Shale gas and Cash-for-Locals?

This week the Parliamentary Select Committee for Energy and Climate Change released its assessment of 'The Impact of Shale Gas on Energy Markets'.

I particularly enjoyed conclusion 5:

One key to community acceptance will be a robust factual response by government to scare stories

I wonder who/what they could be referring to there....

More interesting, in my view at least, is conclusion 6:

Communities who are affected by shale gas development should expect to receive, and share in, some of the benefits of the development

or, as the Guardian would put it: Fracking firms should offer sweeteners to locals. It's an interesting idea, but I'm still torn between whether it is a good one or not.

In the US, mineral rights are generally owned by the person that owns the land. This means that if your farm sits on top of some shale gas, you stand to benefit directly from royalties from the gas development (try sticking the default numbers into this calculation engine). As a result, shale gas is generally wildly popular among rural American communities.

However, in the UK, in most cases the mineral rights being to the Crown Estate (i.e. 'er maj, gawd bless 'er), meaning that royalties from gas production goes straight to central government, rather than via local people.

Of course, that's not to say that shale gas development will not benefit a local community. While many of the jobs involved are high tech, and as such cannot be easily accessed by local people, there are plenty of roles for relatively unskilled workers, particularly in construction and haulage. Moreover, however the influx of skilled workers need places to stay, to eat and to drink, to do their laundry. They need to buy petrol, buy stuff from convenience stores, the list goes on. In Pennsylvania you hear of companies block-booking whole hotels for 6 month stretches to house the workers, restaurants full to bursting every lunchtime and bars full in the evenings.

However, UK public opinion continues to waver in regards to shale gas development. So, is it right to consider setting up community benefit schemes, whereby some of the profits from gas development are injected directly back into the local community? Or is this all a bribe to get people to accept something that they'd otherwise not be comfortable with?

In all honesty, I'm not sure I know the answer to this. On the one hand, shale gas development will involve some local disruption. Not the scare stories of exploding taps, blighted aquifers and general geological disruption - the so-called 'geological dread factor' - but increases in traffic, construction sites, laying new pipeline etc. Therefore it does seem reasonable that a community should receive some recompense for that. On the other hand, offering what could easily look like little more than a bung could make it look like shale gas has something to hide, when so long as the government ensures that there is 'a robust factual response by government to scare stories' it shouldn't have to.

It is worth noting at this juncture that such schemes seem to be common for wind farms (see here and here for two randomly selected examples) and nuclear power stations. I have enjoyed seeing how the language changes depending on your preferred form of energy, particularly wind farm proponents who have touted these community wind farm benefits as a great example of how wind can benefit a community, while if shale gas companies suggest the same thing then it is little more than a bribe.

So I'm still not sure whether this is a good idea or not. Regardless, in the meantime, IGas have drilled two exploration wells in Lancashire.







  

Bristol's shake table

Shake tables are used to simulate the effects of earthquakes on structures. Engineers use them to simulate the effects of earthquakes on structures, so that they can design buildings to withstand shaking.

You can program in the earthquake of your choice, put your structure on the table, and see how well it does. Today I got to visit the Bristol Engineering Dept shake table. Here's some video:

The Maximum Magnitude Conundrum

I talked in my last post about seismicity (i.e. earthquakes) induced by subsurface fluid injection. In fact, there are many human activities that have the potential to cause earthquakes, including:

• mining
• waste fluid injection
• carbon capture and storage
• fracking
• nuclear waste storage (potentially at least)
• reservoir impoundment (for hydro-electricity and/or pumped storage)
• geothermal energy
• conventional hydrocarbon production

So it seems that whether you are a climate-change denier who just wants to keep on mining coal and burning oil and gas, an advocate of tech-based solutions like CCS and nuclear, or a total greenie who sees our future energy needs met by geothermal energy, hydro-electricity, and other renewables that require efficient energy storage mechanisms (i.e. lots of pumped storage reservoirs), it seems that your preferred energy source comes with a risk of generating earthquakes.

