Methane emissions by oil and natural gas extraction

Production, processing, transmission, and distribution of oil and natural gas are the second largest anthropogenic methane source globally. About 88 billion m3 are released annually. In Russia and Ukraine, in 2000 an equivalent of 69.1 and 16.4 Mio t CO2, respectively, was set free. In the U.S. oil industry by petroleum systems in 2005 methane emissions were about 28 Mio t CO2-eq. (EPA, 2007b).

In petroleum systems methane emissions are primarily associated with crude oil production, transportation, and refining operations. Methane is released as fugitive emissions, vented emissions, from operational upsets, and from fuel combustion. Production field operations account for over 97 percent, from which vented emissions are 90 percent. Most dominant are offshore oil platforms, field storage tanks, and natural gas powered pneumatic devices.

Methane losses from natural gas systems account for 15 percent of total worldwide methane emissions. Emissions vary greatly from facility to facility and are largely dependent on operation and maintenance procedures and equipment conditions. Primary contributors are normal operations, maintenance, and system upsets. In field production which is the initial stage of the natural gas system, one-third of the total emissions are released. Fugitive and the emissions from pneumatic devices are major sources. During the processing, where a pipeline quality gas is produced, further 12 percent of the emissions occur, mostly fugitive. Methane emissions from transmission and storage account for another third of the emissions. The distribution system, through which the natural gas is transported to the end user, also accounts for one-third of the emissions.

Considerable reduction is possible through upgrading of technologies or equipment and by improved management and operational procedures. Examples are low-emission regulator valves, operational procedures to reduce venting, leak detection, and more precise measurement.

An example of possible effects of such measures is an emission detection program at Cherkasytransgas, one of six Ukrainian gas system subsidiaries. After running measurement studies it was determined, that 3 Mio m3/a natural gas were leaking from only two compressor station sites. After repairing, leakage of two-thirds of this amount was prevented. The programme continues to permanently monitor and improve all compressor stations (Mandra, 2004).

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