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Un d e r s t a n d i n g t h e e n v i r o n m e n t a l i m p a c t s o f s h a l e d e v e l o p m e n t

Daniel J. Soeder*, South Dakota School of Mines and Technology, Rapid City, South Dakota 57701, USA; and Douglas B. Kent*,
U.S. Geological Survey, Menlo Park, California, 94025, USA

ABSTRACT and constantly introduces new chemicals. resulted in the production of economical Photograph by Dan Soeder
Development of shale gas and tight oil, Geoscientists responding to questions quantities of natural gas from the Barnett
or unconventional oil and gas ( UOG) , has about the risks of UOG should refer to Shale, initiating modern shale-gas and Photograph by Dan Soeder
dramatically increased domestic energy recent, rigorous scientific research. tight-oil development ( Soeder, 2017) . Most 10
production in the U.S. UOG resources are INTROD UCTION estimates suggest that many decades of 2 * *RR
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typically developed through the use of energy supplies are available from uncon- 1
hydraulic fracturing, which creates high- Large-scale scientific and engineering ventional oil and gas ( UOG) resources at
permeability flow paths into large vol- investigations into the natural gas poten- current usage rates ( USGS, 2015) . 7
umes of tight rocks to provide a means for tial of organic-rich shales began after the The commercial development of shale
hydrocarbons to move to a wellbore. This 1973–1974 OPEC oil embargo ( Soeder, gas and tight oil requires drilling, frack- 8
process uses significant volumes of water, 2017) . The Eastern Gas Shales Project ing, production, and transmission of oil/
sand, and chemicals, raising concerns ( EGSP) was funded from 1977 to 1992 by gas, management of waste streams, and 12 3
about risks to the environment and to the U.S. Department of Energy ( DOE) well-closure ( Fig. 1 # 1–7) ( USEPA, 2016) . 6
human health. Researchers in various dis- with the goal of adapting engineered The scale of development has raised ques-
ciplines have been working to make UOG hydraulic fracturing treatments, also tions about possible risks to air, water, 5
development more efficient, and to better known as “ fracking,” to create flowpaths landscapes, ecosystems, and human health Fa lt ul au t 11
1
understand the risks to air quality, water from natural fracture networks within the ( Soeder and Kappel, 2009; Soeder et al., F
quality, landscapes, human health, and shales to vertical wellbores. The EGSP 2014) . Large drill rigs ( Data Repository
2
ecosystems. Risks to air include releases field experiments showed that fracking Fig. S1 ) are required to install the long, 9 12
of methane, carbon dioxide, volatile alone was insufficient to produce econom- deep laterals. The land-clearing and pad
organic compounds, and particulate mat- ical amounts of hydrocarbons from verti- construction activities needed to accom-
ter. Water-resource risks include excessive cal wells ( Soeder, 2017) . modate such equipment often modify
withdrawals, stray gas in drinking-water By the mid-1990s, technical advances in landscapes and watersheds ( Fig. 1 # 10) .
aquifers, and surface spills of fluids or directional drilling for deep-water oil and Fracking involves injection of large vol- 4
chemicals. Landscapes can be signifi- gas, along with improvements in down- umes of water ( ~ 0.1 to > 10 million liters)
cantly altered by the infrastructure hole bit navigation ( Rao, 2012) , enabled with sand to prop the fractures open and
installed to support large drilling plat- Mitchell Energy to bore long, horiz ontal chemical additives such as friction reduc-
forms and associated equipment. wells called “ laterals” into the Barnett ers, corrosion inhibitors, anti-scale agents,
Exposure routes, fate and transport, and Shale in the Fort Worth Basin of Texas. and biocides ( USEPA, 2016; https://fracfocus
toxicology of chemicals used in the These laterals, which contacted a much .org/) . The water, sand, and additives are
hydraulic fracturing process are poorly greater volume of the shale formation than pumped into wells under pressures that Site or figure number
understood, as are the potential effects on vertical wells, were stimulated with a exceed rock-strength to create fractures 4 1. Well-pad construction
terrestrial and aquatic ecosystems and series of staged hydraulic fractures care- ( Figs. 1 # 3–4 and S2 [ see footnote 2] ) . High-pressure 2. Drilling
High-pressure
human health. This is made all the more fully spaced into discrete z ones along the Many of the risks at each step of UOG injection 3. and 4. Completion
injection
5. Natural gas production
difficult by an adaptable and evolving lateral. The combination of horiz ontal development are known while others S an d nd 6. Crude oil production
Sa
industry that frequently changes methods drilling and staged hydraulic fracturing remain poorly understood ( Table S1 [ see 7. Plugged and abandoned well
illustrating leaking casing
8. Wastewater disposal
GSA Today, v. 28, https://doi.org/10.1130/GSATG361A.1. Copyright 2018, The Geological Society of America. CC-BY-NC. g u l P g u l P 9. Induced seismicity
10. Landscape disturbance
11. Potential upward transport pathway
Proppant in fracture
Proppant in fracture
* Emails: dan.soeder@ sdsmt.edu; dbkent@ usgs.gov. 12. Water supply wells
1 The term “ frack” ( with the k) is commonly used by shale gas opponents ( “ fracktivists” ) in reference to the entire drilling, stimulation, and production process. Pro-
ponents use the spelling “ frac” ( minus the k) in reference only to the stimulation step. The word has no standard spelling, but for phonetics and consistency with similar
words ( e.g., crack) we have chosen to include the “ k” but limit the use to the stimulation process.

2 GSA Data Repository Item 2018251, six tables and eight figures with supporting information, is online at www.geosociety.org/datarepository/2018/.

4 GSA Today | September 2018