Which in turn begs a really important question - for a given operation, what (if anything) will determine the maximum possible earthquake magnitude that your activity will produce? This is a really important question both for human activities, as well as seismologists who work on natural seismicity: what is the largest earthquake possible in a given setting?

Before I get into this, a word on earthquake magnitudes (skip this if you already know about magnitudes). Most people are familiar with the Richter magnitude scale running from 0 (i.e. very very small, basically undetectable) to about 9 for the biggest quakes we've ever had. Most people are also aware that it is a logarithmic scale, meaning that an M2 event is 10 times as large as an M1 event, not twice the size. In fact, the Richter scale, which was essentially an arbitrary scaling function, has largely been supplanted by the Moment Magnitude scale, which relates more directly to earthquake physical processes. More specifically, Moment Magnitude is calculated from the seismic moment (Mo), according to:

                       Magnitude = (2/3) log(Mo) - 16.1,

This equation was deliberately scaled so that it followed the Richter scale, so that seismologists (and the public) could still understand magnitudes in the same way. In turn, the seismic moment is defined by the size of the rupture during the earthquake, according to:

                       Mo = G A D,

where G is the shear modulus of the rock, A is the cross-sectional area of the earthquake rupture, and D is the average dislacement that one side of the fault moves relative to the other. So you can see that, if there is no limit to the size of a fault (which controls the rupture area), there is no limit to the maximum magnitude that an earthquake can be. In reality, however, the the thickness of the earth's crust probably imposes an upper limit on the size that an earthquake can be, which is why even the largest earthquakes (on Earth at least - who knows, a planet with a thicker crust could probably have larger earthquakes) don't ever seem to get much bigger than M9.

Now, back to human activities triggering earthquakes. It's unlikely that any of the activities listed above could trigger a crustal-scale fault capable of triggering an M9 earthquake. So what controls the maximum magnitude that could be triggered by mankind's operations? In my last plot I showed the graph used by Art McGarr to explain induced seismicity in the USA and around the world:

BUK is the famous fracking-induced Blackpool earthquake. RMA is the Rocky Mountain Arsenal. YOH is Youngstown Ohio. PBN is Paradox Basin, Colorado. GAK is Guy, Arkansas. BAS is Basel, Switzerland. GAR is Garvin County, Oklahoma. STZ is Soultz, France. RAT is the Raton Basin, Colorado.

McGarr adapted the long established McGarr equation, which originally stated that the total seismic moment released is proportional to the volume of rock extracted during mining (multiplied by G):

            TotalMoment = G x VolRockMined.

This equation was soon adapted to cover seismicity induced by fluid removal and/or injection, with VolRockMined being replaced by dV: the volume of fluid injected. The physical basis for doing so has always been slightly dubious, but empirically it seems to do a reasonable job. After the recent induced seismicity incidences, the McGarr equation has been modified again: now G dV gives not the total seismic moment released, but the magnitude of the largest event alone. This modification should only be strictly true in situations where the single largest event completely dominates the total seismic moment released. So we end up with the modified McGarr equation for injection-induced seismicity:

          MaxMo = G dV.

This is the equation plotted in the above figure, and you can see that it does a good job of fitting the data. But the key thing to note with the McGarr equation is that it is empirical, it does not have any real physical basis - i.e. it is something that is observed, but it doesn't really explain WHY the maximum magnitude should be controlled by the volume of fluid injected (instead of, say, the rate of injection or the change in pore fluid pressure).

A new model for Mmax has been developed by Serge Shapiro of the Freie University, Berlin, which I find very interesting. The Shapiro model suggests that Mmax should be controlled by the size of the fluid-affected zone.

A large earthquake can't just happen anywhere - a pre-existing fault plane must be present on which the quake happens. As an approximate scaling, the maximum earthquake magnitude created by a circular shaped fault with radius r can be approximated as:

          Mmax = 2 log(2r).

