Cottonwood is the first field development in deepwater Gulf of Mexico operated by Petrobras. It consists of three subsea wells in water depths of 670m (2,200 ft). Two wells presently produce gas-condensate, with high wax deposition potential. The wells are connected to a fixed platform in East Cameron 373 Block, 27.2 km (17 miles) away, through a piggable loop with flowlines of 15.2 cm (6”) nominal and 12.2 cm (4.8”) ID. During a pigging procedure in December 2007, a rigid, 12.9 cm (5.1”) elastomer pig got trapped halfway in the East segment of the loop, after traveling through the West segment. In front of the pig a slug of paraffin was formed and impeded its passage. During two years the production continued through the still open West segment of the production flowline. A wax mitigation plan was implemented, consisting of continuous paraffin dispersant injection. Meanwhile, low-cost, advanced technology-based methods to remove the obstruction were pursued, as an alternative to the high-cost whole or partial East flowline substitution. The procedures attempted were, first, the controlled pressurization of the flowline, second, the application of associated vibration and pressurization. These methods, along with paraffin solvent soaking procedures, helped to release the pig in February 2010, making both segments available for production. However, a layer of wax was formed inside the flowline loop and pig fragments might still be present in the East segment. A cleaning operation was performed to further clean both flowline segments. The operation consisted of injecting sea water mixed with a dispersant, an approach, to our best knowledge, not attempted before in such a long subsea tie-back. The formulations used were thoroughly laboratory tested. The operation demanded noticeable logistics planning and execution, due to the flowline volume (4000 bbl) and the number of volumes circulated (circa of 10). The operation was a success, thereby allowing the restoration of production with full flowline diameter availability and the resumption of routine pigging of the loop.
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