Permian: Treating Produced Water for Discharge Reduces Injection
As oil production in the Permian Basin continues to rise, the consequent rise in produced water volumes is placing a financial squeeze on operators in the region. Figuring out what to do with this water is a challenge every operator faces. Given the potential seismicity and capacity issues surrounding saltwater disposal, reusing that water has become a viable solution for reducing costs and limiting water-sourcing constraints—last year Wood Mackenzie estimated a potential savings range from $1.00 to $2.50 per barrel. However, another solution could provide additional relief: treating water for discharge, effectively creating fresh water that can be used for irrigation and uses in other industries.
“The numbers are very great,” said Lnsp “Naggs” Nagghappen, vice president of Veolia North America. “Every day those numbers are changing, and it’s only going up. Operators contact us every day asking what they can do with this water.”
Speaking at the 2019 Permian Basin Water in Energy Conference, Nagghappen outlined the benefits and challenges in treating water for discharge. On top of reducing disposal volumes, he said transporting treated water to a midstream asset is a “less risky” proposition than transporting produced water. The short-term costs may be high in some cases, but it can be a cost-effective management option in the long term.
The process itself should be familiar to any company that treats its water for reuse. It requires pretreatment with a scale inhibitor suitable for use in fracturing fluids to remove the high levels of scaling ions often found in produced water. The water is then treated through a desalination process such as reverse osmosis, nanofiltration, or thermal distillation.
Then comes the tricky part. Treated produced water with high levels of total dissolved solids (TDS) can be used as the base fluid for hydraulic fracturing with no adverse effects on treatment pressure or the ability to place proppant. Water designated for other purposes, or water designated for discharge to surface water bodies, requires a higher level of treatment. So, while post-treatment processes do not need to ensure water clean enough for humans to drink, they still need to provide water that does not reach a certain level of toxicological danger. This means removing some troublesome ions such as boron, a commonly known water contaminant.
While boron plays an important role in the metabolism of plant carbohydrates, the line between efficiency and toxicity is thin, and too much of it can have a negative impact on plant growth. Several technologies are available to remove boron from produced and flowback water, but anything beyond selective removal can be expensive and require significant chemical demand. Boron is one of a handful of contaminants that require a large capital investment for removal, and Nagghappen said that commitment may scare some operators off.
“We have to remove a lot of contaminants from the water,” Nagghappen said. “You have particulates and other stuff from the discharge like boron. Boron is not toxic to humans, but it’s highly toxic to plants, and when you’re trying to use this water for irrigation, it is highly important to remove them. There’s also ammonia—how do you remove ammonia from water?”
Veolia has a number of technologies designed for high TDS recovery rates such as the OPUS (Optimized Pretreatment and Unique Separation), a process for desalination of feedwater with high concentrations of silica, organics, hardness, heavy metals, boron, and particulates. Veolia installed OPUS at Chevron’s San Ardo field in southern California. The field now generates up to 50,000 B/D of produced water for surface discharge and an additional 75,000 B/D for steam generation, allowing Chevron to return additional water to aquifer recharge basins and avoid deep well injection. Historically, water not recycled for steam generation was sent to local US Environmental Protection Agency Class II injection wells for disposal, but the injection zone capacity at San Ardo was limited, and that had constrained full-field development.
Veolia’s four primary areas of service for San Ardo included daily plant management and handling of treated water. The post-treatment water was discharged to constructed wetlands that drain into aquifer recharge basins. The company also provided engineering support. For instance, when hurricanes delayed deliveries of hydrochloric acid (which had been required for the regeneration process of softeners used in the OPUS system), it developed a different formula to maintain ongoing operation of the treatment facility.
Nagghappen also discussed Veolia’s produced water reclamation facility at Plains E&P’s Arroyo Grande field in San Luis Obispo County, California. Like San Ardo, the facility utilizes the OPUS system, providing 20,000 B/D for surface discharge and an additional 25,000 B/D for use as steam. The facility’s effluent-to-steam generators provide an absolute barrier to free oil and solids, reducing the maintenance costs generally associated with steam generators. The field, which contains heavier oil (12 to 16 °API gravity) with well depths averaging 1,700 ft, requires continuous steam injection to operate. The facility helps “de-water” the reservoir, reducing formation pressure and boosting crude oil production.
Veolia is also developing a treatment complex in Applachia, agreeing in 2015 to a deal with Marcellus/Utica producer Antero Resources for the construction and operation of a new plant located in Doddridge County, West Virginia. It will eventually treat up to 60,000 B/D of produced water using a moving bed biofilm reactor, clarification technology, and Veolia’s CoLD process, a proprietary crystallization method that the company said can desalinate high-TDS produced water containing significant quantities of chloride salts. Naghappen said the plant is scheduled to come online later this year.
Nagghappen referenced these case studies in his presentation as examples of what the company hopes to accomplish in the Permian.
“It’s not that it’s not been done,” Nagghappen said. “It’s that we have to bring it to the region that makes the most sense and validate it. All produced waters are different. We trial for 3 to 4 months, but still there are so many things we must solve because of the variability of the water. We know what it takes now to treat these waters, but it’s not easy. However, when it’s done, it’s the ultimate solution for disposal.”
Case Studies in Produced Water Treatment
Three papers selected from 2018 SPE ATCE look at the challenges and approaches to the treatment of increasing volumes of produced water.
Fit-for-Purpose Water Treatment in Permian Shale
Sourcing water for hydraulic fracturing, and disposing of produced water, are constraints and significant cost items in the Permian Basin. Some of the produced water can be treated and reused by using a water life cycle approach..
Testing of Two-Stage Biofiltration Unit for Mitigation of VOC Emissions
Volatile organic compounds (VOCs) present in crude oil can be released to the atmosphere from storage tanks, waste waters, and equipment leaks. A pilot-scale sequential biotrickling/biofiltration unit was designed and tested for removal of VOCs from a wastewater sump.
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