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Effect of Brine Salinity on the Stability of Hydrate-in-Oil Dispersions and Water-in-Oil Emulsions

Aman, Zachary M., Haber, Agnes, Ling, Nicholas N. A., Thornton, Alexandra, Johns, Michael L., May, Eric F.
Energy & Fuels 2015 v.29 no.12 pp. 7948-7955
calorimeters, dispersions, emulsions, ions, nuclear magnetic resonance spectroscopy, oils, petroleum, risk, salinity, sodium chloride, surfactants
The stability of hydrate-in-oil dispersions is a critical parameter in assessing the risk of flowline blockage due to particle aggregation or wall deposition. Many studies of hydrate particle transportability have used deionized water to form the dispersion; however, the resulting lack of ions means that the crude oil’s natural surfactants will be less active, which does not represent production conditions. This study presents a new investigation of both hydrate-in-oil dispersion stability and water-in-oil emulsion stability, measured with a differential scanning calorimeter (DSC) and low-field nuclear magnetic resonance (NMR) apparatus, respectively. The results show that hydrate-in-oil dispersion stability increases directly with sodium chloride (NaCl) mass fraction in the aqueous phase; above 5 wt % NaCl, the dispersion was observed to be stable over ten hydrate formation–dissociation trials. This was comparable with the dispersion stability observed previously when an ionic surfactant was dosed at 2 wt % into the same crude oil. In contrast, only 0.1 wt % NaCl was required to stabilize water-in-oil emulsions over a four day observation period. This comparison suggests that, for crude oils containing natural surfactants, the risk of hydrate blockage may decrease as brine salinity increases from 1 to 10 wt %, without affecting the stability of the water-in-oil emulsion. The results demonstrate that experimental studies on hydrate- or water-in-crude oil systems should be performed with realistic values of brine salinity, to accurately capture dispersion stability.