Field Evaluation of a Tide-Driven Siphon Biostimulation System for Subsurface Hydrocarbon Remediation in Opu-Nembe, Nigeria

This study designs, constructs, and field-validates the long-term performance of a zero-power, Tide-Driven Siphon Biostimulation (TDSB) system.

The installation is configured to accelerate the in-situ degradation of persistent total petroleum hydrocarbon (TPH) mass entombed within low-permeability cohesive clays following the 38-day uncontained wellhead blowout at the Santa Barbara South Well-1 (OML29) in Nembe, Bayelsa State, Nigeria.

A pilot-scale field implementation was executed across three independent, randomized treatment plots containing nested monitoring clusters.

Subsurface fluid delivery lines were charged with an amphiphilic rhamnolipid biosurfactant and dissolved macronutrient solution (C:N:P 100:10:1).

Soil cores (n=9 replicates per milestone) were extracted from a core depth profile of 0.75m to 1.25m over a 24-month horizon.

Residual hydrocarbon concentrations were quantified via gas chromatography-mass spectrometry in compliance with US EPA Method 8015C standards.

Changing structural soil parameters were derived using triaxial shear cell testing under ASTM standard guidelines.

Field data confirm that the system successfully harnessed the natural potential energy of local semi-diurnal spring tides (2.2m maximum head).

When the rising tide head differential breached the network's check- valve activation threshold (ÄHtidal > + 0.4m) , the gravity feed lines automatically pulsed the remediation solution into the clay matrix, overriding capillary entry resistance.

Over the 24-month monitoring timeline, the TDSB network dropped mean subsurface soil TPH concentrations from an acute baseline of 42,500±1,850mg/kg down to 92±8mg/kg, successfully clearing the national EGASPIN intervention target limit (5,000mg/kg), while traditional natural attenuation control fields remained stalled at 8,450±520mg/kg due to severe macronutrient exhaustion.

This accelerated hydrocarbon removal eliminated internal pore-fluid blocks, driving an increase in structural mineral confining stress from a liquefied state of -20.0kPa back to a consolidated baseline of +33.4kPa to stabilize the slopeface against further erosion.

These pilot-scale findings suggest that leveraging natural hydrostatic cycles provides a viable, zero-power mechanism to remediate deep contaminant sinks in isolated basins.

Coastal remediation frameworks should incorporate tidal potential head variations to eliminate the need for external electrical grids during in-situ soil remediation campaigns.