1.4.1 Types of Well Stimulation Technologies

Not all fracking is the same. There are several means and media that can be pumped into a rock formation under great pressure to enhance permeability in rock formations. A compilation of various technologies was compiled by the European Commission Joint Research Centre (Gandossi 2013), which divided the technologies by the method of fracture development including hydraulic fracturing (water), pneumatic fracturing (air), and fracturing with dynamic loading (i.e. explosive and electric fracturing), among other methods (Table 1.1). Many of the technologies discussed are in the conceptual phase, but the compilation shows that there is more than one way to enhance production of oil and gas – all have advantages and disadvantages or limitations.

Hydraulic fracturing is the most common and widespread technique and essentially makes use of a liquid to fracture the reservoir rock. Wells may be drilled vertically hundreds to thousands of feet below the land surface and may include horizontal or directional sections extending thousands of feet. A fracturing fluid is essentially the sum of three main components: the base fluid, proppant, and additives. The proppant is a solid material, typically sand, treated sand of man‐made ceramic materials, which are designed to keep an induced hydraulic fracture open both during and subsequent to a fracturing treatment. These fractures can extend several hundred feet away from the wellbore, and the proppants such as sand, ceramic pellets, or other small incompressible particles hold open the newly created fractures. Upon completion of the injection process, the internal pressure of the rock formation causes fluid to return to the surface through the wellbore. This fluid is known as both “flowback” and “produced water” and may contain the injected chemicals plus other constituents such as naturally occurring materials such as brines, metals, radionuclides, and hydrocarbons. The flowback and produced water is typically stored on‐site in tanks or pits before treatment, disposal, or recycling. In many cases, it is injected underground for disposal. Since injection is not always an option, the flowback and produced water may be treated and reused or processed at a wastewater treatment facility and then discharged to surface water.

The most commonly used fracture method in the oil and gas industry is hydraulic, since water is generally available, can be recycled or treated, and is an uncompressible compound. Water can withstand pressures and temperatures found in the subsurface, and it can double as a carrier fluid for chemical additives and proppants. The term “hydraulic fracturing” is widely used to mean the process of fracturing rock formations with water‐based fluids, albeit hydraulic does not necessarily applied to strictly water and includes all techniques that make use of liquids (including foams and emulsions) as the fracturing agent. This is of environmental interest since public pressure on operators to conserve water resources during the hydraulic fracturing operations have been well documented will continue, and improvements in the efficiency of the process are likely with the addition of green chemicals, gases, foams, and gels to lower the overall water use during the fracturing operations. There are several hydraulic fracturing techniques afforded to the operator based on site‐specific conditions. These techniques include the use of water‐based, foam‐based, oil‐based, acid‐based, alcohol‐based, emulsion‐based, and cryogenic‐based fluids. Cryogenic‐based fluids include such gases as carbon dioxide gas, nitrogen gas, and other compounds.

Slickwater fracturing is probably the most basic and most common form of well stimulation in unconventional gas, being used for more than 30% of stimulation treatments in 2004 in North America. The fracturing fluid is composed primarily of water and sand (>98%), with additional chemicals added (namely, friction reducers, surfactants, and possibly other contents such as polyacrylamide, biocides, electrolytes, and scale inhibitor in variable quantities) to increase fluid flow velocity and sand transport and to reduce friction, corrosion, and bacterial growth, among other benefits during the stimulation process. Conventional fracturing is typically used in both vertical and horizontal wells and in low‐permeability or “tight” reservoirs (i.e. sandstone), generally below a depth of 3000 m. A water‐based gel fluid is used with a medium proppant loading and 4–5 pumps operating at a combined rate of up to 5 m³ of water per minute. This technique creates long, very fine fractures. The volume of fluid is usually <1000 m³ per fracture treatment. High‐volume or “super” hydraulic fracturing commenced in 1968 and is commonly used in the United States for shale gas extraction in very‐low‐permeability reservoirs (i.e. shale and coal) at various depths, usually below a depth of 800 m. Large volumes of water with a low proppant loading are used, with over 20 pumps operating at a combined rate of 24 m³ of water per minute. This technique produces very long, fine fractures and is often used in conjunction with horizontal drilling for shale gas extraction. Skin fracturing is used for small‐scale fracture operations in order to bypass near wellbore damage. Typically used in high‐permeability reservoirs, this technique produces short, wide fractures. Acid fracturing is used in carbonate formations with a mild acid‐based fluid that etches the rock and does not require a proppant.

