**1. Introduction**

Hydrofracking is a simple technique that has revolutionized oil and gas production and transformed the USA into the world's largest oil producer, and yet the technique remains controversial. Along with the promise of increased production comes the real threats of surface water and groundwater pollution. An additional threat is posed by the release of methane, a potent greenhouse gas. Modern hydrofracking combines horizontal drilling through thousands of feet of hydrocarbon-bearing rock with a formation fracturing injection of high-pressure fracking fluid. The fracking fluid is both the elixir that unlocks the tightly held hydrocarbons and the source of potential pollution. It is a mixture of millions of liters of water under extreme pressure to fracture the rock, sand grains to prop the new fractures open, lubricants to decrease friction and better deliver the pressurized water to the rock, and toxic chemicals to

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prevent microbial growth. There is a worldwide debate related to the environmental impact of hydrofracking causing some countries to ban the practice, and some countries to declare a moratorium on hydrofracking. Even in the USA, where hydrofracking was invented, there are states and even counties within states that have banned hydrofracking.

The limits to fossil fuel production in such a well are the thickness of the formation that is screened, tens to hundreds of feet, and the ability of the hydrocarbons to flow through the solid rock. To glean natural gas or oil from a shale formation offers a unique challenge due to the size of the rock's pores. Normally, reservoir rocks have pore throat openings in the range of 2 μm or more. Hydrocarbon-rich shales have pore throat openings in the range of

Effect of Hydrofracking on Aquifers http://dx.doi.org/10.5772/intechopen.72327 35

These inherent limits on production of hydrocarbons from shale are overcome with the combination of horizontal drilling and high-volume hydraulic fracturing. In this technique, a well is drilled vertically down to a few hundred feet above the top of the reservoir rock then bored in an arc towards horizontal, then continuing as a horizontal borehole. The horizontal borehole is positioned to be somewhere in the middle of the depth of the reservoir rock and extended thousands of feet horizontally through the formation. The entire length of the horizontal borehole through the reservoir rock will eventually be screened and open for hydrocarbon flow. To overcome the low pore size and porosity of the shale, portions of horizontal well casing will be perforated, and then the rock surrounding the well bore will be fractured using high-pressure water. The fracturing creates interconnected secondary porosity that allows hydrocarbons to flow toward the thousands of feet of horizontal well. This combination of horizontal drilling and high volume hydraulic fracturing is what has converted shale gas into

**4. Effect of hydrofracking in the USA and worldwide oil and gas** 

gas production in 2003 to over 65% of US natural gas production in 2015.

projects that US oil production will reach 10 million barrels per day by 2018 [3].

The rapid rise of combined horizontal drilling and high-volume hydraulic fracturing has opened up large, previously unavailable natural gas and oil resources within the lower 48 states of the USA. The opening-up of unconventional "tight gas" formations to exploration and production has greatly increased estimates of technically recoverable US shale gas reserves. Geologists at the US Geological Survey, US Energy Information Administration, as well as in academic settings and energy producers have known the vast natural gas resource locked within the tight shale formations. It is only with the development of horizontal drilling and the perfection of hydrofracking that portions of this resource have been converted to proven reserves, that is, portions of the resource that are able to be economically extracted. **Figure 1** shows the increase in shale gas as a percentage of all natural gas produced in the USA between 2000 and 2015 and indicates the dramatic rise from less than 3% of US natural

The technological revolution that has increased US natural gas production in the USA has spilled over into and dramatically increased US oil production as well. Oil exploration and extraction are a mature industry in the USA, having begun in the 1860s. US oil production, as well as US proven reserves, had been in a long-term steady decline since 1970. That decline was reversed in 2008, and since 2014 more than half of the oil production in the USA comes from hydrofracked wells. In fact US oil production increased from under 5 million barrels per day in 2008 to over 9 million barrels per day in 2015, and the US Energy Information Administration

0.1–0.005 μm [2].

a recoverable resource.

**proven reserve**

One of the many risks and concerns of hydrofracking is methane releases and its impact on climate change, but the biggest concern expressed in both the popular press and scientific journals is the contamination of groundwater. One aspect of the debate related to the contamination of groundwater to be explored in this chapter in more detail is the argument that the hydrofracking is happening kilometers below the ground level, and therefore the hydrofracking layer is separated from usable aquifer layers by more than a 1000 meter of impermeable bedrock. In this chapter the authors will lay out the history of hydrofracking and the technological improvements that have optimized the process. The authors will describe the real and perceived threats to the environment and communities within the path of the hydrofracking boom.
