Single Trip Pigging of Gas Lines during Late Field Life

摘要

For flowlines used to tieback marginal fields, pigging is anrnessential component of the associated flow assurance solution.rnSingle trip pigging using a single line is being pursued by thernoffshore industry as an economical alternative to round triprnpigging using dual flowlines because of the potential savingsrnin CAPEX and OPEX. Recently, the industry has developedrnsubsea pig launchers which are specifically designed forrndeepwater and ultra-deepwater applications. However, therernare significant operational challenges associated with singlerntrip pigging that need to be resolved.rnThis paper draws attention to potential difficulties in thernpigging of multiphase gas lines during late life field conditionrnwhen the line is likely to hold a large amount of liquid. A pigrntravelling through such a flowline is likely to stall at the basernof a deepwater riser due to the buildup of high static head ofrnliquid column in front of it and insufficient drive energyrnprovided by the reservoir fluid. There are some options suchrnas using gas lift at riser base, which are available to deal withrnthis problem. Pigging with bypass is another cost effectivernmethod to mitigate this problem. Using a hypothetical field,rnpigging simulation results from OLGA 2000 are presented torndemonstrate how inclusion of 10 to 15% bypass in the pigrnbenefits the pigging operation. Typical pipe cleaning pigs arernlimited to 3 to 5% bypass.rnAnother associated issue is the challenge of handling largernquantities of liquid arriving rapidly on the platform topsidernduring the pigging operation. The platform topside processrntrain is generally not designed to handle liquid inflow at suchrnhigh rates. Some potential solutions to this problem have beenrndiscussed. The optimum solution for liquid handling will havernto be developed using the field specific data.