Increasing production by applying field-proven active slug suppression

  • Lacy C
  • Groote G
  • Chao R
 et al. 
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Abstract

In mature fields, wells and pipelines are often oversized for the current operating conditions. This is because they have been primarily designed to handle early and midlife production, which may lead to slugging issues in later field life. The resulting flow fluctuations frequently lead to liquid handling problems caused by excessive liquid levels and pressure surges in the first stage separator. This can be an important source of downtime due to facility trips and deferment from sub-optimal facility operations. Furthermore, slugs travelling through topside piping can cause integrity issues when they impact bends. In flowline-riser systems, riser-induced slugging can lead to large slugs, especially in deepwater systems. These can usually not be contained in a platform-based separator. In such cases gas lift and conventional choking are often used to mitigate slugging. These two methods have drawbacks, however. For gas lift a source of compressed lift gas must be connected to the riser base and the volumes required to mitigate slugging may cause constraints in gas handling. Conventional choking leads to production deferment due to the backpressure imposed by a partially closed choke. In recent years “active” slug control methods have been developed to overcome these drawbacks. One such system is a relatively inexpensive solution developed by Shell Global Solutions known as the Smart Choke. This system has been installed at several locations worldwide and has been proven to be very effective in stabilizing slugging in flowlines and risers. Here, the topside choke is actively controlled to mitigate riser-induced slugging and acts only if flow surges are observed, reducing the peak flow rate into the separator. Between slugs, the choke opens, reducing the imposed backpressure. Since flow fluctuations are reduced, a flowline can be operated at higher average flow rate as the topside facilities can be operated at higher throughputs without risking excessive separator liquid levels. Field data from case histories in the GOM, Malaysia and Nigeria indicate that production gains of 10% are often possible. This paper presents the modeling, implementation and the data obtained from operations of the Smart Choke implementation for a deepwater facility in Nigeria. The objective of the Smart Choke is to stabilize the flow from the riser and to reduce the gas lift requirement. A feasibility study was performed to analyze the slugging behavior of the pipeline and the impact of no control, gas lift and, the combination of gas lift and Smart Choke. Upon favorable modeling results, the Smart Choke was moved to the project stage and implemented. Field data are presented to demonstrate how the Smart Choke was able to control the slugs, reduced gas lift rates and resolve separation issues. As slugging issues become more common worldwide, active slug control methods can provide a low-cost method to mitigate slugging. The effectiveness of such methods in flowline-riser systems has been proven in practice. This technology may provide effective slug mitigation in a wider range of applications in the future, such as horizontal wells suffering from terrain slugging.

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Authors

  • C E Lacy

  • G A Groote

  • R Chao

  • Shell Projects

  • E Osemwinyen

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