Study focused on the Permian Basin, long a prolific oil production region that has seen resurgence with the advent of horizontal drilling.
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.
Further findings showed that the produced water from unconventional wells is largely injected into non-oil-producing geologic formations—a practice that can increase pressure and could potentially result in drilling-induced earthquakes.
To mitigate such seismicity, UT-Austin scientists pointed out that rather than injecting the produced water into these formations, operators could potentially reuse the water from unconventional wells to hydraulically fracture the next set of wells. Enough water is produced in the Midland and Delaware basins in the Permian to support hydraulic fracturing water use, and the water needs only minimal treatment (clean brine) to make it suitable for reuse, scientists found.
Marc Engle, the chief of a U.S. Geological Survey program on water use associated with energy production, said the UT-Austin study yields a comprehensive, data-driven look into how water is managed in the rapidly changing Permian Basin.
“This work by Scanlon et al., for the first time, provides interested stakeholders with a detailed view of water inflows and outflows from the Permian Basin,” Engle said. “Moreover, the work captures temporal trends through an important period where the industry shifted from vertical wells in conventional reservoirs to vertical then horizontal wells in continuous reservoirs.”
Despite those positive findings, there’s little incentive for wildcatters to employ the reused water method. While enough produced water for reuse is available, Scanlon said issue related to infrastructure, questions about produced water ownership, and low cost of fresh or brackish groundwater may keep disposal practices as they are currently practiced. But as unconventional operations in the Permian grow, reusing produced water may become more appealing, the study’s author’s concluded.
The study was funded by the Cynthia and George Mitchell Foundation, the University of Texas Energy Institute, the Tight Oil Resource Assessment consortium and the Jackson School of Geosciences.
>>> Image: A map showing the Permian Basin and the distribution of oil wells in the region. Bridget Scanlon/UT Austin.
Source: The Patch
Compiled and Published by GIB KNIGHT
Gib Knight is a private oil and gas investor and consultant, providing clients advanced analytics and building innovative visual business intelligence solutions to visualize the results, across a broad spectrum of regulatory filings and production data in Oklahoma and Texas. He is the founder of OklahomaMinerals.com, an online resource designed for mineral owners in Oklahoma.