A study of decommissioned onshore oil and gas wells in the UK found that 30% were leaking methane. But the average leak produced lower emissions than a breeding dairy cow.
The research, published today in the journal Science of The Total Environment, concluded that the leaks were caused by well integrity failure and that wells were most likely to leak within 10 years of being abandoned.
The industry body, UK Onshore Oil and Gas, said the study should reassure people. But Greenpeace said it raised questions about the development of fracking in the UK.
The study was by the ReFINE research consortium on fracking, led by Newcastle and Durham Universities and funded primarily by Centrica and INEOS.
Details
Researchers selected 102 wells from four onshore UK oil and gas basins in the Weald, North Yorkshire, the East Midlands and Wessex.
The wells were chosen to give a range of conditions and they varied in age from eight to 79 years. They had all been decommissioned in line with best practice in the UK. They had been cut off, sealed and buried in soil to 2m. Another well, drilled in 1917, was included because it had not been decommissioned properly.
The study analysed soil gas above each well and compared it with a nearby control site of similar land use and soil type.
- In 31 out of 102 wells (30%) the soil gas methane was significantly higher than control sites
- In the most extreme example, the methane was 147% greater than the control
- In 39 out of 102 (39%) wells the soil gas methane was significantly lower than controls.
- Leaks from the well that had not been decommissioned properly were more than 10 times higher than the average
In the wells that were leaking, the researchers said:
“The estimated fugitive emissions from decommissioned wells are less than that for the agricultural activities that would take place on the reconstituted land.”
However, the researchers acknowledged that they looked only at vertical emissions from well integrity failure and not at the potential for diffuse leakage into surrounding groundwater or over a broad area.
They estimated emissions to be on average 364+/-677kg CO2 equivalent per well per year. The paper compares this with emissions for dairy cows and ewes.
“For dairy breeding herd the CH4 emissions factor (enteric and manure sources) is 128 kg CH4/head/year (2944 kg CO2eq/head/year) while for a breeding ewe the value is 8.9 kg CH4/head/year (205 kg CO2eq/head/year)”.
A DrillOrDrop reader has calculated that based on the figures in the paper the average leaking well could produce emissions just over 1/10th that of a single cow.
The researchers said wells did not appear to leak more as they got older:
“The relative CH4 [methane] concentration above wells did not significantly increase with the age of the well since drilling and 40% of the most recent wells surveyed showed leaks implying that leaks develop early in the post-production life of a decommissioned well.”
They said lower soil gas methane levels than the control indicated that soils on some decommissioned sites acted as a net methane sink.
Well integrity failure
The industry stresses the importance of well integrity to prevent contamination. At a meeting in North Yorkshire last Friday, Ken Cronin, chief executive of the industry organisation, UK Onshore Oil and Gas, told local councillors:
“The most fundamental and important thing about any oil or gas operation is the integrity of the well. If you get the design and creation of that well correct from the start then you reduce the environmental impact of fracking.”
Well integrity failure happens when barriers of cement or steel casings fail, allowing pathways for fluids and gases to groundwater, surface water and the atmosphere.
In today’s study, the researchers said:
“We interpret elevated soil gas CH4 concentrations to be the result of well integrity failure but do not know the source of the gas nor the route to the surface.”
They added:
“Oil and gas wells are typically constructed with multiple barriers to maintain well integrity and prevent leaks, thus well integrity failure is a consequence of complete barrier failure.”
“A loss of well integrity is important because it represents an uncontrolled release of fluids – whether liquid or gas – which could pose a risk to groundwater supplies and air quality.”
The importance of monitoring
Leaks of methane can have important consequences for climate change because the gas has a warming potential 28-36 greater than carbon dioxide over 100 years.
Another ReFine study in 2014 found only two confirmed cases of well integrity failure in the UK in 143 active onshore wells but it revealed that there was no monitoring of abandoned wells. Of these 65% were not visible, while 35% had some evidence at the surface of previous drilling activity.
One of the authors of today’s study, Professor Fred Worrall, told the BBC:
“The point is that even with proper decommissioning you will still have those wells that leak as cement cracks and steel corrodes and so monitoring is important,”.
“Overwhelmingly wells are properly decommissioned and our study shows that when methane does leak the levels are low, for example when compared to methane produced by the agricultural use of the land”.
Reaction
Ken Cronin, of UKOOG, said:
“What ReFINE has shown is that the public should have no health or environmental concerns about emissions from properly decommissioned wells adhering to current industry standards.”
“Indeed the research has found that in the minority of cases where they have recorded some methane emissions from decommissioned wells, these emissions are typically less than one would get from just a handful of livestock grazing in the same fields.”
