What is Induced Seismicity?
Induced Seismicity is just another way to say ‘man made earthquakes’ and are sometimes referred to “induced earthquakes”. Induced Seismicity can be caused by many things humans do including:
- damming rivers for hydro power build a vast water weight behind the dam which was not their previously
- having old mine shafts collapse
- draining of underground water reservoirs
- tunneling / boring for transit systems
but the focus of this article is Induced Seismicity caused by oil and gas exploration and production. There are some unexpected results in the latest research that governments and citizens should be aware of.
The picture to the right is the standard graphic used by industry to explain that when we search for or produce oil and gas near existing fault lines, the added (or reduced!) pressures can cause the faults to activate resulting in earthquakes. Nowhere has this been more pronounced than in Oklahoma over the previous decade and their citizens and governments are taking it very seriously.
What are the Main Causes of Oil & Gas Related Induced Seismicity?
The two major causes of oil and gas related Induced Seismicity are:
- Fracking HORIZONTAL wells
- Waste water disposal wells
What is Fracking?
Hydraulic Fracturing or “fracking” is simply the process of injecting materials (often including water, sand, chemicals, CO2…) into a well under very high pressure. The idea is to crack the rock and release the oil and gas contained.
Contrary to conventional wisdom fracking is nothing new. The first use of modern fracking occurred in the Hugoton gas field located in Kansas in 1947 and it became a popular technology in the 1970’s. However, few earth quakes were attributed to fracking before the mid 2000’s, so what changed?
What is Horizontal Drilling?
The oil and gas industry figured out how to turn a drill bit when it reaches a desired depth so it can run along an oil or gas field rather than just punching a single hole through it as is done in conventional vertical drilling. There are several major benefits to horizontal drilling:
- Because the the drilling extends into the underground oil or gas field, a single well can produce substantially more product than a traditional vertical well
- A drill can be placed in one location but extract oil or gas from a completely different location more than 1 kilometer away
- Local citizens and environmentalists are kept happy because they do not see drilling
- A single horizontal well “pad site” can now receive oil or gas from a reservoir that used to require dozens of vertical wells
- Horizontal drilling allows ready access to otherwise inaccessible (or very expensive) locations like under rivers and buildings
- Fracking a horizontal well makes much more financial sense because it is breaking the rock along a much larger area (potentially over a 1 kilometers), compared to a traditional vertical well that might cut through a few hundred feet of an oil or gas field
This light video explains horizontal drilling and fracking in the simplest terms:
It is clear that adding such massive amounts of pressure to crack rock that is millions of years old can cause “Induced Seismicity”, but surprisingly that is not the major cause of man made earthquakes in the oil and gas sector.
What Are Waste Water Disposal Wells?
Fracking fluids are dangerous and must be permanently sequestered deep in the ground in what are called “waste water disposal wells”. The name pretty much says it all. What is not obvious is that waste water disposal wells operate for years… many years… taking more and more fluid. One company is dumping as much as 300 Olympic sized swimming pools of fracking fluid into one of their disposal wells EVERY DAY. That is a lot of material to jam into the ground and eventually something is likely to give… like the earth. When the pressure gets to great, the ground shifts causing an earthquake until a pressure equilibrium is regained.
What Can Be Done To Reduce Induced Seismicity?
What has changed since the mid-2000’s is the advent of horizontal drilling with fracking. That outputs vast amounts of fluids which are pumped back into the disposal wells. The graph to the right shows that from 2005 to 2015 the OK state went from 1 notable earthquake per year to 850 per year.
To be clear, Induced Seismicity is typically counted as an earthquake only when it is a magnitude 3 or greater because that is the point where humans start to feel it and structures (buildings, roads, pipelines…) might be damaged.
In an effort to reduce Induced Seismicity, governments have brought in regulation limiting fracking and more notably waste water disposal wells primarily near known faults. You might think that would be the end of the story… but it isn’t.
The problem with limiting fracking and more notably waste water disposal wells is that the experience in Oklahoma is not the same as Ohio or Pennsylvania or many other locations around the world in that they have not seen any notable increase in earthquakes after fracking or waste water wells have been used. Worse, the most current research shows that places like Oklahoma that have limited such activities near known faults, have not substantially reduced the incidents of Induced Seismicity. This was quite unexpected.
It turns out that “known faults” are not a good predictors of induced earthquakes.
We recently attended a Canadian Society of Exploration Geophysicists (CSEG) luncheon with a presentation by Mirko van der Baan, Professor Exploration Seismology at the University of Alberta in which he explained that research now shows we need to look at a MUCH bigger picture that local fractures. We need to consider the earthquake hazard maps of Canada and the United States below:
From these maps we can see that places like Saskatchewan and Ohio have low likelihoods of earthquakes so it is no surprise that fracking operations in those regions are not causing any notable Induced Seismicity. This stands in contrast to Alberta and Oklahoma in which Induced Seismicity can be a serious problem.
… Contrary to Oklahoma, analysis of oil and gas production versus seismicity rates in six other states in the United States and three provinces in Canada finds no state- or province-wide correlation between increased seismicity and hydrocarbon production, despite 8- to 16-fold increases in production in some states. However, in various areas, seismicity rates have increased locally. A comparison with seismic hazard maps shows that human-induced seismicity is less likely in areas that have historically felt fewer earthquakes.
Professor Mirko van der Bann has all the numbers to back this up and if you have further interest we suggest you contact him as he is an excellent speaker.
As a result of this research, places like Oklahoma have very recently introduced regulation mandating across the board cuts to waist water wells, regardless of their proximity to known fractures and that seems to be making a difference.