Dynamic Response and Stress Impact Analysis of Production Riser under Severe Slug Flow

摘要

Equipment integrity and systems reliability are of paramount interest inoil and gas industry as they guarantee not only the safety of personnelworking in the field but also for the protection of environmentaldegradation that could inadvertently occur due to unprecedentedequipment failure. This paper presents a finite element analysis of theriser base that is subject to repeated loading resulting from severe slugflow in an offshore production flowline-riser (TTR) system.Commercial software packages used in this simulation study arePVTsim 20, OLGA 7 and ABAQUS 6.14-1. The typical flowline-riserpipe system was modeled with a 10 inch (0.254 m) nominal pipe size(NPS) of wall thickness 0.562 inch (0.0143 m) and of API 5L Grade X-65 steel material. PVTsim was used to generate the PVT properties ofthe fluid model which is a typical heavy oil of API gravity in the rangeof 23-27 degrees and hence the preparation of fluid table files for themultiphase simulator. Slug tracking module in the program was used totrack the severe slug development in the flowline-riser system for atypical oilfield producing at the rate of 10000 barrels of oil per day(bopd) (1584 m~3/day). Pressure-time series prediction by themultiphase simulator at the riser base was used to plot the pressureamplitude loading curve in ABAQUS for the structural analysis.Numerical results from multiphase simulator shows that severeslugging occurs in the riser at that production rate and the riser baseexperiences the most pressure loading during the slug buildup in theriser and as well as the cyclic loading behavior of severe slugging in theriser, while that of ABAQUS implicit dynamic analysis shows thedisplacement mode of the structure and stress distributions in the finiteelement model of the riser base during the peak of the severe sluggingfor 5 cycles period of the severe slug flow. The results of this numericalstudy will provide a technical data for the enhancement of the design ofa riser pipe especially the 10 inch nominal pipe size considered in thispaper which has substantial application in deepwater offshore fielddevelopment.