Graphically Speaking: Fracking and Injection Wells

Mark Green
Posted June 20, 2012

Last week’s National Research Council report on hydraulic fracturing and earthquakes pretty much ends up where a number of scientists are on the correlation between fracking and quakes: that energy development from shale formations poses a low risk for tremors of significance. The report said more attention should be given to injection wells, which are used for waste disposal by a number of industrial enterprises, not just the oil and natural gas industry. AP science writer Seth Borenstein’s take on the report is here.

API, America’s Natural Gas Alliance and the American Exploration & Production Council have produced a couple of informational tools on hydraulic fracturing and seismic activity and underground injection control (UIC) wells that are especially timely with release of the council’s report. 

Highlights from the fracking document:

• Hydraulic fracturing is done with a mixture of more than 99.5 percent water and sand. The other one-half of 1 percent is chemical – including anti-bacterials and lubricants. See the FracFocus.org site for more on fracking fluids.
• Fracturing that occurs thousands of feet below the surface (and below groundwater aquifers) is carefully mapped with sophisticated equipment to optimize recovery of the oil and/or natural gas and to monitor the well itself. In other words, microseismic activity associated with fracking is thoroughly understood.

• One study of several thousand shale fracture treatments across North America showed the largest micro-quake measured about 0.8 or about 2,000 times less energy than a magnitude 3.0 earthquake. The chart below shows that most of the micro-quakes in this study were 10,000 to 1 million times smaller than a 3.0 earthquake, which is roughly equivalent to the passing of a nearby truck:

Highlights from the UIC document:

• The U.S. has about 151,000 Class II UIC wells used by the oil and natural gas industry, of which only a handful are being studied for possible links to earthquakes. These wells are a subset of more than 800,000 injection wells nationwide used to dispose of a variety of industrial wastes and for development of various minerals and geothermal energy sources. Here’s a map that shows the state-by-state well distribution:

• Injection wells are regulated by EPA under the Safe Drinking Water Act. In many cases EPA has delegated authority for the UIC program to the states, with 39 states having primary authority over 95 percent of all UIC Class II wells.
• Literature published in the past five years shows that less than 40 incidents of seismic activity felt on the surface were associated with Class II injection wells.

Injection wells pump fluids into deep rock formations (see graphic). It’s unusual, but in some cases a quake can occur when a number of geological and operational factors come together – especially the presence of hard, dense and brittle crystalline “basement rock.”  These quakes are almost always small, below the level that would be felt on the surface.

For more information, check out the Energy From Shale website.