Not since cable tools gave way to rotary
drilling almost a hundred years ago has there been a revolutionary
change in drilling methods — but one may be coming.
It will, indeed, if researchers studying the potential
of "Star Wars" military laser technology for use as a new drilling
technique are successful.
The concept was largely a pipe dream of petroleum
engineers until significant advances in laser technology were made
in the 1980s and 1990s as part of the military's missile defense
Now researchers believe that state-of-the-art lasers
have the potential to penetrate rock 10 to 100 times faster than
conventional boring technologies — a huge benefit in reducing drilling
And, obviously, reducing drilling costs could make
previously uneconomic gas or oil reserves commercially viable.
The Gas Technology Institute initiated a two-year
study in 1997 to examine the feasibility of adapting high-powered
military lasers for applications in hydrocarbon exploration and
production — including applications in drilling and perforating
oil and gas wells.
According to a previous GTI study, 50 percent of
drilling time is spent on making hole, 25 percent on tripping and
25 percent on casing and cementing. A conclusion: Major reductions
in drilling costs can be achieved by faster drilling techniques
and reduction in the requirements for drill string removal, bit
replacement and setting casing.
So this basic research project examined the feasibility,
costs, benefits and environmental impact of using lasers to drill
and complete oil and gas wells.
Some of the concerns in drilling operations are rock
destruction and removal, drilling time and cost, rig size and transportation,
hole shape and deviation, fishing for stuck pipe, and tripping and
drilling in hard formations like granite.
"This first study was an exploratory mission to broadly
look at a number of parameters and answer questions as to whether
this is a feasible technology for drilling applications," said Brian
Gahan, principal technology manager for the Gas Technology Institute.
"In the late 1960s and again in the 1980s some published reports
maintained that lasers were not effective tools for drilling, because
the lasers would melt the rock resulting in high energy consumption,
and penetration rates would be too low. These early authors saw
lasers as a means of assisting mechanical drilling methods rather
than as a stand-alone system.
"We felt that was a restrictive view of how lasers
might be employed in drilling," Gahan continued, "and when researchers
from the Colorado School of Mines brought this research concept
to us we were very interested in pursuing it."
Can It Work?
Here's what they found: Depending on the rock type,
drilling rates can be significantly reduced using lasers when compared
to conventional drilling rates.
For example, lasers can penetrate hard rock — say,
granite — at about the same rate as conventional techniques would
penetrate soft rock.
A report on the initial research by Ramona M. Graves
and Samih Batarseh with the Colorado School of Mines found that
new technologies and tools operate using basic rock destruction
mechanisms like thermal spalling, fusion and vaporization, mechanical
stresses and chemical reactions.
"All of these destruction mechanisms," the authors
wrote, "can be achieved using lasers."
At low laser power, the report said, spalling or
chipping can be achieved. Increase in the laser power, with a fixed
beam diameter, results in phase changes and reactions in rock, like
dehydration of clays, releasing of gases and inducing thermal stresses.
At high laser powers, the rock will melt or fuse,
and at even higher levels the rock will vaporize.
"Laser technology applied to drilling and completion
operations has the potential to reduce drilling time, eliminate
the necessity to remove and dispose of drill cuttings and improve
wells performance through improved perforation operations," the
We Need An Answer ...
The experimental research was designed to answer
questions posed by the oil industry about laser applications in
drilling. Some of these questions were:
- What is the effect of laser power on rate of penetration and
specific energy in different rock types?
- How does lasing a rock change the permeability, porosity and
- What is the mechanism of rock destruction?
- What is the effect of lasers on fracture formation in different
- What is the effect of beam type - chopped, pulsed or continuous?
- Can vertical and horizontal holes be lased with the same result?
- What happens when saturated rocks are lased?
- Does stress have an effect on laser-rock interaction?
Results from this initial two-year study determined
that calculations significantly overestimated the energy required
to spall, melt or vaporize rock.
Regarding the initial laser drilling experiments:
- U.S. Army's Mid-Infrared Advanced Chemical Laser (MIRACL) and
the U.S. Air Force's Chemical Oxygen-Iodine Laser (COIL) systems
were used. Both systems operated in the infrared optical region
with power delivery capacities of one megawatt and 10 kilowatts,
- Both lasers delivered only continuous wave beams (the COIL
is now capable of pulsed beam delivery, however).
- Laboratory tests were performed on about 150 rock samples to
analyze the changes in rock properties caused by lasers. Laser-rock-fluid
interactions also were studied.
- Laser parameters like power, beam type and direction were varied.
- Rocks used in the study included Berea sandstones, Mesaverde
shaley sandstone, reservoir limestone and granite.
- For comparison, rock properties such as porosity, permeability
and acoustic properties were measured before and after lasing.
Rocks were also analyzed using a scanning electron microscope
combined with an energy dispersive system, thin section, X-ray
diffraction and differential thermal analysis.
- Analysis also was done under various test conditions such as
type of beam, horizontal and vertical rock penetration, purge
gas, saturation with water and hydrocarbons and confining stress.
Fast penetration speeds were obtained as well as
some fundamental changes in the properties of the samples. For example,
the porosity surrounding the lased hole in a Berea sandstone sample
Also, the experiments indicated that at such high
powers there were deleterious secondary effects that increased as
hole depth increased. These effects included the melting and remelting
of broken material; exsolving gas in the lased hole; and induced
fractures, all of which reduced the energy transfer to the rock
and, therefore, the rate of mass removal.
"However, the initial study clearly showed that laser
technology is more than sufficient to break, melt or vaporize any
lithology that may be encountered in the subsurface," Gahan said.
"It showed that the energy required to accomplish these varies as
much within lithologies as between them."
However, no quantitative results as to minimum power
required or determination of factors that control power requirements
"It became clear from these experiments, for example,
that there is a need to control the amount of material melted during
the laser exposure," he added, "as well as to determine quantitatively
the minimum laser power needed to drill rocks for oil and gas applications."
Currently GTI, under a one-year U.S. Department of
Energy cooperative agreement with Argonne National Laboratory and
the Colorado School of Mines, is performing additional experiments.
A primary objective: Obtain much more precise measurements
of the energy requirements needed to transmit light from the surface
lasers down a borehole with enough power to bore through rocks as
much as 20,000 feet or more deep.
GTI identified the specific energy requirements to
remove rock from test samples of sandstone, shale and limestone.
Another aspect of the current study is to determine
if sending the laser light in sharp pulses rather than as a continuous
stream could further increase the rate of rock penetration. Pulsed
lasers have been used for better performance in cutting steel, for
example. It may be likely that the pulsing action will flex and
break the physical bonds between the rock grains, boosting the cutting
Another element is to determine if lasers can be
used in the presence of drilling fluids. The technical challenge
will be to determine whether too much laser energy is expended to
vaporize and clear away the drilling fluids where the actual drilling
Later in the project, researchers could examine other
uses for lasers in oil and gas drilling — such as in perforating