Methane Emissions from Natural Gas Systems: A Comparative Assessment for Select Industry Segments

摘要

The recent rapid expansion of natural gas developments and utilization worldwide are bringing into focus the need to improve understanding and characterization of greenhouse gas emission sources, including methane, associated with petroleum and natural gas systems. New production technologies and practices, including those involving hydraulic fracturing, necessitate a thorough review of existing quantification methods for fugitive methane emissions from venting, flaring, and equipment leaks associated with petroleum and natural gas systems and operations. In the past few years widely divergent estimates have emerged regarding methane emissions from the U.S. natural gas industry sector. Some discrepancies noted by industry surveys have led to a thorough review of newly available information and are leading to the improvement of estimation methods and emission factors associated with activities that comprise natural gas systems. This has manifested itself in the engineering estimations that are used for compiling the national U. S. GHG Emissions Inventory and in the methods used by companies for reporting under the U.S. Environmental Protection Agency mandatory Greenhouse Gas Reporting Program. This paper will present results of a comparative analysis of GHG emissions data, including methane, for key industry segments such as on-shore natural gas production and natural gas processing and their contribution to the so called “petroleum and natural gas systems”. The data analyzed will contrast the “top-down” assessments used in developing the U.S. GHG Emissions Inventory with the “bottom-up” estimation of actual emissions as reported under Subpart W of the GHGRP. The analysis will provide a comparison of the estimation methods and evaluation of the contribution of key sources to overall methane emissions. The ultimate goal of this effort is to incorporate the new information that is becoming available into consistent methods that can be used both for national GHG inventory development and for corporate reporting. Harmonization of these methods is expected to contribute to informing the public debate on natural gas use and its role in mitigating overall GHG emissions.