Permeability estimates from microseismic data

Those who've followed this blog for a while will know that my attitude to open access publishing is luke-warm at best. However, today I can claim that I'm doing my bit for OA, because a colleague has had a paper published in the 'International Scholarly Research Network' Geophysics Journal. Which means you can read it free of charge here.

Personally, I would have preferred to submit to a more established journal. ISRN Geophysics has published a total of 9 papers ever in its history. Geophysics (published by the SEG) has published about 30 papers a month since 1936. I doubt this paper will ever win me any points in a REF submission. However, it'll be interesting to see whether the fact that it is open access leads to a higher number of citations down the line.

What I will say is that I was very impressed by the speed at which Hindawi Publishing turned the article around. I have an article still awaiting publishing in Geophysical Prospecting that has taken more than a year and is still not yet available. This article was submitted in mid December, and is now available online with DOI number by mid-February, which is frankly pretty damn good.

Anyway, since it is openly available to you, I thought I might try to explain what we have done in the paper. So here goes:

One of the crucial things that reservoir engineers always want to find out about a reservoir is the permeability, because this controls how fast the gas and/or oil will flow to the well. There are a number of ways permeability can be estimated, but my colleague Doug Angus at Leeds University has been coming up with a way to estimate it using microseismic events.

During hydraulic fracturing (fracking), microseismic events are triggered by the pulse of fluid pressure moving out from the wellbore. Much as the speed of the gas going into the well during production will be controlled by permeability, so the speed of the pressure pulse moving away from the wellbore during fracking will be controlled by permeability. So by tracking the distance of the microseismic events from the well through time, we can estimate the permeability.

Much of the work on this has been done by Serge Shapiro of Freie Universitat Berlin. The Shapiro method assumes that microseismic events are triggered by small pore pressure perturbations, and solves the diffusion equation to determine how quickly events should move out from the injection well. However, what this doesn't take into account is the deformation of the rock itself. The increases in pressure will be causing poro-elastic deformation as well. An alternative model developed by Alexander Rozhko of Schlumberger incorporates the triggering of microseismic events through stress changes produced by poro-elastic deformation.

In this paper, Doug compares the two models, using them to predict the microseismicity induced during a multistage fracking operation, where in one stage water was used as the fluid, and in the other CO2 was used. Despite the different fluid properties, both methods should in theory recover the same permeabilities.

The following figures show how the two different models fit the data (first the Shapiro diffusion model, then the Rozhko poroelastic model):
Note that while both models fit the data reasonably well, both make very different predictions for what would happen to the microseismicity though time had the injection continued. With the diffusion model, event-injection point distance keeps increasing, with the poro-elastic model it becomes capped.

The permeability estimates for both models are broadly consistent - approximately 50-100 milliDarcies (no, not a small Colin Firth). However, the estimates from the poro-elastic method are more consistent and more stable. Therefore, based on this dataset at least, this method is Doug's preferred choice for permeability estimation using microseismic event locations.

So there you are - my first OA paper, and an attempt to explain it in layman's terms. I hope you made it to the end.

Geologists and shelf stackers

Apart from the coal, the oil, the gas, the plastics, the minerals, the water, the understanding of natural hazards, the evidence for evolution, what have geologists ever done for us?

The geo-twitter-sphere has exploded in the last couple of days with irate geologists. You'd have thought that it would take a lot to upset such a group of usually 'rock-solid' people, but Iain Duncan Smith's comments that shelf-stacking is just as important as geology, has clearly upset a lot of geologists.

I think we all know how important geology is to the way the world works - that's why a geology degree can be a really useful thing. (In case you're not sure, check out the GeolSoc twitter feed for the many comments explaining exactly why geology is important for putting food on the shelves).

But I think we all might be over-reacting just a little bit to IDS's comments. My twitter stream has been full of little else in the last two days. The Geol Soc has even felt compelled to do a press release on the matter, now reported on by the Mail, Independent and Guardian among others.

I don't think IDS was really trying to belittle the importance of geologists, and I hope most of us are smart enough to realise this. Clearly he was trying to suggest that we should not be so disdainful of low-paying, so called 'menial' jobs, and the people that do them. Moreover, that taking any job is better than being unemployed.

We could be talking about the bigger issues relating to this incident - is it right that we expect benefits claimants to take on work experience when/where available? If so, can we structure it so that it is a little smarter? For instance: it might be best for someone who sits on the sofa doing nothing all day to be compelled to work in a supermarket. However, for someone already volunteering in a museum, shelf stacking might not be the best use of their time.

Finally, is it right that a private company (Poundland) gets to benefit from essentially free labour? Surely Poundland should at the very least be paying their benefits (or even paying them a proper salary) for the duration that they work there?

Instead, we're all upset about IDS apparently showing disrespect to geology, with the overdone, slightly-fake-seeming howls of outrage (like a footballer going down for a cheap free-kick), to the point that our principal learned society has felt the need to put out a press release on the issue. I think we as a community look more than a little silly and oversensitive.

When 7 of the world's top 10 companies by revenue are oil and gas companies (so have geology at the core of their business), I think we can afford to be a little more mature, and a little less quick to take offence if someone inadvertently implies that we're not that important.

Update (17:00, 20.02.2012): There's another piece in the Guardian on the IDS comments issue. It raises the salient point that it is important that we as geologists remind the world of our relevance from time to time, that much of the public have little idea about what we do. Perhaps the majority assume that all we do is fossils and volcanoes? If that's true, who's fault is that? Whenever I see geology outreach being done, it's either about volcanoes or it's about fossils (or, to be really exciting, both at the same time).

