Master-5C. Baker Hughes, Sugar Land, TX, https:// oilandgas.ohiodnr.gov/portals/oilgas/_MSDS/ baker-hughes/ClayMaster5C_US.pdf. Baker Hughes Inc. 2013.
7 Hydraulic Fracturing from the Groundwater Perspective Ruth M. Tinnacher, Dipankar Dwivedi, James E. Houseworth, Matthew T. Reagan, William T. Stringfellow, Charuleka Varadharajan, and Jens T. Birkholzer CONTENTS 7.1 Hydraulic Fracturing for Hydrocarbon Recovery ..................................................................................................... 99 7.2 Hydraulic Fracturing for Enhancing Groundwater Yields..................................................................................... 100 7.3 Hydraulic Fracturing Operations for Hydrocarbon Recovery ............................................................................... 101 7.3.1 Typical Phases in Hydraulic Fracturing Operations ................................................................................... 101 7.3.2 Hydraulic Fracture Geomechanics and Fracture Geometry ...................................................................... 102 7.4 Composition and Potential Hazards of Injection Fluids ......................................................................................... 102 7.4.1 Technical Considerations for the Selection of Hydraulic Fracturing Fluids ............................................ 103 7.4.2 Composition of Injection Fluids ..................................................................................................................... 105 7.4.3 Potential Hazards of Injection Fluids ............................................................................................................ 105 7.5 Composition of Flowback and Produced Waters ..................................................................................................... 108 7.6 Potential Pathways for Groundwater Contamination ............................................................................................. 109 7.6.1 Leakage through Hydraulic Fractures............................................................................................................110 7.6.2 Leakage through Failed Inactive Wells ..........................................................................................................111 7.6.3 Failure of Active (Production and Class II) Wells ........................................................................................ 112 7.6.4 Transport through Induced or Natural Subsurface Pathways ....................................................................113 7.6.5 Injection of Produced Water into Protected Groundwater ..........................................................................114 7.6.6 Use of Unlined Pits for Produced Water Disposal ........................................................................................114 7.6.7 Spills and Leaks .................................................................................................................................................114 7.6.8 Treatment or Reuse of Produced Water ..........................................................................................................114 7.6.9 Operator Error ....................................................................................................................................................115 7.6.10 Conclusions.........................................................................................................................................................115 Acknowledgments ..................................................................................................................................................................115 References.................................................................................................................................................................................115
7.1 Hydraulic Fracturing for Hydrocarbon Recovery The extraction of shale gas from formations with lower permeabilities compared to other rock formations has became economical with the emergence of relatively newer technologies such as hydraulic fracturing (commonly known as “fracking”) and precision drilling of wells (Arthur et al., 2008). The extraction of shale gas using hydraulic fracturing has increased estimates of natural gas resources enormously in many countries (Table 7.1), with an overall worldwide increase from 18 to 118 trillion cubic meters (Tcm) (Howarth et al., 2011). Currently, there are only four countries—the United States (U.S.), Canada, China, and Argentina—that
produce shale gas and shale oil commercially (U.S. Energy Information Administration: http://www.eia. gov/todayinenergy/detail.cfm?id=19991). China is estimated to possess the world’s largest shale gas reserves followed by the U.S.; however, the U.S. is the largest producer of both shale gas and shale oil (Howarth et al., 2011). Owing to the high abundance of U.S. shale hydrocarbon resources, combined with its dominance in the production of these resources, the U.S. will be the primary focus in this chapter. The main classes of reservoirs where hydraulic fracturing has been used intensively in the U.S. include verylow-permeability unconventional shale reservoirs and tight-gas sand reservoirs, accounting for over 73% of the hydraulic fracturing activity (Beckwith, 2010). Most of 99
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TABLE 7.1 Estimates of Proven and Technically Recoverable Shale Gas Resources in Trillion Cubic Meters (Tcm)
Countries
Proven Gas Reserves (Tcm)
Technically Recoverable Shale Gas Resources (Tcm)
Mexico France Argentina China Venezuela Canada USA
0.3 0.006 0.4 3 5 1.8 7.7
19 5 22 36 0.3 11 24.4
Increase (Times) 63.33 833.33 55.0 12.0 0.06 6.1 3.17
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Source: Compiled from Howarth, R.W., A. Ingraffea, and T. Engelder. 2011. Nature, 477(7364), 271–275, doi:10.1038/477271a.
