Morphology and Distribution Structure Characterization of Methane Hydrate Formed in the Presence of Amphiphilic Antiagglomerant Additive

Abstract

We investigate the impact of commercial amphiphilic antiagglomerant additive (AA) on the hydrate crystal morphology, size, and dispersion in organic phases, by using optical imaging and Raman spectroscopy. To better reproduce the conditions during oil and gas offshore production, methane hydrates were formed from saline water (5 g/L NaCl) in the presence of AA additive at various concentrations (aqueous solutions of 5 and 7 wt %), by using the Ketrul211 condensate phase (corresponding to a petroleum cut of C 12 −C 14 carbon distribution), under a constant subcooling at 8.5 ± 0.5 K and 70 bar. Two systems have been studied: water-AA/methane and water-AA/ketrul211/methane. By optical imaging observation, the presence of AA additives leads to polygonal periodic crystals (with size ranging from ca. 1 to 10 μm) for the water-AA/methane system and perpendicular needle crystals (with size close to 10 μm) for the water-AA/ketrul211/methane system. In the absence of the AA additive, no polygonal or needle crystal morphology has been observed. With the help of Raman imaging, the methane hydrate distribution has been investigated at a micrometer scale: the formation of methane hydrate aggregates is revealed inside the ketrul211 bulk-phase matrix.