Environmental Fate And Effect Of Contaminants In Produced Water

Abstract

Abstract In 1994, the International Association of Oil and Gas Producers (OGP) issued a report on the fate and effects of constituents produced water in the marine environment, based on information from member companies and the literature (1). The report, which focused on the North Sea, was reviewed and updated in 1998, and is currently subject to a further revision. This new report addresses discharge, fate and potential environmental impact of produced water to the marine environment from a wider, global perspective. The focus of the review is primarily on produced water impact, and takes into account a number of comprehensive studies that have been completed during the past 5 years. In addition, information and data on environmental effects of naturally-occurring, ‘non-oil’, constituents forms an important contribution to the report. It is clear that produced water, in general, poses a limited threat to marine ecosystems. Local effects have been observed in shallow waters. Regulation and legislation practices on produced water vary significantly on a global scale, but in many areas are still based principally on concentration standards of oil in water. In some areas, in addition to performance standards, there is also a requirement for biological testing and discharge modelling studies. Environmental risk and impact assessments have, during the past decade, found broader application in areas such as the North Sea and Gulf of Mexico. The paper will present the results of the review and will serve as a basis for further discussion on produced water environmental management in the industry and in the regulatory and scientific and wider stakeholder communities. Introduction Management of produced water in offshore developments provides distinct challenges for the oil and gas industry. In most areas, discharge of produced water to the marine environment is an option that can be considered as part of a management strategy and any discharge is frequently required to meet an indicative performance standard. The performance standard subsumes elements relating to process efficiency (for separating oil form produced water) as well as environmental protection. Produced water is a complex mixture the detailed constituents of which are determined by the nature of the oil and gas reservoir and to a lesser extent by field maturity. In addition, the composition of discharged produced water and hence its potential impact on the receiving environment, will also be influenced by the processes used to treat water raised from the reservoir. Given the broad diversity of the constituents in produced water, in terms of their presumed fate in the environment, the potential pathways by which these constituents might interact with biological systems and, not insignificantly because of regulatory concerns in some regions, the International Association of Oil and Gas Producers, OGP (then known as the Oil Industry International Exploration and Production Forum - E&P Forum) published a review in 1994 entitled "North Sea Produced Water: fate and effects" (1). In addition, a more focused report on aromatics in produced water was published in 2002 (2). Since the publication of the 1994 review, a wide range of investigations has been carried out on the impact of produced water discharges offshore. These have been in response a desire to understand the consequences of discharges as well as to perceived concerns in the regulatory and external stakeholder communities. The studies have also been able to use more sensitive and specific biological testing methodologies. As a consequence of these new studies, OGP has embarked upon a new review document to update the 1994 study. This paper summarises the work conducted in that review. Composition and Properties Produced water has been in contact with geological formations for millions of years, and contains therefore a wide variety of dissolved inorganic salts and organic compounds characteristic of the geological formation. In addition, discharged produced water contains dispersed (insoluble) oil droplets originating in the reservoir, that surface treatment facilities have been unable to remove. It also contains residual production and treatment chemicals (and their breakdown products) including demulsifiers, corrosion inhibitors, antifoaming agents, etc. It may also contain some corroded material.