Well failure is common, is far more likely with unconventional wells (which are subject to extreme operating conditions), and increases as the wells age.
It can lead to leaks, contamination, and even catastrophe, such as the Deep Water Horizon disaster.
How Can a Well Made of Steel Tubing and Cement Possibly Fail?
This image shows some examples, with big holes in well tubing, and another with a long split. A cross section through cement casing shows cracks in it.
Photographic examples of leak pathways: (a) Corrosion of tubing (b) Cracks in cement (c) Corrosion of casing. (from the paper mentioned below in Marine & Petroleum Geology.)
Drilling a well several kilometres deep, and forming a perfect seal all the way down through the geology, is challenging.
A well is drilled in sections, getting narrower as it goes deeper. Steel tubing is inserted, and cement injected around the tubing, to fill the gap between the tubing and the earth. In theory, the cement bonds to the earth and the tubing, and seals the gap.
In practice, it can be a little more complicated. The tubing might not be perfectly centred, so the casing is thinner on one side. Or the gap might be partially blocked by rocks, or sediment, or drilling muds. Or cement might be lost into the geology. There may be naturally existing fractures in the geology, and so on.
Deep down, at the bottom of a well, is subject to high temperature and pressure. On top of this, fracking involves pumping vast quantities of cold fluid into the well, and pumping to pressures extreme enough to fracture rock. The well contracts, expands, and is stressed, which can break the bond with the cement.
Fracking can cause minor earthquakes, which can of course damage the well, deforming or shearing it. The only high volume fracking to occur in the UK was at Cuadrilla’s Preese Hall well near Blackpool. It caused earthquakes that damaged the well casing by deforming it to an oval shape over 50 metres. They carried on working though, and it was 6 months before it was reported.
“Historical rates of well “failure” in oil and gas fields vary from a few percent of wells with barrier failures to >40%
Since 2005, the state [Pennsylvania] has confirmed more than 100 cases of water-well contamination from oil and gas activities”
– The integrity of oil and gas wells – PNAS (Proceedings of the National Academy of Sciences), July 2014
How Many Wells?
Fracking requires thousands of wells in order to be economically viable, so even if only a small proportion fail, that’s still quite a lot of wells.
“The most recent experience with shale gas wells in the Pennsylvania Marcellus play reflects long term, world-wide industry data with respect to new wells with compromised structural integrity. Operator-wide statistics in Pennsylvania show that about 6-7% of new wells drilled in each of the past three years have compromised structural integrity. This apparently low failure rate should be seen in the context of a full buildout in the Pennsylvania Marcellus of at least 100,000 wells, and in the entire Marcellus, including New York, of twice that number. Therefore, based on recent statistical evidence, one could expect at least 10,000 new wells with compromised structural integrity.”
FLUID MIGRATION MECHANISMS DUE TO FAULTY WELL DESIGN AND/OR CONSTRUCTION: AN OVERVIEW AND RECENT EXPERIENCES IN THE PENNSYLVANIA MARCELLUS PLAY – PSE Healthy Energy (Physicians, Scientists & Engineers)
Well Failure Increases with AgeSchlumbeger is the world’s biggest oil services company. A study in their own journal showed that for wells in the Gulf of Mexico that were new, 5% had well casing failure. For wells that were 6 years old, 1 in 3 had well casing failure. For wells that were 15 years old, the failure rate increased further, to half of the wells.
Far More Common for Unconventional Wells
“Casing and cement impairment in oil and gas wells can lead to methane migration into the atmosphere and/or into underground sources of drinking water. An analysis of 75,505 compliance reports for 41,381 conventional and unconventional oil and gas wells in Pennsylvania drilled from January 1, 2000–December 31, 2012, was performed with the objective of determining complete and accurate statistics of casing and cement impairment. Statewide data show a sixfold higher incidence of cement and/or casing issues for shale gas wells [6.2%] relative to conventional wells.”
Assessment and risk analysis of casing and cement impairment in oil and gas wells in Pennsylvania, 2000–2012 – PNAS (Proceedings of the National Academy of Sciences), June 2014
Well Failures in Europe are Unknown
“The research confirms that well failure in hydrocarbon wells is an issue and that publicly available data in Europe on this seems to be sparse…
… we don’t really know the full extent of well failures. There were unknowns we couldn’t get to the bottom of.”
So if an oil company tells you that well failure in the UK is not an issue (possibly citing gold standard regulation), they are misleading you. There is little evidence to support such a claim.
This paper assessed all reliable datasets worldwide, and found:
“The percentage of wells with barrier element failure is between 1.9% and 75%”
Oil and gas wells and their integrity: Implications for shale and unconventional resource exploitation – Marine and Petroleum Geology
It also points out that most UK onshore wells are now abandoned, and most of them aren’t monitored. Lots of them are “orphaned wells” where the company responsible no longer exists.
So if a company drills in your community, but then goes bust, who pays for the clean up?