But Doug Parr, chief scientist of Greenpeace, said:
“If even an industry-funded study suggests that 30% of conventional wells appear to be leaking, it raises serious questions over the long-term impact of the extensive development of unconventional gas in the UK which is clearly the government’s plan.”
Updated 29/1/16 to include figures for methane emissions and comparison with livestock.
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Categories: Research
DRILL OR DROP? 
With 5.2 million homes at risk of flooding in England ( SOURCE, Flood defence spending in England – Parliament breifing paper 19th November 2014 )
With two thirds of the UK insurance market either refusing cover, or placing special exemptions on the policies of homeowners who live in areas at risk of flooding with fracking sites in close proximity ( 5 miles ).
DEFRA warning of the serious risk to human health from highly polluted fracking waste water.
( SOURCE, Independant Newspaper UK, 9th January 2016, headlined… Householders Face Double Whammy If They Live Near A Planned Fracking Site )
What does the fracking industry intend to do about this ???
The wells tested will have been conventional reservoir geology as so few unconventionals have been drilled. Their productive sections will be linked by natural permeability of pore spaces and jointing to the wider reservoirs. Why would a shale reservoir which must have been actively fractured in order to produce any gas continue to produce gas in any great quantity after it has been abandoned ?
By definition, shale gas reservoirs require an artificial permeability (the enhanced natural and extra man-made fractures) to flow gas. In fact its an achingly frequent criticism that the production lives of these wells are very short and that further producers have to be drilled. This is because the permeable zone, ie the fractured zone near the well, is limited and isolated, surrounded by impermeable unfractured shale which holds onto its gas at virgin pressure.
So what would drive gas to leak from a depleted shale gas well when the fractures have been depressurised as the gas departed and fractures have closed up through natural action of hydrostatic pressure, clay swelling and chemical change ? There is no gas being driven to the well or the well would still be in production.
And then theres the comparison of abandonment techniques and materials used today with wells from 70 years ago, it assumes a standstill in engineering and materials science technology which is naively unrealistic. I see very little use extrapolating leakage rates from elderly conventional reservoirs onto modern unconventional shale reservoirs, there are far too many variables to make this comparison valid.
So Marty Decker, has there been any monitoring of migratory habits of methane along say UK shale for example? So, for example, the explosion in Kellingley colliery two years ago, is there any tracking of how, why, when the methane collected there, and was it a result of underground migration of gas pressured by water?
How much testing has been done of deep underground fossil compounds to find out how inflammatory/explosive they are when combined with others they may be ignited by when forced by water pressure into transmigrating to areas nature kept them separate from?
Not long ago explorers used dynamite to explode large areas all over the planet, in some now realised amazingly exquisitely important places now irreversibly destroyed forever. They in true arrogant know it all forever style, happily blew up everything standing in the way of what they wanted to see and do. Much was learned from this stupidity, and yet lessons seemingly now ignored as the new technology excites those wanting to play with fire while the rest of us get radioactively burned….
You’re comparing a coal mine with a shale gas well? Methane is found in large amounts in coal seams. It collects in a coal mine because the natural water is pumped out of a mine which then is at atmospheric pressure or slightly over. That pressure is lower than the natural hydrostatic pressure in the surrounding rocks and any fluid will obey the laws of physics and move towards the lower pressure, ie into the mine. It is the same way a gas well works, except a gas well is not full of atmosphere because it doesnt need any miners in it.
Methane, or firedamp is why coal mines are heavily ventilated, otherwise the methane will, when combined with the oxygen in the mine, become explosive as it did in Kellingley. All of the methane from every coal mine anywhere is vented to the atmosphere and it always has been for just this reason. Coal mines dont need help to accumulate methane.
You can’t get methane to explode unless there is free oxygen present either. Its only explosive between 4 and 15% methane and above 15% it will extinguish a flame by displacing the oxygen. Inside shale, and in gas wells, there are no big open spaces like mines and all the pores and fractures in rock are filled with salt water. There is not enough oxygen to burn anything.
Also coal is a completely different rock to shale. Shale can have the same permeability as a concrete paving slab, but coal is brittle and full of tiny fractures where gas collects. Its not a case of monitoring of “migratory habits of methane along say UK shale” because thats been known for 300 years since serious mining began. You seem totally unaware that the shale has gas in it BECAUSE water and gas cannot move about in it. Its so impermeable that it needs to be fractured in order to get the gas to move. If gas and water could move about in shale, it would have done so and there would be no gas remaining in it which would make drilling it a bit pointless.
I have no idea what your final paragraph relating to dynamite means. I have no wish to be rude but your post just underlines the danger we have in people with absolutely no education in science trying to drive a debate which requires a moderate understanding of science and technology.
We cannot afford any more fugitive sources of methane. This is not about context. We have to reduce methane full stop and fracking will and is increasing methane emissions.