Environmental Considerations for the Water-Energy Nexus

We have discussed the synergy between energy and water, how this synergy impacts Texas, and the history of energy in Texas. The availability of adequate water supplies has an impact on the availability of energy, and energy production and generation activities affect the availability and quality of water. As these two resources see increasing demand and growing limitations on supply, energy and water must begin to be managed together to maintain reliable energy and water supplies.¹Department of Energy. (2006, December). Energy demands on water resources. Report to Congress on the interdependency of energy and water. To gain insight on the inter-relationship of these resources, let’s now explore how water co-production and production varies as we consume various energy resources.

The inter-relationships between water and energy.

Water Production and Consumption with Resource Extraction

Let’s examine how water is produced (typically brine) as part of the extraction process for several energy resources. We will also look at the water consumed to extract these resource and refine them into products.

Crude Oil 

In 2020, Texas accounted for 43% of the nation’s crude oil production.²Energy Information Administration. (2021, April 15). Texas state profile and energy estimates. https://www.eia.gov/state/?sid=TX Oil production has increased greatly due to hydraulic fracturing and horizontal drilling with the Shale Revolution. Hydraulic fracturing is a method used to stimulate flow within low permeability shale formations. Water is injected at high pressures into a well and creates fractures in the formation, forming flow paths for natural gas to flow through the wellbore towards the surface. According to the American Petroleum Institute, roughly forty million gallons of water are used throughout the life of an individual hydraulically fractured well.³American Petroleum Institute. (n.d.). How Much Water Does Hydraulic Fracturing Use? Energy API. Retrieved July 8, 2021, from https://www.api.org/oil-and-natural-gas/energy-primers/hydraulic-fracturing/how-much-water-does-hydraulic-fracturing-use-2

Water is used in various ways to extract this oil, with the largest volumes used for hydraulic fracturing. However, one of the biggest issues with crude oil extraction is the co-production of water that comes to the surface, termed produced water, often saline and containing other harmful contaminants. That produced water then needs to be managed: either properly treated and disposed of or treated for reuse. Traditional high permeability conventional oil reservoirs in the Texas Permian Basin produced on average 13 barrels of water with one barrel of oil.⁴Scanlon, B. R., Reedy, R. C., Male, F. & Walsh, M. (2017). Water issues related to transitioning from conventional to unconventional oil production in the Permian Basin. Environmental Science & Technology. 51(18). 10903-10912. However, oil production from unconventional shale reservoirs within the past decade generated an average of two barrels of water with one barrel of oil. The volume of water co-produced with oil varies with the type of reservoir, type of production (oil or gas), and geology of the region.⁵Scanlon, B. R., Ikonnikova, S., Yang, Q.  & Reedy, R. C. (2020). Will Water Issues Constrain Oil and Gas Production in the United States? Environmental Science & Technology. 54(6). 3510-3519.

Once this crude oil is produced it must then be liquified into different types of fuel we can use. This process is known as “refining.” Refining oil also requires the use of water. Depending on the design of the facility, water use can vary significantly, but a typical refinery will use about 1.5 barrels of water to process 1 barrel of crude oil.⁶Weaver, L.E., Henderson, R. & Blieszner, J. (2016, January). Potential vulnerability of U.S. petroleum refineries to increasing water temperature and/or reduced water availability. U.S. Department of Energy. https://www.energy.gov/sites/prod/files/2016/03/f30/US%20DOE%20Refinery%20Water%20Study.pdf The following list demonstrates everything that can be made from just a single barrel of crude oil (42 gallons):⁷Desjardins, J. (2020, June 17). What Can Be Made from One Barrel of Oil? Visual Capitalist. https://www.visualcapitalist.com/can-made-one-barrel-oil/.

