Deep water: the Shell experience
31 January 2014
Kilometres below the sea’s surface, near-freezing temperatures cause oil to congeal and gas to form ice crystals. Extreme pressure and sea swell also poses challenges. Shell is using technology to overcome these challenges and unlock new resources from deep water. Thousands of technologies are needed to tackle the challenges of freezing temperatures, high pressure and storm conditions.
Perdido is situated in 2,450m of water - Photo: Shell
Examples of innovations developed by the group to facilitate operations in these extreme conditions include new chemicals based on fish protein which are injected into the underwater pipes to stop oil from congealing and ice-like gas hydrates forming in the extreme cold.
Safety in deep water
Safely drilling a well far below the ocean surface in extreme pressures demands strict safety procedures and rigorous design, construction and maintenance standards.
Strict standards for drilling in deep water require wells to have at least two independent physical barriers to safeguard against blowouts. These can include heavy fluids that exert downward pressure to contain the oil or gas, and mechanical barriers – such as cement plugs and rubber-and-metal seals. If for any reason well control is lost, mechanical barriers such as blowout preventers are designed to seal off the well.
Before drilling can begin, the well design and drilling plan goes through several stages of review, including engineers from Shell and its drilling contractor drilling the well “on paper” to ensure the well design, drilling plan and the agreed safety measures are adapted to the conditions. The process is also used to check that everyone is clear on roles and responsibilities on everyone who will work on the drilling rig.
Shell’s technical approach to the safety of wells is combined with extensive safety training of its well engineers. They must complete an externally-recognised four-year training programme, in addition to their initial Bachelor or Masters degree. The programme includes detailed modules on safety and deep-water drilling. Simulators allow trainees to practice managing well-control incidents, such as a surge of high pressure gas to the surface.
Shell has a number of deep water projects under development or in production. Here we look at two of the most significant.
The Perdido oil and gas platform is moored in 2,450 metres of water and is located 320 kilometres off the coast of Texas in the Gulf of Mexico, further from land — or another installation — than any other offshore production platform. It sits on top of a giant floating steel cylinder — or spar — designed to stay upright in storms.
Nine mooring lines hold the Perdido spar in place, each more than three kilometres long. Beneath the spar a network of 35 wells and pipelines on the seabed connects three separate fields in the near-freezing water under immense pressure. Oil and gas are separated on the seabed before powerful pumps push them up from the low-pressure reservoirs to the surface.
The Perdido platform peak production will be 100,000 barrels of oil equivalent a day. The oil and gas fields beneath the platform lie in a geological formation holding resources estimated at upwards of three billion barrels of oil equivalent.
The Perdido project involves the development of three fields — Great White, Silvertip and Tobago — spread over 70 square kilometres. The Perdido platform is equipped with its own drilling rig and can move directly above the wells in the Great White field with winches adjusting the tension of the mooring lines.
The remaining 13 wells are in the more distant Silvertip and Tobago fields. They tie into the same network on the seabed beneath the spar through a system of valves and fittings that control the flow of oil and gas.
In December 2008, the project set the world record for the deepest completed offshore production well at 2,852 metres below sea level. Another well in the Tobago field is being drilled at a depth of 2,925 metres.
Perdido produces oil production from rock that is less porous than other formations in the Gulf, so oil and gas flow less easily. To combat the low pressure in these reservoirs, Shell has five electric pumps on the seabed to bring the oil to the surface. The gas is separated from the oil and flows up to the spar through risers. From the spar, the oil and gas are pumped through separate pipelines for treatment on the shore.
Powerful storms pose serious technical challenges. In 2008, three quarters of the oil production in the Gulf of Mexico had to be suspended because of hurricanes Gustav and Ike. The Perdido spar’s nine mooring lines are designed to withstand the type of storm likely to occur once in 1,000 years, such as the most destructive hurricane in US history, Katrina.
The spar is designed to stay upright even if it disconnects from its moorings. It moves up and down only a few metres with the ocean’s swell during storms. The heavy bulk below the waterline gives it the stability to keep it straight; it is designed to tilt no more than 14 degrees in the heaviest storms.
On March 31, 2010, when first oil flowed to the platform, Perdido beat the water depth record for an offshore oil drilling and production platform by over 50%. Now Shell’s Stones project, also in the Gulf of Mexico, will be in 2,900 metres of water, making it the new deep-water record holder when it comes on stream in 2016.
Stones is a phased development that will ultimately have eight subsea production wells tied back to a Floating Production Storage and Offloading (FPSO) vessel and host facility. The reservoir depth is around 8,077 metres below sea level and 5,181 metres below the mud line.
An FPSO design was selected to safely develop and produce the Stones ultra deep-water field. This concept design can handle a relative lack of infrastructure, a complex seabed, and unique reservoir properties. Tankers will transport oil from the Stones FPSO to US refineries, and gas will be transported by pipeline.
The Stones FPSO will use a special type of flexible pipe that carries oil and gas to the FPSO for processing and transport, known as lazy wave risers. These were pioneered by Shell and are made of steel with extra buoyancy. An arch bend absorbs the motion of the FPSO and boosts riser performance at extreme depths.
The FPSO will also contain a turret with a detachable buoy that allows the vessel to turn in place during normal weather conditions. If a heavy storm or hurricane approaches, it can disconnect its mooring lines and risers from the well system and sail to safe areas.
Stones will be twice as deep as BP’s Macondo field, where a blowout in April 2010 killed 11 men and spewed crude into the sea for nearly three months. Shell is confident that its technologies, systems and staff are up to the task of ensuring the safe development of ultra-deep hydrocarbon resources, and has recently announced the expansion of its deepwater operations off Brazil and a new find in the Gulf of Mexico.
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