**3. Purpose of hydrofracking and typical geologic targets**

Horizontal drilling followed by high-volume hydraulic fracturing is an expensive, heavy technology, potentially polluting activity, so why has it become popular? Comparing the process to conventional drilling explains the overwhelming benefits of the technique in the appropriate geologic setting.

In a conventional oil or gas production setting, a well would be advanced from the ground surface vertically down through overlying sediment and rock layers and ultimately through the oil- or gas-bearing formation. Typically, the target would be an oil- and/or gas-bearing sandstone or limestone layer of rock possibly tens to hundreds of feet thick. The portion of the well casing within the hydrocarbon-rich zone would be perforated or screened. The relatively large pores in the sandstone or limestone would allow the fluid to flow toward the well.

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 0.1–0.005 μm [2].

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

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

What is called hydrofracking in the popular vernacular is actually two technologies. It is a combination of horizontal drilling and high-volume hydraulic fracturing. The first is horizontal drilling, in which the well drills horizontally through the oil- or gas-bearing rock layer. The second is high-volume hydraulic fracturing in which highly pressurized water is used to fracture the oil- or gas-bearing rock formation and sand transported with the high-pressure

Neither is an entirely new technology. Directional drilling was used to drill for offshore oil in southern California in the 1920s. Drillers would drill vertically from an onshore location and then cause the drill bit to angle west to tap formations below the ocean [1]. From that time the technology has steadily advanced until the present day where drillers have excellent control of the depth and angle of the turn from vertical, the ultimate depth of the horizontal portion,

Horizontal drilling followed by high-volume hydraulic fracturing is an expensive, heavy technology, potentially polluting activity, so why has it become popular? Comparing the process to conventional drilling explains the overwhelming benefits of the technique in the

In a conventional oil or gas production setting, a well would be advanced from the ground surface vertically down through overlying sediment and rock layers and ultimately through the oil- or gas-bearing formation. Typically, the target would be an oil- and/or gas-bearing sandstone or limestone layer of rock possibly tens to hundreds of feet thick. The portion of the well casing within the hydrocarbon-rich zone would be perforated or screened. The relatively large pores in the sandstone or limestone would allow the fluid to flow toward the well.

**3. Purpose of hydrofracking and typical geologic targets**

states and even counties within states that have banned hydrofracking.

to the environment and communities within the path of the hydrofracking boom.

**2. History of hydrofracking technique**

water props the fractures open.

34 Aquifers - Matrix and Fluids

and the 3D orientation of the drilling.

appropriate geologic setting.

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 a recoverable resource.