So an M3 quake needs a fault of radius 15m, and an M6 quake needs a fault of radius 500m. So, could the size of the area stimulated by fluid injection control the size of the earthquake? Lets consider fluid injection into a completely homogeneous porous rock. The fluid-saturated zone will spread as a sphere (assuming it has similar density to the in situ fluid). The radius of this sphere can be easily calculated from the volume injected. Shapiro argues that the size of the largest fault that can be triggered must scale with the radius of the injected fluid volume.

If a fault is significantly larger than the radius of the injection zone, only a small portion of this will be influenced by it, and this will not be sufficient to trigger rupture. Failure will only occur on faults where the majority of the fault is influenced by injection. As a result, we have a reason to scale Mmax with injection volume. Do the maths and you end up with:
         
           RADIUS = (3/4)*VOLUME^(1/3)

so
           Mmax = 2 log((3/4)*VOLUME^(1/3)).

In the plot below, the green circles show Mmax for the McGarr data, which I have calculated using the Shapiro model. You can see that, much like the McGarr model, they fit pretty well. So do we now have a better model to explain Mmax?

Unfortunately, I don't think we do. When you look in more detail at the induced events, you can see that some of the key assumptions of the Shapiro model are not met. The Shapiro model requires that events occur within the immediate radius of the injection zone. The figures below show induced seismic events from Arkansas, Oklahoma and Colorado, with the injection wells marked.

A common theme is that the majority of events occur well below the injection point. Perhaps some of the initial seismicity is triggered in the injection interval, but the majority of the triggered faults lie outside the zone that is directly influenced by injection. The Shapiro model explicitly assumes that the triggered faults lie almost completely within the injection-influenced interval. I think that the Shapiro model is a great attempt to simplify a difficult problem, but to me it seems that more complicated effects involving stress transfer through many layers of rock are acting, and need to be taken into account, to understand the triggering of these faults.

This takes us back to the title of this post: predicting Mmax is still a conundrum. The McGarr model seems to fit the data, but it is only empirical, there is no real physics behind it. The Shapiro model also fits the data well, and has a physical mechanism of control. However, the suggested controlling mechanism doesn't stack up when the events are studied in more detail.

A physically realistic, empirically verified model to predict Mmax still eludes us. We are usually able to  explain post hoc why a particular operation triggered an event. However, we are still not very good at predicting in advance whether a project will induce larger seismic events. If you can come up with a better method, then do get in touch, because a solution will be extremely valuable in a range of industries as discussed above.

In the meantime, we are left with the empirical McGarr equation as our main guide. It should of course be remembered that the McGarr equation does not tell you the maximum magnitude you will get in an operation. The maximum magnitude produced during most operations fall well below the McGarr line. The McGarr line tells you the maximum magnitude you could get if you are very unlucky.

Induced Earthquakes in the USA, and some implications for CCS

Here's a recent BBC report on earthquakes induced by oil and gas activities in the USA. As can be expected, the twitter/blogo-sphere has been lighting up over this in the last few days. For me the biggest surprise is that this has only come up in the wider media in last few days: induced earthquakes have been a key topic of discussion among geophysicists for a couple of years now. The USGS has noted an increase in medium-sized earthquakes in the last decade:

The black line shows the total number of earthquakes in the midcontinent USA (excluding the very active San Andreas fault and other active parts on the west coast) greater than M3 since 1970: you can see the increases as the line gets steeper.

The oil industry likes to dispose of waste-water by injecting it into deep-lying saline aquifers. However, it has been well known since the Rocky Mountain Arsenal in the 1960s that deep fluid injection can trigger earthquakes. It is argued that the increase in oil industry injection activities in the last decade has been the cause of the increase in the numbers of earthquakes.

This remains under debate - could the increase be simply that, as more (and better) seismic monitoring networks are installed, we are detecting more earthquakes than we did in the past. The latest news story is a case in point. The paper in Geology attributes an M5.7 earthquake in Oklahoma to injection of waste-water. The Oklahoma Geological Survey has subsequently released a rebuttal stating that as far as it is concerned, there is not enough evidence to tie the quake to injection activities (strangely enough, the OGS rebuttal hasn't been given much of a look-in from the media).

Nevertheless, I think that it inarguable that, in certain cases at least, fluid injection has triggered earthquakes with magnitudes from about M3 to M6.

