| Summary: | Natural gas hydrate is a solid state of gas and water at low temperature and high pressure. Gas hydrates are known to form hydrate plugs in production line, and has thus generally been considered a problem to the oil industry. However, the energy stored in gas hydrates is vast, and as the global energy demand increases, focus is shifted on gas hydrates as a potential energy resource. The work presented in this thesis is a series of experimental studies of hydrate formation and dissociation kinetics in porous sandstone. The overall objective was to provide an improved basic understanding of processes involved with formation and production of methane (CH4) gas hydrates within porous media and to obtain data for numerical modelling and scaling. CH4 hydrate has been formed repeatedly in Bentheim sandstone rocks to study hydrate formation patterns as function of initial water and gas saturations and salinity, and to prepare for subsequent lab-scale gas production tests using two different production schemes: 1) CH4 production by carbon dioxide replacement, and 2) CH4 production by dissociation of hydrates through depressurization. Salinity impacts on induction time and hydrate growth pattern has been investigated through six different experiments, looking at the effect of salinities ranging between 1 wt% and 10 wt%. Salts are well known hydrate inhibitors and may affect both induction time for nucleation and hydrate growth pattern. These results show that salinities below 4 wt% NaCl do not seem to affect the hydrate formation rate significantly. However, at higher salinities (4.5-10 wt% NaCl) the inhibition is evident. The results show a reduction of the amount of water converted to gas hydrates and an increase in induction time with increasing salinity. Depressurization is by many considered the most promising production method, and is the only successful production method to date on field scale (The Messoyaka field located in the eastern Siberian permafrost). This production method is based on dissociation of gas ...
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