The Potentials and Problems of Expanding Use of Shale Gas in the Continental U. S



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III. Costs of Shale Gas

1. Environmental Costs


Several elements of the process of hydraulic fracturing are inherently hazardous to the health of human beings. These include the silicate used to hold shale pores open during the drilling and operation of a fracking well, the methane extracted by the well (as well as the methane that escapes during the extraction process), and the chemical mixture used to treat the well for maximal efficiency (henceforth referred to as fracking fluid). Silicate is a known carcinogen and irritant, while methane exposure can be toxic to humans, and fracking fluid may contain several hundred distinguishable chemicals, including carcinogens, radioactive elements, heavy metals, eye and organ irritants, toxins, and corrosive and volatile chemical agents. The amount of fracking fluid used per well and the composition of fracking fluid is almost always information that is protected by various trade secret regulations, so it is next to impossible to quantify the risk of any specific type of poisoning or sickness induced by fracking fluid exposure. In this section, risks associated with each element will be explained and assessed.

view the data used to make this graph.

Figure . Fatality rates by state, with North Dakota in the lead [49]

Worker Mortality and Morbidity


The hydraulic fracturing process is particularly dangerous to workers based on the volume and inherent hazard of the chemicals whose use in the process is unavoidable, as well as the exemptions from worker safety regulations to which oil and gas industries in the United States are privy. The National Institute of Occupational Safety and Health places the national average for worker deaths in the oil and gas industry in 2012 at 27.5 per 100,000 workers, where the national average of workplace fatalities for all industries was only 3.4 per 100,000 workers. However, regionally, rates of fatalities among oil and gas workers were extremely variable. In North Dakota (a region where extraction of gas predominately uses the hydraulic fracturing technique), the average rate of fatalities among oil and gas workers was 75 out of every 100,000 workers, while in Texas, the state with the greatest number of oil and gas worker fatalities, the rate of fatality was 27 deaths per every 100,000 workers, much nearer to the national average. However, West Virginia was the state with the highest rate of death per active drilling rigs, with 10.6 deaths per 100 active rigs in 2012. To give an idea of the scale of the yearly number of deaths related to oil and gas extraction, the total number of reported fatalities in the United States oil and gas industry in 2013 was 112, down from 142 in 2012 [49].

The leading cause of worker death associated with oil and gas production is transportation-related. Between 2003 and 2012, 38.2% of oil and gas worker deaths were related to transportation, 26.2% were related to contact with objects and equipment, while 13.2% were related to fires and explosions, 7.9% were related to materials exposure, and 5.8% were related to falls or slips. An additional 0.5% of deaths (6 deaths total) were related to violent injuries by persons or animals.

Although the vital role trucking and transport plays in the extractive industry (particularly in the case of natural gas extraction via hydraulic fracturing, in which roughly 600-900 truck trips occur per well per fracturing event) can partially explain the high rate of transportation-related deaths in the oil and gas industry, policies exempting the oil and gas industry from standard transportation safety regulations potentially exacerbate the problem. While drivers of most commercial vehicles must spend at least 34 hours off duty in order to reset their accumulated hours (above which they are not permitted to work), drivers of commercial motor vehicles that are exclusively used for oil and gas-related transport are permitted to reset their cumulative hours worked after only 24 hours. Additionally, while time spent waiting is usually considered “on-duty” and therefore counts towards the maximum 14 hours that a driver may consecutively spend behind the wheel, time drivers spend waiting at gas sites counts as “off-duty” and does not count towards workers’ consecutive hour counts [50]. This means that oil and gas drivers may be expected to (alertly) wait for an unspecified number of hours, then expected to drive up to 14 consecutive hours afterwards. This increases the risk of driver inattentiveness and rate of fatigue among drivers, increasing the risk of accidents.

