The science of oil drilling goes deep
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Energy Quarterly
The science of oil drilling goes deep Philip Ball Advanced techniques can characterize the physical and chemical properties of oil and the porous rock containing it, but the proof is in the drilling. Spills are an inevitable risk, but natural microorganisms that feed off the hydrocarbons can help to clean them up.
O
ne of the few useful outcomes of BP’s Deepwater Horizon fiasco is that now everyone can appreciate how difficult it is to drill in deep water. But as about half of the world’s undiscovered oil is thought to lie offshore, deepwater drilling will continue despite the risks. Some estimates indicate that oil extraction from deep offshore reservoirs might double by 2015. Yet while oil spills capture the headlines, some of the biggest risks in oil exploration are more mundane. Because full-scale drilling costs billions of dollars, it is vital to know in advance that the effort will bring rewards. Even if exploratory drilling at a candidate site hits oil, how do you know how much there is and what sort it will be? The need to answer those questions is now driving the development of innovative scientific tools that regard an oil reservoir as a complex materials system.
Making oil
The abundance of oil below the sea is unsurprising, since that is where oil formation begins. The raw organic material that gets broken down, by geothermal heat, pressure, and time, into hydrocarbons comes mostly from dead microscopic marine life: algae and plankton that rain down onto the ocean floor to form sediments. Ocean productivity is particularly high just offshore on the continental shelf, fed by nutrients in rivers and wind-stirred sediment. And so a significant number of new oil discoveries —around 20% of the total in 2009—are on these shelves at a relatively shallow depth. The big rivers that empty into the Gulf of Mexico, along with its relative isolation from the open ocean, make this region a particularly fertile hunting ground for offshore oil. Yet many new discoveries—typically between one-third and one-half of the annual totals in the past decade—are in deep water. In 2006, the U.S. Bureau of Ocean Energy Management, Regulation and Enforcement estimated that there are 66.6–115.3 billion barrels of oil and 326.4–565.9 trillion cubic feet of natural gas still undiscovered offshore and technically recoverable by conventional means in the United States and Canada, about 60% of the total oil and 40% of the total natural gas in undiscovered North American fields.
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MRS BULLETIN
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VOLUME 35 • DECEMBER 2010
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www.mrs.org/bulletin • Energy Quarterly
The exploration process
Discovering a new reservoir usually begins with a seismic survey of a candidate site to identify geological structures that can trap hydrocarbons. Seismic waves may reveal their approximate boundaries, since hydrocarbons (particularly gas) in the porous rock alters the way seismic waves travel through it. Seismology has been supplemented in recent years by “electroseismology,” which exploits the way seismic waves can induce elec
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