laser drilling experiments in 1997 used the U.S. Army's Mid-Infrared
Advanced Chemical Laser (MIRACL) and the U.S. Air Force's Chemical
Oxygen-Iodine Laser (COIL) systems -- both of which were used in
tests on cores of sandstone, limestone, shale granite, salt and
those early tests showed conclusively that:
Modern lasers have more than enough power
to spall or cut, melt and vaporize rock.
could be cut without melting, and rock properties had actually improved.
type of rock tested did not significantly change the amount of energy
needed to cut or melt it.
tests were very dramatic demonstrations that big lasers can easily
penetrate rocks," said Claude B. Reed with the Argonne National
Laboratory. "But what the researchers found was that while these
big lasers were good for demonstration purposes, it was difficult
to do scientific investigations, because parameters such as the
power of the laser, the beam on time, or the power density were
all the necessary parameters it is difficult to understand how the
laser beam actually does its work of fracturing rock or cutting
an oil field far, far away ... the future is about to arrive.
is poised to be the first fundamental change to the rotary drilling
concept since its inception nearly 100 years ago.
say, it's about time.
studies of laser drilling possibilities date to the 1960s and 1970s,
but these were primarily theoretical -- physical tests were limited
by the laser technology and low power available at that time.
then-Gas Research Institute (GRI; now the Gas Technology Institute)
resurrected the idea of using lasers to drill oil and gas wells
in 1997, when the institute initiated a two-year study to determine
the feasibility of using the high power lasers developed by the
U.S. military as part of the Reagan-era Star Wars Defense Initiative.
steps investigated the interaction of lasers with different rock
lithologies as the first step toward determining the energy required
to remove rock with laser beams.
began in earnest when the Star Wars effort was winding down and
some in the industry realized these big, high-powered military lasers
could provide sufficient power to blast through rock," said Claude
B. Reed, with the Argonne National Laboratory. "So GRI, along with
the Colorado School of Mines, got access to two military lasers
and ran some initial tests."
a paper updating the status of laser drilling at the recent AAPG
Mid-Continent Section meeting in Tulsa.
said, was keen to continue its work with lasers, but the large military
lasers were not readily available or reliable enough to mount a
systematic test program. Plus it was realized that industrial lasers
had enough power to perform additional tests.
Argonne, because we have two of the largest industrial lasers in
the country," Reed said, "and we have quantified the power levels,
the shape of the beam and other parameters necessary to calculate
just what you have done with the laser."
Argonne, GRI and the Colorado School of Mines again joined forces
under a U.S. Department of Energy National Energy Technology Laboratory
agreement in an effort to more quantitatively determine the energy
required for lasers to remove rock.
Energy Services and Petroleos de Venezuela-Intevep, SA, were industry
partners on the project.
identified the specific energy requirements to remove rock from
test samples of sandstone, shale and limestone using a 1.6 kilowatt
pulsed neodymium aluminum garnet (Nd:YAG) laser, according to Reed.
general, shales required the least energy to remove a unit volume
of rock by an order of magnitude -- good news, since 70 percent
of the rock drilled in most oil and gas wells is shale, according
to the study.
sandstone samples exhibited higher specific energy values than
the shales, although still quite low compared to mechanical drills.
energy requirement differences between spalling or cutting the
rock and melting the rock became more defined -- particularly
in the shale samples, where clear and sharp increases in the specific
energy values of melted samples were observed.
samples showed more of an increasing trend in specific energy
values at the onset of melting, not the sharp definition seen
in the shales.
limestones seemed to spall through a thermal dissociation mechanism
rather than breaking or melting, so the onset of melting was not
the different regimes for vaporizing rock, melting rock or spallation
was important," Reed said.
occurs when the laser beam heats up moisture, which is present in
virtually every kind of rock. The moisture is heated to the point
it causes a steam explosion that acts as a subsurface explosion
to fracture rock and spall off the surface layer.
that you can get the lowest specific energy in this spallation regime,"
Reed said. "That means you would be drilling the largest hole with
the least amount of energy if you could set your parameters to spall
but not melt the rock."
the consortium followed that study with a series of experiments
lasing multiple holes into rock samples to determine effects of
continuous beam exposure time on a single point increased, the
probability of melting and observing higher specific energy values
the depth of a single point hole increased relative to its diameter,
deleterious secondary effects contributed to a higher specific
eight-inch diameter beam that can provide the required power density
to spall rock the full length of the well is not technically feasible
with current technology.
the beam in a pattern necessary to create the hole may prove too
complex in powering and maintaining the rasterizing mechanism
downhole, and an alternative method would be preferable.
focused on a laser-based drilling system making use of multiple
beams of near-infrared energy placed adjacent to one another, collectively
creating a hole. The size of the hole would then depend on the number,
arrangement and burst frequency of the beams.
the set up was not unlike a mechanical drill bit that uses individual
teeth or cutters to chip small pieces of rock as the bit turns under
the weight of the drill string. In both cases, a specific amount
of controlled energy is repeatedly delivered from the system to
a point on the rock, causing the rock to fail in a predetermined
used both the Nd:YAG pulsed laser and a six kilowatt carbon dioxide
gas-type laser capable of both continuous wave and super-pulsed
beams. Both lasers are located at the Argonne laboratory.
series of tests repeated application of laser energy on one spot
with varying amounts of time between laser exposures. The second
series created two spots, varying the spacing between the spots
and the time between repeats. The third series created three spots
arranged in an equilateral triangle, and four spots in a parallelogram.
on sandstones were encouraging, in that both the two and three spot
tests indicate that the weight loss levels off as the number of
bursts per shot increases. The two-shot tests indicated a precipitous
increase in specific energy before the leveling occurs, but the
three-shot tests indicate a very small increase in specific energy,
which seems to be related to the relaxation time.
samples cut more easily than the limestone or sandstone, but specific
energy values were significantly higher than the optimized single
shot, single burst tests done in the earlier study. The specific
energy behavior of the shale samples was similar to those of the
recent tests are encouraging, a great number of questions must be
answered before a laser drilling system can even be field tested.
we are starting to look at what happens when you have moisture in
the wells and then with high pressure liquids, because that is what
you must deal with in the real world," Reed said. "Our early work
was dedicated to dry rocks, but we know that if you drill a hole
in the ground you are going to have water in it. We have to be able
to deal with that.
are future hurdles to clear, but first we have to understand what
is the best we can accomplish in an ideal environment," he said.
"So far, we have seen nothing to tell us that we shouldn't move