Existence and Prediction of Severe Slugging in Toe-Down Horizontal Wells

Abstract

Severe slugging is an important flow assurance issue, typically observed in offshore pipeline-riser systems. The consequences of severe slugging include flooding of downstream production facilities and an overall decrease in productivity. It had been previously thought that severe slugging would be limited to systems with a downward inclined pipeline and vertical, catenary or lazy-S shaped riser. This paper presents the results of an experimental and modeling study, which demonstrates the existence of severe slugging in systems with upward inclined lateral flow paths such as a toe-down well. The severe slugging phenomena described in this paper was observed in a large scale experimental facility constructed for the purpose of studying flow behavior in horizontal wells. The facility enabled the study of the effect of the completion parameters like end of tubing location and the presence of a packer. Various gas and liquid rates were tested in the facility, and slug flow was the dominant flow pattern in the lateral section. The facility was also designed to test gas lift performance in horizontal wells. Therefore, the effect of gas lift on the severe slugging phenomenon was also studied. Based on the experimental observations, two severe slugging prediction models were developed. The first was a transient model based on the Balino et al. (2010) model. The second was a single point criterion based on the Bøe (1981) criterion. The constitutive equations and modeling results are also presented in this paper.