A drilling riser is a large pipe or conduit used to encapsulate drilling equipment during undersea operations. These risers allow workers above the surface of the water to drill deep into the sea floor. A drilling riser is commonly used to drill for oil below the sea, or to simply explore the sea floor and the earth below. After the conduit has been positioned in the water, the drill itself is dropped down through the center of the conduit to access the sea bed.
Companies can choose from two basic types of drilling risers depending on the needs of each application. Marine drilling risers are used with floating platforms or boats, and include a blowout preventer placed below the surface of the water. When working from a fixed oil platform, companies rely on tie-back drilling risers. These systems include blowout preventers located above sea level, which protect workers and equipment from pressure changes or potential explosions.
A drilling riser may terminate at the sea floor, or may extend slightly into the earth to prevent water infiltration. The drill bit itself and all related equipment pass through the riser and continue down below the surface of the earth. Without these risers in place, the drill would be left vulnerable to corrosion and damage caused by the salty sea water. All rock cuttings and other debris would simply be released into the water, leading to pollution that could impact water quality and sea life. The drilling riser helps to contain drilling operations within the confines of the conduit.
During sub-sea drilling, workers pump drilling fluid down through the drill line into the cutting bit at the end. This drilling fluid sprays out of the bit to help reduce heat generated by cutting through stone and hard earth. This fluid then carries rock and other debris back up through the conduit to the surface of the sea, where it can be collected and processed by oil workers. The drilling riser must be sized slightly larger than the drill itself to make room for this fluid.
The use of drilling risers allows companies to drill underwater for extended periods, with little risk of damage to equipment. The drill can be left in place over time without being exposed to saltwater, allowing workers to dig deeper than in previous years. By carrying waste and rocks back to the surface for disposal, these risers help to reduce water pollution and its related effects.