NMR Compatible Cell Design for Thermally Control Hydrate-Bearing Sediments Formation and CO2 Exchange
Abstract
Natural gas hydrate (NGH) have been studied for decades as a vast potential hydrocarbon resource, which also present various economic and technological challenges to exploitation. NGHs, also referred to as hydrate-bearing sediment (HBS), occur naturally in the pore space of various sediment layers, typically at high pressures and low temperature which contain predominately considerable volumes of methane (CH4). In order to recover the hydrocarbons within NGHs, the injection of CO2 has been considered as a potential, thermodynamically favourable, method of enhancing the recovery of the natural gas whilst sequestering the CO2. This exchange process, and the associated heat and mass transfer phenomena in the context of complex porous media, is however poorly understood.
To this end, with the aim of enhancing our understanding of the CO2-CH4 exchange process in complex porous media, various non-invasive Nuclear
Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) measurements will be exploited to essentially visualise the process. This initially has required the design and construction of a hydrate core holder that is able to accommodate the temperature and pressure relevant conditions of the natural gas hydrate system whilst being compatible with NMR/MRI equipment; which primarily necessitated the use of non-magnetic materials of construction in the NMR field of view. The final design included cooling from the centre of the core holder such that an isothermal sediment can be achieved and pressured controlled whilst NMR/MRI magnet temperature was not significantly impacted. Such design was validated using 3-D Finite Element Method (FEM) simulations, where considering a combined material configuration with PEEK, PEEK with 30% of Carbon Fibre and silica aerogel as a thermal insulator, it was feasible not only to optimize the overall thermal conductivity in order to develop a controlled thermal diffusion below -10°C, but also to ensure a robust mechanical integrity capable to comfortably sustain pressure regimes up to 80 bar, both critical factors for promoting gas hydrate formation as well as allowing suitable operation conditions with the NMR/MRI devices.
Initial pressure and temperature testing of the core holder will also be presented along with preliminary NMR and MRI measurements of natural gas hydrate formation and subsequent exchange with CO2 in the hydrate core holder. Future plans will also be detailed in which MRI and NMR relaxometry are used to non-invasively quantify the exchange process. This will be spatially resolved within the hydrate sediment and the role of unconverted water and methane diffusion will be systematically studied.
AAPG Datapages/Search and Discovery Article #90348 © 2019 AAPG Asia Pacific Region Geosciences Technology Workshop, Gas Hydrates – From Potential Geohazard to Carbon-Efficient Fuel?, Auckland, New Zealand, April 15-17, 2019