Life cycle assessments of shale gas activities differ in their findings. Among the various studies, researchers estimate different greenhouse gas emissions, rates of water use, and rates of wastewater production.
Some of the variation in findings is due to the parameters of each study, particularly the life cycle boundary. The life cycle boundary determines which life cycle stages—and which processes attributable to those stages—are included in the assessment. For example, a life cycle boundary for shale gas often includes stages for exploration, drilling, fracturing, well production, processing, and combustion. Attributable processes further define the activities in those stages. However, some assessments omit stages—such as exploration, processing, or combustion—or do not delineate between stages and processes at all. The variations make it difficult to compare assessments and begin a constructive dialogue on strategies that reduce impacts.
This working paper proposes a life cycle boundary for shale gas spanning exploration to well closure/site remediation and from natural gas production to use. It follows the boundary setting guidance given in the Greenhouse Gas Protocol Product Life Cycle Accounting and Reporting Standard, which builds and expands on the ISO 14044 standard for life cycle assessment. In addition, WRI compares its life cycle boundary to those in 16 assessments of the environmental impacts of shale gas production. The findings illustrate significant variations in the scope of such studies, which complicate shale gas discussions. WRI will seek feedback on its life cycle boundary and apply it in a forthcoming working paper that summarizes the findings of previous assessments on the greenhouse gas emissions of shale gas production; estimates the implications on emissions from the Environmental Protection Agency’s revised Greenhouse Gas Reporting Rule; and highlights the potential for additional methane abatement from natural gas systems in the United States.