Effect of pressure vessel size on the formation of gas hydrates

A Seafloor Process Simulator (SPS) has been used for mesoscale experiments investigating the nature of hydrate nucleation and dissociation. The SPS is a 72 L vessel which establishes the pressures and temperatures required for methane and carbon dioxide hydrate stability. This paper describes the experiments that have been performed in the SPS and have been duplicated in the smaller Parr vessel (450 mL). It was found that experiments in the SPS resulted in hydrates consistently forming at lower overpressures and in shorter induction times than equivalent experiments in the Parr vessel. The variability of pressure and/or induction time for hydrate formation was not eliminated by using the SPS, but it appeared to be less dramatic (small coefficients of variation) when compared with a 450 mL Parr vessel. Based on the experiments performed using the SPS this reduction in overpressure and/or induction time required for the accumulation of hydrates may be attributed to increased bubble surface area, increased gas concentration, increased lifetime of bubbles, increased total volume of the SPS, or a combination of the above. Mesoscale experiments, such as those in the SPS, may perhaps be more representative of hydrate accumulation in the natural environment.