Hydraulic Fracturing and the Hydrologic Cycle
Posted on: Wednesday, September 14, 2011
The technology of hydraulic fracturing is responsible for unlocking natural gas that has been hidden away in shale deposits for hundreds of years. However, the hydraulic fracturing process uses water; about 4 to 5 million gallons of water is required to drill and hydraulically fracture one Barnett Shale natural gas well.
While this sounds like a lot of water, it has to be put into perspective. The natural gas industry in North Texas is not a significant user of water. According to the Tarrant Regional Water District or TRWD, only about 1% of the water that they supply to retailers is used for drilling and hydraulic fracturing.
So, what happens to the water once it is used in the drilling and fracturing process? Much of the water remains in the Barnett Shale but some comes back as produced water. While some of this water is recycled, most of it is injected into deep saltwater disposal wells. These wells are drilled to a depth of 10,000 to 12,000 feet into the Ellenberger formation, a saltwater-bearing dolomite. The salt-laden produced water of the Barnett Shale is then injected into the saltier Ellenberger aquifer.
It can be argued that this water is taken out of the hydrologic cycle because it is not allowed to evaporate into the atmosphere. While this argument is true, it doesn’t take into consideration the water vapor that is created when natural gas is produced. It is a give and take process: if water had not been used in the hydraulic fracturing process, then this natural gas would not have been produced. Additionally, the water that is produced when natural gas is burned is water that would not have been in the atmosphere otherwise.
It has been calculated that for every one million cubic feet of natural gas that is combusted (assuming that the gas is the standard 95% methane), approximately 10,675 gallons of water is produced (Matthew Mantell, P.E., GWPC, “Deep Shale Natural Gas and Water Use,” September 28, 2010). This is due to the scientific fact that, like all fossil fuels, natural gas produces H2O when combusted. Since the typical Barnett Shale well produces in the range of 2 MMCF per day, the typical Barnett Shale natural gas well creates a little over 20,000 gallons of water each day, assuming that all of the gas is combusted. Therefore, if it takes 5 million gallons of water to drill and fracture a Barnett Shale gas well, it will take just 250 days of production and combustion to replace the water that was used.
Since a Barnett Shale natural gas well will produce for 20 or 30 years (or longer), each Barnett Shale natural gas well is contributing far more water back into the hydrologic cycle than it used to drill and fracture the well.