Worker deaths related to blowouts, explosions, and contact with object equipment can also be at least partially attributed to loopholes in safety regulations (such as a lack of criminal penalties around workplace safety-related negligence in the Illinois regulations of hydraulic fracturing) and sporadic enforcement of safety standards. Wiseman et al mentions that in some states, violations of environmental and workplace safety regulations may be reported as “alleged violations,” which give the violator time to respond to the inspectors’ allegation and do not necessarily require the violation to be fixed, whereas if they were reported as “violations,” a penalty such as a consent order, a fine, or the institution of a remediation plan would be levied. Additionally, safety and environmental regulations around the fracturing process which are most heavily punished are often procedural violations rather than substantive violations [51]. While OSHA has begun to pursue criminal prosecution of workplace safety violations by the oil and gas industry that result in worker mortality, no further level of protection exists in many states’ legislation of fracking. For example, under Illinois’ regulations on fracturing, there is no criminal penalty for failing to build wells to API construction standards in order to minimize the risk of blowouts and explosions. Additionally, Food and Water Watch reports a “culture of fear” in fracturing-related workplaces, where requests for appropriate safety materials such as hazmat suits are not taken seriously. Accounts of workers expected to climb into produced water tanks and trucks in order to clean them are routinely issued “ ‘a paper jumpsuit, a hard hat, no mask, essentially no protection’ ” are extremely common [52]. In many instances, such blatant violations are not prosecuted simply because they are not inspected: AFL-CIO reports that it would take OSHA (given current levels of staffing and inspection) 131 years to inspect each workplace under its jurisdiction once, meaning that while perhaps a sample of fracking-related workplaces may be inspected by OSHA yearly, there is currently no system in place to police every potentially-hazardous extraction-related workplace for violations of workplace safety.

The total reported number of workplace deaths that occur from exposure to hazardous materials related to hydraulic fracturing is misleading, because some of the hazardous materials to which workers are exposed are carcinogens expected to cause solid tumor formation over the course of many years, Therefore, we can assume many cancers and chronic diseases that would result from hazardous materials exposure such as exposure to airborne hazards such as silicate and carcinogens such as benzene go unreported. Additionally, illnesses and injuries that are unpleasant but nonfatal (such as chemical or thermal burns, crushed fingers or radiation poisoning) are often not reported or self-reported, because the number of reported accidents can play a role in an employee’s future employment prospects (employees who report a high number of on-the-job accidents may be less desirable than those who report none) [52].

One good example of the system of problems described above is the issue of airborne silicate near fracturing sites. Several tons of silicates are generally used as a proppant in each well that is fractured. Silicate particles, up to 100 times smaller than naturally-occurring sand, is highly respirable, and exposure without proper ventilation masks may result in health problems such as thickening of the pulmonary arteries, right heart problems, renal failure, chronic obstructive pulmonary disorder, lung cancer and tuberculosis [53][54]. Rosenman reports that 84% of a representative sample of fracking wells at which airborne silicate levels were measured exceeded maximum permissible levels laid out by OSHA [55].


Fracking Fluid Effects on Public Health


Fracking fluid, the chemical mixture that is injected into fracking wells, includes anywhere from dozens to hundreds of substances. One estimate places the number of chemicals used in fracturing a single well at 750. These chemical agents include (but are not limited to) corrosives, corrosive inhibitors, intensifiers, bacterial control agents, clay control agents, surfactants, friction reducers, gellants, thickeners, buffers, and gel breakers. Many of these chemicals are known to be hazardous to human health. Some examples of toxins commonly used in the hydraulic fracturing process are ethylene glycol (a chemical commonly used in antifreeze that causes renal and cardiopulmonary failure in humans), BTEX compounds (benzene, toluene, ethylbenzene, and xylene, which are known carcinogens and also have adverse nervous system effects), formaldehyde, arsenic, uranium-238, and other known carcinogens such as lead, naphthalene, and diesel [56][57]. In fact, some chemicals used in fracturing are unknown, due to trade secret protection clauses in the Energy Policy Act of 2005. Although these chemicals are not necessarily known, the American Association of Pediatrics advises exposure to fracking fluid either directly or through tainted wellwater or air may have negative neurological, respiratory, cardiovascular, gastrointestinal, renal, urological, reproductive, immunological, mucocutaneous, dermatological, hematopoietic, oncological, and endocrine-related effects [58][59].

Since the Energy Policy Act of 2005 effectively stripped federal-level environmental regulations such as the National Environmental Policy Act, the Safe Drinking Water Act, the Clean Water Act, the Clean Air Act, the Resource Conservation and Recovery Act, Comprehensive Environmental Response Compensation and Liability Act (Superfund), and the Toxic Release Inventory of their potency, companies practicing hydraulic fracturing are exempt from federal minimum standards for contamination, toxic disclosure policies, research and testing requirements, and impact statement requirements [60]. Although states may pass their own regulations for companies wishing to use hydraulic fracturing to extract natural gas, states often lack the resources to enforce such policies. Furthermore, states have a vested interest in the creation of lax regulations, because loosely-regulated areas are seen as more appealing (less costly) to business [61].

