Abstract

This paper presents the results of an in-depth study concerning the composition of produced waters and dispersion in a tropical offshore marine environment. Effluent waters from three outfalls situated in the Java Sea, Indonesia were subjected to a detailed chemical analysis to determine the presence and concentration of contaminants. This information was used to target a detailed literature review to determine priority contaminants for investigation and to determine their geochemical behavior. Combining this information with a detailed hydrodynamic model of the region allowed simulation of the initial dilution and subsequent predictive dispersion of effluent from three fluid process complexes with six outfalls, each exhibiting different outfall characteristics, flow rates, discharge depths and contaminant concentrations. The modeling was calibrated using results from dye tracing experiments that included chlorides and temperature testing conducted at one of the process facilities. Once calibrated, the model has been run for a range of scenarios representing changes in conditions thus allowing the environmental impact of the effluent stream to be predicted and assessed. The observations made from the modeling and the associated field measurements point to the possibility of impact due to plume component concentrations and contact time. Investigation of possible impact forms the basis of effluent discharge studies currently underway.

Introduction

One of the most significant Exploration and Production (E & P) waste management problems is produced formation water. With maturity of offshore operations the ecotoxicological impact and long term sublethal chronic effect of discharged fluids become critical due to increasing pressure to reduce discharge pollutant concentrations and discharge volumes.

The E and P industry's limited ability to respond to real and perceived problems is a result of limited research in produced water impact and an inability to accurately predict plume impact area and content. In particular, there is a paucity of information on differing effects based on effluent volumes (volumetric load), pollutant concentrations, temperature and synergy of pollutants. Most importantly, correlation of numerical modeling to the discharge observed is limited and difficult to use where available.

Background

Pertamina/Maxus Operation Area. Pertamina/Maxus operations are located within the mining contract zone (WKP) designated as Southeast Sumatra. All Pertamina/Maxus SES facilities are offshore on the Java Sea side of the Sunda Straits north of the island of Java and Southeast of the island of Sumatra (Fig. 1). The contract area covers 11,000 square kilometers and adjoins to the Pulau Seribu, national marine park and resort area.

Pertamina/Maxus operates sixty-three platforms in water depths between 70 feet (21.3 m) and 100 feet (30.5 m) with fifty-four unmanned. Produced fluids from the platforms are interconnected via subsea pipeline to three process platforms. The processed hydrocarbons are forwarded to the floating storage facilities.

The produced formation water is removed from the gas and oil stream and "polished" before discharge to the sea. The process platforms of Cinta, Widuri, and Krisna discharge the polished effluent from open-ended and skimmer pile (Fig. 2) outfalls situated between 3 and 15 meters below the sea surface. Discharge rates from these outfall locations vary between 165,000 BPD (26,235 m3/day) to 775.000 BPD (123,225 m3/day) with a total yearly discharge rate of 360 million barrels (57.8 million m3). The salinity of these effluent varies from 8 ppt to 12 ppt with an average dispersed oil content of 15 mg/l.

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