Quantifying sorption-diffusion processes at nanoscale using neutron scattering on coal analogues

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Embargoed until 2022-08-11
Copyright: Vu, Phung Nhu Hao
With the current increase in demand for cleaner energy sources and natural gas in particular, the requirement for better understandings of fluid transportation in porous media is also on the rise. This thesis is focusing on the sorption and diffusion process of hydrocarbon in different formations, a process not well understood in the oil and gas industry. In the first major section, this thesis addresses the main disadvantages of the current models for the sorption/diffusion process, which is the independence of diffusion rate with respect to time and the saturation of gas in the adsorbent. Furthermore, these models assume all the pore sizes within the coal are of constant size, which is not representative of the real rock. We propose a new model based on the reaction-diffusion theory to improve upon the popular unipore model. The model separates the adsorption process from the effective diffusivity by coupling in a reaction term. Moreover, this model also describes the dependence of the gas transportation rate on temperature, activation energy, and gas concentration rate. Together with the new model, a hypothetical experimental and analysis procedure is presented to validate this modification. The new findings of the latter part of the thesis call, however, for an extension of this approach. In the second part of the thesis, Transmission Electron Microscopy (TEM) and Guinier Analysis on Small-Angle Neutron Scattering (SANS) data were performed, revealing the complex nanopore structure of the silica aerogel at 3 different sizes: 3 nm, 9 nm and 0.18 nm. Contrast-match (CM) SANS was employed to investigate the sorption behaviour of methane in these pore regions, using CD4 with fluid pressure up to 1 kbar. The CM-SANS experiment discovered the following sorption behaviour of CD4 in the pore region of 3 nm and 9 nm: (1) all the pores are accessible to CD4, (2) CD4 pressure within the pore is equal to the bulk CD4 pressure, and (3) no adsorption layer on the pore-matrix interface was found. Analysis of SANS data for the 0.18 nm pores indicates capillary condensation is the major factor controlling the CD4 sorption behaviour. After the pressure cycling process to up to 1000 bar, when returning to vacuum, the silica structure at this scale is permanently damaged due to the invading gas
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Vu, Phung Nhu Hao
Regenauer-Lieb, Klaus
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Masters Thesis
UNSW Faculty
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