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52- www. world- petroleum. org 5.1- Technology: pushing boundaries Interpretation, the final step, is a science and an art. A seismic picture is actually of in-terfaces - between, for example, two layers of rock or between the seabed and the water. Differences in interfaces cause a reflection in the way light reflects off a surface; seismic, therefore, provides information about the dif-ference between rock layers, but no informa-tion about the rocks between. " It's like get-ting a bank statement that says you have $ 400 more than last week, but doesn't tell you how much you have in total - it's all very relative," says Walker. Geophysicists take the data and try to assemble a picture of the likely physical characteristics of rocks and fluids that could have produced the seis-mic record they are analysing. This is where computers have made such a big difference. Says Walker: " When I started in this industry about 25 years ago, we used to print off 2- D data [ a less data- intense form of seismic] on paper and interpreters had col-oured crayons and spent their day drawing on the various interfaces and trying to work out what the geology was." Now computers can manipulate 3- D images in seconds, enabling geophysicists to visualise the reservoir. " It's like being paid to play with some of the big-gest games consoles in the world." Improvements in recent years in the qual-ity of seismic imaging have been so spec-tacular that it may soon be possible to see through hitherto impenetrable substances, such as basalt, a volcanic rock. Other imaging techniques are emerging to complement seismic. These include elec-tromagnetics. Specially generated electrical currents can help identify specific rocks and fluids by measuring the resistivity character-istics of subsurface rocks. Alternatively, geophysicists can take ad-vantage of the steady stream of electro-magnetic radiation from the sun that propa-gates into the earth. The changing of the tides Explorers are also starting to make use of natural seismic noise from inside the earth to see the distribution of oil and gas and how they move. And reservoir engineers moni-tor the pressures of oil and gas and water, which regularly change minutely with the rise and fall of the tide and onshore with the rise and fall of the moon - another source of guidance for the future. ?? Geophysics enters a new dimension Time- lapse 3- D seismic ( sometimes called 4- D seismic) could lead to a significant rise in the world's recoverable reserves; today, much less than half of the oil in a typical oil field is produced. The technique is utilised to monitor the production and depletion of an oil field over time and involves running more than one 3- D survey on the same spot, but with an interval of a year or more. Data compari-sons - 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. Typically 30- 40% of the oil in a field is produced and 60- 70% is left in the ground. However, an estimate by an-alysts at Cambridge Energy Research Associates suggests 4- D seismic could re-sult in a leap in overall recovery factors of 8% worldwide. That implies producible re-serves could rise by a colossal 20%. In addition to 3- D surveys, much less data- intense two- dimensional surveys con-tinue to be shot, especially in highly spec-ulative areas in order to assess whether it is worth stumping up the investment needed for a 3- D survey. ?? It may soon be possible to see through hitherto impenetrable substances, such as basalt, a volcanic rock

53- www. energy- future. com 5.2- Technology: pushing boundaries Offshore marvels Designing and building offshore platforms are among the greatest engineering challenges in the oil and gas industry - or any sector Compare the aeroplane piloted by Orville Wright in 1903 - in the first control-led, powered flight - with a Boeing 747. The 747 entered commercial service just 67 years after Wright's historic achievement, but the differences between his aircraft and a modern airliner are simply staggering. Or compare the 1946 Electronic Numerical Integrator And Computer, the first general-purpose electronic computer, with the latest laptop. And what would Alexander Bell have made of an iPhone? The same breathtaking rate of develop-ment has been achieved in the offshore oil industry. It began more than a century ago when a well was drilled at the end of a pier stretching about 100 metres into the Pacific Ocean, off the Californian coast. The earli-est offshore platforms consisted of wooden derricks mounted on barges that could oper-ate in a metre or two of water. By the mid- 20th century, these rudimen-tary systems had been replaced by plat-forms supported by tubular steel members that extended to the seafloor. In 1947, Kerr- McGee spudded the first well from a fixed platform beyond the sight of land, a techno-logical breakthrough that marked the begin-ning of the modern offshore industry. Fast forward to 1995 and the launch of Norway's Troll gas platform, a 0.656 mil-lion tonne concrete structure. At 472 me-tres, it's the tallest installation ever moved by humans - and 30 metres taller than the Empire State building. It's not just the scale of modern oil and gas platforms that's impressive, it's what they can do. BP's Thunder Horse facility in the Gulf of Mexico, the world's largest deep- water pro-ducing platform, pumps out about 260,000 barrels of oil a day - more than Colombia consumes. The largest floating, production, storage and off- loading vessel, the Kizomba A platform, offshore Angola, can store up to 2.2 million barrels - roughly equivalent to Iraq's daily oil production ( in mid- 2009). Daunting burden And the physical burden platforms must deal with are daunting. Consider the 1.2 million tonne Hibernia platform: its gi-gantic concrete base is designed to re-sist the impact of drifting icebergs off the Newfoundland coast. In 2003, US oil major Chevron drilled a well in 3,051 metres of wa-ter in the Gulf of Mexico. The depth of that well, a record, is around six times the height of the world's tallest building - Taipei 101. Petrobras, a Brazilian oil company, has just started producing oil from a well at an oil field called Tupi that involves drilling down through 2,000 metres of water and a further 19031970