AUSTIN, TX — A University of Texas at Austin study has found that reusing the large amounts of water rising to the surface at oil exploration sites is not only efficient, but a way to potentially reduce the chances of inducing earthquakes from horizontal drilling activity.

The university's study centered on the Permian Basin, an expansive oil field sprawled over large swaths of land in Texas and New Mexico. The focus also was on hydraulic fracturing—a practice more commonly known as "fracking"—that involves drilling down to search for oil but then proceeding in a horizontal fashion beneath the earth's surface, cracking through rock and sediment to get to oil pockets in crevices otherwise not able to be extracted via conventional drilling techniques. But at fracking becomes more widely practiced, the incidence of man-made earthquakes heightens. The UT Bureau of Economic Geology led the study highlighting key differences in water use between conventional drill sites and sites that use hydraulic fracturing rapidly expanding in use in the Permian Basin.

The study was published in Environmental Science & Technology on Sept. 6, with results indicating that recycling water produced during operations at other hydraulic fracturing sites could help reduce potential problems associated with the technology, university officials said. Among the drawbacks studies were the need for large upfront water use and potentially induced seismicity or earthquakes, triggered by injecting the water produced during operations back into the ground.

"What I think may push the reuse of produced water a little more are concerns about over-pressuring and potential induced seismicity," said lead author Bridget Scanlon, a senior research scientist and director of the bureau's Sustainable Water Resources Program. "In the Permian we have a good opportunity for reusing or recycling produced water for hydraulic fracturing."

Scanlon co-authored the study with bureau researchers Robert Reedy, Frank Male and Mark Walsh. The bureau is a research unit of the UT Jackson School of Geosciences. The Permian Basin has long been a fruitful area for extraction of oil using conventional methods, with production peaking in the 1970s and the output from the region accounting for nearly 20 percent of U.S. oil production. Since the advent of horizontal drilling technology, oil production in the region is nearing a level as prolific as the 1970s peak. Increasingly, the oil industry has turned to horizontal drilling to get at the less permeable shale formations found in the region.

To give an idea of the horizontal drilling success: The U.S. Geological Survey estimates that the Permian's Wolfcamp Shale alone could hold 20 billion barrels of oil, the largest unconventional resource ever evaluated by the agency.



As part of the UT-Austin study on the amounts of water at the drilling site, a decade's worth of water data from 2005 to 2015 was examined. The researchers tracked how much water was produced and how it was managed from conventional and unconventional wells, comparing those volumes with water use for hydraulic fracturing.

Not surprisingly, hydraulic drilling was found to use exponentially more water than conventional vertical drilling. The average volume of water needed per well, the study found, has increased by about 10 times during the past decade, with a median value of 250,000 barrels or 10 million gallons of water used per well in the Midland Basin in 2015. Yet unconventional wells produce much less water than conventional wells do, averaging about three barrels of water per barrel of oil versus 13 barrels of water per barrel of oil from conventional wells. In conventional operations, produced water is disposed of by injecting it into depleted conventional reservoirs, a process that maintains pressure in the reservoir and can help bring up additional oil through enhanced oil recovery, officials noted. Unconventional wells generate only about a tenth of the water produced by conventional wells, but this "produced water" can't be injected into the shale formations given the low permeability of the shales, the study found.