Thursday, September 12, 2013

The Failure of Fracking - Betting Our Futures on Well Bore Integrity

As a geoscientist with nearly three decades of experience in the oil industry, I have been watching the debate on fracking (or as we called it, "fracing") with great interest.  After a recent discussion with someone who stated that there had never been a blowout related to fracking like there was on BP's Macondo well, I thought that it was time to help explain exactly what fracking is and where the potential problems lie from a geoscientific viewpoint. 

Production of hydrocarbons from a reservoir requires both porosity (the holes in the rock) and permeability (the measure of how connected those pores are to each other).    When I'm explaining the use of hydraulic fracturing to laypeople, I always use the analogy of a sponge.  Hydrocarbons are found in the pores of the sponge but, unless those pores are connected to each other, the hydrocarbons will not flow to the surface.  In the case of shale, the porosity is very high, often in the order of 30 percent or more compared to half that in many sandstones and limestones, however, the pores are not interconnected meaning that the permeability is very low.  In those cases, hydraulic fracturing techniques are used to connect the pores to each other, allowing the oil or natural gas to flow to the surface.

Fracking is a production enhancement technique that has been in use for decades in low permeability reservoirs.  Twenty years ago (or even less), fracking involved pumping what we considered to be large volumes of sand or gel (the material that would help connect the pores) in a semi-fluid state under high pressures through holes that were perforated in the production casing.  This "cracked" the rock and, after the fluids that contained the sand flowed back out of the hole, the sand (the proppant) was left behind in the formation, enhancing the permeability.  Over the past decade, fracking has changed a great deal.  Rather than a single frac, oil companies are now using multi-stage fracs that require massive volumes of water and chemicals to enhance permeability in formations that were once considered to be non-productive.

Many of us have heard of the unfortunate souls that live in areas where fracking is now commonplace (i.e. Pennsylvania, parts of southern Alberta etcetera) that find themselves with tap water that is contaminated with natural gas as shown here:

The oft-heard mantra is that the source of the methane is biological (i.e. it is sourced from decaying plant life close to the surface of the earth), however, that is not necessarily the case.  Let me explain why.

When the oil industry drills a borehole to depth, as you can imagine, the sides of the borehole are very unstable and rock continually sloughs into the hole, causing all manner of problems.  To alleviate these problems, a long string of hollow steel production casing of varying diameters is run into the hole to the total depth of the well (or somewhere below or at the depth of the producing formation depending on the type of well).  The diameter of this casing is somewhat smaller than the diameter of the borehole; the space between the two is known as the annulus.   Once the casing is in place, cement is pumped down the casing and flows back up the well between the casing and the sides of the borehole through the annulus.  The cement is allowed to harden and tools are run to ensure that the "cement job" is sound.  The purpose of the cement is three-fold; it holds the casing in place, it prevents the fluids used in the well completion operations from flowing to the surface and it prevents fluids from inside the borehole from flowing into the surrounding formations once the well is completed and on production.  For example, if there is a water-bearing formation above the productive zone, the production casing and cement will seal off that formation, preventing the formation water from flowing into the well bore.

Here is a cross sectional diagram showing a completed coal bed methane gas well and its components:

So, what could possibly go wrong?  Sometimes, the cement fails to displace the drilling mud in the annulus and completely fill the void between the casing and the formation and other times it fails after a period of time.  This situation allows the formation fluids, which are under pressure because of the weight of the rock that lies on top of them, to flow through the annulus to the surface where the air pressure is far lower.  It is this exact situation that can result in contamination of near surface aquifers even when hydrocarbon-producing formations are many thousands of feet below the source of groundwater.

How prevalent is the issue of failed well bore integrity?  Before you continue reading the accompanying data, please keep in mind that this data is oil industry-sourced; it is not sourced from any anti-fracking lobby with an axe to grind.  Let's start with a graph that shows the rate of sustained casing pressure (i.e. failed well bore integrity) in wells in parts of the Gulf of Mexico from the Autumn 2003 edition of the Oilfield Review to us some idea of how common the problem is:

The well bore integrity in five percent of these wells can be expected to fail immediately ramping up quickly to 40 percent in eight years.  From fourteen years and onward, half or more wells are expected to lose integrity.

In case that isn't enough proof for you, here is a slide from a 2011 presentation by Archer, a global oilfield service company, showing the percentage of wells with integrity failures in the Gulf of Mexico and the North Sea in both Norway and the United Kingdom:

I find it stunning that 45 percent of wells in the Gulf of Mexico had integrity failures.  Archer also states that 20 percent of wells with integrity issues are cement integrity and an additional 41 percent are related to failures of the equipment in the hole (tubulars).

