Pulsed Lasers Drill Rock for Fuels
Brent D. Johnson
Once believed to be a pipe dream, drilling for oil and natural gas with lasers now shows great promise and is receiving the attention of researchers. A team at Argonne National Laboratory is investigating the use of pulsed CO2 and Nd:YAG systems for the petroleum industry.
In 1995, researchers at the Gas Technology Institute of Des Plaines, Ill., completed a study that led them to reconsider the application of traditional tungsten carbide drill bits in favor of a laser-based alternative that would drill faster and wear longer without repeated replacement.
In proof-of-principle experiments starting in 1997, the researchers investigated the interaction of lasers with samples of rock, using high-power systems obtained from the military. They discovered that, as it drills, the laser exposure creates a glass or ceramic liner that potentially could replace the steel casing now required in boreholes.
Researchers are investigating the laser drilling of rock, with a goal of developing systems for the petroleum industry. Courtesy of Claude B. Reed.
Eliminating the need for 10,000 feet of steel pipe would be a big savings, said Claude B. Reed of the Argonne lab, who presented a study with Zhiyue Xu at ICALEO in October on the drilling of rock with a superpulsed CO2 laser. Reed and his colleagues are experimenting with a wide variety of laser parameters for rock drilling, studying different lithologies, including shale, limestone and sandstone. They are using a 6-kW Rofin-Sinar CO2 and a 1.8-kW Electrox pulsed Nd:YAG.
So far, pulsing seems to be beneficial, Reed said. When the 1-cm-diameter beam is pulsed circumferentially, the rock absorbs the energy and fragmentation occurs. The researchers get better penetration and fracturing with this method than they would by continuous pumping with a CO2 laser, which dumps too much power into the rock, causing it to melt and vaporize.
They are capable of drilling 3 to 6 inches in a few seconds, depending on the type of rock. Shale, for example, drills readily with a pulsed laser, but limestone is more difficult. They also have discovered that, in narrow, deep holes, fragments of rock can block the beam, wasting energy. Multiple holes side by side with a drill hole diameter of 8 inches work better and can be achieved with 1-inch-diameter collimated beams.
The scientists believe that they can drill 10 to 100 times faster with a laser than with conventional methods. Another benefit of laser drilling is that it can improve the flow of liquids from the reservoir to the borehole -- in sandstone, for example --by changing the porosity and permeability of the rock so the oil will flow faster.
Options for development
The researchers are considering fiber optic delivery for an Nd:YAG laser drill. For such an application, the fiber would be 10,000 feet long. Thus far, however, the longest fabricated has been less than 1000 feet. They also would need to determine the attenuation issues in this arrangement.
High-power diode lasers may be another option, Reed said. Using a laser head the size of a coffee can, they could put the power directly into the well bore. But the lasers would need to produce approximately 10 times the power that they currently do, and cooling the laser head might raise difficulties.
Reed estimated that the system is five to 10 years away from being used in the field, depending on the amount of investment. Halliburton Energy Services and Royal Dutch/Shell Group are looking at spin-off technologies.
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