For these reasons, it is nearly impossible to find unbiased, peer-reviewed or agency-sponsored data on the rate of well and groundwater contamination by fracking fluid [62]. Reviewing the effects on public health is equally difficult, especially because proponents of unconventional gas extraction are quick to publish industry-sponsored reports that deny the potential of any contamination or environmental toxicity. Thus, the following paragraphs must be considered in light of the fact that more independent research to determine the extent to which fracking fluid may be able to contaminate water supplies and have detrimental effects on public health absolutely must be carried out.

While negative public health effects that are anecdotally attributable to the contamination of water wells by fracking wells are widely documented, there is a conspicuous lack of research demonstrating correlation or causation. For example, it is widely suspected that proximity to fracturing wells has a statistically significant positive correlation to rates of leukemia, which is associated with benzene exposure. Additionally, proximity to drilling at Flower Mound, Texas has been correlated to statistically-significant increases in rates of breast cancer. However, these studies have been subject to much criticism, because they do not appropriately take into account life history variables, meaning they might be over-attributing increased rates of cancer to fracking well proximity. Additionally, the Flower Mound research efforts were short-term studies, which is problematic because solid tumors that develop as a result of chemical exposure may take as long as twenty years to develop. Therefore, the possibility that the Flower Mound studies are in fact underestimating the correlation between well proximity and rates of various cancers is also very real.

Another set of issues which has successfully been linked to well density and proximity are birth defects, specifically congenital heart defects and neural tube defects [58]. A 2014 study of rural Coloradans found babies born to mothers in the top tertile of well exposure (based on both density and proximity of wells within a 10-mile radius from maternal residence) were 30% more likely to have congenital heart defects than babies born to mothers with no wells in a 10-mile radius. The same study also found the risk of neural tube disorders such as spina bifida in babies born to mothers in the top tertile of well exposure to be 2 times as high as for mothers who did not live within a 10-mile radius of any wells [63]. These findings are corroborated by Lupo et al’s 2010 study, which found that mothers living in the areas of Texas with the highest rates of environmental benzene (0.9-2.33 ppbv) were 2.3 times more likely to have babies with neural tube defects [64]. Additionally, Wennborg et al’s 2005 study of Swedish mothers showed a significant correlation between the rate of neural tube defects in the children of mothers who were exposed to benzene, and those who were not exposed to benzene. In this study, children of mothers exposed to benzene were 5.3 times more likely to be born with neural tube defects than children of mothers not exposed to benzene [65].

While extensive research relating real-world fracturing wells to negative health outcomes is limited, exposure to many of the chemicals used in fracking are known to cause a number of deleterious effects in humans affecting every major system of the body. The American Association of Pediatricians New York branch suggests that in light of a lack of human-based research, veterinary medicine “provides a sentinel for potential human health outcomes, and reveals reason to be concerned.” [58][66]


Value of Health and Human Lives


Determining the monetary value of a human life is one of the most difficult ethical challenges associated with economics and policy. It is important to note that valuations of human lives made by government agencies are the value of statistical lives rather than individual lives; rather, the value of a human life is actually an estimate of how much people are willing to pay for small reductions in their risk of dying. These values are reported as the aggregate dollar amount that a population would be willing to pay for a reduction in their individual risk of dying in a given year, so that on average, one fewer person from that population per year would die. For example, if a group of 10,000 people were on average willing to pay $1000 to decrease their risk of dying by 1/10000 (0.01%), the value of a statistical life would be set at $1000/person * 10,000 people , or $10 million. When people actually pay to reduce their risk of dying, they usually do so by shouldering a greater cost for goods or services associated with regulations meant to increase safety and reduce risk, or in taxes meant to support the implementation of such regulations [67].

It is important to note that quantifying human value is also a deeply political issue. In policy-related situations, dollar-number estimates of the value of human life ought to be thought of as the aggregate amount of money that a population is willing to spend to prevent one death. Since government agencies consist largely of appointed officials, their values often shift according to the agenda of the political regime under which they operate. For example, one administration might prioritize economic growth or corporate development over environmental protection. This administration would appoint officials likely to set a lower value for human life in order to encourage business (because regulations meant to make businesses take the burden of paying to prevent deaths off the government would be less significant if each life were valued more cheaply). In an administration that prioritized worker safety or environmental protection over the expansion of business, officials likely to set higher values of human lives are appointed (in order to create appropriate economic grounds for strong environmental or workplace safety regulations) [68]. One good example of this effect is the discrepancy between United States’ Environmental Protection Agency’s estimates for the value of human life under George W. Bush’s pro-business administration ($6.8 million) and Obama’s pro-environment administration ($9.1 million). Estimates also vary between agencies due to different agency priorities. For example, the Department of Transportation thinks of prevention of death in terms of vehicular accidents and vehicle safety standards, as well as speed regulations and signage, while the Environmental Protection Agency thinks of prevention of death in terms of pollution cleanup and prevention. Since humans can die in more or less costly ways (cancer deaths, which are lingering and is costly in terms of healthcare versus a traffic accident death, which is instantaneous), agencies must also consider the type of death they are paying to avoid. For this reason, the Environmental Protection Agency consistently assigns higher values to human lives than the Department of Transportation, because deaths associated with environmental pollution are typically more prolonged and costly to the system than deaths associated with transportation. Additionally, the Environmental Protection Agency has added a cancer differential to its estimate: this additional clause stipulates that up to 50% more should be paid to prevent cancer-related deaths than instantaneous types of death [63].



