are located in an oil field on the seabed 110 vertical riser towers are provided at 112 and 114 for conveying production fluids to the surface and for conveying lifting gas injection water and treatment chemicals such as methanol from the surface to the seabed the foot of each riser 112 114 is connected to a number of well heads injection sites 100 to 108 by horizontal pipelines 116 etc further pipelines 118 120 may link to other well sites at a remote part of the seabed at the sea surface 122 the top of each riser tower is supported by a buoy 124 126 these towers are pre fabricated at shore facilities towed to their operating location and then installed to the seabed with anchors at the bottom and buoyancy at the top a floating production unit fpu 128 is moored by means not shown or otherwise held in place at the surface fpu 128 provides production facilities storage and accommodation for the fluids from and to the wells 100 to 108 fpu 128 is connected to the risers by flexible flow lines 132 etc arranged in a catenary configuration for the transfer of fluids between the fpu and the seabed via riser towers 112 and 114 individual pipelines may be required not only for hydrocarbons produced from the seabed wells but also for various auxiliary fluids which assist in the production and or maintenance of the seabed installation for the sake of convenience a number of pipelines carrying either the same or a number of different types of fluid are grouped in u201c bundles u201d and the riser towers 112 and 114 in this embodiment comprise each one a.