Innovative Solutions to Manage Slug Buildup in Multi-Phase Pipelines through Bypass Pigging

Abstract

One of the major challenges in multi-phase pipelines is to manage slug during pigging to ensure safe and smooth operation of downstream facility. The liquid slug accumulated during pigging can result in process upset, shutdown if the downstream facilities are not designed to handle the anticipated slug volume. This paper discusses the benefits of by-pass pigging to efficiently handle the slug volume resulting in optimal use of assets and without compromising the field production. By-pass pigs are specially designed pigs with holes on the discs that allow part of the fluid to move from behind to the front of the pig. This design feature helps minimize the liquid slug accumulation in front of the pig and significantly reduces the slug volume as compared with conventional pigs. Dynamic Flow Simulator is used to analyze the performance of bypass pig. However, the use of bypass pigs involves careful assessment with respect to well fluids impurities such as presence of wax, solids or high asphaltenes which may block the holes and thus influence the operational efficiency. The liquid slugs generated during pigging operation can cause severe operational problems in terms of level and pressure fluctuations in a separator leading to poor separation, potential liquid flooding, increased flaring, emergency shutdown and production loss. In order to minimize the slugging impact, sufficient buffer volume is provided in the slug catcher/separator to accommodate the slugs generated in the pipeline during various operations. However, considering surge volume in existing separators, Brownfield Projects can impose risk due to space constraints. To mitigate the risk, production levels are normally reduced during pigging operations leads to production deferment. However, during revamp of existing facilities for higher production capacity or changed operating conditions where existing equipment sizes impose constraints, bypass pigging has been shown to provide useful and practical solutions. This option can also useful in providing reduced slug catcher sizes for "Greenfield Facilities" as well. Very importantly, the bypass pigging operation eliminates production loss with no facility upsets. The benefits of this technique are established through transient simulations, before being adopted in facility design and operation. This paper discusses the related case studies. This paper discusses the benefits of bypass pigging and the challenges to accommodate the increased surge volume in the existing slug catcher/separator system during pigging operation. The application of bypass pigging to limit slug volume is demonstrated using Dynamic Multiphase Flow Simulator and compares the results with conventional pigging operation. The proposed design solutions are based on NPCC's extensive and successful experience in tackling challenges in design of slug handling facilities especially in Brownfield projects.