With nitrogen gas fracking, some or all of the fluid used in hydraulic fracturing is replaced by nitrogen gas that has the ability to fracture rock at high pressure much like water. While nitrogen (N₂) is a gas at room temperature, it can be maintained in a liquid state through cooling and pressurization. The three types of nitrogen gas fracking are identified based on the percentage and state of nitrogen used in the fluid (i.e. pure nitrogen gas fracking, nitrogen foam fracking, nitrogen‐energized fracking). Pure nitrogen gas fracking uses nitrogen almost exclusively, with only negligible amounts of water present. The nitrogen is maintained in a gaseous state, meaning it is low density and compressible. Due to compressibility, pure nitrogen gas fracking is ineffective at great depths. Its low density and viscosity also make it a poor proppant carrier. As a result, pure nitrogen gas fracking is an efficient method of production for only very specific types of formations such as for CBM, tight sands, and shales, and at depths <5000 ft deep. Nitrogen foam fracking is a more widely used form of nitrogen gas fracking. Instead of pumping almost pure, compressible nitrogen gas into the rock formation, nitrogen is mixed with water and other additives and then cooled to form a denser foam‐like liquid. Nitrogen foam fracking fluids are made up of somewhere between 53 and 95% nitrogen gas, with the percentage depending on proppant type and characteristics of the formation. The higher density and viscosity of nitrogen foam mean that it is a better proppant carrier and is capable of fracturing at greater depths than pure nitrogen gas fracking. On the other hand, it is not a completely waterless technique. Nitrogen‐energized fracking is carried out using a fluid made up of <53% nitrogen. The remaining fraction of the fluid is again made up of water and small amounts of chemical additives. The smaller amount of nitrogen is used to energize the liquid‐phase fluid, increasing flowback and allowing less water to remain trapped in the ground during fracturing of low‐pressure formations. Nitrogen‐energized fracking can be used at even greater depths than either pure nitrogen gas or nitrogen foam. While it is not as water efficient as higher nitrogen content fluids, it is a vast improvement on standard HFS.

Nitrogen gas fracturing is used primarily for water‐sensitive, brittle, and shallow unconventional oil and gas formations. The use of nitrogen prevents clay swelling that would otherwise be caused by slickwater. Pure gaseous nitrogen produces best results in brittle formations that have natural fractures and stay self‐propped once pressure pumping is completed. This is because nitrogen is an inert and compressible gas with low viscosity, which makes it a poor proppant carrier. In addition, due to the low density of gaseous nitrogen, the main applications for nitrogen gas fracturing are shallow unconventional plays, namely, CBM, tight sands, and shale formations up to 5000 ft (1524 m) in depth. Formations best suited for nitrogen gas fracturing also tend to have low permeability (<0.1 md) and low porosity (<4%) (Air Products 2013).

1.4.2 Terminology

Before we can discuss the technical merits and environmental impacts of hydraulic fracturing, let us come to terms as to as to what we are discussing – a topic that can also be deemed controversial – that being what exactly are we talking about? Fracking or fracing is short for hydraulic fracturing. For those politically inclined, it is inferred to be an attempt to control the debate, anti‐fracing groups prefer the term “fracking” (spelled with a “k”) because of its negative connotations (i.e. smack, whack, profanity, etc.) – similar to the term “peak oil.” “Peak oil” became politically charged to try and move the United States from a hydrocarbon‐based fossil fuels to other energy alternatives. The 1978 Battlestar Galactica series further introduced us to the term “frak” as a fictional censoring substitute for that other four‐letter f‐word. Pop culture has cultivated the term as homage to the Syfy series and a way of being obscene without technically being obscene. Simply defined – and with a wide choice in source material ranging from The Dictionary of Oil Terms to the Urban Dictionary – we decided to go with something in between.

