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Abstract The Greening the Desert initiative explores opportunities to re-use water produced from hydrocarbon fields in arid areas around desert oil fields. Where water does not serve any purpose for reservoir management, re-use is envisaged to be an enabler for new value creation by stimulating opportunities such as agriculture or forestry. An oil field in the south of Oman produces in excess of 200,000 m/d of brackish water, the larger part of which is disposed of through re-injection into deep aquifers. As an alternative the operator has embarked on reed bed pilots later followed by pilots on bio-saline agriculture and forestry. Also a pilot has been executed for the purification of the effluent water from the reed beds by a Solar Dew® membrane system, allowing a.o. fresh water agriculture. Pilots for the different Greening the Desert schemes are aimed at developing a portfolio of technical solutions for produced water re-use in desert environments. The paper presents operating envelopes and limits of technical performance. The selection of technical solutions for a large-scale project may then be based on the best total lifecycle value balancing cost, benefits and risks, and meeting aspirations for sustainable development.
Introduction Water produced during the recovery of hydrocarbons is usually separated at central processing facilities. From these facilities, the water may be directed to destinations, such as water injection wells for reservoir flooding or for downhole disposal, overboard discharge or re-use at the surface. In land-based operations, water is generally disposed in aquifers underneath the producing formation or in shallow aquifers of high salinity marked as unsuitable for re-use. Mature oil fields generally produce large volumes of water, for instance the Nimr oil field in south Oman produces daily more than 200,000 m of wastewater. Currently, this water is discharged into a deep aquifer at costs as high as $0.10–0.15/m.
The volume of water not needed for reservoir management is more and more becoming a subject of debate as questions arise concerning the sustainability of current disposal methods. As alternative to discharging water as a waste, the Greening the Desert concept (GtD) promotes water re-use in areas that are short of water. Potentially, access to water could convert a dry arid environment into one of economic prosperity through agriculture, forestry and associated developments. The project began in the late 1990s, and since then pilots were aimed at the conversion of produced water into a usable resource at a cost lower than that of disposal. Re-use includes water for rig operations and agriculture using water to grow selected salt-tolerant crops or forestry. Also, systems that produce fresh water for irrigation or domestic use are considered, such as the Solar Dew® collector, as well as a water usage-network enabling inter-asset transfer of water for reservoir flooding.
The paper presents the operating envelops and the limits of technical performance for the different Greening the Desert schemes, i.e., for water clean-up schemes like reed beds and Solar Dew® and bio-ponds, and for water re-use agriculture and forestry schemes. Screening the different schemes for large-scale deployment is based on the best total lifecycle value. Providing sustainable solutions to the large volumes of produced water may offer opportunities for local economy, as well it debottlenecks water disposal facilities, the failure of which imparts on oil production.
Technology Options for Water Re-use As delivered from the processing facility, produced water is still contaminated with oil and dissolved and suspended solids, making it unsuitable for re-use without further treatment. Current separation techniques remove dispersed oil to a concentration below 200 ppm, a typical value for injection water. The path towards water re-use comprises various techniques to reduce oil and salt concentrations to a level suitable for irrigation, or even for consumption by livestock.
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