The future of offshore pipelining

The Saipem 7000 was tapped to lay the Blue Stream pipeline from Turkey under the Black Sea to Russia in 2,160 m water depth.

In 1990, coal represented about 24% of all energy sources, and oil and gas represented 50%. The world's primary annual energy demand is about 10 gigatons of oil equivalent. This is estimated to double in the next 50 years, barring technological breakthroughs in nuclear energy, and assuming there is no consensus to drastically reduce carbon emissions from current levels.

The prevailing view is that there will be no shortage of oil and gas in the next 30 years. The places where new reserves are found will be increasingly harder to get to, and much effort will be spent on commercializing new and renewable forms of energy. Fuel efficiency will increase through technological advances, such as the use of fuel cells in automobiles and more efficient lighting and heating systems and appliances. Oil and gas consumption will grow considerably over the next 30 years and beyond, but the focus will increasingly be on gas. The developing world will show a more rapid economic growth as it attempts to catch up.

Transportation needs

The need for pipelines to transport oil and gas includes offshore field-related flowlines and pipelines required to get the oil to a storage vessel or tanker loading facility, and the gas to an existing pipeline or to shore. These are usually rather short lines of limited diameter, but the water depths in which these are installed are increasing. Developments are taking place in depths of 1,500 m, and this will go to 3,000 m or deeper over the next 30 years.

Installation of such lines and the attendant tie-in systems and risers will require specialized deepwater vessels, of which a number are now or will shortly be in service. This market will grow as the offshore potential of West Africa, Brazil, the Gulf of Mexico, and other areas is tapped. Deepwater field developments will increase substantially in number and water depth. From a pipeliner's point of view, this is a mixed blessing, as the lines are short and actual pipeline installation is only a small part of the required activity.

Several pipelines are proposed to cross the Mediterranean Sea. The blue lines are existing pipelines, and the red are some of the proposed lines.

In addition, these projects require the combination of specialized design and project management, as well as installation capability, and are often contracted on an engineering, procurement, and construction basis. It will be a market segment high in engineering and project management content.

The market for long-distance pipelines will be dominated by gas. Over the next three decades, more gas production regions will have to be connected to markets over lengthening distances. This will be stimulated by offshore pipelines' advantage over onshore lines. Offshore lines minimize issues of land ownership and concerns of political instability. The industry's improving ability to install pipe in very deep water also contributes to the advantage of offshore lines.

The deep work will require specialized deepwater lay vessels capable of installing pipe at close to vertical departure angles. Increased demand will prompt the building of additional vessels. There will be a need for deepwater gas pipeline installation of the largest diameter possible.

Projects under consideration

A number of deepwater gas pipeline projects are being given serious consideration and will likely be completed in the next decade:

• Middle East to India and Pakistan through the Arabian Sea along the path of the originally proposed Oman-India pipeline
• Several pipelines across the Mediterr-anean, including the Medgas line from Algeria to Spain, which is in the preparation stages, the Libya to Sicily line, which begins construction soon, the planned Morocco to Spain line, and a planned line from Algeria to Italy via Sardinia and Corsica
• Pipelines from northern Russian fields to Western Europe through the Baltic Sea
• The Asian Gas Grid from Natuna Sea to South and East China
• Pipelines from Eastern Siberia and China to Japan.

Beyond these projects, one can imagine others across the Bay of Bengal, between Australia and Southeast Asia, along the Brazilian coast, and so on.

Long distance transport

Transporting oil over long distances is still done primarily by tanker, but compared to tankers, pipelines are a much safer means of transport, as marine mishaps demonstrate. The distances over which oil is transported are such that pipelines are not an economic alternative unless the cost of tanker transport increases and the pipeline cost drops.

The Saipem 7000 laid two 24-in. lines, along with Saipem's Castoro Otto, which will be used for shallow water pipelay work from 170 m water depth to the shore.

