Wanted: Drilling Rigs for Mars
by Richard Mason
|Tuesday, January 20, 2004
Engineers are exploring a number of systems to drill extraterrestrially. Some of these will have direct application for drilling practices on the home planet.
It's going to take more than Bruce Willis.
Sure, the Hollywood star gave one of his more sympathetic performances as an oil field toolpusher in Armageddon, the 1998 sci-fi thriller that follows a team of misfit oil patch workers into space where they drill a hole to house a nuclear device that will disintegrate an asteroid before it hits Earth.
But drilling in space presents a much greater challenge than hopping on the space shuttle and jetting off to a planetary body.
On the other hand, the concept is no longer simply fodder for Hollywood plots. Some of the best and brightest minds in aerospace engineering--and the oil patch--are working on the concept right now.
One of the primary goals of drilling in space is to determine whether the conditions for life are present, or have been present in the past, and this usually involves exploring for water. But other more prosaic goals include sampling the extraterrestrial geology. Still, the new science should provide benefits for the pursuit of hydrocarbons here on Earth.
Drilling on Mars is complicated by limitations. In theory the drilling unit will weigh less than 550 pounds, be autonomous, or able to work and repair itself automatically, and demonstrate the ability to conduct self-correcting workarounds for problems.
Low weight is necessary because it costs about $1 million per kilogram of weight to transport something to the Red Planet.
It must also operate on low power. Guidelines call for units that can operate on 100 watts per hour, or less, and under 1,000 watts of total power consumption per day. Despite these constraints, it is necessary to develop a unit that will take coring samples, stabilize the well bore, remove downhole cuttings, conduct measurements while drilling, log the well, and be able to complete a mission in 200 days or less.
The solution calls for a lightweight autonomous drilling system that will act as a robot after the eight-month journey to Mars. One project calls for drilling as deep as 600 feet into the Martian surface and, through a phased approach, eventually penetrating up to several kilometers in future explorations.
Initial studies at Los Alamos National Laboratory for the Mars deep drilling project surveyed 36 drilling systems used on Earth, which it whittled down to a short list of 15 potential systems that fit general guidelines regulating weight and power. The study eliminated items used in conventional drilling such as fluids for cooling the bit and removing downhole cuttings.
The Los Alamos study developed three models. One is patterned on the coiled tubing unit used in the oil patch. The unit would convey a hydraulic powered motor with a rotary diamond coring bit coupled with a PDC reamer. It will use a liner to seal the hole, reduce heat from friction, and serve as the conduit to carry cuttings to the surface.
A second system employs a wireline-deployed cable tool percussion drill teemed with a second sonic core drill. The instruments are lowered via wireline into the borehole. For well stabilization, the device injects a liquid or slurry that freezes or dries on the wall of the hole. The percussion drill can operate through mechanical reciprocation while the sonic drill runs off electricity and uses a bucket augur and compressed air to remove downhole cuttings.
The third system employs a segmented drill stem electric motor with a top drive and a rotary core bit. Essentially a micro-PDC rotary drill slices cuttings that are blasted to the surface via pulsed air. An umbilical system conveys wireline for telemetry and tubes for high pressure pulsed cuttings flow. The system would use a casing style drilling system to stabilize the well. The core bit would be run on a downhole motor.
These are not the only systems on the drawing boards. Other investigations include the Autonomous Mars Drill, which has been an active joint project between the Johnson Space Center and Baker Hughes since 2001. The concept employs an electrically powered downhole tractor that is lowered by cable into the borehole. Essentially the unit attaches to the sides and grinds its way down as far as a kilometer or more using a derivative of the diamond drill bit common in coring retrieval. The drill slices a thin section of rock, which is cored and transported to the surface by cable, along with well cuttings. The system will not use drilling fluids because of the weight factor, so ROP (rate of penetration) will be very low.
Prototype testing of the drilling unit will begin as early as this summer on Ellesmere Island, an environment that presents similar conditions to what will be found on Mars. The Ellesmere Island location will provide an opportunity for researchers to extract core samples from permafrost millions of years old, which will be examined for microbial activity.
Other alternative approaches include rock melters; inch-worm modeled structures that work their way down a borehole; lasers to vaporize the rock, then spectroscopy to analyze the atoms from the disintegrating compound. This latter methodology is labeled laser-induced breakdown spectroscopy (LIBS). The unit can be attached to a Rover that can navigate around the Martian surface, though it would not be used for deep drilling on the Red Planet.
Companies involved in the various programs include Honeybee Robotics, Baker Hughes, Inc., Halliburton, SpaceDev, Tempress Technologies, and Canada's NorCat in addition to the various branches of NASA.
The systems evolving for use on Mars are total opposites of Earth-based systems, which rely on power and weight to bore through the surface.
Earth-based systems also use one other methodological component: people.
Comparison with the Martian system makes Earth's common drilling rig seem quite humble. But picture it instead as a multimillion-dollar portable, self-contained industrial system that is assembled in remote sites, generates its own power, and bores a mile or more into the planet's surface, creating much more energy than it will ever use. This industrial system works 24 hours a day rain or shine and is operated by an experienced crew.
For this, operators here on Earth pay a mere $350 an hour or so.
Compared to what will be done on Mars, it represents a good bargain.
On the other hand as the current edition Mars Rover proves--and the trailer for Armageddon says: It is closer than you think.