Riser pipes are used to connect a well at the seabed and a floating rig. In deep water, the cold seawater temperature can cause congealing of the drilling fluid, such as mud or brine, within the riser pipe. The riser pipe typically has a diameter of around 0.5 metres or larger. Therefore, with this large flow area and a more viscous fluid, the pumping capacity is typically insufficient to achieve the turbulent flow required to displace all of the existing fluid from the pipe. Rather, fluid returning to the surface tends to channel through the colder and therefore more viscous existing fluid.
Consequently, it can take several stages, and between two and four days, depending on the depth of the seabed to displace the existing fluid. This represents a significant waste of time for the drilling operation, which is inefficient and costly.
It is desirable to provide a tool which more effectively removes existing fluid from the riser pipe.