Dissociation of Fresh- And Seawater Hydrates along the Phase Boundaries between 2.3 and 17 MPa

Natural gas hydrates are increasingly encountered in offshore projects as they move into ever deeper water. Occurring from the seabed until several hundred meters in depth, hydrates are metastable, and dissociate back to gas and water if their high pressure- and low temperature stability conditions are affected by any kind of intervention. Hydrate dissociation weakens the seabed severely, and therefore, it is important to know accurately at which local pressure and temperature condition it is taking place. Experimental data on the phase equilibrium of seabed hydrates in the presence of porous media are at present limited to 11 MPa. This study presents a novel method of determining the hydrate phase boundary in porous media by controlled dissociation. Experimental phase boundary data of freshwater and 3.03 wt % NaCl hydrates up to 17 MPa pressure have been determined. The freshwater and seawater hydrate phase boundaries in porous media fit a set of simple empirical equations.