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67- www. energy- future. com 5.3- Technology: pushing boundaries strong, yet lightweight, to avoid snapping, up-rooting the wellhead, or exerting too heavy a downward drag on the rig. Shell, for example, uses a so- called lazy- wave steel riser on its deep- water projects in Brazil; this shape pro-vides buoyancy and takes some of the load off the floating structure and the set- down point. Much scientific research has gone into composite materials for risers: most consist mainly of steel, but in regions where either the oil or the seawater is especially corrosive, for example, they have rubber linings. Considerations like this exemplify the challenges facing all subsea equipment: wellheads, trees and tubes all have to be exceptionally durable, as well as sophisti-cated, to work properly under the weight of up to 3,000 metres of water. The kit needs to be able to withstand the weather extremes that nature frequently throws at it - strong tides, waves, and currents; and hurricanes, earthquakes and icebergs, to name a few. And it needs to meet increasingly tough en-vironmental and safety requirements, and run for years with minimal maintenance. Then, as Schlumberger's Hendricks points out, there is the problem of the oil itself. It might be too cold or too viscous to flow on its own, requiring the assistance of giant electri-cal pumps or heat- transmitting pipes that are lowered down to the seabed. On other occa-sions the oil will be found at high tempera-tures, or in a highly acidic state, posing more problems for a producer's equipment, both under the sea and on the platform. Not surprisingly, oil firms have teams of R& D specialists engaged in devising clever solu-tions. Norway's FMC Technologies, a pioneer of subsea technology, recently developed an electrically driven, centrifugal gas compressor capable both of extracting the very last drops of oil from mature fields in shallow waters and of working for several years without mainte-nance at depths of 3,000 metres. Schlumberger has developed a remote-monitoring technology capable of measuring objectively the relative flow contribution of different operators to common pipeline net-works in areas such as the North Sea and the Gulf of Mexico - and, therefore, the share of the financial spoils owed to each producer. Sometimes, subsea solutions are primarily chemical in nature. Schlumberger recently unveiled Futur, an active set- cement technol-ogy that automatically self- heals in the pres-ence of hydrocarbon leaks coming through cracks in subsea wells that can occur in ex-tremes of temperature or water pressure. Many companies have invested in re-motely operated vehicles ( ROVs). These are robotic pieces of equipment performing tasks on the deep- sea floor that in times past ( or in much shallower waters) might have been carried out by human divers. ROVs come in a range of shapes, sizes and func-tions, from simple eyeball- camera devices to multi- purpose, multi- appendage mainte-nance vehicles. Subsea engineers are also engaged in developing cables, tethers, bu-oys and other mooring technology that will keep platforms and production vessels sta-ble in the roughest deep- water seas. Deep- water applications attract the head-lines, but David Pridden, chief executive of Subsea UK, an industry body, says subsea techniques are ideal for tapping relatively small pools of oil and gas in mature areas such as the North Sea, particularly when wells can be tied back to existing production and pipeline infrastructure. Nearly half the relatively shallow UK continental shelf's out-put comes through subsea wells, he says. In an era when the more accessible and relatively easy- to- produce discoveries have been made, and oil producers have long since started looking beyond dry land in their quest for fossil fuels, the role played by subsea tech-nologies has never been more vital. ?? Oil companies have teams of R& D specialists engaged in devising clever subsea solutions

68- www. world- petroleum. org 5.4- Technology: pushing boundaries Producing clever There is plenty of oil left, but it's not necessarily easy to produce. That's where the clever stuff comes in It's a surprising fact that most of the oil in a reservoir is usually never retrieved. Eventually, it becomes too expensive to pro-duce and, at that point, it's time to abandon the project. Perhaps the oil or gas is con-tained in small, separate compartments, obliging the operator to drill numerous - and expensive - wells to get at the various pockets of hydrocarbons. Occasionally, as much as 70% of the oil can be pumped out. But in most cases it's much lower - perhaps just 5%. On average, the worldwide recovery factor is about 35%. Any technology that can step up the re-covery rate and allow the operator to con-tinue pumping oil is valuable for the com-pany producing the oil; increasing recovery at existing fields is cheaper and less energy-intensive than making and developing new discoveries. It's good for the government re-ceiving taxes from the production too. And it's important to world energy supply. According to BP, a 1% increase from its res-ervoirs alone would yield an extra 2 billion barrels of oil equivalent. On a worldwide ba-sis, a 5% increase in recovery would yield an additional 300- 600 billion barrels of oil equivalent, the company says. That would equate to 10- 20 years' of oil supply at to-day's consumption rate. And, with oil prices of, say, $ 70 a barrel, the economic value of such an uplift would be staggering. " There is a significant amount of oil out there in fields that we already know where they are," says an enhanced oil recov-ery ( EOR) specialist at US oil company It's about teamwork The effectiveness of EOR technologies depends on the effectiveness of other branches of the science of oil production - geological understanding and the ability to monitor the subsurface, for example. Part of the problem with improving sweep is it's difficult to know which bits of rock are being swept well and which aren't. If the injection well is in a place that doesn't come into contact with untapped pockets of oil, it doesn't matter how clever the recovery technologies are. Understanding the geology, so you can predict where the oil's going to be held up, and seeing the subsurface - through ef-fective seismic imaging, say - will allow the drilling of optimally placed infill wells that allow your sweep to get at the maxi-mum number of juicy pockets of oil. Time- lapse 3- D seismic ( sometimes called 4- D seismic) is a particularly effective tool in mapping the movement of liquids through a reservoir over time, helping scientists un-derstand how a particular geological struc-ture works. The technique involves running more than one 3- D survey on the same spot, but within an interval of a year or more. Data comparisons - made by subtracting one data set from the other - can show areas of the field that have been depleted over time and highlight areas where in- fill drilling would be useful to tap pockets of bypassed oil. New surveying techniques, such as elec-tromagnetic ( EM) surveys and its marine offshoot, controlled- source EM, are also making waves in the field of mapping the lo-cation of fluids. ?? Visualisation of a 3- D seismic survey in the Gulf of Mexicco