The most important contribution of natural gas related to carbon emission
reduction is the substitution of gas for coal. For example, this could be very
significant in China where natural gas is desirable for replacing direct coal
combustion for industry and heating in urban areas, where it causes serious
air pollution problems.
Nevertheless, natural gas transportation is always a source of potential methane emission. There are large opportunities to reduce methane emissions from this source by promoting the more widespread use of available technologies and practices in the production, transmission, storage and distribution of natural gas (US EPA, 1993). The largest emission reductions can occur from using or reinjecting gas associated with oil production, rather than venting or flaring this gas. Flaring is preferable to venting because even an inefficient flare will convert the majority of the methane (usually more than 98 per cent) to a less harmful greenhouse gas (CO2). Around 5 per cent of world natural gas production goes to flaring and venting (80% and 20% respectively). A similar amount, 6 to 7 per cent of world production, is thought to be reinjected. Encouraging the use of natural gas and developing the infrastructure to do so can help reduce emissions from oil production. Estimates are that a 50 per cent reduction in emissions from venting and flaring is readily achievable (US EPA, 1993). Thus, technologies are readily available to reinject gas or to efficiently flare when necessary. Large oil corporations could show leadership and actively stimulate the use and dissemination of these technologies (see Section 5.4).
Other measures to reduce losses during natural gas treating and transport have been developed. For example, the Natural Gas Star Program at the US EPA has documented a variety of best practices such as (US EPA, 1997):
An important issue regarding natural gas transportation is pipeline leakage.
This is a serious problem in the Former Soviet Union (FSU), particularly in
Russia and the Ukraine, through which passes a significant share of European
gas from Russia, but these leakages can be mitigated (Strategic Development
of the Russian Gas Industry, 1998).
Another source of greenhouse gases is the CO2 that is co-produced with oil or natural gas. The CO2 is usually removed by amine scrubbing. Rather than release the CO2 to the atmosphere, CO2 can be reinjected. Excess CO2, extracted from natural gas, is being injected into a shallow underground aquifer in the Sleipner Field in offshore Norway (Baklid and Korbol, 1996; US DOE, 1997). In this development, 1 TgC per year are being re-injected.
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