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Hydrocarbon Adsorption Characteristics and Absolute Adsorption Estimation in Shale Nanoporous Media from Statistical Thermodynamics Approaches
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- Author / Creator
- Pang, Wanying
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Shale gas has become a very important unconventional energy resource and significantly increased the global energy supply. Due to the presence of large amount of specific surface area and nanopores in shale rock, the phenomenon of gas molecules accumulation on the solid surface is the so-called adsorption. The enhanced storage capacity of shale will control the production and provide additional gas during depletion. Therefore, understanding the sorption mechanism in shale nanoporous media and accurate characterization of methane absolute adsorption (mabs) play an important role in the gas-in-place estimation and prediction of well productivity.
In the proposed dissertation, we first perform grand canonical Monte Carlo (GCMC) simulation to investigate the methane adsorption in organic mesopore at various pressures. Based on the density distributions, we characterize the transition zone between the first adsorption layer and free gas phase, then a modified Ono-Kondo (OK) lattice model with multilayer structure is proposed for accurately estimating mabs converted from experimentally measured excess adsorption (mex) to better account for the effect of transition zone. In addition to methane which contributes shale gas compositions, propane is one of major heavier constituents in shale gases which can have multilayer adsorption behavior on the surface. Therefore, by studying the propane adsorption behavior from GCMC simulation, we propose a multi-layer OK model considering the correlation effect arising from the strong adsorbate-adsorbate interactions beyond mean field theory (MFT) to regress mex and subsequently obtain the mabs. However, shale has a widespread pore size distribution (PSD) and the adsorption behavior varies in micropores and mesopores. Based on the varying density profiles in different sized of nanopores obtained from GCMC, we propose the corresponding methane adsorption model in each nanopore. Combining the actual PSD and different adsorption behaviors in varying pores, by fitting mex in nanoporous media, OK lattice model can readily obtain mabs. Large number of randomly generated PSDs are used to validate our model. Then, we assess various commonly used methods converting the mex to the mabs systematically and comprehensively and give suggestions in experiment measurements. Furthermore, considering the continuous pore size distribution in shale, the OK model utilizing PSD lumping method has been proposed to account for the specific adsorption behavior in series of adsorption types over different range of nanopores. Lastly, since inorganic clay minerals are observed to also be responsible for gas adsorption, the methane adsorption capacity controlled by both complex confinement effect and heterogeneous rock type has been studies by molecular simulation. Then, we propose the OK-dual heterogeneity (OK-DH) model to consider the heterogeneity of shale rock arising from various rock type and pore sizes. The proposed model can account for different fluid-surface interactions between methane and substrates and thus provide accurate prediction of adsorption behavior in not only shale matrix but also in specific rock and pore sizes. -
- Subjects / Keywords
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- Graduation date
- Fall 2021
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.