A Case Study in Wax Removal From a Subsea Flowline

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 105048, "A Case Study in the Removal of Deposited Wax From a Major Subsea Flowline System in the Gannet Field," by H.A. Craddock, SPE, K. Mutch, and K. Sowerby, Roemex Ltd., and S. McGregor, J. Cook, and C. Strachan, Shell UK Ltd., prepared for the 2007 SPE International Symposium on Oilfield Chemistry, Houston, 28 February–2 March. The following stages were key to the successful wax-removal operation: selection and design phase of the chemical application, the environmental chemical-selection criteria, the development of the work scope, and the logistics of the chemical application. The wax-removal process was deemed successful and offered the client significant benefit in terms of increased oil production. Reduced pipeline differential pressure and increased fluid arrival temperatures also indicated that the wax restrictions in the flowlines had been removed. Introduction The control and mitigation of wax deposition and its concurrent problems rapidly are becoming critical challenges facing the oil- and gas-production industry as the industry explores and develops in increasingly challenging environments, such as deepwater and subarctic conditions. Wax deposits can occur widely in the production process and often are considered the organic equivalent of scale formation. Field Description The Gannet field is 180 km east of Aberdeen in a water depth of approximately 90 m. Since the field was originally discovered, in the 1970s, several satellite fields have been tied into the Gannet facilities. Gannet D is an oil field 16 km northeast of Gannet Alpha. Production is from five wells, with oil transported back to the Gannet Alpha facilities by two looped 6-in. subsea flowlines referred to as Riser 31 and Riser 32. The crude from these reservoirs typically is 41°API, with a wax content of approximately 7% and a wax-appearance temperature of approximately 35.5°C. The Gannet G field also is produced by this system with a single 6-in. flowline tied in at the base of Riser 32, 0.5 km from the Gannet Alpha platform. Riser 31 carries Gannet D crude only, and Riser 32 carries Gannet D and G crude topside onto the Gannet Alpha processing facilities, where the oil is commingled with other Gannet fluids before being exported to the Fulmar platform.