Predictive Modeling of Hydrodynamic Dispersion for High-Pressure Atomized Crude Oil Plumes During Tidal Phase-Lag Loops in Santa Barbara Estuaries, Nigeria

Okuroghoboye Diepreye Itugha

This study models the multi-phase hydrodynamic atomization, near-surface jet shattering, and transient longitudinal advection-diffusion transport of high-pressure crude oil plumes within a tidally driven tropical estuary. It maps the 38-day uncontained wellhead failure at the Santa Barbara South Well-1 (OML 29) in Opu-Nembe, Bayelsa State, Nigeria, to quantify sub-surface contaminant migration paths. Hydrodynamic and chemical concentration data were compiled across a 10 km × 1 km estuarine corridor enveloping 47 remote communities. Ambient water samples (N = 120) were extracted from the water column using decontaminated Niskin sampler grids, stabilized, and processed via Gas Chromatography-Mass Spectrometry (GC-MS) to quantify Total Petroleum Hydrocarbons (TPH). Estuarine water surface elevation and multi-directional flow profiles were captured via a bottom-mounted Acoustic Doppler Current Profiler (ADCP). A two-dimensional depth-averaged finite-difference hydrodynamic model (x = y = 50 m) was coupled to an isentropic choked-jet discharge algorithm to calculate transient plume dispersion across a 12.4-hour Semi-diurnal tidal cycle. Thermodynamic derivations show that the reservoir pressure (4.2 MPa) drove a choked multi-phase discharge velocity (vjet  145.24 m/s), producing aerodynamic Weber numbers far exceeding critical breakup thresholds (We  100). This jet velocity shattered the liquid stream into ultra-fine droplets, driving immediate emulsification and chemical dissolution into the sub-surface water column. The cross-validated model isolated a strong phase-lag dynamic controlling transport. Flood-tide vectors drove the dissolved plume upstream, while ebb-tide drawdown compressed the mixing column, funneling persistent hydrocarbon matrices directly into low-velocity intertidal mangrove channels. This mechanism matched a peak measured near-source TPH concentration of 52.40 ± 2.62 mg/L at station AQ-01, representing a five-fold exceedance of national regulatory acute aquatic hazard boundaries. Model cross-validation yielded a Mean Absolute Error (MAE = 0.024 ± 0.003 mg/L), a low Fractional Bias (+0.012), a FAC2 index of 0.945, and a Nash-Sutcliffe Efficiency (NSE = 0.912). Conventional spill models that assume simple surface-slick transport underestimate the spatial extent and velocity of sub-surface estuarine plume migration. Upstream maritime contingency frameworks must shift from surface booming loops to implement real-time hydro-telemetry tracking grids. Environmental impact criteria should mandate continuous downhole automated isolation systems to prevent sub-surface resource fouling within vulnerable coastal delta networks.