Shale Gas Produces Half the GHG Emissions and Consumes Half the Freshwater of Coal

by Shannon Julius

The long term environmental concerns having to do with shale gas development are primarily greenhouse gas (GHG) emissions and freshwater consumption, as other forms of environmental degradation can be remediated over time. Ian Laurenzi and Jersey Gilbert (2013) of the ExxonMobile Research and Engineering Company performed a life cycle assessment (LCA) of both GHG emissions and freshwater consumption of Marcellus shale gas. The life cycle begins with well drilling and ends with burning the fuel for power generation. Using their elaborated system boundaries, the researchers found that a Marcellus shale gas well releases 466 kg of carbon equivalent units per megawatt hour of power produced (kg CO2eq/MWh) and consumes 224 gallons of freshwater per megawatt hour of power produced (gal/MWh) over the course of its lifetime. The biggest contributor to both GHG emissions and freshwater consumption is power generation. The result of this study are highly dependent on the variables chosen to represent the shale gas well life cycle, especially the expected ultimate recovery of natural gas. Despite the potential for variability of results, the result of 466 CO2eq/MWh is consistent with other published life cycle assessments for conventional and shale gas, and almost all of the 14 other studies fall within the 10%–90% range of 450–567 CO2eq/MWh. Even considering factors that can increase total results, this study shows that average GHG emissions from shale gas are 53% lower and freshwater consumption is 50% lower than what is required for an average coal life cycle. Continue reading

Shale Gas Development Poses Threats to Regional Biodiversity

by Shannon Julius

Shale gas development physically and chemically alters the surrounding landscape, and native plants and animals can be particularly susceptible to these changes. In the Marcellus and Utica shale region—a largely forested area that encompasses the states of Pennsylvania, Ohio, and West Virginia—shale gas wells are being drilled with increasing density. A shale gas installation, including the well pad, compressor station, and storage areas, requires 3.56 ha on average. If an edge effect is considered, installations can affect approximately 15 ha of forest per site. Kiviat (2013) reviewed the potential ways that shale gas development can impact biodiversity. The most serious threats are physical alteration of terrestrial landscapes, chemical contamination of water and soil, and alteration of regional hydrology. Terrestrial alterations include construction of well installations, which cause deforestation and habitat loss, and construction of roads and pipelines, which create forest fragmentation. Chemical contaminants come from fracturing fluid and recovered wastewater. Hydrologic alterations are caused by water withdrawals and an increase in impermeable surfaces. Minor impacts on plant and animal health can come from noise, light, and air quality. Certain species are particularly at risk from shale gas development activities and some are able to thrive in the altered conditions. Continue reading

Disclosure of Hydraulic Fracturing Chemicals

by Shannon Julius

Hydraulic fracturing requires a large quantity of fluid; most estimates place the amount at 2 to 4 million gallons per well. This fluid is composed of 90% water, 8–9.5% proppants (sand which is needed to keep fractures open once hydraulic fracturing occurs), and 0.5–2% chemicals. Companies that perform hydraulic fracturing invest time and resources into creating their fracturing fluid formulas, so they insist on keeping those formulas proprietary because revealing the information could cause the company to lose its competitive edge. However, some common fracturing chemicals have been identified and are known to cause adverse human health effects, so keeping the composition of fracturing fluid confidential could be dangerous in the case of an emergency situation. Even in normal operating circumstances, these fracturing fluids could theoretically make their way into surface water or groundwater because hydraulic fracturing creates new flow paths through deep shale formations and speeds up the natural flow of fluids closer to the surface or aquifers. Maule et al. (2013) investigated recent efforts to regulate the disclosure of fracturing chemicals. Current systems in place include a voluntary reporting website, limited state regulation, and no federal regulation. Regulation efforts have faced problems of exemptions or loopholes, inadequate or incomplete information reporting, lack of enforcement, and competing state and federal interests. Continue reading

