The Government Accountability Office (GAO) recently released an analysis of technologies available to cut water use in hydraulic fracturing and thermoelectric power plant cooling to identify how water-scarce areas of the country could benefit from these technologies (GAO-15-545).
Perhaps of special interest to readers is the GAO analysis of waterless and low-water stimulation fluids.
GAO concludes that water-free hydraulic fracturing techniques are either unproven or are applicable to only specific geologic formations. However, strategies to use produced or flow-back water or brackish water have proven effective in reducing water use. These have the added benefit of cutting costs and reducing disposal volumes. However, there are some arid areas where water consumption for hydraulic fracturing stresses subsurface aquifers.
Thermoelectric plant cooling, which represents 38 percent of U.S. water withdrawals, seems like a logical topic for GAO to pair with hydraulic fracturing because natural gas combined cycle (NGCC), the most water-efficient fossil-fuel power generation technology, has blossomed with the growth in natural gas production from hydraulic fracturing.
In NGCC a gas turbine generates electricity and the waste heat is used to make steam to generate additional electricity via a steam turbine. The gas turbine does not require water for cooling but the steam generation portion often uses wet cooling. Natural gas (including hydraulic fracturing and NGCC) reduces water use in power generation by up to 60% relative to coal and nuclear plants (Scanlon, 2015).
Natural gas power generation is now about 50 percent above levels in 2003, and more than 80 percent of natural gas power generation comes from NGCC (Energy Information Administration, EIA).
Of course, wind and solar photovoltaic use little water, and energy efficiency technologies that cut energy consumption unsurprisingly save lots of water.
Reduced- or Waterless Stimulation Fluids
GAO investigated the use of gases in place of water—liquefied petroleum gas (LPG, propane or butane), nitrogen and CO2—as well as foams, and the technique of channel fracturing.
LPG, nitrogen and CO2 are used with water-sensitive shales and in under-pressured formations. Operators reported to GAO that initial tests of LPG-based fracturing in south Texas have shown a notable increase in production of oil and gas. The cost of LPG, the lack of long-term production data, and the safety risks in using a flammable gas have limited the use of this technology.
Foam-based fractures have generally been used in under pressured and water-sensitive formations. The foams are composed of water, a foaming agent, and nitrogen or CO2. The U.S. Department of Energy developed foam-based fracturing for use in low-pressure Devonian, Appalachian basin shales in the 1970s. However, it proved unsuccessful in higher-pressure formations, such as the Barnett, that were developed in the 1990s. GAO predicts that foam-fracturing technology is unlikely to expand except in low-pressure formations unless water consumption becomes a larger issue.
Channel fracturing is an alternative formation stimulation technology to increase oil and gas production while reducing water consumption. The technique uses injection of proppant-laden fluid followed by injection of proppant-free gelled liquid. The technique creates open flow channels through proppant-filled fractures. Channel fractures have been shown to increase oil and gas production and reduce water and proppant consumption in Eagle Ford, Barnett and Marcellus wells (Altman et al. 2012). Analysts and operators reported to GAO that the technique has not been demonstrated in enough regions or over sufficient time to determine its full impact. GAO also reported that some operators consider channel fracturing as just one of many enhancements that are improving the efficiency of hydraulic fracturing.
Water treatment, recycling and reuse are important to reducing costs, improving efficiency and reducing demand for fresh water. GAO reports studies that showed that ten percent of the operating costs of a Marcellus well go to water management and handling. GAO reports a Texas study that showed that freshwater use varied from 20 to 95 percent across different plays. The balance of water was recycled or brackish. Data on other basins show that essentially all water produced from the Marcellus formation and in the Piceance basin is reused.
Thermoelectric Plant Cooling
Coal-fired thermoelectric power plant cooling systems generally are either once-through or recycling systems using water to cool and condense the steam that is produced to drive turbines. Thermoelectric power plants in general and once-through cooling systems are more common in areas where water is plentiful.
Dry and hybrid cooling systems are used in areas of water scarcity, but the systems use more land and require additional fuel per unit of electricity produced. An additional problem is that these low-water systems cannot be retrofitted on existing plants. However, newer NGCC plants generally use dry cooling for the steam-generation part of the system.
The GAO report also describes a number of emerging cooling technologies that are not commercially proven but may be effective are reducing water consumption in the future.