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Tapping into deep-water reservoirs
Breakthrough technology and the innovative use of undersea equipment normally found onshore or on sea-level platforms is making oil production possible from the Parque das Conchas project.
The location of the fields 120 kilometres off the coast of Brazil, the water depth of nearly two kilometres and the scattered nature of the reservoirs posed daunting technical challenges. So too did the low reservoir pressure — meaning the oil would not flow freely — and the near-freezing temperatures on the seabed. Shifting sands and the powerful swell of the Atlantic Ocean added to the hurdles.
To develop the fields economically, three reservoirs of Parque das Conchas were connected through a single production process centred on a specially-converted floating, production, storage and offloading vessel.
Drilling through shifting sands
Gunnar Holmes, former Senior Operations Geophysicist and Lee Stockwell, former Senior Petrophysical Engineer, Shell Brasil, talk about drilling challenges in soft sand kilometres below the ocean’s surface (2009).
The sand that forms the layer containing oil and gas at Parque das Conchas has travelled a short distance in geological terms from Brazil’s coastal mountain ranges, 1,000 metres above sea level, to fill the Campos Basin. The steep angle of the flow — down to 2,000 metres below sea level in just 120 kilometres — has left the sand relatively little time to settle, making drilling more difficult.
“Drilling down thousands of metres into the uncompacted seabed in the Campos Basin is like trying to dig a deep hole in beach sand,” said Gunnar Holmes, former Shell Brasil Senior Operations Geophysicist. ”As we drill down thousands of metres, sand and water pour back in.”
To prevent sand, mud and shale from filling the well while drilling, Shell pumped a mix of synthetic oil with additives under high pressure to shore it up before installing steel casing to hold it back permanently. Engineers then installed perforated pipes covered by several layers of mesh that acts as a sieve to stop sand from flowing into the well, but allow oil and gas to enter.
Tools that can make electronic and microscopic measurements helped engineers drill with pinpoint precision. For the first time Shell used technology that gives a detailed picture of geology three to five metres away from the well while it is being drilled. This technology allows engineers to steer drills in response to a continuous flow of geological information.
“That means we can steer the path of the well as we drill and stay in the best reservoir,” says former Shell Senior Petrophysical engineer Lee Stockwell.
First oil and gas separators on the seabed
Remote-controlled submarines helped to install 1,500-horsepower electric pumps on the seabed — each with the power of a Formula 1 engine — to push oil to the surface as the natural pressure inside the reservoirs is too low. Just as a fast-flowing river resists freezing, the six pumps on the seabed help prevent the oil from freezing. They also stop wax from forming under the high pressure and low temperature in the 78-kilometre network of production pipes. This was the first use of electrical submersible pumps in a full-field development.
In another industry first, machines separate oil and gas on the seabed, rather than on the surface. Without first separating the oil and gas, the electric pumps — designed for liquids — would struggle to force oil to the surface. Any gas entering the pumps could cause damage and lead to pump failure.
The reservoirs in Parque das Conchas are up to 20 kilometres apart. Shell developed special umbilical cables to keep the power supply running and to feed chemicals to the seabed production system. The 25 centimetre-wide cables also carry sensors that convey vital temperature and pressure information back to engineers on the surface. The six cables, which stretch for a total of 54 kilometres, supply electrical and hydraulic power to the wells, manifolds and pumps. The chemicals prevent frozen solids from forming in the oil.
Steel pipes that bend
Former Parque das Conchas Project Manager Kent Stingl reveals how technologies met ultra-deep-water challenges (2009).
The constant swell of the ocean posed another challenge. Shell designed risers — pipes connecting the equipment on the seabed to the surface — that can move with the swell. They are rigid steel pipes several kilometres long with a bend which flexes when the sea level rises and drops, helping to prevent fractures and metal fatigue.
A floating production, storage and offloading vessel (FPSO) receives the oil at sea level because of the remote offshore location of Parque das Conchas, a long way from other producing oil fields and established pipelines. Building a platform or new pipeline network would have been too costly.
The Espírito Santo is among FPSOs moored in the deepest water in the world. It is as long as seven Olympics–sized swimming pools and as tall as a 33-storey building. It is a former crude oil carrier refurbished to include new tanks and collision-resistant buffers around the vessel. The Espírito Santo has the capacity to generate 68 megawatts of power — equivalent to the peak output of about a dozen heavy diesel-electric locomotives — to supply the deep-water oil and gas separation machines and high-pressure pumps on the seabed.
Most of the technology hardware used on the seabed was built in Brazil. But the submersible electrical pumps and umbilical cables were built in the USA, the tubes for the cables in Europe, and the cables’ copper cores were made in Colombia. The FPSO was built in Singapore. At peak, some 3,000 people worked on the FPSO at the Keppel Tuas shipyard in Singapore before it set sail in 2008 on a 16,700 kilometre journey to its final mooring in the Campos Basin.