ABSTRACT

Slug flow is a flow pattern commonly encountered in offshore Multiphase flow lines. It is characterized by an alternate flow of liquid slugs and gas pockets, resulting in an unsteady hydrodynamic behavior. All important design variables, such s slug length and slug frequency, liquid holdup, and pressure drop, vary with time and this makes the prediction of slug flow characteristics both difficult and challenging. This paper reviews the state of the art methods in slug catcher sizing and slug volume predictions. In addition, history matching of measured slug flow data is performed using the OLGA transient simulator.

This paper reviews the design factors that impact slug catcher sizing during steady state, during transient, during pigging, and during operations under a process control system.. The slug tracking option of the OLGA simulator is applied to predict the slug length and the slug volume during a field operation. This paper will also comment on the performance of common empirical slug prediction correlations.

INTRODUCTION

There is an increasing need to develop more oil and gas design and development of economical offshore production fields in harsh offshore environments. The special problems associated with offshore operations pose new challenges in the systems. In an offshore environment the transient effects during start-up and shut-down of the production system become more pronounced. New transient simulation tools such as OLGA andPLAC are being used more in the design and modeling of these transient effects

Slug flow is one of the most common flow patterns. It is characterized by an unsteady, alternating flow of liquid slugs and gas pockets. Due to its highly complex nature, the prediction of slug length, slug frequency and pressure drop by thematically means is almost impossible. Due to its impedance to oil and gas production operations, many studies have been camied out and empirical and mechanistic models have been developed. "Steady state" slug flow can be classified as either hydrodynamic or terming induced slugging. "Transient" slugging can also occur in pipelines as a result of changing operating conditions, pigging or duringstart-up opemtions. Empirical correlations based on field or labotary data have been developed to predict the transition to slug flow, the slug velocity, the slug length, the slug frequency, and the statistical distribution of slug lengths.

Hydrodynamic slugging is the normal slugging pattern enounced in flowlines. Most of the empirical methods developed for predicting the tradition to slug flow were developed for horizontal or near horizontal pipes. The most often used slug length prediction methods in the industry for large pipe diameter are the rilll correlation and its revisions, such as the Norris2 correlation, and the Scott et. al.3 Correlation. Terrain induced slugging is induced by low points in the flowline which may shrink, or grow after the dip. It is more dynamic and less understood compared with hydrodynamic slugging. Every flowline through hilly termin has its own elevation profile, therefore has its own slugging characteristics. The worst kind of terrain induced slugging is severe slugging.

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