Geology Reference
In-Depth Information
using traditional drilling techniques. From the industry's perspective, the advant-
ages of directional drilling are many.
First, horizontal drilling allows companies to hit oil or gas reservoirs that are
difficult to access, and to stimulate them in ways that simple vertical wells can-
not. Some shale reservoirs are located in places where drilling is difficult or not
allowed—such as under a school or city. But if drill pads are located on the edge of
a city, such as those that ring the Dallas-Fort Worth Airport (DFW), in Texas, and
their wells are drilled at an angle that intersects the reservoir, it is feasible—and
legal—to tap into it.
Second, horizontal drilling permits the drilling of multiple wells—often six at
a time—from a single pad, reducing the cost and environmental impact of energy
projects. In 2010, the University of Texas at Arlington made headlines when re-
searchers there ran 22 wells from a single pad to pull natural gas from a 1,100-acre
shale formation beneath the campus. (The pad is on state-owned land, and isn't
bound by local municipal rules governing urban gas drilling. Carrizo Oil & Gas
operates the wells on university property, which have produced some 110 billion
cubic feet of gas). 11 But such schemes can be controversial. In 2013, students, cit-
izens, and environmentalists protested the fracking of gas beneath a pristine, biolo-
gically rich, 8,000-acre tract of forest land owned by the University of Tennessee
in Knoxville. 12
Additionally, while horizontal drilling is technically complex, time-consuming,
and expensive—a directionally drilled, hydrofracked shale well can cost two or
three times as much per foot as a standard vertical well—the wells tend to be more
productive than vertical wells, and the extra cost is made up for by bigger gas or
oil yields. 13 The reason for this is that the size of a well's “sweet spot” or “pay
zone” becomes much larger. A vertical well drilled through a 50-foot thick section
of shale will produce a pay zone that is 50 feet wide. If the well turns sideways
halfway through the vertical section and runs horizontally for 5,000 feet, then the
sweet spot full of gas bubbles will be 5,000 feet long, which greatly increases its
productivity.
Horizontal wells can also be safer. In the case of a well blowout—which occurs
when pressure-control systems fail, and natural gas is released in an uncontrolled
way (blowouts can be explosive and spew fracking fluid into the air and onto the
ground)—directional drilling can provide a relief well, which intersects it, allow-
ing rig workers to relieve pressure and control it or seal it. 14
Search WWH ::




Custom Search