If we as geologists have an image problem (and I'm really not sure that we do), the outreach we do should highlight the role of geology in supplying the raw materials needed for this modern life of ours. Rather than waiting for the next ministerial slip-up to advertise our subject....

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.

New BGS shale gas estimates leaked: and there's a lot of it!

Breaking news from the Times this weekend. I should add as a caveat that I have no idea how they got hold of the figures, as they haven't been officially released by the BGS yet. However, several sources seem to have confirmed the numbers.

The UK is sitting on 1,300 - 1,700 TCF (trillion cubic feet) of shale gas. For those who don't know how much a TCF is, a useful comparison is the since we started producing gas from the North Sea, we have produced 83TCF, while the Norwegians have produced 57TCF. So 1,300TCF is A LOT.

At this point it is necessary to point out that this figure is the resource. Only a portion of this will be economically extractable - say 10% as a ball-park figure. But even 10% of 1,300 TCF is 130TCF, which is approximately the amount extracted from the North Sea over the last 40 years.

The main article is hidden behind the Times paywall, and I have no desire to put any more money into Mr Murdoch's pocket. However, I've picked up a little more of the article via the No Hot Air website:

Britain could have enough shale gas to heat every home for 1,500 years, according to new estimates that suggest reserves are 200 times greater than experts previously believed. The British Geological Survey is understood to have increased dramatically its official estimate of the amount of shale gas to between 1,300 trillion and 1,700 trillion cubic feet, dwarfing its previous estimate of 5.3 trillion cubic feet.

According to industry sources, the revised estimates will be published by the Government next month, fueling hopes that new “fracking” techniques to capture trapped resources will result in cheaper energy bills.

It is thought that it will be technically possible to recover up to a fifth of this gas, making Britain’s shale rocks potentially as bountiful as those in the US. Experts stressed that it was still much too early to say how much of the gas it would be economic to get out of the ground to heat homes and help to generate electricity.

However, in the interests of balance, I must take the Times to task for their headline. Claiming that we have enough gas for 1,500 years is inaccurate, as only a small amount of the BGS resource estimate will be extractable. Moreover, if we are still relying on gas as the dominant fuel in 1,500 years time then  I would be extremely surprised!

As for the influence of this find on domestic gas bills, I think that is still anyone's guess. Increasing supply will reduce prices - that much is basic economics. But it may not reduce them by much, unless other countries also develop shale gas, as demand is also likely to be high. But it's worth bearing in mind that if global gas prices do remain high, then we as a country can make lots of money producing and selling the gas, while if they drop, we as consumers benefit from cheaper energy. Regardless of what gas prices do, a find this large is a win-win situation. The question now is whether the BGS will confirm these numbers?

Between a rock and a hard place: Welcome to the blogosphere

Just a short note to welcome a new Bristol Earth Sciences blog to the blogosphere. Between a Rock and A Hard Place is being written by some of our Earth Science PhD students.

I look forward to seeing what you produce while avoiding writing up your theses. A blog as the ultimate procrastination tool is a fabulous idea. Marvellous. Good luck.

Artists tour of shale gas in Pennsylvania

In order to draw attention to the danger of fracking, Josh Fox took the Artists Against Fracking on a tour of the Pennsylvania shale gas fields. Here's the video:


Seems innocuous enough. But this little tour has been all over the web garnering controversy, so I guess I might as well jump on the bandwagon. The tour was lead by Vera Scroggins, a local anti-gas activist. Here's what she had to say to Phelim McAleer, the director of FrackNation, when he turned up to try to interview some of the celebs:



Fairly shockingly xenophobic! Funnily enough, this doesn't make it into Josh Fox's AAF video.

Anyway, the main part of the visit was to the Mannings in Franklin Forks, which presents another interesting fracking story, fairly representative of how much things have deteriorated in these parts. I think, whether you are pro or anti, you'd have to agree that the debate surrounding it is now a big murky mess, and any semblance of trust has evaporated on both sides.

The Manning's water well began behaving strangely, with high levels of methane, and bursting from the top, as you can see in this video. Gas drilling has occurred nearby (note that the video has been posted by Ms Scroggins, her of the Irish-drunks tirade above):

Of course, WPX, the gas drilling company disputes that they are the cause of contamination. They argue that shallow natural gas accumulations are common in the area - indeed records of shallow gas seeps are found as far back as 1921, and water quality in the area is reportedly poor anyway.

WPX also claim that the strange bursting behaviour of the well is not due to the gas but due to a mechanical fault in a pump. There's video been posted video of WPX employees demonstrating the problem and attempting to fix it:

What's interesting is that there was more than one video camera at this little shindig. Vera Scroggins was there to stir the pot a bit:

The upshot now is that the lawyers are involved, and WPX employees are no longer allowed on the property.

The first thing that strikes me about these videos is that everyone has now resorted to shoving cameras in each other's faces. Everyone filming everyone else. A complete lack of trust all round.

Isotopic testing of the gas appears to suggest that the gas has a shallow origin (i.e., is not from the shale formations). However, the only results published are from WPX testing, everyone is still waiting on DEP results.

All in all, I think this shows what a mess the situation appears to have become. Communities are tearing themselves apart over this, and that's due in equal measure to the activities of both the pro- and anti- sides.

Determining water that is often naturally bad from water contaminated by fracking (and many, if not most, oil and gas fields have naturally occurring shallow accumulations) is not an easy problem. And it's a situation that is wide-open to manipulation and distortion from both sides. Plus, America being full of lawyers, things get even more complicated, to the point where everyone now seems to be videoing everyone else.

Certainly, the classic tale of little local people defending themselves from nasty big corporations is not really applicable, despite how attractive that story may be to the big Hollywood names on a day-trip from NYC. I don't think the AAF video even touches the complexity of the situation.