Environmental Effects Of Discharge And Reinjection Of Produced Water.

Abstract

There has been much focus on possible acute toxicity of produced water and which natural components and chemicals contributes most to the toxicity. This paper describes a method for risk analyses of discharges to sea based on exposure dose instead of the more common method using concentration. Results are presented from such analyses for the produced water from 4 Norwegian oil/gas fields. A comparison of environmental effects of discharge and reinjection of produced water is also presented based on available methods for assessment of environmental impacts. Introduction Since new, strict regulations for oil content on drill cuttings were introduced in 1993, produced water has become the major contributor of oil to the sea from the Norwegian oil industry. As a consequence, there has been much focus on possible acute toxicity of produced water and which natural components and chemicals contributes most to the toxicity. The amount of produced water from the fields in the Norwegian part of the North Sea is steadily increasing as new fields come on stream and the water cut increases on older fields. Currently. the yearly discharge is approx. 30 Mm3, and is expected to increase to around 90 Mm3 by the year 2000. Typical discharge volumes are from 500 m3/day to 25,000 m3/day from one platform. Produced water composition Typical values for the most important components in the produced water are shown below. The concentration of the chemicals in the discharge water depends both on the amount used and how they follow the gas, oil and water phases. Spreading of produced water Field tests have shown that the produced water is more rapidly diluted than earlier anticipated. These field tests have been used to calibrate computer models. A simplified formula for calculating the spreading is: where c0 concentration of a component in the discharge c(x) concentration at distance x x distance from discharge point Q0 discharge volume pr time unit (flux) U current velocity Kz vertical diffusion coefficient (typically 0.01 m2/s) P. 471

Probabilistic Risk Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Produced Water

“…A 100% gastrointestinal absorption is considered, as the cancer slope factors were estimated based on administered dose of PAHs. The BTEX aromatic compounds are prominent in produced water, but evaporate rapidly as soon as they are discharged close to the sea surface or from the positively buoyant plumes (Furuholt 1996). For these reasons BTEX were excluded from this study.…”

Characterization of the microbial community structure and the physicochemical properties of produced water and seawater from the Hibernia oil production platform

“…A modeling study by Somerville et al (1987) found that even at a 10, 000-m 3 /day discharge rate, a 100-fold dilution was estimated at 50 m from the platform, and a 2800-fold dilution was estimated at 1000 m from the platform. Another modeling study at a low discharge rate (2000 m 3 /day), Furuholt (1996) estimated a 1000-fold dilution would be found at 50 m downstream from the discharge point. Our findings measured similar dilution factors as those predicted by the modeling studies, suggesting that using this detection method, we could obtain measurements comparable with the predicted dilution factors for discharge models.…”