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Steerable drill bits allow lots of control while drilling horizontal wells. Benefits: Faster penetration and long lateral wells drilled with pinpoint accuracy.

Courtesy Schlumberger.

  A crude story
 


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A well is drilled vertically, and then veers off toward horizontal, following the oil reservoir.

Horizontal drilling
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.

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."

  Once upon a time, drillers extracted oil with this Swiss cheese routine; new techniques reduce the need for wells.

Image courtesy of the United States Department of Energy.

 

A hillside covered by old oil drills and shacks. 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.

  This roller cone drill bit was adapted from one used by 19th -century dentist (NOT). Use it to cut hard and/or abrasive rock.

Courtesy University of California-Berkeley petroleum engineering program.

 

A big bit. 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.

  Trans-Alaskan pipeline

Image courtesy of the
Alaskan Division of
Trade and Development.

 

Gas-to-liquid
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.

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?

       
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