Safer, cheaper deep-sea drilling
24 Apr 2001
Researchers at the US Department of Energy's Idaho National Engineering and Environmental Laboratory and the University of Arkansas have developed two technologies that may enable safer and more economical deep sea oil and gas exploration.
The INEEL-led research team has developed new seismic source technologies - devices used to create shock waves that travel below the drill bit through the ground. Drillers then record the resulting acoustic data to gain insight into the location of high- and low-pressure areas before they drill.
Researchers tested two new technologies - the Regenerative Combustion Source and the Capacitive Discharge Source - in August 2000, at a hydrology research park and compared the results against standard commercially available technologies.
The patent-pending Regenerative Combustion Source creates shock waves by supplying hydrogen gas and then sparking it with an electric fuse, creating a controlled explosion in the borehole below the ocean floor. The second technology, called a Capacitive Discharge Source, uses an electric spark to create an arc. The result is a steam bubble that bursts, creating a shock wave.
Deep water drilling is said to be a delicate procedure, heavily dependent on how much the drilling crew knows about subsurface pressures at the drill site. By drilling into the sea floor, drillers create a well borehole that has lower pressure than the surrounding area.
They keep the ocean sediments from collapsing the well by using a slurry of mud, which maintains the pressure inside the hole just slightly greater than outside the well. However, if pressure in the mud slurry is less than pressure in the sediments, the subsurface fluids will flow into the well, causing a blowout. Blowouts are extremely dangerous situations for both the personnel on the drilling ship and the environment.
To prevent blowouts, drillers case the well by cementing a pipe into the well as a liner. As they drill deeper into the ocean floor where the pressure becomes progressively higher, drillers must use increasingly smaller-diameter casing pipes to compensate for the pressure.
Casing at deep ocean depths can take days because the cement has to dry before drilling can continue. 'When you consider that a drilling rig costs between $150,000 and $200,000 a day, fewer lengths of casing means less pipe and less time,' said INEELs' Dave Weinberg.
'With energy prices getting as much attention as they are today, technology to help the US produce more oil and gas must be a priority,' said Barry Short, INEEL's director of Energy Efficiency and Natural Resources.