the unconventional shale reservoirs contain natural gas, with the exceptions of the Eagle Ford, which produces oil in the shallower portion of the formation, and the Bakken and Niobrara plays, which mainly contain oil. Shale gas resources are found in a variety of basins including the Barnett Shale (Fort Worth Basin, Texas), Haynesville Shale (East Texas and Louisiana), Antrim Shale (Michigan), Fayetteville Shale (Arkansas), New Albany Shale (Illinois Basin), Bakken Shale (North Dakota), and Marcellus Shale (Pennsylvania). The Marcellus Shale probably represents the most expansive shale gas play in the U.S., with recoverable reserves as large as 13.8 Tcm (Kargbo et al., 2010). According to a report submitted to the U.S. Energy Information Administration (EIA), technically recoverable shale oil resources amount to 23.9 billion barrels in the lower 48 states, with California providing the largest reserve amounting to 15.4 billion barrels (~64%) (U.S. Energy Information Administration: http://www.eia.gov/analysis/studies/usshalegas/pdf/ usshaleplays.pdf). Currently, hydraulic fracturing is used to produce a significant amount (~20%) of oil and gas in California with most of the production occurring in the San Joaquin Valley. It is important to note that each shale formation has unique geologic, chemical, mineralogical, and physical properties (Arthur et al., 2008; Kargbo et al., 2010) that need to be considered for hydraulic fracturing operations.
sedimentary or crystalline-rock aquifers (Banks et al., 1996). Crystalline-rock aquifers, in this context, refer to fractured igneous and metamorphic rocks with negligible porosity and permeability. In these aquifers, groundwater flows through fractured crystalline rocks. Typically, one or two high-yielding fractures that are interconnected through a wider fracture network supply the vast majority of water from a successful borehole (Gustafson and Krásný, 1994). In sedimentary aquifers, water supply wells are frequently clogged due to chemical (e.g., mineral precipitation), physical (e.g., suspended solids), mechanical (e.g., gas entrapment), or biological (e.g., growth of algae) processes (Martin, 2013). Hydraulic fracturing artificially enhances fractures or cleans out non-water-producing veins that are clogged, thereby providing a clear transport pathway for groundwater flow into the well. Additionally, hydraulic fracturing is also used for effectively increasing groundwater recharge (Martin, 2013). For these groundwater-related applications, hydraulic fracturing is a two-step process that involves the setting of packers, followed by high-pressure pumping (Figure 7.1a). First, the inflation of packers is used to seal the borehole hydraulically. Then, a high volume of water (~5000 gal) is pumped into the borewell at high pressure (~3000 psi) through a pipe connecting the packers. This process induces new fractures, or opens and clears previously obstructed fracture paths (Figure 7.1b) (Banjoko, 2014). For the remainder of this chapter, we will focus on hydraulic fracturing in the context of enhanced hydrocarbon recovery, and its implications on groundwater (a)
(b) Bedrock
Water
Water
Bedrock
Although hydraulic fracturing is primarily used for the extraction of hydrocarbons, this technique can also be applied to enhance groundwater yields from
Water
Bedrock Water
Water
Casing Packer
Obstruction
7.2 Hydraulic Fracturing for Enhancing Groundwater Yields
Casing
Fracture Water
Fracture Water
Water
Obstruction Fracture Bedrock
Fracture Bedrock
Bedrock
FIGURE 7.1 Hydraulic fracturing process for enhancing groundwater yields: (a) packers and packer piping are used to open and clear clogged fracture paths and (b) hydraulic fracturing results in enhanced groundwater flow into the bore well. (Adapted from Banjoko, B., Handbook of Engineering Hydrology: Environmental Hydrology and Water Management, CRC Press, Boca Raton, FL, 2014.)
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and VanBriesen, 2012; Vidic et al., 2013; Brantley et al., 2014). Warner et al. (2013) studied the effluent from a brine treatment facility in Pennsylvania and found an increase of salts downstream, despite significant reduction in concentrations due to the treatment process and dilution from the river. Moreover, radium activities in the stream sediments near the point of discharge were 200 times higher than in upstream and background sediments, and were above radioactive waste disposal thresholds. Much of the research on disposal has focused on produced water constituents and not specifically on stimulation chemicals commingled with produced water.
