Environmental Risk Management of Produced Water - A Demonstration of the CHARM Model Used for the Ula Field in the North Sea
Authors: Bakke S. , Ofjord G.D. , Vik E.A. , Sande A. 
Published: December 2007

This paper gives a demonstration of environmental risk analysis and risk management by use of the CHARM (Chemical Hazard Assessment and Risk Management) model for making cost/environmental benefit evaluations of produced water handling. The BP operated Ula field in the North Sea is used as a demonstration case. The CHARM model is developed by Aquateam, Norway and TNO in the Netherlands on behalf of the oil operators, chemical suppliers, and environmental authorities in the North Sea countries. The CHARM model has been discussed and is accepted by the Oslo and Paris Commission (OSPAR). The environmental risk analysis demonstrated in this paper covers evaluation of the environmental impact of the produced water discharges, including chemicals and natural constituents from the Ula platform. The environmental risk analysis was performed for various environmental management options. Two options were elaborated for comparison to a reference situation. The Ula produced water constituents demonstrated variable contributions to the total environmental risk. The environmental risk was slightly reduced by improved water treatment, but the most significant reduction was seen for the option of produced water reinjection (PWRI). PWRI reduced the produced water discharges with 90%, indicating that the environmental benefit was superior. PWRI was also able to compete economically with the other options. It should be noticed that the PWRI option did not reduce the production capacity at Ula. If so, the economic situation would have been significantly different.

Introduction

The produced water discharges to the North Sea are steadily increasing as the oil producing fields are becoming more mature. The discharges were 187 million m3 in 1993 and are expected to culminate at a level of 340 million m3 in 19971. As the oilfields mature, the produced water volumes will increase, more chemicals will be used, and hence, the environmental risks related to produced water discharges will increase. The environmental risk can be reduced by choosing less harmful chemicals, improving the water treatment, reinjecting the produced water or selecting alternative (e.g. corrosion resistant) materials. These choices are, however, not always clear cut. Which option is the better for the environment and to which cost? The optimum choice will, however, be site specific.

Traditionally, risk is a product of consequences and probability. The use of risk analysis within safety management has been applied for a long time. This method has recently also been introduced in the environmental field for evaluation of environmental risk of acute incidents in Norway. In the offshore industry, environmental risk analysis is normally associated with accidental oil spills. The environmental risk discussed in this paper is, however, related to continuous discharges of produced water and includes the combined risk of residual chemicals and oil as well as natural organic and inorganic constituents in the produced water.

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