organic components can be achieved by combining these two methods. In this work, mechanical properties and chemical characteristics of four shale samples with different thermal maturities were investigated. Generally, this study had two objectives: (1) Characterize the mechanical properties of shale samples with different maturity levels through the novel AFM method, and (2) Explore the underlying cause for the change in elastic properties of shale samples from a chemical perspective through the complementary Raman and FTIR methods.