Seabed factory of the future

If you told a process engineer that you proposed to share your production pipe with a lot of unwanted by-products, he would think you were mad.

Jul 1st, 2001

If you told a process engineer that you proposed to share your production pipe with a lot of unwanted by-products, he would think you were mad. The logic of separating the by-products as close to their source as possible is incontestable. Despite this, the offshore industry continues to pump huge quantities of unwanted gas and water to the surface from subsea wells. This may or may not be a major drawback in shallow water, but as we move into deeper seas, the practice can cost serious amounts of money.

This is hardly an original observation. Most oil companies have been thinking about the problem for several years and have largely accepted that, sooner or later, they must adopt some form of processing on the seabed or downhole.

Nevertheless, it takes a substantial leap of faith to visualize relocating the production hardware of a floating production, storage, and offloading (FPSO) vessel, for example, to a cold, dark seabed thousands of feet below the waves. Yet, that is what must come about if the industry is serious about operations in deepwater, and wants to profit from them.

Easier said than done? That depends. The important thing is for engineers to take their minds out of any straitjacket and consider the challenge rationally. When a processing plant is out of reach on a seabed far below, its operator loses the option of tweaking it with a spanner if something needs adjusting.

Although remotely operated vehicles (ROVs) are very advanced, they are still not ideally suited for intricate operations. So, this means that any worthwhile maintenance or modification must be done topsides.

For this to be possible, no seabed processing plant can bear any resemblance to its cousins on the surface. Power and control distribution is another area of concern because traditional land-based methods of layout are totally impractical for a seabed application. Switchgear and speed control systems, for example, cannot be reliably treated as separate entities from the processing requirements.

Having been a champion of the cause of seabed processing of subsea hydrocarbons for as long, if not longer, than most others, it has become obvious to me that the only way to ensure complete reliability and to minimize both capital and operating expenditures is to take a "system-modular" approach to the problem.

To build and maintain a "factory" on the seabed by removing sub-systems and individual items of equipment, such as pumps and compressors, for maintenance is totally impractical. It is far more logical to install and operate the system as a complete module. This ensures that it can be worked on in safety with the entire system fully tested before it is returned to the seabed. If the installation features a second module, this can remain on the seabed and maintain production until the other is returned.

Component insert retrievable methods require many wet mate-able interfaces. Cause-and-effect is difficult to determine when a piece of equipment fails unless the whole system can be tested. The time and cost implications of this approach are horrendous and make it more logical for a system to be packaged into conveniently sized system-modules. This minimizes the wet mate-able interfaces and allows testing and run-in to be undertaken in the benign environment of a land-based workshop, where all tools and test equipment are readily available.

The engineering for such a concept is not easy. System modularity opens an entirely new and exciting future. This is due to the ability to control wells and processes remotely. When electrical power and control cables are necessarily linking all of the process and manifold functions on the seabed, they are also providing the communications conduits that link the module's brain with its operator on the surface.

Distance ceases to be an issue, and for the first time, the freedom and flexibility of a network, using nodes similar to the Internet, becomes a reality for oil field operators.

Others are in agreement. For example, Dick Olver, Technical Vice President at BP, in announcing his company's plans for the North Sea, clearly feels that some changes are overdue. "We are going to re-engineer the North Sea," he said. "We'll do this subsurface, on the seabed, and on the surface. Imagine a future where platform integrity and downhole and surface control are possible from shore, and all our technical experts are connected in a virtual network."

Some years ago I visited one of the UK's network of underground command bunkers built to survive a nuclear holocaust. I was intrigued by the fact that the computer network linking it with all of the other bunkers around the country was the precursor to the Internet that is now familiar to us all. It was a technical concept that has been proved to work beyond a doubt. It is fascinating to think that this legacy of cold war paranoia could extend its influence a step further.

With each modular seabed system acting as its own command and control center, we also have the opportunity of building an indestructible global network of fields, capable of being operated from anywhere in the world and capable of supporting each other in a global communications network.

Downhole data becomes available to anyone who requires it, wherever he might be, in real time. Wells are operated, and fields are controlled by someone in a distant office who has one finger on the pulse of the oil market and another on his computer mouse, ready to direct production accordingly.

David Appleford
Alpha Thames, Ltd.
London, UK

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