A natural filter for water

The Nimr reed beds facility

The reeds themselves form a wetland covering around 5.1 million square metres of previously arid desert. They are irrigated by water that is a by-product of oil production activities in Nimr, carried out by Petroleum Development Oman (PDO) in which Shell holds a 34% interest. The field has long been characterised by the high percentage of water that also comes to the surface with the oil.

Since 2011, a sizeable proportion of Nimr’s produced water – currently some 175,000 cubic metres of it per day – has been flowing into a special treatment plant operated on PDO’s behalf by the environmental services company Bauer Nimr. The facility incorporates a clever settling tank and centrifuge systems that remove any residual traces of oil (which are reclaimed) before the water flows into the beds to be cleaned by microorganisms that live among the roots of the reeds as well as by algae.

Because the whole facility is constructed on a man-made slope, the water requires no pumping or other mechanical stimulus to flow through it, making the plant both highly energy-efficient and extremely reliable.

Thanks to this unique, natural process the water taken from the beds is pure enough to be used for drilling new wells, which saves pumping clean water from shallow aquifers. PDO also draws on it to help make up the polymer mixtures used in its chemical EOR (enhanced oil recovery) project in Mamul, and it can be used for hydraulic fracking, which is a process by which high pressure water injection is deployed to fracture reservoir rock in order to improve its permeability.

Assessing the potential for Nimr-wetland by-products

Outside of oilfield operations, PDO is investigating the potential of earmarking some of the water to irrigate crops that are tolerant to high levels of dissolved salt – so-called biosaline agriculture.

PDO and Bauer Nimr have been running a three-year research project to study the impact of treated produced water on 13 different plant species and its commercial viability. For example, eucalyptus, acacia, conocarpus, casurian and prosopis are being grown on a 20-hectare plot and cotton has also been harvested there. It has seen promising plant growth from numerous crops with the potential for commercial application as well as the possibility of producing biomass and oil seeds.

PDO is also working with Sultan Qaboos University in Muscat to use local soil and low-salinity treated produced water to manufacture compressed stabilised soil blocks. The bricks, which could reduce building costs, are currently being tested for their strength and thermal conductivity.

After all these practical uses have taken their share of water, any remaining liquid is passed into giant evaporation ponds to let nature take its course. PDO then plans to harvest the salt deposits left behind.

An award-winning project

Since the Nimr reed beds opened, PDO has been able to shut down high pressure pumps that it uses to dispose produced water from the field into deep-lying aquifers (ensuring it is kept well away from drinking water supplies), achieving a 98% reduction in energy requirements (source: PDO Sustainability Report 2018).