Asphaltene Solvency and Stability of Water in Oil Emulsion: A Case Study of Two Nigerian Crudes

Abstract

The effect of asphaltene solvency on the stability of water-in-oil emulsion was investigated using crude samples from two Nigerian oil wells, namely Okoro oil well (crude A) and Okpoho oil well (crude B), chosen because of their varying resin and asphaltene content. Solvency of the emulsion was modified by addition of heptane, toluene, and their blend (heptol) in various proportions. The effect of aqueous phase pH on the stability of the emulsion was also studied. The results showed that the Okoro well crude oil which has higher asphaltene content of 3.2 wt% and lower resin/asphaltene ratio of 1.15 formed a much more stable emulsion than that of Okpoho oil well which has 1.9 wt% asphaltene content and 3.16 resin/asphaltene ratio. It was also noticed that the emulsion became more destabilized at basic pH range. A model was developed which can be used to predict the stability of the water/oil emulsion in period of time beyond the study range.

Keywords: water-in-oil emulsion, stability, asphaltene, resin, solvency, aromaticity