The recent trends of increasing energy demand led the industry toward the development of heavy oil unconventional resources. However, the production and transportation of such heavy oil is a challenge due to the lack of understanding of the two-phase flow behavior under the condition of high viscosity liquid phase. The objective of this study is to physically understand and quantify the effect of liquid viscosity on slug length and develop two- phase slug length correlation for high oil viscosity. The developed slug length correlation can improve the existing mechnistics two-phase flow models in the development and maintenance of heavy oil fields. Experimental high viscosity (0.181-0.589 Pa.s) two-phase air/mineral viscous oil slug length data is acquired in a horizontal 0.0508-m ID pipe. Data analysis showed a one third reduction in the average slug length compared to the average slug length under low viscosity condition. Furthermore, statistical analyses showed a significant effect of liquid phase viscosity on slug length distribution including maximum slug length and slug length variation. High speed recorded flow visualization revealed the effect of liquid phase viscosity on the scooping and shedding processes at the front and back of the slug, respectively; which is speculated to reduce the slug length. In addition, a proposed physical model suggests that the thick liquid film in the Taylor bubble zone and the short slug mixing zone result in a fully developed velocity profile at slug back stabilizing the slug at a shorter length. A new dimensional analysis based model is proposed to predict average slug length for high viscosity liquid slug flow. A validation and comparison study of the proposed correlation showed the best performance amongst the existing correlations.
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