Hydraulic fracturing or fracking is a controversial technology used to extract shale gas. By effectively shattering the shale around a drill hole, fracking improves the rock’s permeability so that the gas trapped within the rock can be released. Used in combination with another technique, known as horizontal drilling, the technology allows otherwise uneconomic reserves of natural gas to be commercially exploited. First used commercially on the Barnett Shale in Texas in 1998 (Fig. 19C), these technologies have led to an economic boom in natural gas exploration in the United States and elsewhere.
Figure 19C: Texas Natural Gas Boom.
The dramatic increase in the number of wells in the Barnett Shale, Texas, between 1997 and 2010, was made possible by fracking and horizontal drilling (red dots).
Hydraulic fracturing is the cracking of a rock by a pressurized fluid, and occurs naturally in when dikes and veins form (see Chapter 4). When the process does not occur naturally, it is often referred to as fracking. When energy companies participate in fracking, they artificially create fractures around a borehole by injecting a fluid, known as “slickwater,” into the well at very high pressure. This fracking fluid is largely water, but also contains a range of chemical additives to facilitate the process, and “proppants,” such as sand, to keep the fractures open once they have formed (Fig. 19D).
Figure 19D: Fracking.
By shattering the shale around a horizontal drill hole and then keeping the fractures open by pumping in proppants, such as sand, fracking improves the rock’s permeability. In this way, the gas trapped within the shale can be released.
Horizontal drilling is the technology that allows a vertical borehole to be continued horizontally once the target shale has been reached. Drilling can then be continued in any direction and a pattern of holes can be drilled that radiate horizontally from a single wellhead (Fig. 19E). The single wellhead is referred to as a pad and the process is called pad drilling.
Figure 19E: Pad Drilling
In the technique known as pad drilling, up to 10 wells radiate horizontally for distances of up to 10 kilometers from a single site, or pad.
The advantage of fracking is an economic one. It allows energy companies to extract vast quantities of natural gas from otherwise inaccessible reservoirs. Some 1.7 million jobs have been created by shale gas development with a total of 3.5 million projected by 2035, and, without fracking, it is estimated that the United States would lose almost 50 percent of its domestic natural gas production.
Fracking is not without significant environmental consequences, the most worrying of which is the potential for groundwater contamination by fracking fluid. There is also a risk of surface contamination and the millions of gallons of fracking fluid used in every well must be subsequently treated or disposed of safely. The exploitation of shale gas can also have a major impact on the landscape (Fig. 19F). As a result of these concerns, fracking has become a highly contentious issue, pitting industry against opposition in an emotionally charged public debate. This has led some local governments in North America to introduce new legislation, while some European countries have banned the process altogether.
Figure 19F: Jonah Field, Wyoming.
The heavy development of the Jonah natural gas field near Pinedale, Wyoming, illustrates the impact that gas shale development can have on the landscape.