ABSTRACT

Multiphase production systems face many challenges from the design to production phase. Transport of multiphase streams involve phase mixing, different flow patterns, mass transfer and, phase changes which make the system hydrodynamic very complex. All this complexity and chaotic state could lead to operational issues in the production and processing facilities; thus, it is very critical to understand what the expected behavior of the system is and how it would affect the production. In multiphase transporting systems, situations such as severe slugging in pipelines, risers, and receiving facilities can generate harsh transient events which could jeopardize the integrity of the system. Thus, this paper presents a multiphase assessment of an offshore production facility including its major component and a multiphase trunkline. The studied pipeline operates with three phases: oil, water, and gas; thus, flow patterns vary from stratified to severe slugging for some operating conditions and locations. A flow assurance study was conducted to improve the design and reliability of the off-shore transporting multiphase system. The study included a production development from an offshore production-separation platform which is located at approximately 55 miles offshore. The production of different wellhead platforms convey in the platform and then a multiphase stream is transported via a 30-in pipeline to a separation processing plant on-land. A detailed hydrothermal model of the entire system was developed and different operating conditions were evaluated considering the worst case scenarios for slugging and liquid accumulation. Different gas oil ratios were evaluated to determine the most optimum and safe operating conditions for the system based on a slugging analysis and severity scale. Slug severity statistics and system hydrodynamics were used narrow down critical conditions that should be avoided as well. This paper presents the methodology used in the assessments as well as the results obtained for the steady state and transient cases. In addition, some recommendations for improving the design and operation of the system are provided.

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