Direct conversion of water droplets to methane hydrate in crude oil

Water droplets suspended in a crude oil were converted to methane hydrate by pressurization in an autoclave cell. Droplet size distributions were monitored using a focused beam reflectance method (FBRM) particle size analyzer as the water converted to hydrate. The droplet size distribution did not change significantly during conversion of nearly all the water to hydrate. The preservation of the distribution during conversion indicates that water droplets act as individual reactors and supports a hydrate shell formation model. Water droplet size distributions were measured with the FBRM probe at multiple shear rates in four crude oils (Albacora Leste, Conroe, Petronius, and a West African oil) with various surface tensions and viscosities. The water droplet size distributions, and thus hydrate particle distributions, were found to be lognormal with breadth increasing with mean. A correlation model has been developed to predict the entire size distribution of water droplets in these oils as a function of viscosity, interfacial tension, and shear rate. The model has been extended to represent gas hydrate particle size distributions in oil after conversion.