Modelling the Fate of Produced Water Discharges on the Nigerian Continental Shelf

Produced water, the largest volume waste stream from offshore oil and gas production, is discharged to sea from Nigerian continental shelf platforms in quantities that have received limited independent scientific scrutiny regarding their cumulative environmental fate and impact at the ecosystem scale. This dissertation develops a comprehensive fate and transport modelling framework for produced water constituents on the Nigerian continental shelf, validated against original field monitoring data and applied to evaluate cumulative environmental impact under current and projected future production scenarios. Produced water characterisation is conducted through analysis of 240 samples collected from 12 platforms across Nigerian oil mining licences during quarterly sampling campaigns in 2023 to 2024, quantifying dissolved organic matter, total petroleum hydrocarbons, polycyclic aromatic hydrocarbons, heavy metals, naturally occurring radioactive materials, and scale inhibitor chemicals using standardised analytical methods. The validated hydrodynamic model of the Nigerian shelf (ROMS, calibrated in companion research) is coupled with a particle-tracking and dilution-dispersion module to simulate produced water plume trajectories and dilution under the full range of tidal, wave, and seasonal current forcing conditions. Sediment accumulation of hydrophobic constituents is modelled through a coupled sediment transport and chemical partitioning module. Ecological risk assessment using species sensitivity distributions for key Nigerian shelf organisms (crustacean zooplankton, bivalve larvae, demersal fish) determines safe dilution thresholds. A Monte Carlo uncertainty analysis quantifies the confidence bounds of modelled environmental concentrations. The regulatory implications for mandatory produced water treatment standards under the revised Petroleum Industry Act are assessed. Keywords: produced water, fate modelling, Nigerian shelf, ecological risk, offshore discharges