By Marcus George on Dec 11, 2019
In the deep south of Oman a patchwork of lush green pastures stands out from the arid plains that dominate the vista. This is no recreational park or remote garden nursery but an innovative project that plays a unique role in the oil industry, the country’s most important economic export.
At the nearby Nimr oil field, lots of oily water comes to the surface when crude oil or natural gas is produced. Previously this fluid, called produced water, was disposed of in deep wells in a costly, energy-intensive process. Today, these 12 square kilometres of reed beds and evaporation ponds make up the Nimr Water Treatment Plant, the world’s largest constructed wetland. At the heart of the project are the reeds which naturally break down hydrocarbon molecules, cleansing the water in the process.
Announced in 2009 and launched two years later, a new phase of the plant started up in May, expanding its capacity significantly.
“This is a unique project. When I look back, it’s incredible to think we have created this oasis in this remote place,” says Fahad Al Rawahi, operations team leader for Bauer Nimr, the company which designed and built the treatment plant for Petroleum Development Oman (PDO). PDO is a joint venture between the government of Oman, Shell, Total and Partex. “The most exciting moment for me was seeing the water flow into the beds for the first time. We worked so hard on it. We were confident it would work but there was no guarantee until we saw the reeds growing and treating the water.”
Today, the reed beds are in good shape. They tower up to five metres tall and have attracted more than 130 different species of birds which have come to nest and feed. Currently 145,000 cubic metres of water is pumped from the Nimr oil field into the plant every day, enough to fill more than 50 Olympic-sized swimming pools.
The initial treatment stage is to separate as much oil from the water, a process which reclaims up to 500 barrels of crude a day.
The water then drains into the buffer pond where skimmers remove a further oil layer, before it flows, thanks to gravity, into a cascade of reed beds where nature takes over.
Periphyton – or algal and bacterial biofilms – attached to the submersed leaves and stems of the reeds trap the oil and break down hydrocarbon molecules, cleansing the water further.
The water outflow then drains into evaporation ponds and ends up little more than whitish salt crystals.
It wasn’t always like this. Prior to the treatment plant, some 275,000 cubic metres of produced water was pumped into deep wells by pumping stations operating most hours of the day. “Deep well disposal was a major headache. Not only did the pumps consume lots of energy, but if the system failed and we couldn’t fix the problem within 27 minutes, we had to slow or stop oil production,” says PDO’s Ahmed Al Ajmi.
A DEVASTATING WORM
Today, the difficulties Ahmed faced as a production team leader at Nimr are a distant memory. Over the coming year, the plant will process some 175,000 cubic metres of produced water a day and with no interruption to oil production. The remainder of the water produced at Nimr is reinjected into reservoirs to maintain pressure and improve production. Given its success, PDO is now looking to develop similar water treatment plants other key oil production areas.
But it hasn’t all been plain sailing. The biggest threat to the reed beds was an outbreak of African armyworm – a form of moth larva, which devastated 80% of the young Phragmites reeds planted in the second phase of the project in 2012. After tests, Bauer Nimr found that combining alternative species of aquatic reeds – Juncus, Typha, Schoenoplectus and Cyperus – made the beds resilient to attack.
LIFE IN THE DESERT
Fahad and his Omani colleagues work on rotation, spending two weeks on site and two weeks at home. For many of them, outside working hours life revolves around watching or playing football.
Hewn out of the red dirt to one side of the nursery where reeds are planted and grown is a makeshift pitch. “We didn’t just create the world’s largest constructed wetland, we also created Bauer Football Ground,” he says with a smile. “I dreamt of being a professional football player when I was young. These days, after the day is done, I live those dreams on this pitch.”