MEMO
To:
From:
Subject:
Fracking Expert Group
Gene McManus
Concerning fracking failures
Date: 4 June 2014
We’ve had several papers on fracking1,23 giving background, economics and potential
availability of oil and gas reserves in Nova Scotia. However, what I’ve yet to see is a
consideration of the threat posed by fracking, and the potential dangers.
Advocates of fracking suggest it is “safe”, that we have nothing to worry about. But
Three Mile Island was supposedly “safe”4; Deep Water Horizon was supposedly “safe”,
but it failed catastrophically5. Chernobyl was supposedly “safe”6. NASA and its
contractor North American Aircraft designed the space shuttles to be “safe”; yet two of
them failed catastrophically7. The Titanic was supposed to be “unsinkable, yet never
completed it’s first trip8.
The lesson is “Nothing lasts forever”. Translating this into more precise language,
“everything has a failure rate”. From this we can calculate several important terms:
1. The cumulative probability that a well will fail catastrophically
2. The time at which the cumulative probability of failure is 0.50.
The cumulative probability of well failure
Assume for a fracking sell, a probability of failure pf in a year. Then the probability that
the well will still be functioning after a year is ps, where ps is given by
ps = 1-pf.
The expression for the well to be functioning after t years is
Ps = (1-pf)t
The cumulative probability of failure of a well is then
Pcum.=[1-Ps]
Or
Pcum = [1-(1-pf)t]
Note tat as time passes, Pcum approaches 1.
Setting Pcum equal to 0.5 and solving for t will give the time at which the cumulative
probability of failure for a well is equal to 0.5:
0.5= [1-(1-pf)t]
Or 0.5 = (1-pf)t
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Take logs of both sides:
Log (0.5) =t x log (1-pf).
Solve for t 0.5:
t 0.5= log(0.5)/log(1-pf)
Empirical data, based non observed well failures, can be used to estimate pf.
If there are N wells, the binomial probability distribution can be used to estimate the
probability of 1, 2, 3 …N wells failing, as a function of time. This distribution is
tabulated for various values of N and pf, in standard statistics books. It can also be
calculated directly using the BINOMIAL function in EXCEL For N wells the expected
number of failures is given as
E(Nfailures)=N x pf
Note that as time passes, pf approaches 1.0, so the expected number of well failures
approaches N. Sooner or later they will all fail.
Earthquakes
Goggling fracking and earthquakes yielded 921 000 results. Certainly no one is going to
read all of them. For the most part, they seem to focus on three occurrences: in Ohio, in
Oklahoma, and near Dallas, Texas. The Ohio event, near Youngstown, was found by
geophysicist, geologists and other experts to have been highly correlated with the drilling
of fracking wells. Likewise, the events near Dallas were highly correlated with an
increase in wells, particularly fracking wells. The correlation in Oklahoma is not as
strong as in Ohio and in Dallas, but this is understandable, given that petroleum wells
have been drilled in Oklahoma for decades.
Let’s try to construct a plausible qualitative model that might explain the correlation
between fracking and earthquakes.
In a pristine environment, gravity, the flow of water and weather bring the earths surface
and subsurface into what might be considered a minimal energy configuration. This
typically, but not always, occurs as the form of layers of roughly slimier material, similar
in terms of density and mechanical characteristics. Left undisturbed, this configuration
may, over time, slowly reconfigure to a comparable minimal energy configuration. Now
introduce an extractive process. Subsurface material is being removed, and replaced with
perhaps nothing (as in an abandoned mine), or with a material that has a density and
mechanical properties different from the material that had been extracted. Gravity, the
flow of water and weather will now act to reconfigure the surface and subsurface
relationships, toward another minimal energy configuration. If the subsurface structures
tend to be brittle and unbending, the result may, in the future, result in an earthquake, as
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subsurface structures suddenly snap. If the subsurface structures tend to be ductile,
earthquakes would be less likely to occur.
