GAS HYDRATE FORMATION AND DISSOCIATION FROM WATER-IN-OIL EMULSIONS STUDIED USING PVM AND FBRM PARTICLE SIZE ANALYSIS Boxall, John A.; Greaves, David P.; Mulligan, James; Koh, Carolyn A.; Sloan, E. Dendy
An understanding of the mechanism for hydrate formation from water-in-oil emulsions is integral for progressing from preventing hydrate formation through expensive thermodynamic means to hydrate blockage prevention. This work presents hydrate formation and agglomeration in a stirred system studied using two complementary particle size analysis techniques, a Particle Video Microscope (PVM) and a Focused Beam Reflectance Measurement (FBRM). The PVM provides qualitative visual information through digital images in the black oil illuminated by a series of lasers. The FBRM provides a quantitative chord length distribution of the particles/droplets in the system. Three sets of experiments were performed using two different Crude oils, Conroe with a very small asphaltene content and poor emulsion stability, and Caratinga with a much higher asphaltene content and emulsion stability. The first experiments looked at ice as an analogy to hydrates, studying the morphology with both the PVM and FBRM. The second experiments looked at the effect of droplet size on hydrate formation and agglomeration, and the third set of experiments studied the dissociation process using a combination of the PVM and in situ conductivity measurements to determine the continuous phase. For hydrate formation, droplet size was found to have a major effect on whether or not agglomeration will occur. During dissociation agglomeration is extremely dramatic due to the creation of surface water on the particles. The dissociation of these agglomerates results in a significant destabilization of the suspension into a water/hydrate phase at the bottom of the cell until dissociation is complete. The dissociation conceptual picture presented illustrates an important implication when operating a flow line with hydrates present; dissociation within the pipeline should be prevented until the hydrates are out of the flow line.
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