GSA Critical Issue: Hydraulic Fracturing
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Potential Environmental Issues
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HYDRAULIC FRACTURING’S HISTORY AND ROLE IN ENERGY DEVELOPMENT
Photo of first hydraulically fractured well, from Howard, G.C. and Fast, C.R., 1970. Reproduced with permission of SPE; further reproduction prohibited without permission.
Hydraulic fracturing has been commercially applied since the 1940s (fig. 7). Over a million wells in the U.S. have been subjected to hydraulic fracturing, most of them conventional vertical oil and gas wells . Hydraulic fracturing became even more important in the 1990s, when improved technology allowed its application to horizontal wells in developing tight gas and oil reservoirs, particularly for shales. The technological combination of hydraulic fracturing, the chemistry of the fracturing fluid, and the use of horizontal wells is rapidly evolving. Traditional wells are drilled vertically (usually several thousand feet) and penetrate only a few tens or hundreds of feet of the reservoir rock. Horizontal wells start vertically, but then at a kickoff point are directed laterally (or horizontally) within the reservoir rock. The horizontal legs of these wells may extend as much as 10,000 feet through a reservoir rock, thus accessing a far greater volume of the reservoir than a traditional vertical well that only taps one vertical thickness of the reservoir rock. This replaces the need for multiple, vertical wells spaced closely on the land surface to tap the same reservoir volume. Because multiple wells can be drilled from one horizontal well pad, this further decreases the total amount of land needed for the drilling platform (called the “footprint”) and subsequent surface production equipment, although a horizontal well pad is typically much larger than a traditional vertical well pad. Because horizontal wells have both a vertical and a horizontal leg, and more contact with the reservoir rock than a traditional vertical well, horizontal wells typically require a larger volume of water than traditional vertical wells [6, 17, 18]. This may be due to larger volumes of oil produced and not just the hydraulic fracturing requirements; one study compared the ratio of water use to oil produced for two different shale plays and found it was within the typical range for vertical, conventional oil wells over their lifespans. In a horizontal well, hydraulic fracturing usually occurs sequentially in several stages along the horizontal well bore (these are sometimes referred to as “staged treatments”), generally 10 to 15 pumping intervals, and sometimes as many as 50 . Hydraulic fracturing of each stage may last from 20 minutes to four hours to complete .
Figure 8: Well drilling into Marcellus Shale, from Pennsylvania Independent Oil &Gas Association; www.pioga.org.
In the past three decades, hydraulic fracturing has been increasingly used in formations that were known to be rich in natural gas that was locked so tightly in the rock that it was technologically and economically difficult to produce . The application of hydraulic fracturing to tight sands revitalized old fields and allowed establishment of new fields. Subsequently, the application of hydraulic fracturing to shale opened up huge new areas to development, including the Marcellus Shale in the eastern U.S, the Barnett Shale in Texas, and the Fayetteville Shale in Arkansas (Figs. 4, 8). The rise in production of natural gas from these and other shale plays was dramatic, to the point that natural gas prices have dropped and become more stable. Natural gas has become a major source of electrical power, and the U.S. may become a net natural gas exporter , if markets and regulations are favorable. [57, 58, 59]
While hydraulic fracturing has had a huge impact on natural gas production, the same techniques have been applied to oil fields [18, 19, 21], leading to increased production from formations such as the Bakken and Three Forks Formations in North Dakota and Montana, and the Eagle Ford Formation in Texas. U.S. oil production from tight formations grew rapidly over the past several years. Future growth projections are uncertain, as the industry is influenced by global demand, prices, a social license to operate, regulations, well production life spans, and technological improvements that increase the percentage of recoverable hydrocarbons (22).