Subsea risers need to accomplish a lot. Not only are they responsible for transporting your media from the well fields on the seafloor, but they also deliver control and injection fluids to undersea equipment. So, it stands to reason that this vital link between the subsea field and the drilling and production facilities can come in a variety of options. Here’s a guide to some of the basic kinds of risers and their roles.
Primarily used in fixed platforms, these types of risers include attached, pull tube, catenary and top-tensioned risers and are usually preferred for their dual-use of support and fluid transportation. Most of these can handle small degrees of motion, but too much can give rise to issues. In particular, top-tensioned risers can use buoyancy cans and motion compensators to minimize stress. Riser towers also fall under this category.
While once being used mostly as a supplementary riser, these are now occasionally used as part of the primary system since they can withstand more movement than their rigid cousins and are usually lighter. Some even include buoyancy modules, which can help extend the life of the riser and relieve some of the stress on the platform themselves. Some companies are developing a riser monitoring system to help manage buoyancy automatically. These risers are primarily used in floating platforms, which take advantage of their wider range of motion.
Usually used during preliminary site preparation and production, drilling risers are largely used for neither support nor fuel transportation. Instead, these temporary risers typically transport silt and other material away from the drill site. Additionally, they pull drilling fluids from the wellbore to the surface, keeping the water free from contamination.
Depending on the type of offshore platform, your riser needs may vary. Often, these riser types will even be used in conjunction with each other, such as pairing flexible risers with riser towers to try to capture the best of both worlds.