Well integrity: Separating fact from fiction
September 8th, 2014
A Twitter user recently made the claim that ‘all wells fail’ – just like that, with no proof, no evidence and no examples.
When we challenged the Tweeter to come up with the goods to back their claim that all wells fail, their response was to ask for proof that wells don’t fail.
And that’s the problem with social media – emotive claims, with no justification, can be easily made in 140 characters.
Showing the true story can take a little longer. So, here we go.
Straight to the issue – do oil and gas wells fail?
The Society of Petroleum Engineers – eminently qualified to address such questions – found in 2013 that:
“..actual well integrity failures are very rare. Well integrity failure is where all barriers fail and a leak is possible. True well integrity failures are two to three orders of magnitude lower than single barrier failure rates”.
So what does that mean?
To understand the statement, you need to understand how a well is designed and engineered.
Gas wells are designed to ensure that the gas stays contained within the wellbore, and that the surrounding subsurface layers, including aquifers, are protected.
As this handy graphic shows, layers of steel and cement are used to construct a typical well.
You can download the image here: Coal Seam Gas Well Graphic
In Australia, there are a number of safeguards and measures that are put in place when drilling and completing a well.
These guidelines are based on world best practice standards developed by the American Petroleum Institute (API), and that have been used extensively by oil and gas producers around the world.
In Australia, State Governments have set down the technical requirements for the design, construction and operation of wells, along with the procedures that need to be followed when wells are decommissioned, plugged and abandoned.
Read the NSW Government’s Code of Practice, the Queensland Code of Practice, and a fact sheet about Western Australia’s requirements.
So what protects the well?
Put simply, its multiple layers of steel and API certified cement, engineered and constructed to ensure the integrity of the well.
And the issue has been studied extensively. In the United States, the Ground Water Protection Council, a group of state regulators whose mission is “to mutually work toward the protection of the nation’s ground water supplies”, found wells casing failure rates to be minuscule.
Their 2011 study looked at more than 34,000 wells in Ohio from 1983 to 2007 and more than 187,000 wells in Texas between 1993 and 2008. The study found a well failure rate of 0.03 percent in Ohio and only about 0.01 percent in Texas.
And a 2014 report from Durham University, which examined 25 separate datasets from around the world on well integrity and well failure rates, found variable failure rates – some as low as 1.9% in developed countries.
What does all that mean?
Simple really – there is no evidence to back the claim that ‘all wells fail’.