Worldwide, the produced water to oil ratio is 3-to-1. In the U.S., the ratio is 8-to-1.
by Bill Charneski
July 7, 2015

Freshwater and produced water are the two major sources for water applications in the oil and gas industry. As freshwater becomes scarcer, the industry must focus more on treating, recycling and reusing produced water. Produced water is trapped in underground formations and brought to the surface during well operations. This water contains traces of hydrocarbons and other chemicals. Worldwide, the produced water to oil ratio is 3-to-1. In the U.S., the ratio is 8-to-1. Older wells tend to generate more water.1

Smart Wastewater Management

From sourcing freshwater to trucking away wastewater for disposal, water management places a heavy financial burden on fracking operations. In the U.S. alone, costs average $9 per barrel of water, with a high of $26 recorded by Jefferies analysts.

Nowhere is the pressure to reduce water costs felt more than in the Middle East and North Africa (MENA), where the share of natural gas in local electricity supply is expected to hit a staggering 70 percent by 2035.2 The MENA region is the most water scarce on the planet, with per capita freshwater supplies well below the "poverty" line of 1,000 cubic meters per year.3

New technologies are driving down the cost of treating water for reuse, making the practice cost competitive with traditional disposal methods. The hydraulic fracturing industry—already well established in the U.S.—is just beginning to see the need for strategies to meeting growing water regulations. As hydraulic fracturing moves beyond its infancy stage in the MENA region, producers are seeing the value of smart wastewater management strategies.

Treatment Costs

Oil and gas wells generate two types of wastewater—flowback and produced water. Flowback, which resurfaces a few weeks after injection, accounts for about 25 percent of water used in fracking operations. Produced water naturally comes to the surface with oil or gas. Both types of wastewater carry chemicals from the surrounding formation and fracturing operations, which makes them unsafe to return to the natural water cycle. After extraction, wastewater is traditionally transported off-site and disposed of in evaporation ponds and disposal wells. These options require operators to use trucks to and from the disposal sites, incurring significant transportation and disposal costs. According to Jefferies, these costs for U.S. operators can range from $1 to $17 per barrel. Operators must then purchase and truck freshwater back to the wellhead to restart the cycle, with current freshwater costs ranging between $0.75 and $9.75 per barrel in the U.S. In the MENA region, wastewater disposal regulations can be particularly stringent, adding even greater costs. In Oman, for example, regulations prohibit the discharge of wastewater or sludge into the environment when it has a high pH value or a high concentration of metals. In addition, wastewater may not be discharged when reuse is possible.

Electro-Coagulation Systems

Electro-coagulation systems are an effective method to clean wastewater on-site, especially when combined with other processes. One such technology takes a distinct approach using three separate phases that occur in two hardware stages to clean water: electro-coagulation, electro-flotation and electro-oxidation. Before entering the first stage, contaminated water and oil or gas from the wellhead typically pass through a three-phase separator, or American Petroleum Institute (API) skim tank. The separated water, still contaminated with suspended solids and 1 to 2 percent oil, then enters the treatment system. Electro-coagulation destabilizes emulsion and neutralizes the electro-static charge of non-soluble hydrocarbons and suspended solids. In this stage, solids and organic contaminants clump together through agglomeration and flocculation. The stream of clumped particulates then flows into the second hardware stage. In the electro-flotation chamber, less dense materials, such as organic contaminants, are lifted from the stream for extraction, while heavy solids settle out for evacuation. Electro-oxidation resulting from previous stages disinfects bacteria and oxidizes dissolved organic materials and hydrocarbons. A supervisory control and data acquisition (SCADA) system controls the process. The SCADA system monitors specific water parameters and makes real-time adjustments to ensure maximum efficiency and minimum energy usage. It also controls the production and propulsion of the high-density bubble flotation employed to improve effluent water quality. The configuration of the anodes and cathodes is essential to energy-efficient electro-coagulation technologies. The proper deployment and use of donating and non-donating anodes can minimize power use and optimize contaminant removal. The system can be configured to integrate with downstream polishing technologies to create an end-to-end water treatment solution.

Case Study: Gulf Energy

Gulf Energy, a major oil services company that has customers in Oman, Yemen and Saudi Arabia, announced a plan to reduce costs and environmental impact. The company will implement a low-energy, primarily chemical-free system that efficiently removes oils and suspended solids, insoluble chemicals and bacteria from flowback and produced water across its operations. A 5,000-barrel-per-day unit is being designed as a field-scale, mobile system. The company selected the proprietary three-phase electro-coagulation system based on demonstration results across the U.S. The water at each wellsite has unique salinities, oil levels and contaminants that can change daily. At each site, the system was able to treat different water qualities, enabling operators to manage variances easily and still produce effluent water. Results of the technology to date:

  • Colorado: The system successfully removed 99.8 percent of turbidity, 100 percent of suspended solids and 99.2 percent of oil from the water.
  • Texas: In the Permian basin, the system was coupled with ultrafiltration on produced or flowback water from local wells. Turbidity varied among truckloads, from 300 to 1,400. In all cases, turbidity dropped to essentially zero through the system configuration.
  • California: For an exploration and production (E&P) operator in the Monterey basin, 99.9 percent of turbidity and suspended solids was removed. Oil and grease were non-detectable.
References
  1. netl.doe.gov/research/coal/crosscutting/pwmis/intro
  2. iea.org/publications/freepublications/publication/WEO2011_WEB.pdf
  3. brookings.edu/research/opinions/2014/06/24-water-scarcity-growth-prospects-middle-east-north-africa-devlin