Integrated Environmental Risk Management of Future Produced Water Disposal Options at Draugen on the Norwegian Continental Shelf

Abstract

Cost/environmental benefit comparisons of different produced water disposal options were performed for the Draugen platform on the Norwegian ContinentalShelf. Comparison of the environmental risk for the year of maximum water production, as well as the integrated environmental risk for the predicted lifetime of the field was made for the different produced water disposal options. Discharges of natural constituents, as well as residual production and injection chemicals in produced water were included in the risk assessment. High level cost environmental benefit evaluations have been carried out. A Base Case, meeting the present oil in water discharge permit was defined. Differences in cost/environmental benefit of the potential disposal options were quantitatively compared to the Base Case. Uncertainties in the figures are discussed. The work presented here is one of the inputs to the Draugen produced water disposal programme. Feasibility studies will develop more reliable cost and performance data. Decisions on future produced water disposal at Draugen will be based on the final results and recommendations in the produced water programme. An approach has also been suggested and used for weighting potential long-term effects of the discharges. This provides important additional information to the risk assessment results. Introduction The Draugen platform operated by A/S Norske Shell E&P (Exploration and Production) is located on Haltenbanken, an environmental sensitive area on the Norwegian Continental Shelf. The platform is located at a 250 m water depth. Oil production started October 1993 and is predicted continuing until year2012. Seawater injection was initiated in 1994 to maintain the pressure in the reservoir. Water production started on a continuous basis in 1998. In September1999, 2% water cut was reached. The water cut in later field life is expected to reach ~88%. The maximum water production is expected in year 2006 (35–40 000m3/day). As the water production increases, it is expected that the existing produced water system will not meet the present discharge quality requirement(40 ppm oil in water - OIW). A produced water programme was initiated in 1998 to meet future environmental and technical challenges. Cost and performance efficiency of different disposal options have been evaluated. Environmental risk over the predicted lifetime of the Draugen field was determined for the different disposal options using the internationally accepted PEC/PNEC (PEC: Predicted Environmental Concentration, PNEC: Predicted No Effect Concentration) approach for the different natural constituents and residual chemicals present in the produced water. Several different produced water disposal options were evaluated. The presently available risk assessment methodologies are only feasible for evaluating environmental risk over a relatively short time-span. An alternative approach has therefore been proposed for evaluating the potential long-term effects of the discharges (open sea risk assessment).

Hydrogen Sulfide Forecasting Under PWRI (Produced Water Reinjection)

“…1 have been evaluated in a previous study where preliminary evaluations of PWRI operations have already been completed. A more thorough characterization of the produced water has been accomplished in the 1999 produced water project 13 . This paper specifically deals with the theoretical assessment of the potential hydrogen sulfide production that can be expected under PWRI based on the application of Sawyer and McCarthy`s hydrogen sulfide model for forecasting the maximum H 2 S generation potential in PWRI systems 14 .…”