Methods and apparatus for a subsea tie back

A flow assurance system includes an inner pipe (70) disposed within an outer pipe (50) to assure flow through the outer pipe (50). During installation an d relative axial movement with the outer pipe (50), the inner pipe (70) is nearly neutrally buoyant or fully neutrally buoyant in the fluids of the out er pipe (50) and may extend partially or completely through the outer pipe (50) . The inner pipe (70) may be anchored at one end within the outer pipe (50). T he inner pipe (70) is preferably composite coiled tubing that is installed usin g a propulsion system. The system may allow fluids to flow through the inner pipe (70) and commingle with the fluids in the outer pipe (50) or may flow fluids through the inner pipe (70) to the exterior of the outer pipe (50). H ot fluids may pass through the inner pipe (70) to maintain the temperature of t he fluids flowing through the outer pipe (50) and chemicals may flow through th e inner pipe (70) to condition the fluids in the outer pipe (50). Tools may be attached to the end of the inner pipe (70) for conducting flow assurance operations within the outer pipe (50).