Steerable drill bits allow lots of control while drilling horizontal wells. Benefits: Faster penetration and long lateral wells drilled with pinpoint accuracy.
Courtesy Schlumberger.
More bright ideas
Horizontal drilling
So if you're interested in oil, you gotta make house calls. Translated:
You gotta drill right into the reservoir. Not only can it be a tiny target,
but even if you hit a bulls-eye, the well may be unproductive. Say a vertical
drill pierces 5,000 feet of rock into an oil reservoir that's 20 feet
thick. Because oil moves slowly, the 20-foot exposure would not tap much
oil.
Over time, of course, more oil would seep toward the well, Bergt says.
"If you could wait one million years for nature to refill it, that would
be great." But drillers can't wait that long, and "In the old days, you'd
move 200 feet and drill another well."
We talk about "pools" of oil, but in fact the stuff exists
between the grains of porous rock like sandstone. Oil can travel through
rock, but so slowly that it would probably lose a race with a whip-tailed
paramecium.
Image courtesy of the United States Department of Energy.
Do the math. In a big field, thatsa lotta holes. Expensive holes.
With horizontal drilling, the entire picture changes, Bergt says. "Instead of drilling 20 wells, you'd drill two or three for the same recovery." On land, the technique also reduces the "footprint," the area damaged by drilling operations. At sea, it allows drilling many wells from a single platform.
Bent pipe solution?
Because the pipe that drives oil drills is surprisingly flexible, a horizontal
well can snake around to reach isolated pockets or follow a reservoir
that meanders across the terrain.
Horizontal drilling has evolved over the past 25 years, and even though it remains more expensive than vertical drilling, greater productivity led to rapid acceptance. Between 3,000 and 4,000 wells are drilled annually with the technology. The record hole is a long-haul monster that wanders almost 7 miles, on the coast of southern England in the Wytch Farm oil field.
Courtesy University of California-Berkeley petroleum engineering program.
Coil
tubing
Traditionally, oil bits were driven by 30-foot sections of steel pipe.
Pulling a bit up for sharpening involved hours or days of yanking pipe
out of the ground and unscrewing it. In the past five years, drillers
have come up with an alternative -- coil tubing.
Packed in giant reels holding 4,000 feet of tubing, the stuff is simply unreeled and lowered into the hole. Instead of rotating the tubing to spin the bit, high pressure drilling mud is sent, as usual, through the tubing. At the other end, however, is a hydraulic motor that rotates in response to mud pressure.
Peter Meenan says coil tubing also lends itself to scavenger operations -- tapping pockets of petroleum that seismic techniques show are near to existing wells. Meenan, who directs the Oil and Gas Institute at the University of Aberdeen, Scotland, says coil-tubing drilling, combined with steerable drill bits, may be used when a new pocket of hydrocarbons is discovered, say, 1,000 feet from a deep well. Rather than drill from the surface, it's possible to start drilling part-way down and veer off to reach the new deposit.
Image courtesy of the
Alaskan Division of
Trade and Development.
Gas-to-liquid
But gas is also expensive to ship by ship, and big steel pipelines cost
a bundle. Now to the rescue comes a technology pioneered to supply Hitler's
Luftwaffe -- converting natural gas to a liquid fuel.
"It's been talked about for so long that some people think it's like
turning lead into gold," Nation says. The problem is efficiency: Most
processes need high temperatures. To the rescue come catalysts -- chemicals
that help other chemical reactions occur without getting consumed in the
process.
There are signs that gas-to-liquid could be ready for prime time. A pilot
plant has begun operation in Bellingham, Wash. More ambitiously, Chevron
and Sasol, a firm in South Africa that once tried to convert coal into
oil, are collaborating on a $1-billion plant for Nigeria.
The technology could be used to convert gas that's now burned off at
oil wells into a usable fuel. In a larger sense, it could convert isolated,
or "stranded," gas into a usable product. "If you found a huge gas field
in the South China Sea," says Nation, "it might not justify building a
billion-dollar pipeline to transport it. And if it's not economical, the
gas might as well just not be there." If gas-to-liquid works, however,
a ship housing the conversion machinery could tread water above the wells,
feeding tankers that would haul the fuel to market.
Similarly, a large amount of gas remains on the North Slope of Alaska,
without any way to get it to market, Nation says. "If you could turn it
into liquid, you could put it into the Aleyska pipeline" and pump it south
to the port of Valdez.
Speaking of gas, have you heard of the newest energy source, gas
hydrates?
What to do about all the natural gas that accompanies oil
in remote regions? Gas, after all, is an incredibly useful material that
contains lighter hydrocarbons like methane. The ancient Chinese delivered
natural gas through bamboo pipes and burned it for lighting.
©1999, University of Wisconsin, Board of Regents.