Oil production releases more methane than previously thought

A new study from the IIASA Air Quality and Greenhouse Gases Program, which for the first time takes into account different production management systems and geological conditions around the world, shows that global methane and ethane emissions from oil production between 1980 and 2012 were far higher than previously thought.

Methane is a potent greenhouse gas, which scientists rank as the second-most important contributor to climate change after CO₂. Yet, while methane concentrations in the atmosphere can be easily measured, it is difficult to determine the contribution of different sources, whether human or natural. This information is necessary for reducing emissions.

The layer of gas that is present above the oil in an oil reservoir, has a methane content of 50 to 85%. When the oil is pumped to the surface, this gas also escapes. In oil production facilities in North America, almost all of this gas is recovered and the portion that is not is mostly flared to prevent leakage and potential explosions, while a very small fraction is simply vented. In other parts of the world where recovery rates are lower, much larger quantities of this gas are released into the atmosphere.

Previous global bottom-up emission inventories of methane used rather simplistic approaches for estimating methane from oil production, merely taking the few direct measurements that exist from North American oil fields and scaling them with oil production worldwide. This approach however, leaves considerable room for error, which prompted an IIASA researcher to develop a new method that could better account for the many variations in oil production around the world.

In a paper on this work that was published in the journal Environmental Research Letters [1], global methane emissions from oil and gas systems in over 100 countries were estimated over a 32-year period. A variety of country-specific data was used, ranging from reported volumes of associated gas to satellite imagery that can show flaring, as well as atmospheric measurements of ethane, a gas which is released along with methane and easier to link more directly to oil and gas activities.

Graph showing the sources of methane from oil production since 1980.

The study found that, especially in the 1980s, global methane emissions were as much as double the amount previously estimated. The results also show that the Russian oil industry contributes a large amount to global methane emissions. A decline in the Russian oil industry in the 1990s contributed to a global decline in methane emissions, which continued until the early 2000’s. At the same time, methane recovery systems were becoming more common and helping to reduce emissions. Yet, since 2005, emissions from oil and gas systems have remained fairly constant, which according to the research, is likely linked to increasing shale gas production that largely offsets emission reductions from increased gas recovery.

The study points out that these estimates are only as good as the data allow and that there is still uncertainty in the numbers. To improve the data, a close collaboration between the scientific measurement community and the oil and gas industry would be needed to make more direct measurements available from different parts of the world.