What I find even more concerning is this:

...and this:

Horizontal drilling and hydraulic fracturing - coming soon to a shale basin near you!

The red blobs on the first map outline the world's major shale basins that have been assessed as containing economic volumes of shale gas.  In total, 32 nations have a projected 5760 trillion cubic feet (TCF) of technically recoverable natural gas on top of the 862 trillion cubic feet in the United States.  With the U.S. consuming 25.5 TCF in 2012, that's a 33 year domestic supply.  As well, the U.S. Energy Information Administration (EIA) projects that 14 percent of global natural gas supplies will be sourced from shale by the year 2030 and the U.S. Department of State notes that this will provide "...the reserve base necessary for expanded consumption in a business as usual scenario."  I guess there is no need to conserve after all!  Thank goodness fracking will be there to bail us out!

Lastly, according to the Society of Petroleum Engineers, over the next decade, the oil industry will drill more wells than they have in the last 100 years and that of the world's current inventory of 1.8 million wells, roughly 35 percent have integrity problems.

I find those observations to be most disturbing, particularly given that so much of our energy future is now hinging on the ramping up of hydraulic fracturing.  We're betting our future on a very risky energy pathway, one that depends heavily on improvements to well bore integrity.


  1. Thanks for the very informative post. just because we can reach these supplies does not mean we should rush to "exploit and waste" them. As much concern as many of us have the political and economic desire to rip into these resources as a easy way to mask other problems is very real. I have heard how this can effect ground water but any idea as to what these up to now contained gases will do to the atmosphere?

  2. Bruce

    Methane is considered to have 25 times the global warming potential of carbon dioxide. Methane is also the most common component of natural gas. I think that answers your question!


    1. I though so, I was troubled by this so after all this time I wandered back to your article. Very troubling. The sad thing is how much waste of natural resources still occurs. As you noted in another article we are also busy fouling and wasting water with this process.

  3. Fossil fuel companies are undergoing a campaign to convince us that society is in transition from dirty fossil fuels (e.g. coal) to cleaner fossil fuels. In truth, the real transition that is happening is from fossil fuels to green technologies. Most of the new power installations are using green technologies. Our government needs to come up with a master plan on our energy sources and use. We cannot let the fossil fuel companies determine this plan, because they will surely act in their own interest. Unfortunately, they are currently the big gorilla in the room, and they are succeeding in deciding for all of us our energy policies.

  4. This is an interesting topic, but I notice that your graphs are related to casing failure in sea-borne wells, versus onshore shale wells. Are there any data on the incidence of failure specifically for fractured shale wells?

  5. Its a good article on reasons not to drill, or alternately on reasons to improve the quality of annular cementing operations. However I don't see the link between annular isolation failure and fracturing.

  6. When annular isolation fails, fracking fluids can work their way up through the failed cement/casing interface since they will follow the path of least resistance. When that happens, the fluids used can end up anywhere in the stratigraphic column (i.e. in aquifers).

  7. Your article is very informative. The key to the problems of contamination, as you point out, is well bore integrity. There are many ways to "design" the well to protect the shallower water sands. Additional casing strings are normally added to protect shallow and intermediate water producing formations. Proper cementing techniques and close supervision of the cement job is essential (this is a key point). Cement bond surveys can be taken to determine if the casing is properly cemented prior to the fracture treatment. No human endeavor is 100% certain, but a good wellbore design and proper supervision can reasonably eliminate contamination.

    The current paranoia about fracking is based mostly on fear, fiction, distrust of oil companies, and in many cases motivated by groups with their own monetary agendas. Until viable energy sources are developed we are dependent on hydrocarbons. We can't just say no more development of hydrocarbon resources.

    Retired Petroleum Engineer

  8. why is the north sea way lower then the golf of mexico in there integirty issues

  9. what is this supposed "monetary agenda of environmental groups fighting on behalf of communities (often pro bono) and grassroots community groups who are fighting to transition to alternative energy and stop more oil? Please provide concrete (pun intended) evidence.

    There IS financial motivation to deny of these problems; Oil companies have been known to offer large sums to scientists willing to produce research to back their claims.Just a few examples (google provides plenty of support)

    and a piece on Dr. Willie Soon, (leading climate science denier) an astrophysicist at the Harvard-Smithsonian Centre for Astrophysics, was paid $1 million over 10 years to express the view that CO2 emissions are not the cause of global warming.