Unconventional oil and gas extraction using a combination of hydraulic fracturing and horizontal drilling has transformed natural gas and oil production in North America and raised public concern about its intense water use and potential hazards, including drinking-water contamination. Such extraction is thought to pose no safety concerns for drinking water if it occurs many hundreds of meters to kilometers underground, yet no comprehensive analysis of hydraulic fracturing depths existed until publication of a new article in the journal Environmental Science & Technology. Based on reports of fracturing depths and water use at 44,000 wells in the United States between 2010 and 2013, the analysis finds the average fracturing depth was 8,300 feet and the average water use was 2,400,000 gallons per well. Many of these wells (6,900 or 16 percent) were fractured less than a mile from the surface; 2,600 wells (6 percent) were fractured above 3,000 feet. Because hydraulic fractures can propagate 2,000 feet upward, the analysis indicates that shallow wells may warrant special safeguards, including a mandatory registry of well locations, full chemical disclosure, and, where horizontal drilling is used, predrilling water testing to a radius 1,000 feet beyond a well’s greatest lateral extent.
Nicholas Institute for Environmental Policy Solutions