Another method of calculating the value of a human life is the insurance-calculation method. This is better suited towards the calculation of an individual’s monetary potential at any given point in time, based on tax rate, health, projected income, and amount of productive time left in the workforce [69]. We will not use this method because our cost-benefit analysis is meant to provide insight into appropriate risk-reduction policies around unconventional natural gas extraction, rather than around individual remunerations for extraction-related injuries.

Potential Effects on Water Resources


One of the greatest arguments against the extraction of natural gas from American shale plays is the negative impact hydraulic fracturing can have on water resources. The argument that fracturing for natural gas is detrimental to water resources has several facets: first, the amount of water used in the fracturing process is extremely large. Second, water used in fracturing cannot necessarily be returned to the water cycle due to the toxicity it gains from being mixed with other chemicals during the process of fracturing. Third, there is no method of fracturing which guarantees methane and other chemicals do not seep into the water table (either during the fracturing itself, or from wastewater disposal wells), causing environmental toxicity and potentially destruction of natural filtration systems.

Resource-Intensiveness of the Hydraulic Fracturing Process


The process of hydraulic fracturing is extremely resource-intensive, especially in terms of water. It is estimated that 2-12 million gallons of water are required to fracture a single horizontally-drilled well, with different amounts of water required for varying depths of wells, which translates into the creation of approximately 882 billion gallons of “produced” water, or post-fracturing wastewater per year in the United States alone [70]. This amount is especially significant in light of the fact that fracking wastewater ought not to be returned to the water cycle, because no technologies currently exist to thoroughly remove toxins. As the global population increases, so does the demand for fresh water, which is used for direct human consumption and agriculture. Critics of fracturing claim the process jeopardizes freshwater resources in three major ways: first by using freshwater in a way which renders it toxic and largely untreatable, second, by allowing it to leach into groundwater and surface water reserves, rendering them toxic and unusable; and third, allowing a large fraction of the water used to be re-injected or simply left in the ground, rendering it unusable [71].

Toxicity and Obstacles for Treatment of Wastewater


Although most industrial and non-industrial uses of water are such that the water can be treated in municipal water treatment facilities, then effectively returned to the water cycle, wastewater produced in fracking poses several additional problems which prevent it from being effectively treated.  Post-fracturing wastewater is comprised of the injected freshwater, the chemical mixtures injected, meaning fracking wastewater must be treated of several hundred (potentially toxic, carcinogenic, or radioactive) chemicals, but is also briny and somewhat radioactive. Currently, produced water is dealt with in one of the following ways: disposal by injection in deep underground wells; disposal into surface waters such as rivers after some chemical treatment; or recycling into future fracturing efforts, with or without treatment.

The EPA cites several major problems with treatment of fracking wastewater using standard water treatment methods. For example, in chemical wastewater treatment systems, chemicals involved in fracking interact with chemical disinfectants to form complex and toxic byproducts such as trihalomethanes, haloacetic acids, bromate, and chlorite [70][72]. In biological treatment systems, where bacteria are used to remove toxins from water, high levels of chlorides cannot be removed by biological treatment systems. Additionally, high levels of mineral salts in the fracking wastewater change the osmotic pressure of biological treatment systems, killing the operative microorganisms and reducing the efficacy of the treatment system [73].


