Water for hydraulic fracturing

Water is the most commonly used fluid in hydraulic fracturing, and it is used in large quantities. Chemicals are added to the water to aid in fracturing and prevent damage to the reservoir, and normally less than 1 percent of the fluid contents are chemical compounds. Because fracturing involves a large amount of water, innovations to reuse/recycle and safely dispose of the water are an important part of environmental stewardship.

Mechanism

Hydraulic fracturing is the process of pumping fluid into a wellbore at an injection rate too high for the formation to accept without breaking. During injection, the formation’s resistance to flow increases, and the pressure in the wellbore increases to a value called the break-down pressure, which is the sum of the in-situ compressive stress and the strength of the formation. When the formation “breaks down,” a fracture is formed, and the injected fluid flows through it.

Fluid not containing any solid (called the “pad”) is injected first, until the fracture is wide enough to accept a propping agent. The purpose of the propping agent is to keep apart the fracture surfaces once the pumping operation ceases, the pressure in the fracture decreases bellow the compressive in-situ stress trying to close the fracture. In deep reservoirs, man-made ceramic beads are used to hold open or “prop” the fracture. In shallow reservoirs, sand is normally used as the propping agent.

Chemical additives

Water comprises 90 percent of typical fracking fluid, followed by 9.5 percent sand and 0.5 percent other chemical additives. The chemicals serve multiple functions, including limiting the growth of bacteria and preventing corrosion of the well casing. The conditions of the well being fractured determine the number of chemical additives used. Typically, very low concentrations of between 3 and 12 additive chemicals will be used, depending on the characteristics of the water and the formation being fractured. Each component serves a specific purpose. For example, the predominant fluids used for fracture treatments in the gas shale plays are water‐based fracturing fluids mixed with friction‐reducing additives (called slickwater). The addition of friction reducers allows fracturing fluids and proppants, like sand or small ceramic beads, to be pumped to the target zone at a higher rate and reduced pressure than with water alone. Other additives include: biocides to prevent microorganism growth and reduce biofouling of the fractures; oxygen scavengers and other stabilizers to prevent corrosion of metal pipes; and acids to remove drilling mud damage within the near‐wellbore area.

Water sources

Large quantities of relatively fresh water are essential in hydraulic fracturing. Water quality is a key factor in fracturing because impurities can reduce the efficacy of the additives used in the process. Most water used in hydraulic fracturing comes from surface water sources like lakes, rivers, aquifers, and municipal supplies, which may have to be hauled over long distances. But groundwater can be used to supplement surface water supplies where it is plentiful. In some areas, the water used for fracturing is controlled by a river basin commission or water resources board. In other places, water is owned by private individuals who can distribute it as they choose.

Quantity of water used

An average of four to six million gallons of water are used to stimulate contemporary unconventional wells. The amount of water used in hydraulic fracturing, particularly in shale gas formations, appears substantial, but it is small when compared to other water uses such as agriculture, manufacturing, and municipal water supplies. (https://fracfocus.org/water-protection/hydraulic-fracturing-usage) For example, electric generation uses nearly 150 million gallons a day in the Susquehanna River Basin, while the projected total demand for peak Marcellus Shale activity in the same area is 8.4 million gallons per day. Horizontal well high-volume fracturing use has accelerated significantly since 2005. Per a Department of Energy report conducted by ALL Consulting, "Estimates of peak drilling activity in New York, Pennsylvania, and West Virginia indicate that maximum water use in the Marcellus, at the peak of production for each state, assuming 5 million gallons of water per well, would be about 650 million barrels per year. This represents less than 0.8 percent of the 85 billion barrels per year used in the area overlying the Marcellus Shale in New York, Pennsylvania, and West Virginia."

Disposal and recycling of wastewater

Upon stimulation treatment, water used to fracture the well, in amounts as large as 50%, can rise back to the surface, along with the initial production, as flowback water. Flowback and produced waters, both part of the production stream, must be separated from the formation. In most cases, flowback and produced water are disposed into an injection well, put in evaporation ponds, or treated and disposed of according to government regulations. Water management can significantly add to the cost and environmental footprint of oil production and innovations in water management can provide significant economic and environmental gains. New treatment technologies make recycling of water recovered from hydraulic fracturing possible. Methods for recycling fracking water include anaerobic and aerobic biologic treatment, clarification, filtration, electrocoagulation, blending (directly diluting wastewater with freshwater), and evaporation. Recycling of produced water and fracture flowback water for reuse in hydraulic fracturing is on the rise in the development of unconventional resource plays. Factors driving the conservation of water include the limitations in sources of fresh water in areas with a high rate of development, attractive economics of recycling compared with tanker truck transportation costs, minimization of road traffic to reduce environmental impacts, and water disposal costs.

Noteworthy papers in OnePetro

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Online multimedia

Burnett, David. 2012. New Options for Produced Water Treatment and Re-use in Gas/Oil Shale Fracturing. http://eo2.commpartners.com/users/spe/session.php?id=9382

Palmgren, Tor. 2013. Treatment Options for Reuse of Frac Flowback and Produced Water from Shales. http://eo2.commpartners.com/users/spe/session.php?id=11046

External links

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See also

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