• Enough gasoline to drive a medium-sized car over 450km (280 miles).
• Enough distillate fuel to drive a large truck for almost 65km (40 miles). If jet fuel fraction is included, that same truck can run nearly 80km (50 miles).
• Nearly 70 kWh of electricity at a power plant generated by residual fuel.
• About 1.8 kg (4 lbs) of charcoal briquettes.
• Enough propane to fill 12 small (14.1 ounce) cylinders for home, camping or workshop use.
• Asphalt to make about 3.8 L (one gallon) of tar for patching roofs or streets.
• Lubricants to make about a 0.95 L (one quart) of motor oil.
• Wax for 170 birthday candles or 27 wax crayons.

And after producing the above products, there would be enough petrochemicals leftover as a base to make other products, such as:

• 39 polyester shirts or 540 toothbrushes

Now, we just need to figure out what to do with the 2 barrels of produced water!

Natural Gas 

In 2020, Texas accounted for 26% of the nation’s marketed natural gas production.⁸Energy Information Administration. (2021, April 15). Texas state profile and energy estimates. https://www.eia.gov/state/?sid=TX Natural gas production has also increased greatly with the Shale Revolution. As with crude oil, water is used in a variety of ways to extract natural gas, with the largest volume of water consumed by hydraulic fracturing. 

Hydraulically fracturing a well also entails the production of original formation water and a smaller component of fluids injected to fracture the well. These produced fluids must be injected into the subsurface, managed, or recycled. Projections show that hydraulic fracturing in the Permian Basin alone could contribute to production of almost forty million barrels of produced water each day by 2030.⁹April Reese. (2020, February 5). There’s a new boom in the Permian Basin – wastewater. High Country News. https://www.hcn.org/articles/water-theres-a-new-boom-in-the-permian-basin-wastewater

Water Consumption for Electricity Generation

Now, we will compare energy resources based on the water needed to generate one megawatt-hr of electricity for consumption. In these cases, a primary energy source (e.g., natural gas) is used to produce a secondary energy source (electricity). Thermoelectric power plants require water to be withdrawn from sources such as rivers or lakes to cool equipment used during the process of generating electricity. After withdrawal, the water is either consumed (e.g., lost to evaporation), or the water is diverted or discharged back into a body of water. Texas produces more electricity than any other state, generating almost twice as much as Florida, the second-highest electricity-producing state.¹⁰Energy Information Administration. (2021, April 15). Texas state profile and energy estimates. https://www.eia.gov/state/?sid=TX

Natural Gas

What about electricity generation? Natural-gas fired power plants have become increasingly important in the mix of Texas electricity generation. Natural gas demand for electricity generation usually peaks during the summer in Texas when residents increase their air-conditioning use. Natural gas has generated as much as 61% of Texas’s monthly net electricity generation during peak summer electricity demand. Natural gas accounts for a smaller share of the state’s electricity generation during the winter because total electricity demand is lower and demand for natural gas for heating is higher. A natural-gas fired power plant uses 198 gallons of water to produce one megawatt-hr of electricity.¹¹Energy Information Administration. (2021, April 15). Texas state profile and energy estimates. https://www.eia.gov/state/?sid=TX

Wind

What about wind? Wind energy does not require any water. Greater reliance on renewable energy as we move forward will likely have a positive impact on water resources, as wind is far less water intensive than fossil fuels. Texas leads the nation in wind-powered generation and produced about 28% of all U.S. wind-powered electricity in 2020. Wind power surpassed the state’s nuclear generation for the first time in 2014 and produced more than twice as much electricity as the state’s two nuclear power plants combined in 2020.¹²Energy Information Administration. (2021, April 15). Texas state profile and energy estimates. https://www.eia.gov/state/?sid=TX However, reliance on wind alone is likely unattainable in the near future, especially in Texas. 

Rapid growth of renewable energy has outstripped the carrying capacity of transmission lines in West Texas. Even when demand soars and electricity supplies run short, ERCOT must limit the power West Texas wind and solar farms can sell into the grid because of transmission constraints. More than 20,000 megawatts of wind energy alone are generated in the area. Due to transmission line capacity and other technical constraints, ERCOT officials must limit power transmission to less than 12,000 megawatts to keep the lines working properly.¹³Webb, S. (2021, June 4). Wind and solar power is rapidly growing in Texas, but ERCOT limits how much goes to the grid. Houston Chronicle.

