Geology Reference
In-Depth Information
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Let's begin with the equipment. Roughnecks rely on tall metal drill rigs (such as
the rig depicted on the cover of this topic) that rise up to four stories tall, which
lower diamond-tipped drill bits and sections of steel pipe into the borehole.
Other equipment includes a slurry blender, high-volume fracturing pumps, a
monitoring unit, fracturing tanks, proppant storage and handling units, high-pres-
sure treating iron, a chemical additive unit, low-pressure flexible hoses, and gauges
and meters to assess flow rate, fluid density, and treating pressure.
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Once a drill pad has been built and the equipment is in place, drillers use a series
to drill a vertical borehole into a layer of shale, which typically lies a kilometer
widely, depending on the location, geology, stage of drilling, and so on. In the Mar-
cellus Shale, for instance, natural gas wells range from 5,000 to 9,000 feet deep.
(By comparison, most residential water wells lie 200 to 500 feet deep.)
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The second step is to reach that depth and turn the drill bit horizontally and con-
tinue drilling, extending the lateral borehole up to a mile or two long.
The third step is to line the vertical and horizontal borehole with steel casing,
to contain the gas and (so it is hoped) to protect groundwater from pollution, and
cement it in place.
The fourth step is to use explosives to perforate holes into the horizontal section
of the well casing. This is done by detonating a small package of ball-bearing-like
shrapnel with explosives; the shrapnel pierces the pipe with small holes.
The fifth step “completes” the process by using powerful pumps to inject “slick-
water” fluids—a slurry (a semiliquid mixture of soluble and insoluble matter) con-
sisting of water, sand, and chemicals—into the wellbore at extremely high pressure
