Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications

Abstract 136

Gas Hydrate Growth and Dissociation in Narrow Pore Networks: Capillary Inhibition and Hysteresis Phenomena

Anderson, R. Tohidi, B and Webber, J.B.W.

Geological Society of London Conference on Sediment-hosted Gas Hydrates: New Insights on Natural and Synthetic Systems, London, 25-26 January (2006).

The potential role capillary phenomena could play in controlling gas hydrate formation in natural sediments has recently been the subject of considerable laboratory investigation, and there is now a significant volume of experimental clathrate equilibrium data for various (primarily synthetic) media available in the literature. However, studies to date have focussed almost exclusively on hydrate dissociation behaviour in narrow pores, neglecting capillary controls on the equally (if not more) important process of clathrate growth. Here, we report the results of an experimental investigation of methane hydrate growth and dissociation in synthetic mesoporous silicas for a range of Pressure-Temperature (PT) conditions (273-293 K, up to 20 MPa) and sample pore size distributions. Results demonstrate that clathrate formation and decomposition in narrow pore networks is characterised by a distinct hysteresis; solid growth occurring at temperatures significantly lower (or pressures higher) than dissociation. Hysteresis takes the form of repeatable, irreversible closed primary growth and dissociation PT loops, within which various characteristic secondary 'scanning' curve PT pathways may be followed, depending on initial conditions. As far as we are aware, the observed hysteresis has not previously been reported for hydrate equilibria in porous media, although similar behaviour has been observed for ice-water systems, and is common to liquid-vapour transitions in mesoporous materials. The causes of such hysteresis are still not fully understood - our results suggest pore blocking during solid phase growth as a primary cause.

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