Performance Evaluation of Reverse Osmosis Treatment of Oilfield Produced Water for Re-use
a report by Marcel Vasconcelos Melo,1 Oswaldo de Aquino Pereira Júnior,1 Helga Elisabeth Schlüter2 1. Process Engineer; 2. Petroleum Chemist, Petrobas Research and Development Center Rio de Janeiro and Antônio Faria Lima2
Oil and gas reservoirs have a natural water layer (called formation water) that, being denser, lies under the hydrocarbons. Oil reservoirs frequently contain large volumes of water, while gas reservoirs tend to produce only small quantities. Furthermore, to achieve maximum oil recovery, additional water is often injected into the reservoirs to help force the oil to the surface. Both formation and injected water are often produced along with the hydrocarbons and, as an oil field becomes depleted, the amount of produced water increases as the reservoir fills with injected water. At the surface, the water is separated from the hydrocarbons. It is treated to remove oil and then either discharged into the sea or injected back into the wells (called produced water re-injection), with or without further treatment. In addition to this, some installations are able to inject the water into other suitable geological formations.
In what follows the term ‘produced water’ is used to describe the mixture of water (formation and injected) and oil (hydrocarbons) that is either discharged into the sea or re-injected. In other words, it is water from the well that has been subjected to basic treatment but still contains small quantities of oil.1
Water Utilisation and Scarcity
Global water scarcity has already been forecast, figuring as one of the greatest challenges of the 21st Century. This discloses the need for water re-use, which represents a potential for sustainable development. From an industrial point of view, two other issues also related to the utilisation of water must also be taken into consideration:
•
costs associated with the input itself and the steps required to achieve each industry’s particular specifications; and
• the volume of generated effluents, which will represent added costs with water disposal and/or treatment.
The current regulating agency trend is to charge for water impounding and disposal, thus increasing industrial costs.2
In this
context, and of particular concern to the oil industry, produced water re-use is becoming more important as oilfields are reaching their production mid-life or maturity. Water generation associated with oil production is growing considerably; this may drastically reduce the sustainability factor of oilfields.3
Furthermore, the
growing demand for water in industrial processes may affect the local environment in a significant way. Likewise, water scarcity, especially in the semi-arid northeast of Brazil, makes water re-use a factor of high priority and attractiveness.
Initial Project at Petrobras Fazenda Belém Field Six years ago, in order to produce wet steam for oil recovery at Fazenda Belém Field (in Ceará State, Brazil), Petrobras engineers
© TOUCH BRIEFINGS 2010
suggested re-using part of the produced water instead of using water from the Açu aquifer (a valuable freshwater reservoir that supplies the semi-arid northeast of Brazil). This specific project focused on the implementation of a hot softening system in the dissolved air flotation tank and some adaptations in the coagulation/flocculation processes. These implementations were performed at the Fazenda Belém effluent treatment station. They made the produced water suitable for steam generation after a final polishing treatment using an ion-exchange resin (see Figure 1).
The proposal included, among other methods, chemical softening by the addition of sodium hydroxide and separation of the sludge generated via the conventional dissolved air flotation process.
Study Objectives
The objectives of this study were: •
•
to determine the efficacy of a pilot-scale reverse osmosis and nanofiltration system for treatment aiming at the re-use of produced waters from a specific oil field; and
to assess the quality of treated water in terms of physicochemical characteristics influencing re-use of the water for irrigation or other beneficial uses.
Marcel Vasconcelos Melo is a Technical Consultant and Processing Engineer at the Petrobras Research and Development Center and has experience in chemical engineering, with emphasis on produced water treatment working mainly in the areas of primary and tertiary separation processes. He has degrees in chemical engineering from the Federal University of Rio de Janeiro (1999) and a doctorate in science in chemical engineering (2002).
E:
mvmelo@petrobras.com.br
Oswaldo de Aquino Pereira Júnior is a Senior Consultant and Processing Engineer of the Petrobras Research and Development Center and has experience in chemical engineering, with emphasis on produced water treatment, working mainly in the areas of primary and tertiary separation processes. He has degrees in chemical engineering from the Federal University of Rio de Janeiro (1974) and a masters in science in chemical engineering (1985).
E:
oswaldo@petrobras.com.br
Helga Elisabeth Schlüter is a Petroleum Chemist at the Petrobras Research and Development Center and has experience in chemistry, with emphasis on produced water treatment working mainly in the areas of primary separation and desalination processes. She has degrees in industrial chemistry from the Federal University of Fluminense (2003) and a degree in physics (2001) and a masters in science in civil engineering from the Federal University of Rio de Janeiro (2007).
E:
helga@petrobras.com.br
Antônio Faria Lima is a Petroleum Chemist at the Petrobras Rio Grande do Norte Division and has experience in chemistry and chemical engineering with emphasis on produced water treatment in the areas of primary separation and desalination. He has degrees in Chemical Engineering from the Federal University of Sergipe (1982) and a masters in science in chemical engineering from the Federal University of Rio Grande do Norte (1995).
E:
farialima@petrobras.com.br
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HSE – Produced Water
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