BGS shale gas estimates: an update, and other London meetings

I've just got back to Bristol from a very interesting few days in London, first at an AAPG conference on induced seismicity, followed by a BGA conference on geophysics and new energy challenges.

The first item of note was a talk given by Mike Stephenson of the BGS on UK shale gas. He didn't mention any numbers from the upcoming BGS resource estimate, so I took the trouble of asking him for a comment on the numbers published by the Times last weekend. In his words: 'they've simply made those numbers up'.

Fair enough, I guess that'll teach the likes of me to go jumping on every number you see in the press. Of course, he'd have to say that, as it would be embarrassing for the BGS to have had a leak, but either way hopefully the BGS will get around to giving us some figures in the very near future (it was originally supposed to be released in January, and we're still waiting).

I also got to have a good long chat with Huw Clarke, who is Cuadrilla's chief microseismic guy. One thing that noone has really talked about much is the flow rates from Cuadrilla's fracked well.

We've all talked plenty about the earthquake they produced, but we've all forgotten that they successfully completed 6 stages of fracking, and have tested the flow rates they got back after the frack. Whether or not the flow rates are sufficient to be economical will be a key part of whether shale gas extraction will happen in the UK.

Of course, Cuadrilla's flow rates are highly highly highly commercially sensitive, and there's no way Cuadrilla are going to tell anyone what they are. But it's interesting to note that, after having measured the flow rates, Cuadrilla have been happy to pay for a 3D seismic survey, the installation of a dense array of permanent geophone sensors, and a whole heap of PR on the side (as well as leaving the drilling rig parked in Lancashire when it could be drilling holes anywhere in Europe).

These aren't the kind of things you'd do if you have concerns about the economic viability of the gas flow rates from the shale formation, which of course implies that Cuadrilla probably think they're sitting on some pretty significant resources.


Other things that came up in these conferences? One of the major themes can be summarised as 'Induced seismicity, friend or foe', or 'Induced seismicity, the good, the bad and the ugly'. Of course, if you've met many geophysicists, you'll know what the 'ugly' is describing.

Whenever you inject fluids into, or take fluids out of, a reservoir, you change the stress state. This will almost inevitably induce earthquakes. The majority of these are so small (M-3 to M-1) that they can only be detected with sensitive seismometers placed right next to the target of interest. We geophysicists locate the microearthquakes, using them to learn about the stress state and fractures in the reservoir, enabling operators to improve the safety and economic viability of their operations. This is the good, or friend, part of induced seismicity.

However, every so often, as at Blackpool, operations create a larger event, which can be felt by the public. This tends to cause a lot of alarm, and the operators start to feel the regulators breathing down their neck. This is induced seismicity the bad, or the foe.

The big problem is that we're still not really very good at predicting when we'll just get small events, and when we'll get larger ones. Clearly the presence of a pre-existing fault is needed for a larger event. But many operations occur right next to faults without triggering any seismicity.

So it seems we still don't know why 99% of our activities don't trigger felt seismicity, but some do. There are probably about 150,000 waste-water injection wells in the US, and only about 10-20 have induced felt seismicity. There have been hundreds of thousands of fracking stages completed in the US, yet only one in Oklahoma, one in Blackpool, and a few in British Columbia, have triggered felt earthquakes.

So this was probably one of the key aspects emerging from these two meetings: the need to develop improved geomechanical modelling of reservoir activities (whether it be fracking, carbon dioxide injection for CCS, or waste-water injection), so we can predict whether we're likely to trigger a larger earthquake on a fault. So if you are a budding geoscientist or engineer deciding what direction to pursue, I'd recommend looking in to this, because improvements in this area will be really significant for a lot of industries.