Impact of Water Cut on Asphaltene Deposition Tendency

Abstract A systematic lab study was conducted to investigate the impact of water on asphaltene deposition tendency, with emphasis on percent water cut and ion composition. Two crude oils from Gulf of Mexico with different properties were applied as probe oils to study asphaltene deposition using a capillary deposition flowloop. Distilled (DI) water and a synthetic brine with 6.5% NaCl salinity were used to create water-in-oil emulsions to study the impact of water on asphaltene deposition. For one oil sample, it was observed that adding as few as 2 vol% DI water to the oil/n-heptane mixture could cause as much as 56% reduction on deposition rate. When DI water was replaced by the synthetic brine, the reduction in deposition rate decreased. However, when the synthetic brine also contained ferric ion (Fe3+) or aluminium ion (Al3+), the deposition rate was restored back to the same or an even higher level as the base case without water. ICP analysis revealed that deposits collected from tests with ferric ion or aluminium ion also contains significant amount of those two ions, plus remarkable increases on other divalent ions including Ni and V. In the second oil, adding 10–20% synthetic brine also reduced deposition rate 10–25%. With only 10 ppm ferric ion in the brine, the deposition rate for the second oil was largely restored back to the original level without water.