An oil riser is an integral part of a drilling rig, which is a long complex pipe that connects the floating or anchored rig to the wellhead situated below the sea. The subsea well is drilled through the oil riser and enables the drilling mud (a combination of oil, gas, water and sand) to circulate up through the pipe and back up to the rig's separation tanks. It is common knowledge in the oil drilling industry that knowing the condition of the oil riser [and mooring systems] is critical to safe and successful operation and production of deepwater fields..
Drilling in deeper water makes the process more challenging. How an oil riser will function on the job depends on variables and connot be determined until it is used in deep water and at full production. One of the primary failures of oil risers is the lack of preventative monitoring, which may often be left as the last function of operators. There is little doubt that inadequate monitoring of the oil riser and other variables contributed to the tragic explosion and consequent oil spill on British Petroleum's drilling rig in the Gulf of Mexico.
Problems may also occur in offshore drilling due to a flow process called "riser slugging" that may develop in pipelines from wellheads to separation tanks. This occurrence may produce severe oscillations in pressure and flow rates. Stabilizing the intensity of riser slugging may be introduced by employing "anticipatice control actions" on valves located at the gas and oil entrance and exits of the separators.
A common variation and concern in deep water is that the reservoir is not adequately pressurized to allow the flow of oil at satisfactory levels, which may complicate the function of the riser. High flow levels of gas must be accommodated in the risers for further recovery by the gas/liquid separators on the rig's platform prior to recompression and reinjection. If not monitored and processed satisfactorily inadequate riser design and/or lax monitoring may cause excessive pressure that along with the high flow of gas and/or oil may result in an explosion, outbreak of fire and/or possible crew fatalities, all of which occurred on BP's drilling rig in the Gulf of Mexico. It is important that oil risers are monitored more carefully to ensure proper flow and functioning to avoid any future explosive and tragic outcomes.