Date of Graduation
Statler College of Engineering and Mineral Resources
Petroleum and Natural Gas Engineering
Shahab D Mohaghegh
Over the past few years, the production of shale hydrocarbons has seen a renewed interest both in science and industry. Indeed, these fluids today constitute a significant energy and economic stake to compensate for the scarcity of so-called conventional resources. This is due to the fact that shale gases and oils represent enormous potential resources and are present all over the world. In shales, hydrocarbons are generally contained in microporous organic nanopores: kerogen. The kerogen is both the source rock of hydrocarbons and their reservoir. In shales, the extreme confinement of fluids in organic matter, high pressure-high temperature thermodynamic condition as well as very low permeabilities, imply a significant change in the state of the fluids (present in adsorbed form) and its transport mechanisms (diffusive). In this dissertation, we studied the physical properties (adsorption, transport) of kerogen as well as its carbon dioxide sequestration potential. The characteristic scales in the shales are of the order of a nanometer, which is accessible today by molecular simulations on supercomputers or even personal computers. Therefore, we have chosen to study kerogens by molecular simulation. The objective of this work is to stimulate a fundamental research on this subject in order to understand and model the mechanisms encountered in the shales and thus to respond responsibly and sustainably to the energy challenges of the years to come. Initially, the simplified kerogen models (carbon nanochannels and nanocapillaries) are developed and transport and storage of different gases are studied. This part of research is beneficial for developing analytical models of gas transport in organic nanopores. Furthermore, kerogens with different maturities were generated by molecular dynamics simulations under thermodynamic conditions typical of this type of reservoir (338 K, 20 MPa). In our simulations, the microporous network of kerogen is created by the inclusion of dummy particles, which were deleted after kerogen structure is created. The average density of the structures of organic matter created is in agreement with the experimental results obtained on such kerogens. The density is very strongly correlated with the stacking of the kerogenic polyaromatic clusters which is a strong indicator of the coherence of the simulated structures with respect to the experiments. We were interested in the transport of hydrocarbons in the kerogen and have identified the mechanisms of mass transfer through kerogens and we have been able to predict their evolution as a function of thermodynamic conditions (composition and pressure). Based on the results, it is demonstrated that the higher the maturity of kerogen, the higher is its adsorption capability. This is in agreement with experimental results of adsorption on kerogen. Furthermore, it is shown that the permeation of fluid through the kerogen membrane can be described by a diffusive formalism. The heavier alkanes have smaller diffusion coefficients and as a result, they may trap inside organic nanopores. Multicomponent diffusion of mixtures containing water and carbon dioxide is investigated and it is shown that water and carbon dioxide have lowest diffusion coefficients compared with hydrocarbons. The diffusion coefficients of hydrocarbons increases in presence of water due to higher adsorption capability of water and filling the adsorption sites. Adsorption molecular simulations of binary mixture of methane and carbon dioxide demonstrate that carbon dioxide have higher adsorption capabilities than methane. Binary mixture diffusion simulation of these two components also shows that carbon dioxide molecules have lower diffusion coefficients compared with methane. Therefore, injection of carbon dioxide into organic matter causes the methane molecules desorb and produce.;In conclusion, this dissertation work consisted of developing models, algorithms, and methodologies to predict the properties and mechanisms governing the behavior of the organic matter contained in the shales by employing molecular simulations . This work aims to improve our understanding of this type of resources.
Kazemi, Mohammad, "Molecular Simulation of Transport and Storage in Shale" (2017). Graduate Theses, Dissertations, and Problem Reports. 5950.