Abstract
Potential environmental consequences of oil leakages (i.e., continuous uncontrolled releases at low flow rate over a long period of time) need to be taken into consideration in the ongoing development of plug and abandonment (P&A) activities on the Norwegian continental shelf. Regulations of P&A wells employ a "zero leakage" target; however, environmental risk monitoring strategies for permanent abandonment are not yet in place. Predicting and estimating the consequences of adverse environmental impacts through a modeling approach can play a key role in evaluating and monitoring environmental risk. In this paper, we present a modeling study of the fate and effects of an oil leakage from abandoned wells using a theoretical scenario on the Norwegian continental shelf. Environmental impact factors (EIFs) derived from the Dose related Risk and Effect Assessment Model (DREAM), previously designed to characterize the effects of produced water discharges, were used to assess impacts of leakages from abandoned wells. Exposure assessments for the EIFs were modified to include specific hydrocarbon contributions derived from different sized oil droplets from the leakages. Because DREAM is not generally used for chronic low-rate oil releases, an update of the database with chronic predicted no-effect concentrations, as input data for effects modeling, was conducted. In general, EIFs became stable after simulations of 30 d. The area from the release site and up to a few hundred meters southward had the most locations of high impact. Chronic exposure and effects on organisms potentially occurred as a steady-state effect over a long period. Risks, at which more than 95% of species will be negatively affected, appeared surrounding the release site, indicating a need for mitigation measures. These results show that the EIF tool can be used for risk management and P&A regulation by identifying potentially harmful leakages. Integr Environ Assess Manag 2021;17:626-638. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).
Highlights
Abandoned offshore wells have uncertain interactions with the seafloor, the water column, and the sea surface in the marine environment (DNV GL 2016)
Aiming to provide an approach for modeling fate and effects of oil leakages from abandoned wells, the present study has shown that the estimation of biological exposure and chronic effects by continuous low‐rate oil leakages can be achieved through simulation modeling
The novelty of the present study was the use of chronic ecotoxicological thresholds derived from the PETROTOX database, allowing Dose related Risk and Effect Assessment Model (DREAM) to be used in the leakage scenario for specific oil components
Summary
Abandoned offshore wells have uncertain interactions with the seafloor, the water column, and the sea surface in the marine environment (DNV GL 2016). Oil leakages from abandoned wells may be comparable to natural seepages in that the discharge rate is relatively low and the exposure to biota is chronic. Sudden, large releases could occur, but likely under conditions where well barriers are severely degraded or insufficiently constructed. Indicative average gas (methane) flux rates from plugged onshore wells in the Netherlands; Pennsylvania, USA; and the UK were reported as 443, 264, and 41 g CH4 per day (Townsend‐Small et al 2016; Schout et al 2019). Oil rates would require a large buoyancy of gas bubbles to be in the same order of magnitude for equivalent cases
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