Shale Gas Well Drilling and Wastewater Treatment Impacts on Surface Water Quality in Pennsylvania

by Shannon Julius

Shale gas development can affect surface water quality by means of runoff from well construction and discharge from wastewater treatment facilities. Olmstead et al. (2013) conducted a large-scale statistical study of the extent to which these two activities affect surface water quality downstream. This study is different than most current literature related to the regional water impacts of shale gas development in that it focuses on impacts to surface water bodies as opposed to groundwater bodies. Researchers consulted online databases to retrieve locations of shale gas wells and wastewater treatment facilities within Pennsylvania. These were spatially related to downstream water quality monitors using Geographic Information Systems (GIS). Concentrations of chloride (Cl–) and total suspended solids (TSS) were used as indicators of water quality because both are associated with shale gas development and are measured by water quality monitors. Shale gas wastewater typically has a high concentration of Cl–, which can directly damage aquatic ecosystems and is not easily removed once dissolved in water. TSS, which harm water quality by increasing temperature and reducing clarity, can potentially come from the construction of well pads, pipelines, and roads associated with well drilling, especially when precipitation creates sediment runoff. Results of the study suggest that wastewater treatment facilities are responsible for raised concentrations of Cl– downstream and that the presence of gas wells are correlated with raised concentrations of TSS downstream. Continue reading

Marcellus Shale Gas Wastewater Management

by Shannon Julius

Since 2008, the Marcellus shale formation has become the most productive region for extracting shale gas in the US. Managing wastewater for these operations is a challenge not only due to their size and distribution, but also because of the different types of contaminants that are present in various types of wastewater. Rahm et al. (2013) retrieved data from the Pennsylvania Department of Environmental Protection (PADEP) Oil and Gas Reporting website from 2008 to 2011 to look for the trends and drivers of Marcellus shale wastewater management. After analysis using internet resources and Geographic Information Systems (GIS), the authors found that there was a statewide shift towards wastewater reuse and injection disposal treatment methods and away from publicly owned treatment works (POTW) use. These wastewater management trends are likely due to new regulations and policies, media and public scrutiny, and natural gas prices. Research also shows that Marcellus shale development has influenced conventional gas wastewater practices and led to more efficient wastewater transportation. Continue reading

Methane Migration from Shale Gas Extraction Contaminates Drinking Water in Pennsylvania

by Shannon Julius

Perhaps the biggest environmental and health concern related to shale gas development is the possibility of contaminants leaking from the well shaft into nearby groundwater supplies. The first sign of such leakage would be stray methane in groundwater, as methane is a small enough molecule to move through tiny spaces and easily dissolves in water. Jackson et al. explored the possibility of stray gas contamination by testing for concentrations of methane, ethane, and propane in drinking water wells of homes in the Marcellus shale region of Pennsylvania. The researchers generally found higher amounts of dissolved gases in drinking water wells less than one kilometer from a natural gas well. Statistical analysis showed that distance from gas wells was the most significant factor for Continue reading

Impacts of Shale Gas Development on Regional Water Quality

by Shannon Julius

Drilling into shale is a difficult task, as gases are under high pressure and can easily damage the well’s integrity if drilling is done incorrectly. Such damage allows natural gases, particularly methane, to “migrate” through cement seals and into groundwater, which happens with approximately 1–3% of wells in Pennsylvania. The high toxicity of fracturing fluid raises the concern of fluid migration accompanying methane migration, and research has yet to determine the extent to which fracturing fluid can affect groundwater. However, it is highly likely that most of the unrecovered fracturing fluid is absorbed by the shale formation. The remaining fracturing fluid is recovered as Continue reading

According to Life Cycle Assessment, Shale Gas Produces Half the GHG Emissions and Consumes Half the Freshwater of Coal

The increase in shale gas production in the United States has led to an interest in the environmental impacts of this unconventional and largely unstudied source of natural gas. Ian Laurenzi and Jersey Gilbert of the ExxonMobile Research and Engineering Company present a life cycle assessment (LCA) of  both greenhouse gas (GHG) emissions and freshwater consumption of Marcellus shale gas. This assessment includes processes from drilling the gas well to power generation. Using their elaborated system boundaries, the authors found that a Marcellus shale gas life cycle releases 466 kg of carbon equivalent units per megawatt hour of power produced (kg CO2eq/MWh) and consumes 224 gallons of freshwater per megawatt hour of power produced (gal/MWh). The biggest contributor to both GHG emissions and freshwater consumption is the power plant. The results are similar to previous LCAs of conventional and shale gas and are far lower than results from LCAs of coal. Even considering factors that can increase total results, this study shows that average GHG emissions from shale gas are 53% lower and freshwater consumption is 50% lower than required for an average coal life cycle. —Shannon Julius
                  Laurenzi, Ian J., and Gilbert R. Jersey. “Life Cycle Greenhouse Gas Emissions and Freshwater Consumption of Marcellus Shale Gas.” Environmental science & technology 47.9 (2013): 4896-4903.

