Statements made by two oil companies about the recent cluster of earthquakes in Surrey have been challenged by geologists.
Angus Energy and UK Oil & Gas, who operate near the centre of the earthquakes, have both said their operations could not have caused the 14 small earthquakes recorded near Newdigate since 1 April 2018.
Dr Stephen Hicks, a seismologist at Southampton University, tweeted earlier this week that some of the science and facts on Angus Energy’s website “doesn’t completely add up”.
Emeritus Professor David Smythe questioned Angus comments made to a county council meeting that it was “scientifically impossible” for its operations at Brockham to cause the earthquakes. Professor Smythe has also called on UK Oil & Gas to produce evidence of what it described as a “large fault”, around which the earthquakes were clustered.
DrillOrDrop invited Angus Energy and UK Oil & Gas to respond to the challenges. UKOG replied but declined to comment. Angus Energy read our emails but did not reply.
Yesterday at 5.30pm, DrillOrDrop took screen grabs of the Angus Energy web page on the earthquakes. At some point afterwards, the web page was updated and statements challenged by Dr Hicks have been rewritten. (Click on images from the screen grabs taken yesterday, left, and those taken today, right).
Who said what? (and when)
Andrew Hollis, of Angus Energy, said in an advertorial in Surrey Live 10 days ago:
“it is physically impossible for the Brockham field to create an earthquake”.
Paul Vonk, Angus Energy’s Managing Director, told a meeting of Surrey County Council last week:
“It is scientifically impossible for the Brockham oil field to cause the earthquakes. There is no physical connection between the fault at Brockham and the earthquake area”.
Professor Smythe, in a review of the Surrey earthquakes said:
“injected fluid from Brockham BRX-3 could, in principle, flow south (or north) along the high permeability reservoir, crossing through any faults on the way, and aided by confining clays (layers of low permeability) above and below.”
He added that research from the US had shown that fluid pressure from injection was linked to induced earthquakes observed more than 20km away, albeit with large volumes of fluid.
Up to 5.30pm yesterday, Angus Energy said on the FAQ page of its website that the Surrey tremors have “the lowest intensity possible on the Mercalli Scale. The USGS describes all of these earthquakes as “Not felt except by a very few under especially favourable conditions.”
Dr Hicks said:
“The shaking intensity felt during the largest earthquakes in the swarm wasn’t “the lowest intensity possible”. Actually, shaking intensity of level 4 on the European Macroseismic Scale was felt during the 05/07 event and reported by the BGS. This shaking intensity scale goes from 1 (Not Felt) to 12 (Completely Devastating) Other earthquakes in the sequence had ground shaking intensities of level 3; other earthquakes in the swarm were not felt. Shallow depth of earthquakes = higher shaking intensity over a small area.”
At the time of writing, the Angus Energy web page had changed to say:
“All of these tremors were magnitude 3 or below which means that most people would not notice them even if they very [sic] close to the centre. In general, these sorts of tremors would not cause any surface effects.
“Floating on magma”
Up to 5.30pm yesterday, Angus Energy said on its web page:
“Earthquakes and tremors are naturally occurring phenomena. We live on a thin solid crust, plates which are floating on a big layer of molten rock (magma).”
Dr Hicks said:
[The] “earth’s crust does not “float on magma”. Earth’s mantle, which is the layer below the crust, is actually pretty solid. It is not molten. It only flows and creeps very very slowly on geological timescales – over millions of years.”
At some point after yesterday evening, Angus Energy removed the whole sentence on magma from its web page.
Distance from the epicentres
Up to yesterday evening, Angus said on its web page:
“The epicentres of these earthquakes are ~10.5km to the south of the site.”
Dr Hicks said:
“The nearest and best-located earthquakes of the sequence are ~7 km distance from the Brockham drill site – not 10.5 km. Still a fairly long way away, but it’s good to get these distances right so that we’re being consistent.”
Since yesterday evening, Angus Energy changed its web page to say:
“The centres of these tremors ranged from 6.9 to 10.4km to the south of the Brockham Field with the scatter of centres around 9.3km to the South.”
Angus originally said on its web page:
“We couldn’t cause a North-South tremor even if Gareth Southgate told us to. Again, this is plain science.”
Dr Hicks said:
“The phrase “north-south tremor” just doesn’t really make any sense.”
Angus Energy has since removed the reference to the “north-south tremor” and Gareth Southgate. At the time of writing, the web page said:
“To be clear, there cannot be any link between production and water replacement in Brockham and these events. This is because the Brockham field is sealed to the south by a fault. If this fault did not seal there would be no oil there. So oil and water cannot move from the Brockham field anywhere to the south.”
Fracking and earthquakes
Up to yesterday evening, Angus Energy said on the web page:
“It is clear hydraulic fracturing or ‘fracking’ risk creating tremors. Angus Energy does not frack. Nor is there any fracking in Surrey, period.”
Dr Hicks said:
“Yes, hydraulic fracturing and high-rate wastewater disposal are the biggest cause of induced earthquakes in the oil/gas industry, but there is no acknowledgment [in the FAQs] that examples exist of conventional production causing earthquakes e.g. due to reservoir depletion.”
Since 5.30pm yesterday, Angus Energy has removed this reference.
Faults and tremors
Stephen Sanderson, the executive chairman of UKOG, told BBC Radio Surrey:
“the data that I’ve looked at shows that these tremors were actually clustered around quite a large fault which comes to the surface around Russ Hill”
Professor Smythe said he had found no faults near Russ Hill on maps from the British Geological Survey or geological Roam data. He said:
“I therefore challenge Mr Sanderson to produce evidence for his alleged “large fault”. If he cannot do so, the impression seems to be left that he is once more prepared to come out with any old nonsense in order to defend his company and support the share price.”
So what do we know?
Dr Hicks concluded on his website:
“Based on our knowledge of activities at the nearby drilling sites of Horse Hill and Brockham, as well as our knowledge of human-induced seismicity around the globe from the scientific literature, there is no clear reason why these earthquakes should have been directly caused industry. Injection volumes and pressures appear to be too low, whilst the distances and timescales involved do not indicate a clear, physical link.
“Whilst earthquakes have been shown to be induced over long distance and timescales due to fluid injection in Oklahoma, the injection rates and volumes are much higher than what we know to have occurred in the Weald Basin.
“Overall, there is no substantial evidence at present which indicates that these earthquakes have been directly induced by nearby industrial activities.”
Professor Smythe concluded on his website:
“the extreme shallowness of the Newdigate events means that we have a lot to learn about shallow pore pressure, shallow stresses, and shallow faults. The complex tectonic problem to be resolved here lies in the depth zone of the hydrocarbon activity.”
He backed a call for a moratorium on oil operations in the Weald by a group of geologists earlier this month (DrillOrDrop report)
“In view of the clear temporal and spatial relationship to the current exploration and production activity at the two sites in question, I support the call for a moratorium on further hydrocarbon activity made by four expert earth scientists.”
17/8/18 First quote from Professor Smythe changed from “along the low permeability” to “along the high permeability”