Badmos, Sakiru Babatunde; (2020) Structure-Transport Properties of Fluids in Narrow Pores: Relevance to Shale Gas. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Shale gas has attracted significant attention in the past decade. Pioneered by the USA since the 1940s, the production of shale gas in Europe is still in its early stage and has not been attempted in Africa. Oil and gas production from shale is technologically difficult, in part due to very small sizes of pores in shale formations and poor pore connectivity. Experimental characterization has revealed heterogeneous nature of shale, and a network of connected pores is actually not visible at the resolution of tens of nanometers. Poor pore connectivity in shale rocks is responsible for its low permeability. To produce oil and gas from shale formations, more advanced technology such as horizontal drilling and hydraulic fracturing is required. However, recovery is still very low as oil rate drops rapidly. To improve production, enhanced oil recovery (EOR) is proposed. In order to design advanced EOR technologies, fluid–fluid and fluid–rock interactions in nanopores are crucial. This thesis seeks to better understand the behaviour of fluids confined in narrow pores. The techniques of choice are based on molecular dynamics simulations, conducted at the atomic resolution. The pores considered are of slit-shaped geometry and of dimensions as small as 1–2.2 nm carved out of silica, muscovite, MgO, alumina and graphite. The fluids simulated include hydrocarbons, such as n-butane and n-octane, as well as a few other fluids, including H2O, CO2, H2S and N2. The results show, in qualitative agreement with literature observations, that confinement affects the structure of aqueous H2S due to perturbation of water coordination around H2S. It was also found that injection of H2S or CO2 could help to displace hydrocarbon from the confining pore surfaces, and that the performance of the injected gas depends on the chemistry of the surface. CO2 and H2S could displace hydrocarbons from inorganic surfaces but not from organic surface. Analysis of the interaction energy between confined fluids and the pore surfaces shows that the results depend on gas–surface and hydrocarbon–surface interactions. At the conditions simulated, CO2 or H2S suppressed hydrocarbon mobility due to pore crowding. These findings could contribute to designing advanced EOR strategies for achieving both improved hydrocarbon production, acid gas sequestration as well as natural gas sweetening.

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