Most of the general public likely turns to Wikipedia, which defines hydraulic fracturing as the natural propagation of fractures in the subsurface caused by the presence of pressurized fluids (i.e. as in the natural case of the formation of dikes and sills albeit on a much smaller scale), which allows gas and oil to migrate from source rocks to reservoir rocks. “Induced” hydraulic fracturing, or what is commonly referred to as a frac job (aka fracking, fracing, fraccing, the F‐word, or whatever), is when fractures in the subsurface strata are generated from a wellbore drilled into reservoir rocks with the ultimate goal of increasing extraction rates, thus enhancing the recovery of gas and oil. There is also formation fracturing, explosive fracturing, refracturing, vertical fracking, high‐volume hydraulic fracturing (HVHF), or fracturing simulation. The term “fracking” did not start with the controversies that exist today. The term originally made its appearance as the hydrafrac process in a paper published in 1949 (Clark 1949), and in the 1950s “frac” for well stimulation was in common usage. The term frac was also again used around 1981 in an Associated Press story, with continued usage in trade journals throughout the 1980s. For the purposes of this book, we are referring universally to hydraulic fracturing stimulation or HFS, unless stated otherwise.

1.6.1 Environmental Stewardship

In 2017 President Donald Trump’s “An America First Energy Plan,” the stated policies consisted of several key points: to make the country energy independent and secure from foreign oil imports, to create new jobs, to lower energy costs, and maximize the use of resources by unleashing an energy revolution vastly improving the economy. The President also noted “lastly, our need for energy must go hand‐in‐hand with responsible stewardship of the environment.” The concept of environmental stewardship has its beginnings with Aldo Leopold (1887–1949) in his (1949) landmark book A Sand County Almanac. Leopold considered the concept of a “land ethic” and called out for moral responsibility in our understanding and interactions between us and them – the natural world – that being the land, the animals, and the plants that grow upon it. Leopold felt that the relationship between people and the land was intertwined, and the caring for people could not be separated from the caring for the land – it was a moral code.

This concept of land ethic would evolve, and in the 1970s energy production and environmental issues related to technology advancements as it relates to the industrial complex and energy resources began to creep into the public’s consciousness. Former President Richard Nixon established the US EPA in July 1970, while Greenpeace was being formed in Vancouver in 1971. The United States was experiencing the OPEC crisis in 1973 and the Three Mile Island incident in 1979. Environmental concerns would become even more visible throughout the 1980s and 1990s, giving rise to many geoscientists moving into environmental fields.

We currently view environmental stewardship as the crossroads between the environmental, social, and economic systems. The environmental system addresses natural resources usage, environmental management, and pollution prevention. The social system includes standards of living, education, community, and equal opportunity. The economic system addresses profit, cost saving, economic growth, and research and development. All three systems intermingle (i.e. social/environmental, environmental/economic, and economic/social). The area where all three primary sectors meet and interact is referred to as “sustainability” (Figure 1.10). Sustainability is commonly defined as the ability to maintain or improve standards of living without damaging or depleting natural resources for present and future generations. The concept of sustainability was ingrained as a foundation of environmental law with the signing of the 1969 National Environmental Policy Act (NEPA). NEPA established as a continuing policy of the federal government the creation and maintenance of “conditions under which [humans] and nature can exist in productive harmony, and fulfill the social, economic and other requirements of present and future generations of Americans.” The United Nations World Commission on Environment and Development characterizes sustainable development as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.”

Being energy independent, of course, by definition, implies that our energy needs are available, but availability is not sustainability. The concept of availability refers to something that is present and ready for use and is well established in the literature of stochastic modeling and optimal maintenance. Availability of a system is typically measured as a factor of its reliability. Reliability is the ability to be relied or depended upon, in regard to accuracy, honesty, or achievement. As reliability increases, so does availability. Thus, as we move from the concept of availability to sustainability, the concept of environmental stewardship has evolved over the years into the responsible use and protection of the natural environment through conservation and sustainable practices.