To quantify this simple model probably would require at a minimum familiarity with
tensors, fracture dynamics, geology and earthquake prediction; certainly beyond my
capabilities. Let’s take a different tack
Nova Scotia is on the Nova Scotia tectonic plate, which originally was part of what is
now the west African coast. Some several billions of years ago it broke off, drifted
northward, and rammed into the North American tectonic plate, amongst other things
forming the Bay of Fundy. Essentially the Nova Scotia plate ‘floats”, and as such would
tend to be relatively responsive to changes in forces and energy configurations. New
Brunswick, on the other hand, is at the extreme edge of the North American plate, and
would be less likely to respond gently to changes in forces and energy configurations.
This suggests that Nova would be less susceptible to earthquakes than the New
Brunswick Fundy region.
Sink holes
Sink holes, or places where a portion of the earth’s surface drops below the local surface,
are relatively rare, but seem to be occurring with increasing frequency. The generally
accepted cause of a sink hole is the erosion of the earth’s structure below the surface.
This erosion has several causes: underground streams or rivers, abandoned mines that
subsequently collapse, depletion of underground lakes and aquifers, extraction of material
from beneath the surface. Following is a plausible qualitative model of how fracking
might cause or contribute to the creation of a sink hole.
Consider the earth below the surface to consist not of layers of variable consistency and
density, but of a large number of very slender vertical columns, of non uniform
composition. Under normal conditions and use, such a slender column would buckle
under any applied compressive load. However, the subsurface “vertical columns” do not
buckle because they are mutually self supporting, much like when beer cans or pop cans
are filled and packaged in a case of twenty four: the liquid inside the can provides the
rigidity needed.
Under the normal passage of time, surface water trickling downward will erode some of
the material surrounding each “column”, but column buckling will be inhibited because
of the support of material from the surface following the trickling water. Some small
amount of local buckling may nevertheless occur, which accounts for local irregularities
over time in, for example, lawns. People who maintain their lawns periodically have
them “rolled” to remove or minimize these irregularities. The columns are supported by a
base, or foundation, containing gas, petroleum, minerals.
If now is foundation is eroded or depleted by mining, subsurface streams or fracking, the
column will no longer be supported, will collapse downward to fill the new empty area,
and a sink hole will result. This is observed in the vicinity of rivers with subsurface
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branches, abandoned and collapsed mines and more recently, in the vicinity of fracking
wells.
1
Baechler, Fred, et al: Primer on the Process of Hydraulic Fracking; undated
Gardner, Michael, et al; Discussion Paper: Petroleum Operations, Costs and Opportunities in Nova
Scotia, undated
3
Hayes, Bad, Ritcey, et al: Discussion Paper: the Potential Oil and Gas Resource Base in Nova Scotia
Accessible by Hydraulic Fracking, undated
4
The Three Mile Island disaster occurred because two electrical lines, each about a half mile, had been
deleted, to save money. A switch on the Master Control Console was connected to one set of wires.
Activation of the switch sent a command to a relay approximately half mile away. When the relay acted, it
sent a signal back to the console, and energized a light next to the switch. To save money, the contractor
proposed removing the wires back from the relay, and jumpering directly from the switch to the light. The
operator activated the switch, the light came on, but the relay had jammed.
5
In the interest of economizing, Quality Assurance procedures and checks were not performed. As a result,
a breakdown in the well cap was not discovered.
6
The Chernobyl disaster occurred because a simple relay failed to actuate when commanded.
7
Challenger failed because the launch took place in weather that was too cold for the “O” ring in the
booster rocket. The Columbia disaster was caused by a one foot icicle falling on tiles on the leading edge of
the portside wing, breaking them and exposing bare metal to the environment. When re-entry began, hot
gases at approximately 4000 degrees C began to impinge on this section of bare metal, approximately a
square foot. The hot gases acted like a cutting torch; within thirty seconds the port side wing had been cut
off .
8
In the interests of cost savings, rivets in the Titanic were cast iron, rather tan steel. In the icy cold waters
of the North Atlantic, the rivets became brittle, and snapped when they impacted the ice berg.
2
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