                  Laurenzi and Jersey use a “from well to wire” approach to study the carbon and water footprints of Marcellus gas. In this study, the shale gas life cycle is defined to include drilling, well completion, wastewater disposal, transportation of gas from well via gathering pipelines, treatment and processing, transmission, and power generation. It also includes consideration of water consumed for hydraulic fracturing and evaporative cooling at the power plant. Excluded from the study are gas distribution networks, which deliver gas for purposes other than electricity. The GHG emissions are expressed in units of CO2 equivalents based on an IPCC specification. The idea behind this unit is to make the “global warming potential” for all green house gases comparable. This study used 100-year global warming potential values of 25 kg CO2eq/kg CH4 (methane) and 298 kg CO2eq/kg N2O (nitrous oxide). The functional units for the whole study were kg CO2eq/MWh (amount of gas released per unit of power produced) and gal/MWh (gallons of water consumed per unit of power produced).  The authors used data from over 200 Marcellus shale wells in West Virginia and Pennsylvania. Their information largely came from XTO Energy, a subsidiary of ExxonMobil, and where data was not available  they used established standards from different regulatory agencies or publicly available data. Modeling of the power generation stage used a combined cycle gas turbine power plant operating at 50.2% efficiency.
                  The authors’ calculations revealed that the total life cycle GHG emissions of Marcellus shale gasses are 466 kg carbon equivalent units per MWh of power produced. The majority (almost 78%) of emissions occur at the power plant. The second most significant source of GHG emissions are the gas engines that drive the gathering system compressors, which are part of the system that transports gas from the well to a central location. Hydraulic fracturing activities are only responsible for 1.2% of the lifecycle GHG emissions. Only 1.17% of total GHG emissions are specific to Marcellus shale gas production and processing, making the difference between Marcellus shale gas and conventional gas statistically insignificant. Some other sources of emissions are: transmission compressors, transmission losses, processing plant compressors, processing losses, pneumatic devices and chemical injection pumps, and road transportation for well maintenance.
                  The total life cycle water consumption is 224 gallons of freshwater per MWh of power produced, with 93.3% of that total occurring at the power plant. Of the remaining water consumed, 91% (13.7 gal/MWh) goes towards hydraulic fracturing operations. That figure includes water used in the life cycles of gasoline or diesel used to power the fracturing process or for transportation. Water is also consumed during drilling, casing manufacture, and road transportation for well maintenance.
                  The results of this assessment are dependent on the particular boundaries chosen to represent the life cycle of shale gas. The most important parameter is the expected ultimate recovery (EUR) of natural gas from a well, since there will be more greenhouse gases released per unit of power produced if more wells are needed to yield the same amount of natural gas.  The GHG emissions associated with life stages besides drilling and completion are independent of EUR. Still, there is a strong inverse relationship between EUR and total lifecycle GHG emissions. Other important parameters are pipeline length, gas composition, water scarcity in the region, and other infrastructural elements.
                  Another factor that could greatly change the final result is the efficiency of the power plant. This assessment used an efficiency of 50.2%, which is relatively consistent with the 80% of U.S. power plants that operate within the range of 42-48% efficiency. When the authors present a separate GHG distribution using data from the less efficient, currently operating U.S. power plants, they get a distribution that  is wider with a higher average of GHG emissions. Even so, the highest possible level of Marcellus shale gas emissions from this higher life cycle distribution is lower than the lowest possible GHG emission for an average coal life cycle.
                  Despite the potential for variability of results due to the previously stated factors, the result of 466 CO2eq/MWh is consistent with other published life cycle assessments for conventional and shale gas, and almost all of the 14 studies fall within the 10%-90% range of 450-567 CO2eq/MWh. 

Stray Gases from Shale Gas Extraction Contaminate Drinking Water in Pennsylvania

by Shannon Julius
Shale gas is an unconventional source of natural gas recently made accessible by horizontal drilling and hydraulic fracturing. Shale and other unconventional sources of natural gas have caused overall U.S. production of methane to increase 30% since 2005. Despite their increasing importance, the environmental implications of producing unconventional natural gas have not yet been studied extensively. Jackson et al. explored the possibility of stray gas contamination by testing for concentrations of methane, ethane, and propane in drinking water wells near homes in the Marcellus shale region of Pennsylvania. In general, they found higher amounts of dissolved gases in sources less than one kilometer from a natural gas well. Statistical analysis showed that distance from gas wells was a more significant factor for raised levels of natural gas than other potential sources of contamination. Closer analysis into the chemistry of the samples showed that at least some of the natural gases present in drinking water wells came from a thermogenic source, which includes gas wells. The authors suggest that the stray gases could be due to wells with faulty steel casings or cement sealing.
 

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