Reliable and affordable energy is essential to life as we know it. However, behind the convenience provided by today’s technology and innovation, the energy supply chain is quite complex, which begins with a resource exploration and extraction footprint and leads to the development of massive distribution systems, storage, and refining facilities, among others, which all have a footprint of varying dimensions and potential environmental impacts. There is no free ride – it all has a definable impact. As we move into the realm of energy independence and being an energy exporter, it leaves us with two questions: Do the social and economic benefits outweigh the environmental effects? Are the energy sources being developed in the most environmentally sensitive and sustainable manner achievable? These are two very important questions to be addressed.

Anybody can be an environmental steward. All one really has to do is be aware and knowledgeable of the world around you and take the appropriate steps to minimize adverse impact to the environment regardless of the activities or operations in which you are involved. All industrial operations and activities have some environmental impact, and there is little question when it comes to local issues such as noise, air and water quality, traffic, and overall aesthetics. These issues appear to be predominant due to their inherent visibility with the community at large.

In summary, for us humans in social systems or ecosystems, the concept of sustainability is the long‐term maintenance of responsibility, which has environmental, economic, and social dimensions and encompasses the concept of stewardship – the responsible management of resource use. The role we as geoscientists play enhances the lives of everyone and impacts every aspect of American life including conventional, alternative, and renewable energy, the economy, the environment, water and other resources, transportation, social contracts, and overall worker and public health, safety, and welfare, among much more. How we communicate this is crucial in whether we succeed or not. Our efforts to reduce our environmental footprint while maintaining exceptional deliverability and operational results are the ultimate goal – environmental sustainability.

1.6.2 The New Energy Landscape and Environmental Challenges

The phase “It’s the economy, stupid” was made popular by former President Clinton’s campaign strategist James Carville during Clinton’s successful 1992 presidential campaign against George H. W. Bush. Carville was making the case that Clinton was a better choice because Bush had not adequately addressed the economy, which had recently undergone a recession. In the pursuit of energy, the unconventional and alternative energy resources arena is especially susceptible to environmental drivers. With all the regulations and oversight that exist at the federal, state, and local level, it does not take a highly visible incident to make the point that we live in an environmentally conscious world. Environmental concerns drive energy policy, and policy drives the conventional, unconventional, and alternative energy resources, regardless of the merits. How successful we geoscientists will be in developing a national energy strategy that is reasonable and sound depends on how well we communicate with the public, policy makers, and the environmental community at large.

With advancements in HFS, the energy landscape has changed, and areas once virtually void of significant energy plays are now in the forefront. The technological advances in horizontal drilling and HFS has opened up shale deposits across the country and globally, bringing interest in exploration and production to new regions. Geologically, the interest is on gas shales such as the Marcellus Formation throughout Pennsylvania, New York, Ohio, and West Virginia, the Barnett and Woodford in west Texas, or the Bakken in North Dakota and Montana. The Barnett Shale in Texas, using horizontal drilling and HFS techniques, was developed in the mid‐1990s for economically viable shale gas. The Marcellus Shale within the Appalachian Basin (West Virginia, Pennsylvania, and New York) is the most dynamic of the shale plays. Encompassing 54 000 mile² in extent, with techniques pioneered in the Barnett Shale, this play is still in the exploration stage. Currently, most of the activity in the Marcellus is where the shale can be drilled at minimum depth. As of 2011, there were an estimated 74 operators, 8982 active wells, and 3025 violations, totaling about $3.5 million in fines.

These shale formations, among others, have great potential and reserves to provide natural gas for decades and provide the opportunity for many countries, including the United States, to progress toward energy independence. In addition to the high demand for clean burning natural gas, the same areas also require clean surface and subsurface sources of potable water and water for commerce and agriculture. In recent years relating to the boom in shale gas drilling, local citizen groups, environmental activists, regulatory agencies, and governmental agencies have been holding often heated debates and trying to resolve whether the drilling and hydraulic fracturing chemicals are degrading surface water or groundwater supplies.

