Via the Mitchell Foundation, some interesting commentary at the management of water use for shale oil and gas:
The United States is becoming energy independent largely due to a technology that combines horizontal drilling with hydraulic fracturing. At a recent public meeting I posed a question to the audience, “How much water is used in hydraulic fracturing?” I received a quickly delivered, fiery response, “I don’t care—it’s tons of water!”
Even though the process does take tons of water—typically an average of about 20 tons, or ~5 million gallons per well—the emphasis was on the deleterious “I don’t care!”
This public cry helped motivate our team of researchers from the Bureau of Economic Geology as we worked on a study funded by the Cynthia and George Mitchell Foundation that put water use for hydraulic fracturing in context with energy production, water availability, and competing water demands.
Oil and Gas Production from Shale Reservoirs
The recent boom in energy production in the U.S. is from shale, a dense rock so tight that, to release the oil and gas trapped within, the rock must be fractured.
Accessing the shale may involve drilling vertically a mile or two underground, and perhaps one to two miles horizontally. Once drilled, the rock is fractured with small explosives and injected with high-pressure water containing proppants and chemicals. Proppants are small particles, sands or ceramic beads, that ‘prop’ the fractures open, and thechemicals enhance flow to the well.
This technology is considered unconventional when compared to the conventional technologies that consist of vertical wells drilled into more porous reservoirs. Water is necessary to extract oil and gas, and water is also necessary to generate electricity from the gas.
Deep geologic deposits of shale are found across the United States and globally, although 40-50 percent of those containing oil and/or gas, known as plays, are in water scarce regions. Water availability to sustain energy production puts pressure on all water users, particularly at the local scale wherever shale plays are developed.
Water Issues Related to Shale Energy Extraction
In the Eagle Ford Shale in Texas, our team (consisting of Bob Reedy, Bridget Scanlon, and Jean-Philippe Nicot) approached concerns about sustainable water use by addressing the following questions:
- How much water was used during the 2009–2013 period of exponential growth in energy production?
- How does the volume of water used during hydraulic fracturing compare to more conventional energy production?
- Is water scarcity an issue for continued energy production?
- What are the local competing demands on water? and,
- Are there more sustainable practices that can address water constraints?
Working with data available through FracFocus and IHS, we calculated that 40 billion gallons of water were used in the 8,300 wells drilled in the Eagle Ford from 2009 through 2013, and a projected 330 billion gallons of water will be needed over the next 20 years. Water use in 2013 represented 16 percent of total water use in the Eagle Ford play.
As a well is hydraulically fractured the shale also releases brine (ten times saltier than the ocean) that has been held within the geologic formation. This ‘produced water’ waste product is generally disposed of in deep, waste injection wells across Texas.
Comparing Water use for Oil Production — Unconventional Versus Conventional Reservoirs
How much energy does water used for hydraulic fracturing produce and how does it compare with conventional production?
Unconventional, hydraulic fracturing generally uses from 0.4 to 1.4 gallons of water to produce a gallon of oil, which is in the lower range of that used in conventional reservoirs in the U.S. (where the range is from 0.1 to 5 gallons of water per gallon of oil produced. The difference is in the timing of water use over the ~20 year production life of a well. Most of the water use in hydraulic fracturing is in the early stages at well completion versus later stages in conventional reservoirs for water flooding and enhanced oil recovery.
Comparing water demand to water supplies to assess water scarcity
Comparing water demand for hydraulic fracturing relative to water supplies requires quantifying water available in the Eagle Ford play. Groundwater is the primary source of water.
Groundwater storage was estimated from regional groundwater models developed by the Texas Water Development Board Groundwater Availability Modeling (GAM) program with an estimated 10,000 billion gallons of freshwater in the play, much greater than the 330 billion gallons projected for hydraulic fracturing
Reliance on fresh, potable water is not sustainable and competes with other needs and requirements. Recycling produced water is a more sustainable practice growing in application by some operators. Several municipalities have reported to be negotiating contracts to sell their treated municipal waste water to operators to support hydraulic fracturing, including Laredo, but the infrastructure to transport water to the operators has yet to be built.
Brackish groundwater is widely available in Texas aquifers with an estimated 80,000 billion gallons in the Eagle Ford Shale play (estimated from the TWDB Groundwater Availability Models). The Pecan Valley Groundwater Conservation District is taking the lead in fresh water conservation by revising their rules to encourage the extraction of brackish water.
We divided the Eagle Ford play into square mile grids to compare water demand to support hydraulic fracturing and other uses, including municipal, industrial, and irrigation water demands relative to water available to assess scarcity (demand exceeding supplies). We found that water scarcity should not be a concern to the industry, and hydraulic fracturing will not significantly impact other water users, except in Dimmit and Zavala counties in the northwest of the play where irrigation demand is the dominant water use sector.
As groundwater is extracted pressures in the aquifer decline and water levels drop. Reviewing groundwater elevation data monitored by the TWDB shows little impact across the play, however, some areas do show local declines. We estimate that ~6 percent of the western, more arid region of the play has experienced water table declines up to 200 feet in the Carrizo Wilcox aquifer.
Impacts of Hydraulic Fracturing on Water Resources
We also investigated the large scale impacts of shale gas on water resources in Texas by comparing water use for unconventional shale gas extraction to water use in power plants burning this natural gas.
We found that the volume of water used for gas extraction is ~6 percent of the water consumed in power production. In addition, use of natural gas in combined cycle power plants saves water when compared to water use in steam turbine coal, nuclear, and other older natural gas power plant technologies. We estimated that for every gallon of water used for unconventional shale gas extraction in 2011 we saved 330 gallon of water by generating power using natural gas rather than coal or nuclear fuels.
Our conclusions
Our findings indicate that we are using more water for oil and gas production derived from unconventional reservoirs because we are producing more oil and gas, not because hydraulic fracturing requires more water per unit of energy production. We can manage water use more sustainably by recycling water, using brackish groundwater, and reducing competition with freshwater users, such as irrigators and municipalities.
So, what’s the important takeaway from this study?
Although it may seem obvious to most, as we move toward more energy independence in the United States by increasing energy production, we are using significantly more water. New and unconventional technologies allow us to produce more energy with similar water intensities to conventional production, and water resource sustainability is feasible by choosing alternatives to fresh water sources.
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