Unconventional hydrocarbon production sits at the center of several water issues. Hydraulic fracturing requires large volumes of water to permeate the shale formations and release the trapped tight gas or oil. The ensuing production generates between 5 and 15 barrels of produced water per every barrel of oil or per every million cubic feet of gas. This water comes to the surface with a wide range of total dissolved solids (TDS), which have different requirements for treatment and processing. Ongoing production requires more and sometimes increasing volumes of water in order to continue producing hydrocarbons. Therefore, hydraulic fracturing requires thoughtful and effective water management strategies.
There have been significant advances in water management for unconventional oil and gas production. Examples include reuse of produced water in Pennsylvania’s Marcellus shale play where over 90% of the produced water is reused for hydraulic fracturing and this water accounts for up to 25% of the water required for hydraulic fracturing on a statewide basis.
Reuse of produced water is also increasing in the Permian Basin, where produced water volumes exceed the volume of water required for hydraulic fracturing. Advances in hydraulic fracturing fluid design allow use of untreated produced water. Reported costs by some operators associated with reuse of produced water are similar to or less than costs incurred by sourcing and disposing of water.
There are four dominant flowback water management options. First, direct reuse without treatment blends flowback with freshwater for reuse that has minimal costs. Second, on-site treatment and reuse treats water onsite before reinjection with moderate costs. Third, offsite treatment and reuse transports water to a different treatment facility and then back for reuse. The costs for this method is comparable to the on-site treatment method but with added transportation costs. Offsite treatment and disposal transports water to a separate facility for treatment and then either to an injection site for disposal or to an approved discharge facility.
Water recycling can lessen water stress in a region where hydraulic fracturing is occurring. If operators can recycle produced water, then freshwater resources can remain in the hydrosphere. Also, if operators can recycle produced water, they can mitigate their burden for wastewater disposal. This can be a significant cost savings over drilling and permitting a wastewater injection well or treating water to the point at which it can be returned to surface water sources.
On the other hand, recycling water has some risks. Recirculating flowback water through shale formations can hyperconcentrate the TDS in the fluids. Likewise, if the shale formation is rich in naturally occurring radioactive material (NORM), then recirculation can increase NORM levels. If operators at the surface come in contact with the fluid or equipment containing the fluid, they may be exposed to excessive levels of radiation. Also, storage, pumping and transportation of any fluid, whether freshwater, brackish or wastewater, comes with the risk of spills.
Images: “Purple” by John Loo licensed under CC BY 2.0