Coupled Near-and Far-field Modeling Suite for Produced Water Discharges from Offshore Oil Platforms: Integrating TAMOC and OpenDrift's ChemicalDrift for Operational Monitoring

Produced water (PW), the largest waste stream from offshore oil and gas production, is continuously discharged into the marine environment after treatment, introducing polycyclic aromatic hydrocarbons (PAHs), heavy metals, and other contaminants [5], [2]. Accurate prediction of the fate and transport of these substances requires modeling both the initial discharge dynamics and long-range dispersion. We present a coupled near- and-far-field modeling framework that integrates the Texas A&M Oilspill/Outfall Calculator (TAMOC) with OpenDrift's ChemicalDrift module to simulate PW discharges from offshore platforms.

TAMOC's Bent Plume Model (BPM) simulates the nearfield dynamics of PW discharge. The BPM solves conservation equations for mass, momentum, and buoyancy considering ambient stratification and cross flow conditions, capturing the initial dilution and trajectory of the plume [6], [4], [3]. The key outputs transferred to the far-field model include the plume terminal location  and the dilution, which are used to initialize the Lagrangian particle seeding in ChemicalDrift.

ChemicalDrift, a Lagrangian chemical-fate and transport model integrated within the open-source OpenDrift framework, simulates the subsequent long-range advection and dispersion of contaminants [1]. The model tracks advection and diffusion by ocean currents, interaction with surface wind and turbulent mixing. Critically, it implements dynamic partitioning of contaminants between dissolved, particle-bound, and sediment phases, along with their degradation and volatilization. Temperature and salinity dependencies on chemical processes are formulated, enabling enhanced fate predictions in varying oceanographic conditions.

This coupled system is being deployed within the Integrated Monitoring System for the Italian Ministry of the Environment and Energy Security (SIM MASE) for operational monitoring of PW discharges from Italian offshore platforms. The framework enables direct integration of regulatory thresholds from Italian legislation (D.Lgs. 172/2015) and EU Directive 2013/39/EU on priority substances in water policy. Model outputs flag exceedances of Environmental Quality Standards, enabling users to identify when and where contaminant concentrations surpass legal limits, according to the simulations. By separating contributions from multiple platforms and providing spatiotemporal concentration fields, the modeling chain offers decision-makers a tool for compliance assessment and sustainable management of offshore activities.

References

1. Aghito, Manuel, et al. "ChemicalDrift 1.0: an open-source Lagrangian chemical-fate and transport model for organic aquatic pollutants." Geoscientific Model Development 16.9 (2023): 2477-2494.
2. Beyer, Jonny, et al. "Environmental effects of offshore produced water discharges: A review focused on the Norwegian continental shelf." Marine environmental research 162 (2020): 105155.
3. Dissanayake, Anusha L., Jonas Gros, and Scott A. Socolofsky. "Integral models for bubble, droplet, and multiphase plume dynamics in stratification and crossflow." Environmental Fluid Mechanics 18.5 (2018): 1167-1202.
4. Gros, Jonas, et al. "Petroleum dynamics in the sea and influence of subsea dispersant injection during Deepwater Horizon." Proceedings of the National Academy of Sciences 114.38 (2017): 10065-10070.
5. Neff, Jerry, Kenneth Lee, and Elisabeth M. DeBlois. "Produced water: overview of composition, fates, and effects." Produced water: Environmental risks and advances in mitigation technologies (2011): 3-54.
6. Socolofsky, Scott A., et al. "Texas A&M Oilspill Calculator (TAMOC) modeling suite for subsea spills." Proceedings of the thirty-eighth AMOP technical seminar. Ottawa: Environment Canada, 2015.