Contamination of Groundwater


    The object of hydraulic fracturing—creating pathways for natural gas trapped in deposits of shale to reach the surface—is precisely what makes the chemicals and fluids used in the process difficult to contain. Fractures in the rock which allow natural gas to escape and be recovered may also serve as pathways for fracking fluid to travel. Indeed, the fracking fluid often continues to migrate along these pathways even after the process of fracturing is completed, due to the high levels of pressure at which the fluid is injected in the first place.   This is especially problematic when manmade fractures in the rock extend into shallow rock areas used by humans for water resources, or connect with natural flaws in the rock which are linked to underground reserves of water, which not only allows methane to migrate into potential sources of drinking water, but also the chemical mixture used for fracturing itself (see Figure 14) [74][75]. Another way in which fracking fluid or methane might leach into ground water is through the failure of a well casing. Contamination of surface and ground water is a great concern when fracking wastewater is spilled accidentally, when it is improperly disposed of, and when it is allowed to reenter the water cycle without significant treatment.  Some researchers also argue that produced water, post-treatment, ought not to be released into surface waters for fear of contamination of aquatic environments, and increased environmental toxicity [76].

how fracking works

Figure . Pathways for fracturing-related water pollution [133]


Induced Seismicity


Induced seismicity refers to earth tremors and quakes associated with anthropogenic activity. The types of human activity which have historically caused seismicity are generally ones which cause the levels of stress, friction, and porosity of the earth’s crust to vary.

There are two clear ways in which this effect can cause tremors. First, the alteration of underground structures can allow groundwater to seep into faults, changing the pore pressure of the rock along the fault, making it more likely to slip more easily, allowing the fault to fail. Second, changes in the amount of material placing stress on a fault increase the possibility of slipping along that fault. This is especially true in the case of creation of formations such as large surface-level or subterranean lakes through damming or through the deep injection of wastewater. In cases such as these, both ways (seeping water increasing porosity along faults, and change in stress on the fault via increased mass and volume of matter exerting pressure) can increase the porosity of the rock, which allows the rock to slide more easily when shear stress is introduced, allowing the fault to fail [77].

The seismic events which have been shown to have a direct causal link to human activities have historically been of relatively small magnitude, and confined to nearby the site of the manmade activity. Typically, seismic events associated with the drilling and fracturing of a natural gas well are negligible in magnitude. However, the process of hydraulic fracturing has been shown to be associated with the increased magnitude of small-scale seismicity, even in zones that are not typically seismically active. For example,

However, the process of wastewater injection presents a greater seismic risk. Under EPA regulation, wastewater from natural gas production must be disposed of in Class II wells, which are generally 4000-8000 feet deep. There are approximately 144,000 Class II wells currently in operation in the continental United States, of which approximately 30,000 are disposal wells. The injection of fluids into each of these wells creates a network of fractures in the surrounding rocks, and increases the porosity of rock where fluid is injected [78]. This effect itself is associated with increased rates of small-magnitude seismic events, and increased risk of larger seismic events, but the most concerning risk associated with injection of waste fluids is the possibility that these manmade fracture networks may be triggered by large, remote, naturally-occurring quakes. Although large trigger earthquakes would ordinarily apply pressure on natural faults and could cause minor aftershocks, manmade fault networks are more susceptible to major slipping based on high porosity inherent to this type of fault network, and also because there are so many such manmade fracture networks. When one system of manmade fractures fails, resulting in earthquake, the risk of other nearby fracture networks doing the same skyrockets, due to the change in position and pressure of rock along the manmade fault cracks that occurs after the initial earthquake event [79].





Figure . Top: Map of seismic risk by region, taking likelihood and potential magnitude of seismic risk into account. Red indicates highest risk, while grey indicates lowest risk. (United States Geographical Survey, 2014)

Bottom: Map of viable shale plays in the Lower 48 United States. Pink areas indicate shale plays, while purple regions indicate shale basins. (United States Energy Information Administration, 2014)

One example of a large earthquake believed to be caused by this ripple effect was the 2011 M5.7 earthquake in Prague, Oklahoma, which was most likely triggered by an M8.8 earthquake in Maule, Chile. This is notable for several reasons: first, because before the creation of injection wells, Oklahoma had no history of any large-scale seismic activity; and second, because the epicenter of the triggering earthquake was well over a thousand miles removed [77].

Another particularly worrisome possibility pertinent to the process of hydraulic fracturing (which I argue must necessarily include the process of wastewater injection, because no cost-effective alternative exists to dispose of or treat produced water), is that of large-scale natural seismic activity in the central United States, which could trigger a swarm of large-scale seismic events throughout every system of man-made fracture which exists. This possibility is especially concerning because the Wabash and New Madrid seismic zones, spread throughout the southern edge of the Midwestern Marcellus Shale, have been listed by USGS as “high-risk.” Many scientists believe this area is “due” for an earthquake on the scale of M7-M8. Since the most recent major seismic event on the New Madrid fault occurred in 1811, it is quite conceivable that another such event could occur at any time. This large-scale event would have the potential to trigger powerful aftershocks in both natural and anthropogenic faults [80].