This brings me to a couple of asides. Firstly, following on from my last post about bad media reporting of these issues, many reports attributed the quake to injection of waste-water from fracking. This is not the case - the waste water in this case came from conventional oil production. This harks back to an older post I made about the relative risk profiles from fracking in comparison to conventional oil and gas. The need to dispose of large quantities of contaminated waste water is not a new, fracking-related problem in the oil industry. If you are opposed to fracking, you must presumably be opposed to all oil and gas related activity.

Secondly, M5.7 is a large earthquake. It is about 100,000 times larger than the quake induced in Blackpool by fracking. It is larger than any earthquake ever recorded in the UK. Perhaps only a few historical earthquakes in the UK have been of a similar size. An M5.7 triggered earthquake here would be serious news.

So, can we get an estimate of what earthquake magnitude might be triggered by our various activities? Art McGarr, a venerable (and venerated) and highly experienced geophysicist with the USGS has made an effort to do this. McGarr cut his teeth in the 1970s looking at mining induced seismicity, where he noticed a correlation between the total energy released during rock extraction and the volume of rock extracted. He developed the so-called McGarr equation:

Sum(Moment) = G dV

The sum of the released seismic moment equals the volume change (dV) multiplied by the shear modulus (G). It should be noted that this equation is based on empirical observation only. It has subsequently been applied to fluid injection (or mis-applied, some would say, as there is no obvious basis for arguing that physical processes during fluid injection should match those during rock removal (mining)), where dV becomes the volume of fluid injected.

More recently, McGarr has been looking at earthquakes attributed to fluid injection. This includes waste-water injection as discussed above, as well as geothermal activities and, of course, fracking. He has developed the following plot:

Each + represents an injection-induced seismic event. Unfortunately for any non-geophysicist readers, McGarr has given the earthquake sizes in moment, rather than magnitude, but 10^12 is about M2, 10^15 is about M4, 10^18 is M6. I've not found out what all of McGarr's abbreviations are, but

• BUK is the Blackpool earthquake
• RMA is the quake induced by fluid disposal at the Rocky Mountain Arsenal
• BAS is the Basel (Switzerland) earthquake caused by geothermal activity
• STZ is an earthquake caused by geothermal activity at Soultz, France
• RAT (several of them) are earthquakes in the Raton Basin (Colorado) associated with waste water injection
• POK is the Oklahoma earthquake discussed in this blog

You can see a general correlation between the maximum magnitude and the injection volume, following a McGarr-esque equation, replacing the sum of the moment by a maximum magnitude: Mmax = GdV. It should be remembered that this line appears to be describing the MAXIMUM POSSIBLE magnitude. There are over 150,000 waste-water injection wells in the USA, only a tiny fraction of them have caused detectable earthquakes.

So how does this apply to the UK? The first thing to note is that deep injection of waste fluids is not allowed in this country, so we can strike this risk off immediately. What about fracking? A typical frack stimulation uses about 1000 - 5000 metres cubed of water - that's ~10^3. This leaves us with a maximum induce-able moment of ~10^13 (or a magnitude of about M3). We get 30 or so M3 events in the UK every year, so inducing a few more due to fracking isn't going to make much difference.

What about CCS? Carbon capture and storage is a key plank in the UK's CO2 emissions reductions plan. All well and good, but CCS involves the injection of very large volumes of fluid into subsurface aquifers. Could this trigger earthquakes?

I've modified McGarr's plot to add the injection volumes of Sleipner and In Salah, two of the foremost CCS projects currently in operation (as well as changing the scale from moment to magnitude to make life a little easier for non-geophysicists):

You can see that, following the McGarr plot, Sleipner and In Salah have the potential to trigger earthquakes of M5 or larger! Of course, they haven't: Sleipner has barely done anything, while In Salah has triggered at most an M1 event (so small you can't feel it without the aid of sensitive seismometers). The McGarr plot tells you the maximum possible magnitude, not what magnitude you will get. Hence why I have shaded in the area under the line: you could get an event on the line, or anywhere under the line.

