Castrol is exploring a possible return to closed loop systems and use of synthetic control fluids for subsea development.
Since the 1960s, subsea development have been moving further offshore into deepwater, high-pressure, high-temperature environments, said Tony Globe, technology authority for Castrol’s marine and energy lubricant business, in an interview with Rigzone. Oil and gas companies are also trying more difficult things in these challenging, remote locations. Additionally, environmental regulations worldwide are playing a greater role in the chemistry of the products being used.
Initially, conventional hydraulic systems and hydraulic oils were used for offshore production. These systems operated well valves on the surface; operated wells on the seabed were controlled via longer, water-proof hoses. As subsea wells moved further away from the platform, operating this equipment became more difficult in terms of opening and closing well valves quickly due to thicker oil. Globe said. The longer distance also slowed down the systems’ responsiveness, prompting operators to switch to thinner oil-based fluids. Then, a number of oil and gas operators decided to switch to water-based fluids, which have a much lower viscosity, to speed up response. The belief that water-based fluids would be safer to return to the water prompted operators to install valves on Christmas trees so these fluids could be discharged at the actual point of use.
As distances have grown, the technology of this relatively straightforward equipment has been pushed as far as it can, said Globe. To cope, the industry turned to technologies used in military aircraft for long-distance hydraulic control, electrohydraulic multiplex control systems (EMS). The first EMS system was installed in the mid-1980s on Shell’s Cormorant underwater manifold sensor in the North Sea. This system largely removed the restrictions on distances between the host installation and subsea equipment. EMS equipment manufacturers, particularly directional control valve manufacturers, operate this equipment using hydraulic fluids for military aircraft, which are synthetic hydrocarbon fluid.
Synthetic oil is a better lubricant, and much less likely to attack elastometers and plastics. The problem has been that companies preferred to stick with water-based products; since these products could be discharged into the sea, costs could be reduced. Companies wanted to keep using EMS systems, but use water-based products with them. However, water-based control fluids have limitations, particularly in terms of thermostability. This becomes an issue with higher pressure, higher temperature wells. To address this issue, some oil and gas companies are looking to develop fluids that operate at higher temperatures, but are still environmentally friendly enough to be discharged.
Here a dichotomy emerges: the desire for a robust, stable fluid in a system that will fall apart and disappear once it’s discharged into seawater.
“That’s not how chemistry or physics works,” Globe explained.
Synthetic fluid technology lends itself more to that inherently stable fluid that can be broken down in the environment. But changing people’s mindsets is a challenge. Another challenge is that customers wants to see good qualification data, with tests under actual conditions done versus a bench test for a few hours.
Today, the global subsea control fluid market consumes 11 million liters each year; this fluid is being discharged into the sea. Globe said that Castrol anticipates that legislation increasingly based on the Ospar [Oslo Paris Commission] will seek to deter operators from discharging fluids into the sea. Ospar looks at every identifiable chemical in a product; even products that are considered to be biodegradable could contain harmful chemicals.
“We’ve always followed Ospar approach, in which fluids are not recognized as oil or water-based, but as a synthetic product,” said Globe. “The only thing that matters is how those chemicals perform from an environmental perspective. On that basis, an operator could end up with chemicals that are less likely to break down.”
To meet the needs of next generation subsea systems, Castrol sees a need for greater collaboration with vendors and operators to ensure that fluids will always be available for any system design. This includes collaboration on system architecture.
There’s an assumption by equipment vendors is that a control fluid will always be available for any system design, but Castrol believes that will not always be true, Globe said. The company sees a need for better collaboration between operators and synthetic fluid providers to make a system that will work and have the fluid it needs.
“The challenge is tying down what exactly is required and the timescales involved,” said Globe.
The time required for developing a new control fluid – from the initial design to commercial debut – could take years.
“If you’re selling a $60 billion control system, that’s one thing. But developing a new control fluid is another. Sometimes the development cost can be just as high, but the ability to get a return on the investment is less.”
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