Two weeks ago I happened to talk about the responses of water levels in wells to earthquakes and the limits of our knowledge as to how and why this happens over distances of hundreds even thousands of miles. I questioned what this connection of groundwater to earthquakes might mean for groundwater in areas that are fracked. Fracking or hydraulic fracturing as it is more properly known is the pressurized injection of water with chemical additives into a geologic formation. The pressure used exceeds the rock strength and the fluid cracks open or enlarges fractures in the rocks and shale. As the formation is fractured, a “propping agent,” such as sand or ceramic beads, is pumped into the fractures to keep them from closing when the pumping stops and the pressure is released. Natural gas will flow from the fractures in the rock and shale into the wells increasing the recovery of the methane.
In hydraulic fracking in a shale formation to enhance recovery of natural gas on average 2-3 million gallons of chemicals and water is pumped into the shale formation at 9,000 pounds per square inch and literally cracks the shale or breaks open existing cracks and allows the trapped natural gas to flow. While geologists and engineers believe that there is little risk that the fracking “water,” a mix chemicals and water, will somehow infiltrate groundwater reserves though a fissure created by the fracking there are other routes of contamination and impact. It is believed that the intervening layers of rock would prevent a fissure from extending thousands of feet to the water table; there are other risks in how we build wells and fracture the shale. There have been documented cases of seepage into drinking water wells through improperly sealed or abandoned drilling wells. There are also places where groundwater is only several hundred feet above the gas reserves as they are in Wyoming and groundwater is more easily directly impacted by fracking.
The US Geological Survey has been studying the factors that impact the response of groundwater wells to earthquakes, including the magnitude and depth of the earthquake, distance from the epicenter, and the type of rock that surrounds the groundwater. The depth of the well, whether the aquifer is confined or unconfined, and well construction also influence the degree of water-level fluctuations in wells in response to seismic waves. It has been suggested that some aquifers may even act as resonators, which may amplify the response. The US Geological Survey has been able to add more data points to their information base this past week and someday we may know more about this relationship and groundwater itself, but right now all the US Geological Survey can do is observe and collect data.
Dr. Cliff Frohlich of the University of Texas at Austin was part of a team of researchers who studied a series of small earthquakes that struck near Dallas, Texas in 2008 and 2009, in an area where natural gas companies had used fracking. The epicenter of the quakes turned out to be about half a mile from a deep injection well under the Dallas-Fort Worth International Airport used to dispose of the fracking fluid. The largest earthquake of the series measured 3.3 on the Richter scale, a very small earthquake. In a study that was published in the Bulletin of the Seismological Society of America, the researchers also reviewed records from US Geological Survey seismic-recording stations in Oklahoma and Dallas. It was concluded by the researchers that the fracking did not cause the earthquakes, but there seemed to be a relationship to the deep well injection of the fracking fluid to the earthquakes. The water caused the earthquakes.
This past spring, the Shale Gas Subcommittee of the Secretary of Energy Advisory Board was created to identify the measures that can be taken to reduce the environmental impact and improve the safety of shale gas production utilizing fracking. Dr. Mark Zoback of Stanford University was a member of the committee. He has studied the relationship of earthquakes to fracking and is a strong supporter of replacing coal with natural gas. He feels the risk of earthquake from fracking fluid disposal and all other risks from fracking are manageable. According to Dr. Zoback the risk could be mitigated by treating the water on the surface or shipping the water to a disposal well that isn’t near a fault. He felt the risk could be addressed by oil and gas companies identifying faults near potential well sites, and simply staying away from the faults.
Our ability to recover natural gas buried a mile or more beneath the earth has increased. Advances in horizontal drilling which allows a vertically drilled well to turn and run thousands of feet laterally through the earth combined with advances in hydraulic fracking, the pumping of millions of gallons of chemicals and water into shale at high pressure have increased our ability to recover natural gas from shale. Hydraulic fracking is a technology that was unknown 60 years ago. In the past decade the advances in drilling and fracking technology have been adapted to exploit gas in the Barnett shale in the Fort Worth Basin in Texas and applied to a series of major shale gas deposits that could not have been viable without the advances in drilling and fracking. The Fayetteville shale, the Haynesville shale, the Marcellus shale reserves all in the United States and the Horn River shale in Canada are now accessible. At the current rate of natural gas consumption North America is reported to have a 100-year supply of proven, producible reserves and even with expanded use of natural gas, there is more than a generation of currently accessible reserves. This natural gas could profoundly change the future of our nation and would we live in; however we need to be cautious about what other impacts fracking might have especially to hydraulic balance of groundwater.