Neutron scattering studies on the formation and decomposition of gas hydrates near the ice point

Gas hydrates pose a major risk of disruption to the marine pipelines of the oil and gas industry. At the temperatures and pressures in these pipelines gas hydrates can form large solid plugs. A clearer understanding of these processes would allow implementation of effective strategies to avoid production losses in gas pipelines. In-situ neutron powder diffraction was used to study hydrate growth and dissociation for 10% propane-methane gas and D2O ice and liquid water in the temperature and pressure range of 263 – 288 K and 3.0 – 4.8 MPa. Of our three samples one formed a mixed sI and sII hydrate while the other two formed single sII hydrate. Thermodynamic stability calculations could not accurately predict if a mixed hydrate wo uld be formed. Our hydrate dissociation experiments question the relevance of anomalous hydrate preservation in our particular case. Furthermore these experiments elucidate the importance of the heat flow of the reaction processes and the role of a free liquid-gas interface.