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    When the Ground Shakes: Who You Gonna Call?



Cuadrilla Resources found out that the ground shaking in the vicinity of its hydraulic fracturing operation was no coincidence. A member of the team that helped diagnose the company’s problems says Cuadrilla spent millions of pounds to increase the amount of data gathered, which included FMI logging, core analysis, sonic logging, and seismic data from all available stations.

by: Drew Leifheit

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Natural Gas & LNG News, News By Country, United Kingdom, Shale Gas , Technology, Top Stories

When the Ground Shakes: Who You Gonna Call?

If only Leo Eisner had only been there a bit earlier.

Mr. Eisner, President at Seismik s.r.o., was part of the team that helped diagnose Cuadrilla Resources’ earth tremors which were the result of its shale gas exploration activities in the UK.

Seismik focuses on large, felt seismicity in the vicinity of oil and gas reservoirs, events which are typically connected to oil & gas companies. But are seismic events related to what those companies are doing, like hydraulic fracturing?

Cuadrilla was not planning at all to monitor their first hydraulic fracture in April 2011, recalls Eisner, when the British Geological Survey (BGS) reported a seismic event about 2 km away from their well and 10 hours following the second injection.

“At that time, the nearest monitoring station was about 80km away. There had been no seismicity in this area prior to this,” he explains. “It could have easily been a coincidence.”

Cuadrilla reacted, taking pre emptive measures:

“They installed four stations at their own cost to find out whether the events were related to their activities.”

The trouble wasn’t over - a second seismic event happened in May of last year following the fourth injection. Did this have to do with Cuadrilla’s hydraulic fracturing at its Preese Hall site?

Eisner explains: “Cuadrilla found out it was not a coincidence, but no one knew what was going on. They assembled an international team to look at all aspects. The company disclosed the phenomenon and spent millions of pounds to increase the amount of data gathered, which included FMI logging, core analysis, sonic logging, and seismic data from all available stations.”

The big difference between this induced seismic activity and normal earth tremors, according to him, is that there were smaller events preceding the event reported by BGS; the occurrence of these small events had coincided with the hydraulic fracturing.

“This was a wonderful discovery,” Eisner recalls, “because usually you have a large seismic event and then aftershocks. In the Cuadrilla case, there were small events leading up to large ones, and relatively few after that.”

The injection of fluids built up this seismic event and eventually led to creating the big event, which was barely felt on the surface and could not damage any building structure or be a threat to any property, he says.

“However, it was felt and was a concern for the UK’s Department of Energy and Climate Change (DECC), the BGS and the UK government,” he adds.

Previously, there had been no reports of large seismic activity from hydraulic fracturing.

Just don’t call it an earthquake.

Mr. Eisner insists that using the word “earthquake” to describe the tremors caused by the technology is inappropriate. “These are micro earthquakes – they’re something that’s not felt on the surface. At magnitudes around 2 you start to feel events on the surface; that’s when they can be called earthquakes.”

Earthquake or not, what happened in Blackpool, Eisner contends, may not have been so good for Cuadrilla, but did help the company understand that the events were indeed related to their activities.

“We now have measures to mitigate this. Seeing the small movements as a precursor to larger ones, they can stop the fracturing and the injection and take preventive measures like draining the well and reducing pressure.”

Part of the UK government’s recommendation to all future operators will probably be to monitor the injection wells and if it exhibited unusual seismic activity, to stop hydraulic fracturing and drain fluids from the well, according to Eisner.

“This is what they recommend as a process/methodology for fraccing in the UK,” Eisner explains. “It’s in the public domain and open for public discussion, so the Government may allow it going forward.”

According to him, the UK government has acted in a very rational way about what has proven a controversial topic – hydraulic fracturing – and has been listening to arguments from all sides. The study conducted by Cuadrilla has been reviewed by the Government, and by a panel of independent experts, who have pointed out the weak spots.

With a background in research, Mr. Eisner says his main interest is understanding how seismic events are induced and geology’s interaction with injection fluids, recovering the maximum amount of information towards understanding induced seismicity.

He explains: “The problem is if we rely on a quick judgment, because sometimes it’s very biased; to understand whether you are causing tremors requires careful analysis. It’s hard to prove whether or not they’re related – this requires a detailed look at the phenomenon.”

The industry needs the help. Mr. Eisner admits that, “The industry has a bad reputation as it is, a reputation for hiding data.”

“There are always accidents,” he says of industry. “We must accept a level of risk to harness energy. I’m trying to increase the amount of information to prevent future accidents, mitigate hazards and to better understand what we are doing.” 

Now, contends Mr. Eisner, that same approach to seismic activity mitigation could be used by oil and gas explorers across the globe. However, he notes, seismic monitoring has not become mandatory for shale gas explorers.

“Companies are still not doing it - it’s only being done at a fraction of the wells in the US. Few wells are monitored in Europe, but they will be in the UK; it’s not being done in Poland. It’s better to do it ahead of time than after the fact,” he says.

In terms of cost, he says it costs explorers USD 20-30,000/week to do real time seismic monitoring and processing of the data gathered on their wells.

“Compared to the costs of drilling and fracturing, I think this additional cost is negligible,” he comments. “If you have full scale seismic you see more events because you must deploy geophones in the borehole, which can cost USD 200-500,000. You see things in detail and can prevent large events.”

Regarding his native Czech Republic, Leo Eisner says his company Seismik was “almost famous” there, before the Czech government declared a moratorium on hydraulic fracturing.

“We’re sorry that the dialogue over this in the Czech Republic is not more factual and rational. There were three companies granted exploration licenses, but the Ministry of Environment decided to declare a moratorium, saying shale gas needed a better legal framework. This means there will be no exploration in the Czech Republic for 2-3 years.”

Natural Gas Europe asked the expert geologist how crucial he believes seismic monitoring will be going forward for unconventional gas.

“While there’s some excitement over this, there’s also some reality. Seismic monitoring helps in terms of how far to fracture, where the fluid flow is, what is optimal well spacing – there are different strategies,” he says. “This can be done without seismic, but then it’s more trial and error. Seismic monitoring is not mandatory, but E&Ps can get better insight, and those that have that can gain competitive advantage,” concludes Seismik’s Leo Eisner.

“We’re on the best path to helping improve our understanding and mitigating all the hazards.”