Constructed Wetlands for Produced Water Treatment

Location: Nimr oil fields, Oman


Petroleum Development Oman LLC (PDO): a joint venture between The Shell Petroleum Company Ltd and the Government of Oman

Technology provider

BAUER Nimr LLC, Oman (a subsidiary of BAUER Resources GmbH in Germany)

Overview of Project

The challenge

At the PDO Nimr oil fields, a tenth of the total production is crude oil. The remaining production, around 330,000 m³ per day, is water that is brought to the surface together with the oil. This water used to be disposed of by injection into a deep disposal well. To reduce the high costs of treating and re-injecting the produced water, PDO together with BAUER, developed a solution that would reduce or eliminate the power consumption and CO2 emissions associated with the operation of equipment for deep well disposal. The solution was a four-tier gravity-based wetland design.

The solution

The plant layout includes a pipeline, which enters the NWTP system and leads to an oil/water separator. The water is then distributed into a wetland facility where it is channeled through four wetland terraces by gravity feed. Finally, evaporation ponds are used to recover the salt while the biomass is landfilled. Alternative uses of the water and biomass that could offer a variety of environmental and socio-political benefits are being explored.


The constructed wetland is designed to treat close to 200,000 m³ of produced water per day. The facility was constructed under a build-own-operate contract and as such, BAUER designed and built the facility and has been operating the plant since 2010.

Key benefits of the solution

  • Capital expense savings: significant capital cost savings compared to the traditional produced water treatment and injection facility
  • Operating expense savings: the gravity-based wetland design requires close to zero energy for water treatment, thus reducing power consumption by approximately 98%
  • Operational performance: The oil content in the produced water is consistently reduced from 400 mg/l to less than 0.5 mg/l when leaving the wetland system
  • Significantly reduced carbon footprint: CO2 emissions reduced by approximately 98% due to the elimination of electric powered water injection equipment
  • Other benefits: the wetlands provide habitat for fish and hundreds of species of migratory birds

Evaluation of the business opportunity

Frontier team members were involved in the development of techno-economic models to better understand the cost advantages, the technical performance, and the water and CO2 footprint of this wetland facility. Different biomass and water re-use options were evaluated to optimize the project’s NPV and VIR, taking local market prices and potential future penalties related to CO2 emissions and water consumption into account. The team observed that, at a certain scale, the wetland facility can become truly decentralized, i.e. self-sufficient in generating its own power requirements.