Still, I find the potential for induced earthquakes from CCS to be worrying. I think this has been under-appreciated by the UK CCS community. There is a clear need for further study on why most injection sites do not produce seismicity, but a few do? What is it that is different about these sites, and how can we identify this in advance, and only select sites that won't trigger events during CO2 injection. At the same time, we can quickly see that the earthquake risk from fracking has been hugely overplayed in comparison to the risks posed by other activites (geothermal, CCS, waste-water injection, mining, and even hydroelectric energy).

My visit to Glastonbury: Part II - The reaction

I discussed in my previous post my visit to the councillors of Glastonbury to talk to them about unconventional gas extraction, and the potential impact it could have on the area. In that post I gave a summary of what I said in my talk. In this post, I'd like to talk about the reaction.

It should be noted that I didn't go there with the intention of changing anyone's mind. Given that the council had already voted to ban fracking, I hardly thought a 45 minute presentation by a gravitas-lacking 29 year old (even if he does have a good number of letters after his name) would be enough to change their minds (I was more worried about getting out of there without being tarred-and-feathered to be honest).

However, the councilman who had asked me to come give the talk sent me a very kind email afterwards, saying he saw the evening as a total success, at that some members 'had come to confessions and said the presentation had changed their minds'. I wasn't aware that councillors had 'confessions', but I'm very glad that I appear to have had some small effect at least.

Furthermore, there was a reporter from the local paper in attendance, who placed a story on my talk in the Somerset Gazette, which has granted me my first experience of being completely misrepresented by the media (I guess we all get to experience this eventually.

It ran under the headline: 'Expert warns fracking leaks are the result of cutting corners'. Which is true. What is completely missing is the context - the fact that leaks from fracking are not inevitable side effects of the process, but that they can be prevented by a stronger regulatory regime. Also, missing is the context that the majority of companies are not cutting corners, which is why the percentage rate of leakage instances remains very very low.

In my view (perhaps unfairly, I'd love to hear your comments), you could be mistaken for thinking that I am opposed to fracking, based on that article. For instance, the line:

I am here to tell you how the process works and the effects that science has shown that it has on the people nearby and the surrounding areas,

placed without context, suggests that I am saying that science has shown lots of impacts. In fact, in my talk I went on to point out, for example with the Texas and Pennsylvania air quality surveys, that scientific evidence for negative impacts of fracking on water and/or air quality have been remarkably hard to come by, bar a small number of documented surface spill and well integrity cases.  

The final and most important item left out in the story is that I summarised my talk by stating that, while it is not my decision to take, I believe that unconventional gas extraction can be done safely in the South West, and that it will have a beneficial impact on the area. It would have been nice if that could have been reported as well.

 

My visit to Glastonbury

Last week I had the pleasure of visiting Glastonbury, a small town in Somerset best known for its tor and its music festival. Glastonbury Town Council has preemptively declared itself to be 'frack-free'. Much like Frome's similar decision last year, this is more a symbolic gesture, because (a) it's not clear that there is any unconventional gas to be had from around Glastonbury, and (b) if there were, it is unlikely to be developed for many years.

The decision was not a unanimous one. Some councillors felt that the decision had been rushed, having heard only of the negative sides from Frack Free Somerset. Jim Barron, one of the dissenting councilmen, pleaded in the local paper for a more evidence based discussion before any decisions be taken.

As a result, I was asked to come down to Glastonbury one evening after work to give a presentation to the council. You can download the presentation that I ended up giving from here. You might as well read it in full, but here's a potted summary.

I began by explaining what shale gas is, why it is different to conventional gas, and why hydraulic fracturing is necessary. I followed this by explaining the process, including a time-lapse video of a well being drilled and fracked, and an animation showing how microseismic events are used to image where the stimulated fracture is going. I gave a short overview of existing UK onshore oil/gas operations, including the fact that fracking has been done over 200 times in the UK since the 1970s.

