Drilling without fail?
Research on failure of oil and gas wells shows problems are common, and likely to be worse for shale gas wells.
A new review of published research on well failure in the oil and gas industry, produced for Friends of the Earth, indicates that shale gas drilling poses significantly higher risks of leaks than conventional oil and gas wells.
The problem of “well failure”, although long acknowledged within the industry, has until recently received little public attention, although this is starting to change, with a recent research paper from Durham University also highlighting the problem.
Well failure likely to affect hundreds of wells in the UK
The research raises many unanswered questions, with different studies using different definitions of “well failure” – from less serious, contained leaks through only one of the well’s inner layers of casing, to leaks into the air, soil or groundwater. However there is a consensus that well failure of one kind or another is quite widespread, with failure rates of between 5% and 9% being the most frequently cited, rising to above 50% for older wells.
Bloomberg has estimated that between 10,000 and 20,000 wells would be needed in the UK for shale gas production to replace the gas we currently import. This means even at failure rates of 5% the UK would expect to see between 500 and 1,000 failing wells.
Although improvements in drilling technology could reduce some of these risks, a study called “Why oilwells leak” shows how intractable the problem can be. The research describes how the layers of cement used in oil and gas wells tend to shrink over time, opening up channels between the casing and the cement, through which gas can travel up to the surface.
Industry’s preferred figures are not comparing like with like
The oil and gas industry website Energy in Depth often cites figures from the US Ground Water Protection Council showing much lower “well failure rates” of around 0.03 percent. However this is comparing apples and oranges.
The Ground Water Protection Council study looks only at documented instances of groundwater contamination, based on complaints reported by local residents. It does not attempt to measure the proportion of wells actually leaking, and does not include leaks to groundwater which were unreported, or any leaks to air and soil. This study doesn’t debunk other research into well failure – it measures something different.
Fracking associated with increased risks
More worryingly for advocates of shale gas development, the research suggests that the technologies associated with fracking make well failure significantly more likely. There are two main reasons for this.
Firstly, hydraulic fracturing involves injection of fracking fluids at high pressure, placing additional stress on well casing and cement. Research from offshore wells in the North Sea shows that ‘injection wells’, where liquids or gasses are pumped at high pressure, are two to three times more likely to leak than conventional ‘production wells’.
Secondly, shale gas wells tend to be ‘deviated’ – rather than going straight down into the ground, they are drilled down and then horizontally, to access gas over a wider area. Research from Alberta, Canada shows that such ‘deviated’ wells have a failure rate four times higher than for vertical wells. This could be due to cement slumping or being unevenly distributed in curved and horizontal sections.
More research is needed into the likelihood and impact of well failure in UK shale wells. However, if both high pressure and well deviation multiply the chance of well failure, the results are unlikely to reassure a public already strongly opposed to fracking in their communities.
Blog written by Ryan Brightwell, 13 May 2014
