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How it Works: Water for Natural Gas

Contents:
1. Electricity Generation
2. Fuel Extraction
3. Fuel Processing

About one fifth of electricity in the United States comes from natural gas power plants. Water is required first to extract natural gas from its underground source and then to transform the fuel’s chemical energy into electricity.

Electricity Generation

More than 80 percent of natural gas-fired generation in the United States comes from natural gas combined-cycle (NGCC) power plants. The rest are simple gas combustion turbines (5 percent) or simple steam turbines (12 percent).[1]  NGCC plants first use a gas combustion turbine to generate electricity, and then use the waste heat to make steam to generate additional electricity in a steam turbine.  Because gas combustion turbines require no cooling (having no steam to condense), the overall combined cycle system requires much less water for cooling than traditional steam turbine technologies.

Because the amount of cooling necessary is much less per unit of electricity output in NGCC plants than in coal or nuclear plants, dry cooling systems are more economical for NGCC plants than for other thermoelectric options. A dry cooling unit in a NGCC plant need only be one thirdthe size of a dry cooling unit for a coal or nuclear plant with the same electricity output.[2]  Indeed, about 60 percent of natural gas combined cycle plants in the United States use dry cooling technology; most of the remainder (about 30 percent) rely on wet-recirculating systems. Fewer than ten percent use once-through cooling.[3]

Fuel Extraction

Natural gas in the United States has traditionally been extracted from deep vertical wells that require relatively small amounts of water for drilling but that produce more than 200 billion gallons of water per year that surfaces with the gas on extraction.[4] This produced water is often trapped in these underground formations alongside natural gas.[5] The main methods of disposing of produced water involve pumping it back into oil- or gas-producing wells to bolster production, or injecting it deep into other formations below usable groundwater resources.[6]

Hydrofracking Diagram. Graphic Source: ProPublica

In the last few years, major new U.S. sources of natural gas have begun to be tapped from shale gas deposits. These new sources are less readily accessible than conventional deposits, and extracting the gas requires a process called hydraulic fracturing or “hydro-fracking.” The process involves drilling vertically down to where the gas is trapped and then turning to follow the deposit horizontally. A mixture of water and chemicals is then sent through the drill hole at high pressures, creating fractures in the rock and allowing the trapped natural gas to escape to the surface. According to oil and gas industry estimates, 90 percent of currently operating wells have used hydraulic fracturing, and the technique is responsible for 30 percent of total domestic oil and natural gas.[7]

Hydro-fracking has become controversial  because of concerns about groundwater being contaminated with natural gas and the chemicals used in the process.  A single hydro-fracking treatment can yield 15,000 gallons of chemical waste from the fracking fluids.[8] Due to the failure of the industry to disclose the mix of chemicals used in the process and to its successful lobbying to exempt the process from the Federal Clean Water and Safe Drinking Water Acts, concerns have emerged about the ability of local wastewater facilities to properly treat the produced fracking water.[9],[10] Recognizing the potential health and environmental impacts on local water sources, the EPA is studying water impacts of hydro-fracking on gas shale production.[11]

Active Marcellus Shale gas well in West Virginia. Additional water storage pit is not captured in the photo. Photo Source: WVSORO

In addition to concerns about water quality, water quantity is also an issue.  A single hydro-fracked well can require several million gallons per treatment--dozens of times what is used in conventional vertical drilling.[12],[13] Withdrawing this amount of water over a short period of time can strain local water sources.

Fuel Processing

After extraction, an additional 400 million gallons of water per day are consumed for natural gas refining and pipeline operations.[14]