I then outlined what I see as the potential issues relating to unconventional gas extraction: water usage, earthquakes, water contamination, air pollution, and surface impacts. The first, water usage, can be quickly shown to be a red herring: the water lost by SouthWest Water through leakage every day would be enough to frack more than 30 wells. I talked about the Blackpool earthquake, discussing how event magnitudes work (and that the event in Blackpool is so small that most of my real-earthquake-studying colleagues wouldn't get out of bed for something 10 times the size), and looking at evidence for fracking-induced earthquakes elsewhere (of which there are a handful in Canada, but none in the US).

Water contamination is perhaps the major issue for fracking. It is clear that there have been some cases of methane contamination through wells, and of chemical spills at the surface. I listed some of the key incidents taken from this report. However, it is important to point out that where methane leakage has occurred, it is inevitably due to shoddy practice from the drillers: poor or incomplete casing and/or missing cement. Equally, it should be fairly easy not to spill chemicals on pads at the surface, while open tailings ponds (often the most common source of surface contamination) are not allowed in the UK. It is most important to consider the context of these incidents: for example, the Groundwater Protection Council estimate that less than 0.1% of wells have seen a problem.   

With respect to air pollution, I showed a number of studies from both Pennsylvania and Texas, which do not show increases in benzene, ozone or volatile organic compounds (VOCs) before and after drilling. I then looked at a study of employee health statistics for the oil and gas industry in comparison to other sectors. If drill pads are unhealthy places to be, with dangerous chemicals being pumped into the air, then surely the employees should be getting the sickest, given that they might be on site 6 days a week for months on end. In fact, sickness rate in the gas industry is pretty consistent with national average rates, and a lot lower than many other industries.

To demonstrate the surface impacts of shale gas extraction, I showed some photos of what the rigs look like during drilling (on site for a month or two), and what the pads look like once the well is completed, and talked about pad spacing (minimum 2 - 6km as an approximation), as well as pointing out other impacts like new pipelines, and the truck journeys to and from the pads.

I then talked about the public debate around fracking in the US, pointing out that it has become highly polarised, with protest groups, but then anti-protest groups who protest the protest groups. I also showed the data from a Pittsburgh public opinion survey that showed that generally fracking does have more support than opposition (although perhaps the opposition is more vociferous).

Finally, as I like to do, I compared the risks from fracking to the risks from conventional gas extraction. To me at least, if you are opposed to fracking, you should be opposed to all hydrocarbon extraction, so I posed the question to Glastonbury's councilmen: take the scary boogey-word 'fracking' out of the question, and ask what would you do if there was a large conventional gas field discovered under Glastonbury. What would you do?

Coal bed methane in Falkirk

There's been a fair bit of activity down in the SW over UK Methane's plans for coal bed methane extraction around Keynsham. Coal bed methane, like shale gas, uses fracking to extract gas, only from deep coal seams rather than shale beds.

Coal bed methane has already been in operation in Scotland for several years (I wasn't aware of this, and am indebted to Frack-Off for pointing this out).

So, how has CBM extraction affected Falkirk? Has it become an environmental wasteland? Here's the local MP (Eric Joyce) on the issue, writing in the Guardian:

My constituency of Falkirk is home to one of the UK's most advanced coalbed methane extraction projects. As Lord Browne says, the extraction of coalbed methane is a low carbon bridge to future technologies, is unobtrusive and is environmentally safe. I have received a handful of local objections to the project, all from the same campaign group and all reminiscent of the disastrous anti-science, anti-GM lobby of a decade ago. On the other hand, I have received many messages of support from constituents who accept the potentially valuable contribution unconventional gas extraction has to make to the UK's energy mix.

It surprises me how much these onshore unconventional gas developments seem to have slipped under that radar, on both sides of the argument. Councillors and locals with worries about CBM developments in Somerset should be making a bee-line to find out more about how it has impacted Falkirk? Surely that might help improve the quality of the debate somewhat.

As an aside, it is interesting that Eric Joyce draws parallels with the anti-scientific approach of those who oppose unconventional gas with those who opposed GM food a decade ago. He's not the first to make this comparison (nor the second)...

 

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.