Acknowledgments This chapter was supported by the California Natural Resources Agency and the U.S. Bureau of Land Management, under a Work for Others Agreement with the U.S. Department of Energy (DOE) at LBNL, under contract number DE-AC02-05CH11231. We appreciate the cooperation and leadership of Jane Long and Laura Feinstein of the CCST in the execution of this chapter. We also acknowledge partial support from the Scientific Focus Area at LBNL funded by the U.S. DOE, Office of Science, Office of Biological and Environmental Research under Award Number DE-AC02-05CH11231.
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7.6.9 Operator Error Human error during the well completion, stimulation, or production processes could also lead to contamination of groundwater. Operator error could create connectivity to other formations that could serve as transport pathways. For example, poor monitoring or control of the fracturing operation could increase the extent of fractures beyond desired limits. Such errors could lead to an unexpected migration of fluids, or connection between wells that impacts production activities themselves. Fracturing beyond the reservoir bounds due to operator error may also be of particular concern in the case of shallower fracturing operations. An example of operator error during stimulation is a 2011 incident in Alberta, Canada (ERCB, 2012), where a misjudged fracturing depth led to fracturing fluids being injected into a water-bearing strata below an aquifer. A hydraulic connection between the fractured interval and the overlying aquifer was not observed, but groundwater samples contained elevated levels of chloride, BTEX, petroleum hydrocarbons, and other chemicals. 7.6.10 Conclusions Contamination of water supplies due to spills, leaks from surface facilities, disposal of inadequately treated water, leakage from wells, and illegal discharges have occurred. Several plausible release mechanisms and transport pathways exist for surface and groundwater contamination. However, the issue of contamination of groundwater via processes specific to hydraulic fracturing has not been proven to have occurred. It is clear that the hazard exists, and practices that mitigate the potential for contamination should be in place at each step of the process. Additional research on fracture propagation, the hydrological processes in and around unconventional reservoirs, and additional sampling studies to investigate potential transport scenarios are all required to understand the risks associated with the pathways discussed herein.
References Abass, H.H., A.A. Al-Mulheim, M.S. Alqem, and K.R. Mirajuddin. 2006. Acid fracturing or proppant fracturing in carbonate formation? A rock mechanic’s view. In: SPE 102590, SPE Annual Technical Conference and Exhibition, San Antonio, TX. Alley, B., A. Beebe, J. Rodgers, and J.W. Castle. 2011. Chemical and physical characterization of produced waters from conventional and unconventional fossil fuel resources, Chemosphere, 85(1), 74–82. Retrieved from http://www. ncbi.nlm.nih.gov/pubmed/21680012. Arthur, D.J., B.G. Langhus, and C. Patel. 2005. Technical Summary of Oil and Gas Produced Water Treatment Technologies, ALL Consulting, LLC, Tulsa, OK. Arthur, J.D., B. Bohm, B.J. Coughlin, and M. Layne. 2008. Evaluating the environmental implications of hydraulic fracturing in shale gas reservoirs. In: SPE 121038-MS, SPE Americas E and P Environmental and Safety Conference, pp. 1–21, ALL Consulting, San Antonio, TX. Arthur, J.D., B. Bohm, and M. Layne. 2008. Hydraulic fracturing considerations for natural gas wells of the Marcellus Shale. The Ground Water Protection Council 2008 Annual Forum, September 21–24, Cincinnati, OH. Baker Hughes Inc. 2011. Material Safety Data Sheet: Clay Master-5C. Baker Hughes, Sugar Land, TX, https:// oi l a ndga s.oh io d n r.gov/p or t a l s/oi lga s/_ M SD S/ baker-hughes/ClayMaster5C_US.pdf. Baker Hughes Inc. 2013. Master Fracturing Chemical List—Arkansas. Trican, http://aogc2.state.ar.us/B-19/1242_ChemConst.pdf. Balaba, R.S., and R.B. Smart. 2012. Total arsenic and selenium analysis in Marcellus Shale, high-salinity water, and hydrofracture flowback wastewater, Chemosphere, 89(11), 1437–1442, doi: http://dx.doi.org/10.1016/j. chemosphere.2012.06.014. Banjoko, B. 2014. Handbook of Engineering Hydrology: Environmental Hydrology and Water Management, S. Eslamian (Ed.), CRC Press, Boca Raton, FL. Banks, D., N.E. Odling, H. Skarphagen, and E. Rohr-Torp. 1996. Permeability and stress in crystalline rocks, Terra
