How can fracking wells be depleted and still leak methane?

Fracking opponents say shale gas wells are depleted really quickly, but that they'll also leak methane long after they've stopped producing. It can't be both...

 

If you've followed the debate about shale gas closely enough in recent years, you'll no doubt have heard that fracking wells suffer with a significant decline in production after the first 2-5 years, and so give up most of their gas right near the start. Fracking opponents use this to argue that a few years of production doesn't justify the risks (as they see them).

You may have seen graphs produced like this one we've mocked-up that show the really steep decline curve and then the long tail of continuously diminishing volumes of gas over a predicted 30 year lifetime.

Shale_gas_decline_curve_and_leaking_wells.png

But the very same people also like to claim that these rapidly depleted wells will leak methane into the environment years after they have been decommissioned. 

Does that sound odd to you? How can a well that's produced all its gas very quickly then go on to leak gas in the future?

When a well reaches the end of its life, it is plugged at several intervals with a mixture of mechanical and cement seals, then capped-off below ground level too in accordance with best practice. 

But by that point, there shouldn't be any gas left to leak - once it's gone, it's gone. The network of fractures that is created to allow the gas to escape gradually close-up again over time too, and so there's no longer even a pathway to the well. 

This is presumably why the UK's health, safety and environmental regulators haven't all insisted on some sort of "bond for abandonment" - along with the fact that the wells will be engineered and constructed to a very high standard so that there's no risk of a leak in any case.


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