HOW - Hydrofracking: What Everyone Needs to Know - page 20

(over 9,000 pounds per square inch). 5 When the pressurized fluid flows through
the perforations at the end of the wellbore, it fractures the shale rock in which gas
is trapped in tiny bubbles. As the fluids break open the rock, sand and other “prop-
pants”—materials that hold the fractures open—allow gas to flow out; the chemic-
als help the natural gas escape the rock and flow up the borehole to the surface.
The sixth step is the “flowback” phase, in which pump pressure is released, al-
lowing much of the fluid in the well to return to the surface.
The seventh step involves cleaning up the borehole and allowing the well to
start producing gas. This can take several days.
In preparing a well for production, as many as 25 fracture stages may be used,
each of which uses more than 400,000 gallons of water—for a total, in some cases,
of over 10 million gallons of water—before a well is fully operational. 6
The eighth step is to remediate the wastewater a well produces, which I discuss
below.
How Do Horizontal Wells Differ from Vertical Wells?
To answer this, we need to return to the first three steps listed above—the drilling.
To hydrofrack a shale rock formation, boreholes are generally drilled straight down
some 5,000 to 20,000 feet deep. The average depth is 7,500 feet deep, which is
one-and-a-half miles below the surface—equivalent to six Empire State Buildings
or more than 25 football fields stacked up end to end. 7 (The depth is key to en-
vironmental safety, as the industry points out that these wells extend beneath the
water table.)
Since the 1990s, hydrofracking has been combined with “directional” drilling,
in which a vertical well is drilled thousands of feet deep, whereupon the borehole
doglegs and continues horizontally through layers of gas- or oil-bearing shale. In
places like the Bakken Formation, in North Dakota, the lateral leg can extend for
one or two miles. 8
A horizontal well therefore begins as a standard vertical well. A rig will drill
thousands of feet down, until the drill bit is perhaps a few hundred feet above the
target rock formation. At this point the pipe is pulled from the well, and a hydraul-
ic motor is attached between the bit and the drill pipe, and lowered back down the
well. The hydraulic motor is powered by forcing mud (or slurry) down the drill
pipe. The mud rotates the drill bit without rotating the entire length of pipe between