Robert Jackson, an environmental scientist at Stanford Univ., has been immersed in the hydraulic fracturing issue for close to seven years now. His interests lie in how to make the process safe, something he believes can be done. However, what can be done and what is done are often quite different.
“Wells implement many safeguards, first and foremost through good well integrity, the steel casing and cementing that’s used to isolate the oil and gas from the environment,” says Jackson to R&D Magazine. He further says fracking wells should have a depth of at least one mile.
According to FracFocus, steel casings are important in regards to groundwater protection “because they provide for the isolation of fresh water zones and groundwater from the inside of the well.” But cementing is of further importance. “Proper sealing of annular spaces with cement creates a hydraulic barrier to both vertical and horizontal fluid migration,” according to FracFocus. “The quality of the initial cement job is a critical factor in the prevention of fluid movement from deeper zones into groundwater resources.”
In a study, published in Environmental Science & Technology, Jackson and colleagues found around 6,900 oil and gas wells in the U.S. were fracked at less than a mile from the surface. Additionally, “at least 2,600 wells were fracked at depths shallower than 3,000 ft, some as shallow as 100 ft,” according to the university.
Due to fracking, U.S. production of oil rose to 9 million barrels per day by the end of 2014, a number that rivals Saudi Arabia, the world’s largest oil producer. Jackson estimates there are around 1 million oil and gas wells in the U.S. utilizing fracking.
Wells produce “for years, but production drops off much more quickly with fractured wells than with conventional wells,” says Jackson, who is also a senior fellow at the Stanford Institute for the Environment and the Precourt Institute for Energy.
In North Dakota, production drops by 80% or more after the first two years of production, according to the paper. The result is “tens of thousands of unconventional wells must be drilled each year in the U.S. to maintain production through time,” according to the researchers.
“Public concerns over hydraulic fracking include its water requirements and the potential for drinking-water contamination and surface chemical spills, induced seismicity and emissions of air toxics and greenhouse gases,” the researchers write.
Those “chemicals are used as biocides, surfactants, anti-corrosion agents and viscosity adjustors, among other things,” says Jackson.
The study
The study made use of data available from FracFocus and gleaned information from 44,000 fracking locations across the U.S. “Within 3,000 ft of the surface, 2,600 wells were hydraulically fractured, particularly in Texas (850 wells), California (720), Arkansas (310) and Wyoming (300),” the researchers write.
One might think the shallower a well, the less water and chemicals used for extraction. However, the researchers found the average volume of water was indistinguishable from the amount used in deeper wells. The study reports the average volume used to frack was 2.4 million gallons. In Arkansas, wells between 1,000 and 2,000 ft used 5 million gallons, wells between 2,000 and 3,000 ft used 5.1 million gallons and wells deeper than 3,000 ft used 5.3 million gallons.
According to the researchers, only Texas and Colorado have special requirements for shallow hydraulic fracturing.
“Texas prescribes a different casing and cementing process and additional pressure tests and cement evaluations,” according to the researchers. “Colorado has a policy targeting stimulation at depths of 2,000 ft or less” and “requires additional geological, hydrogeological and engineering assessments, based on which the Colorado Oil and Gas Conservation Commission may increase cementing requirements of limit stimulation.”
The authors suggest additional safeguards when it comes to U.S. wells, including more information regarding distances between groundwater resources and potential fractures, state assessments of additional safety measures for wells shallower than 3,000 ft, a mandatory registry of fracking sites, full disclosure of chemicals used and pre-drilling tests of nearby water resources.
“The public pays to clean up acid mine drainage today because of poor practices decades ago,” Jackson said. “What are we doing today that may cause problems tomorrow?”
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