Subsea infrastructure and method of decommissioning subsea infrastructure

Abstract

A method of dewatering a subsea pipeline bundle assembly before lifting the assembly from the seabed and an elongate carrier pipe comprising at least one internal fall that slopes downwardly towards a drainage outlet and at least one venturi formation that is aligned with the drainage outlet. The method comprises adding discrete buoyancy to the elongate carrier pipe that elevates the carrier pipe disposed between drainage outlets of the assembly. Each elevated portion defines inclined falls that slope downwardly in opposed longitudinal directions toward the respective outlets. Water within the carrier pipe drains down the falls toward the outlets. Injecting a dewatering fluid into the carrier pipe promotes expulsion of water from the pipe through the outlets by downward displacement of the water. Drainage may be assisted by a venturi effect driven by accelerating the flow of the dewatering fluid at a location in line with an outlet.