Coal 

Coal is extremely water intensive! According to the U.S. Geological Survey, up to 75 trillion gallons of water are needed each year to produce electricity through burning coal.¹⁴Global Energy Monitor. (2021, April 30). Water consumption from coal plants. Global Energy Monitor. https://www.gem.wiki/Water_consumption_from_coal_plants Think about one megawatt-hour of electricity, which yields enough energy to run two refrigerators for a year.¹⁵Nussey, B. (2020, February 26). What can you do with a megawatt-hour? Freeing Energy. https://www.freeingenergy.com/what-is-a-megawatt-hour-of-electricity-and-what-can-you-do-with-it/ If that megawatt-hour of electricity was produced by burning coal, roughly 600 gallons of water would be consumed at the coal-fired power plant for cooling. More water may need to be withdrawn for mining the coal.¹⁶Scanlon, B. R., Duncan, I. , & Reedy, R. C. (2013). Drought and the water-energy nexus in Texas. Environmental Research Letters. 8(4). 

Nuclear 

At a nuclear power reactor, fission heats water generating steam that then turns a turbine to generate electricity.¹⁷Energy Information Administration. (n.d.). Nuclear power plants. Retrieved July 8, 2021, from https://www.eia.gov/energyexplained/nuclear/nuclear-power-plants.php Large quantities of water are then used to cool the plant, which can take about 460 gallons of water per megawatt-hour of electricity in Texas.¹⁸Scanlon, B. R., Duncan, I. , & Reedy, R. C. (2013). Drought and the water-energy nexus in Texas. Environmental Research Letters. 8(4). In addition, the mining for uranium that is used to create nuclear fission is water intensive. 

Solar 

What about solar energy? Photovoltaic solar does not have water requirements for cooling. However, photovoltaic solar energy may consume ~ 30 gallons of water per megawatt-hour of electricity (to clean the panels).¹⁹Solar Energy Industries Association. (n.d.). Water Use Management. Retrieved July 8, 2021, from https://www.seia.org/initiatives/water-use-management

Hydroelectric 

Hydroelectric power plants use flowing water to generate electricity through the use of turbines. While this type of energy source does not use up water like other forms of energy, hydroelectric power plants do degrade water landscapes and ecosystems. These negative impacts result from dams that are often built to provide the flow of falling water to power turbines. Hydroelectric power plants can also be unreliable in times of drought, such that turbines are unable to spin and initiate electricity generation when flow of water is low or absent. 

Geothermal 

Geothermal energy is the process of using heat from hot water deep within the Earth to generate power. While this water is then recycled back into the earth, additional water is used for cooling purposes. Depending on the cooling technology used, geothermal plants may use as much as 4,000 gallons of water per megawatt-hour of electricity generated.²⁰Union of Concerned Scientists. (2013, March 5). Environmental Impacts of Geothermal Energy. Union of Concerned Scientists. https://www.ucsusa.org/resources/environmental-impacts-geothermal-energy This image shows the largest geothermal power plant in the United States: The Geysers in California.

The natural gas glut resulting from the Shale Revolution drowned out some of the interest in geothermal in Texas. Geothermal energy does not contribute to the state electric grid right now. But that might change. In Texas, a new opportunity for geothermal has arisen. Geothermal technology could potentially repurpose end-of-life oil and gas wells. By drawing heat up from old wells, geothermal energy could alleviate the expense to plug and abandon these wells. This new application could extend the life of these wells as a source for clean energy for decades.²¹ Richter, A. (2021, April 1) Could geothermal energy be a game-changer for Texas? Think Geoenergy. https://www.thinkgeoenergy.com/could-geothermal-energy-be-a-game-changer-for-texas/