Overcome Slug Related Operational Issues in Brownfield Facilities by Using Bypass Pigging

Abstract

Abstract One of the major challenges in the upstream oil and gas industry is de-bottlenecking of existing slug catcher/ inlet separator system during facilities up-gradation or due to changes in production rates for any other reasons. It is often found that upgrades or changes result in increased slug volume from the upstream pipelines thus making existing slug catcher or separators inadequate to handle the increased load. Even in cases of normal pigging not involving debottlenecking of existing facilities, production rates are required to be lowered. This is done as excess liquid slugs generated due to pigging may show 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. The use of by-pass pigs can effectively reduce the liquid arrival rate at the slug catcher over conventional approach by delivering a more uniformly mixed fluid even at relatively higher production rates. It thereby reduces the slug volume and hence, the requirement of increased surge capacity. Further, in brownfield applications, it enables optimal use of existing assets or avoiding new slug catcher. Operators are reluctant to reduce the production flow rate to very low value for pigging, as this normally results in reduction in revenue. Bypass pigging, as compared with conventional pigging, is able to reduce the pig velocity even at relatively higher production rates. It, however, requires careful evaluation and design as in many cases, such as well fluid having wax, solids or high asphaltenes may result in blockage of the bypass holes thus impacting the effectiveness of the operation. Transient modeling and simulation of bypass pigging using OLGA Dynamic Multiphase Flow Simulator has been performed to address such issues. This paper describes the strategies to address de-bottlenecking challenges due to increased surge volumes to be accommodated in the existing slug catcher/ separator system and use of by-pass pigging to overcome these. The application of the technique used i.e. bypass pigging is demonstrated by transient multiphase simulation using OLGA dynamic simulator. Proposed design solutions are based on NPCC's extensive and successful experience in tackling challenging Brownfield projects.