The oil and gas industry is universally recognized as being a vital part of the US economy, both short and long term, and is heavily regulated at the state and federal level and at the local government level. Most of the companies operating in this sector are relatively small enterprises, in addition to the large international corporations. Fundamentally, to commence exploration for oil and gas, the business enterprise must obtain a development permit, a drilling permit, and an operating permit. The requirements for gaining these permits are stipulated at the state level. There must also be a public review period, which is often contentious. All permits must be obtained prior to beginning exploration, and the applicant may face delays and be assessed financial and legal penalties for failure to adhere to permit conditions.

References

1. Air Products (2013). Oilfield Services: Nitrogen Fracking. http://www.airproducts.com/industries/energy/oilgas‐production/oilfield‐services/product‐list/nitrogen‐fracking‐energy‐oilgas‐production.aspx?itemId=396A3CBAB15846BF8FDAEA963586E80D (accessed 5 November 2018).
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Suggested Reading

1. Amico, C., DeBellus, S., Detrow, S., and Stiles, M. (2011). Shale Play: Natural Gas Drilling in Pennsylvania. State Impact Pennsylvania. National Public Radio. http://stateimpact.npr.org/pennsylvania/drilling (accessed 11 July 2013).
2. British Petroleum (1996). Statistical Review of World Energy. Technical Report by British Petroleum Company P.Lc, London. http://www.radialdrilling.com/?page_id=17130 (accessed 5 November 2018).
3. Burke, L.H., Nevison, G.W., and Peters, W.E. (2011). Improved unconventional gas recovery with energized fracturing fluids: Montney example. In: SPE Eastern Regional Meeting. Columbus, OH: Society of Petroleum Engineers.
4. Colorado Oil and Gas Conservation Commission (COGCC) (2014). Risk‐Based Inspections: Strategies to Address Environmental Risk Associated with oil and gas operations. (COGCC‐2014‐PROJECT #7948. Denver, CO: COGCChttps://cogcc.state.co.us/Announcements/RiskBasedInspection/RiskBasedInspectionStrategy.pdf.
5. Gallegos, T.J., Varela, B.A., Haines, S.S., and Engle, M.A. (2015). Hydraulic fracturing water use variability in the United States and potential environmental implications. Water Resources Research 51: 5839–5845.
6. King, G.E. (2012). Hydraulic fracturing 101: what every representative, environmentalist, regulator, reporter, investor, university researcher, neighbor and engineer should know about estimating Frac risk and improving Frac performance in unconventional gas and oil wells. SPE Hydraulic Fracturing Technology Conference, The Woodlands, TX, Society of Petroleum Engineers (6–8 February 2012).
7. Kothare, S. (2012). Economics and applicability of nitrogen for fracking. Air Products and Chemicals, Inc., 2012 (35346) 351‐13‐002‐US, 4 p.
8. Montgomery, C.T. and Smith, M.B. (2010). Hydraulic fracturing: a history of an enduring technology. Journal of Petroleum Technology 62: 26–32.
9. Testa, S.M. (2011). It’s the Environment Stupid: American Association of Petroleum Geologists Energy Mineral Division President’s Message. Explorer (November 2011).
10. Testa, S.M. (2012). Oh, Fraque! Improving Public Perception: American Association of Petroleum Geologists Energy Mineral Division President’s Message. Explorer (May 2012).
11. Testa, S.M. (2017). Being an Environmental Steward: American Association of Petroleum Geologists Energy Mineral Division President’s Message. Explorer (December 2017).
12. United States Environmental Protection Agency (US EPA) (2016). Hydraulic Fracturing for Oil and Gas: Impacts from the Hydraulic Fracturing Water Cycle on Drinking Water Resources in the United States. Washington, DC: Office of Research and Development EPA/600/R‐16/236Fa.