Geological Leaks of Methane in Natural Gas Extraction

There have been many air craft flights of fugitive methane emissions over oil and gas fields in the US and several aircraft expeditions over gas fields in Canada. The US measurements of fugitive methane are summarized for 18 basins. The much fewer Canadian measurements are discussed in that context. The US measurements in the top down mode average about 10% of methane production whereas the bottom up measurements average about 2.5 % of production. This amazing difference has persisted despite the extensive field campaigns. The aircraft large methane measurements are supported by satellite measurements from the SCHIAMACHY and OCO-2 satellite instruments. These will be reviewed in this paper. The obvious answer to this conundrum is that we are missing another source term of about 7%. We propose that this source is underground geological leaks which make their way to the surface far from the wellhead, but in the same geological basin. We think that that the underground leaks are associated with coal beds above the gas beds. The geological basins without coal beds above the lower gas deposits only have leaks of 3 or 4 %. The task at hand is to identify where the large leaks are reaching the surface within the geological basins.