ABSTRACT

A CFD method is proposed to simulate the gas-liquid severe slugging in a pipeline-riser system in the present paper. Based on the consistence principle of the severe slugging formation condition, the 3D flow in a pipeline-riser system is simplified into a 2D flow. The severe slug flow in a pipeline-riser system with a given pipeline declination angle is simulated numerically. The effects of gas-liquid physical parameters on slug flow characteristics are studied and analyzed when the liquids are water, crude oil and kerosene, and the gas are methane and air, respectively. Numerical results show that physical properties of the liquid, including viscosity, density and surface tension, have remarkable influence on the characteristics of severe slugging, including the flow pattern, the period and the pressure fluctuation, whereas the influence of the gas physical properties on the characteristics of the severe slugging is not significant.

INTRODUCTION

The pipeline-riser system, including a downward inclined pipeline and a vertical riser, is needed to transport oil (with water) and associated gas from subsea wellheads up to offshore platform systems in the exploitation of offshore oil and gas (Sertã, 2004). At low flow rates of gas and liquid, one important problem experienced in such a pipeline-riser system is a severe slugging phenomenon that is defined as the buildup of liquid slug that equals to or exceeds the riser's height (Schmidt, 1985; Fabre, 1990). This phenomenon, also called terrain-induced slugging, is a considerably harmful flow pattern in offshore petroleum production systems because of its high potential in causing sudden fluctuations of pressure and flow mass in the pipeline and overflow or interruption of the terminal gas-liquid separator (Sarica, 2000). Such a severe slug flow can thus damage the production equipment and greatly reduce the production capability. The gas-liquid severe slugging in a pipeline-riser system has been studied experimentally in several flow laboratories.

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