The cost of tanker transportation is bound to go up as stricter regulations are implemented to reduce the risk and consequences of oil spills. It is up to the offshore pipeline industry to reduce the cost of pipelines by greater efficiency and productivity, continuing the trend of the last 30 years, and by developing new ideas and techniques.

One such idea is the reduction in wall thickness for deepwater pipelines. The diameter/wall thickness ratio for a pipeline in 2,000 m depth is about 20, a number that has been steadily growing as knowledge of material properties and behavior improves. A 30-in. diameter gas pipeline would need a 1.5-in. wall thickness, something that will not only strain the capabilities of the pipe manufacturing industry, but also the pocketbooks of the investors. For a 1,000-km-long pipeline, this means a total of 727,525 tons of steel.

Wall thickness is governed by the collapse criteria, but if the line were installed flooded with water, the wall thickness would be controlled by internal pressure considerations only, provided that the internal pressure never went below a critical level. For a liquids line, this is not an issue. For a gas pipeline, this is an issue. If the industry can assure that the gas pressure would not go below a certain safe limit, then even a gas pipeline can be installed wet with considerable reduction in wall thickness.

A 30-in. diameter line with 1-in. wall thickness is about neutrally buoyant when empty. When filled with water, it weighs about 388 kg/m, so that in 2,000 m water depth, the installation vessel has to hold up nearly 881 tons of pipe. This should be well within feasible equipment limitations, as even today the equipment needs to be capable of holding on to an accidentally flooded pipeline.

As the water is replaced by gas or air during start-up, the weight of the compressed gas at about 200 bar will give enough added weight to assure stability. The question then becomes how to safeguard the system against accidental pressure loss due to damage to the line or operating error.

Considering what the oil industry has achieved thus far, this does not appear to be an insurmountable problem. But the long-distance oil pipeline issue still has not been resolved. Installing a water-filled line is feasible, and the oil pipeline wall thickness would be even less because the operating pressures are generally lower.

In fact, one could even think of a thin-walled membrane similar in shape to a fire hose that can be reeled off from a surface vessel or a system crawling along the seabed. It would be inflated to its cylindrical shape once oil is pumped into it under sufficient pressure to overcome the difference in hydrostatic head between the seawater outside and the crude oil inside. In 3,000-m depth, this is about 45 bar.

To overcome the difference in gravity, weight would have to be added to keep the line from floating. In a 24-in. inner diameter pipeline, this difference is about 45 kg/m. The pipe material would have to be a flexible thin wall material, such as a high strength metal or a composite or a fabric. To add the necessary buoyancy, and to avoid cracking in the thin wall, small diameter lines would be incorporated in the design.

While the future is being created, let's add another feature to the scheme. The problem with long distance oil pipelines is that they require pump stations at regular intervals, which is impractical along a long-distance deep ocean oil pipeline. Pumping facilities would have to be stationed on the seabed.

Technology is already in an advanced stage of development in connection with long-distance subsea tie-backs. The electrical power to drive these subsea pump stations would be supplied via cables inside the small diameter lines already set to be embedded in the pipeline.

Fiber optic communication cables are rapidly encircling the world. Why not encircle Earth in a network of oil pipelines? Before this can happen, however, it might be better to prove the technology with water pipelines and at the same time provide much needed water to dry regions like the Middle East.

Conclusion

This, then, is the look of the next 30 years:

• Deepwater fields up to 5,000 m with their flowlines, risers, and subsea connections
• Long-distance gas transmission lines in 3,000-4,000 m water depth
• Potential pipeline alternative to tanker transport
• Application of new materials.

Pipelines are more than physical conduits for transport of one commodity or another. They can be links between different worlds, encouraging economic development where it is sorely needed and creating forms of cooperation between societies. In business around the world, the oil and gas industry has the opportunity to improve relations. The business world has always been ahead of the politicians in building such bridges.

Editor's Note: This is an adaptation of a keynote speech that was delivered at the Offshore Pipeline Technology Conference in Oslo, Norway, in 2000.