Another terrifying possibility related to a New Madrid-triggered series of quakes would be that any injection wells even remotely near the Mississippi, Missouri, Ohio, or Wabash River floodplains could increase the risk of soil liquefaction in the case of a large seismic event. It is predicted that in the case of any seismic shock over M6.8, the silty soil and high water table of this region would allow the water pressure to rise to the point where soil particles could move freely, causing the foundations of bridges and other architectural foundations to become extremely unstable. Soil liquefaction could cause the collapse of many man-made structures, increasing the potential of earthquakes in this region to cause widespread loss of property and loss of life. Liquefaction also has the potential to disrupt any drilling or hydraulic fracturing wells in the region, to cause methane leaks as a result of compromised wells, and to cause leaks of highly radioactive, toxic produced water, which could permanently contaminate surface and ground waters.


Greenhouse Gas Footprint


Natural gas has been widely touted as a “bridge fuel” meant to ease the transition between traditionally “dirty” sources of energy such as coal and “cleaner” sources such as renewables without provoking the economic and infrastructure stresses a complete renouncement of fossil fuels would. It is also widely stated in the popular sphere that natural gas has a smaller greenhouse gas footprint (and therefore a smaller potential to cause global warming) than other fossil fuels such as oil and coal. This is because when natural gas is burned, fewer units of carbon dioxide are produced per unit energy than when coal or oil is burned, as well as fewer additional pollutants. Per megajoule of energy produced, coal emits 92g of CO2, oil emits 78g, and natural gas emits 56g. However, the assertion that natural gas is overall “cleaner” is problematic because it neglects lifecycle methane emissions associated with natural gas [69].

Natural gas is composed primarily of methane, itself a potent greenhouse gas. In terms of potential climate effects, methane is 25 times as potent as carbon dioxide (one mole of methane in the atmosphere would cause roughly 25 times the warming effect that one mole of carbon dioxide would) [81]. Once natural gas is burned for energy production, the most serious greenhouse gas byproducts which remain are carbon dioxide, meaning that the releasing a quantity of unburned natural gas into the atmosphere is actually worse on a short time frame than burning the same quantity of natural gas. However, carbon dioxide takes roughly 120 years to decay in the atmosphere, methane takes only roughly 10 years to decay. These measures of potency are complicated by the fact that methane reacts photochemically in the earth’s atmosphere to form ozone (O3), carbon dioxide (CO2), and water vapor, all of which have additional global warming effects. For every mole of methane present to undergo the photochemical reaction, roughly one mole of CO2 and 0.7 moles of O3 would be formed [82]. Therefore, if natural gas that is mostly composed of methane is spilled in the production process, the relative “cleanliness” of the natural gas in respect to global warming outcomes may be somewhat lessened. Accounting for the varying time scales of greenhouse gas decay, Rodhe estimates that on a timescale of 100 years, methane leaks from natural gas production must be limited to less than 4% of total natural gas production in order to “break even” in terms of greenhouse gas outcomes: that is, if natural gas was to be as clean as oil in terms of greenhouse gas production, no more than 4% of the natural gas present should escape via leaks or vents. If a timescale of less than 100 years is considered, the estimate shrinks to less than 3% because methane decay can be discounted less in the short term than in the long term [84].

Currently, 3.6%-7.9% of methane involved in the life cycle of an unconventional gas well escapes into the atmosphere [84]. This is at least 30% more than rate at which methane escapes from the average conventional gas well (conventional gas wells have lifetime fugitive emissions that range from 1.7%-6%, largely because no leaks occur during the flowback period, because no flowback period exists). Based on the current rate of methane emissions from shale gas wells, Howarth, Santoro, and Ingraffea argue that on the 20 year timescale, shale gas has a greenhouse gas footprint between 20% and 100% greater than that of coal’s, while on the 100 year timescale, the greenhouse gas footprints of coal and shale gas are roughly equivalent [82].

Reducing atmospheric methane leaks in the natural gas sector is accomplishable to some extent by altering management practices (such as increasing inspection at pipe joints or areas where leaks are likely)or equipment types (such as making sure all pipes and seals are as efficient as possible), and reducing venting. However, leaks which occur during the drilling process, during the flowback process, and after the well has supposedly been sealed are largely unavoidable [85].


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