Investigation and Prediction of High-Viscosity Liquid Effect on Two-Phase Slug Length in Horizontal Pipelines

Abstract

Summary The recent trend 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 because of the lack of understanding of two-phase flow behavior under the condition of high-viscosity liquid phase. The objective of this study is to physically understand the effect of liquid viscosity on slug length and develop an empirical two-phase slug-length correlation for high oil viscosity. The developed slug length correlation can improve the existing two-phase flow models often used 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. High-speed recorded flow visualization revealed the effect of liquid-phase viscosity on the scooping and shedding processes at the slug front and back, respectively, and liquid film thickness in the Taylor bubble zone. Data analysis showed a one-third reduction in high viscosity (0.181–0.589 Pa.s) average slug length compared with low viscosity (0.001–0.017 Pa.s) average slug length. Furthermore, analysis of slug-length distributions revealed that as liquid viscosity increases, slug length distribution deviates from the log-normal distribution to a trancated positively skewed distribution. As a result, the average, the variance, and maximum slug-length values vary with liquid viscosity. On the basis of these experimental observations, a physical model is proposed which suggests that the thick liquid film in the Taylor bubble zone and the short slug-mixing zone at the slug front result in a fully developed velocity profile at the slug back, stabilizing the slug at a shorter length. A new dimensional-analysis-based empirical model is proposed to predict dimensionless average slug length for high-viscosity liquid slug flow. A validation and comparison study of the proposed correlation showed the best performance among the existing correlations.