Assessment of Shallow Drilling Geohazards for Safe Well Placement from Seismic Data in the Tano Basin, Offshore Ghana

Abstract

The increasing global demand for oil and gas underscores the need for comprehensive assessments of geohazards in offshore drilling operations to ensure safety and efficiency. This study investigates shallow drilling hazards in the Tano Basin, offshore Ghana, focusing on geologic structures and conditions that pose risks to well placement. Utilising high-resolution 3D seismic data, seabed features and subsurface horizons were mapped, and structural depth analyses were performed to evaluate potential drilling risks. The study identified a northwest trending canyon with steep flanks prone to sliding or rotation, posing a risk to wellbore stability. Faults were prevalent in Unit B, with significant gas accumulations associated with an unconformity at Horizon 1. This unconformity serves as a potential trap for gas, elevating the risk of blowouts during drilling activities. Minor gas accumulations were also detected between Horizons 1 and 2, indicating drilling hazards. Key recommendations include avoiding well placements near seabed canyons, fault zones, and areas with gas accumulations. These regions are susceptible to mass movements, explosions, and structural instability, which could compromise drilling operations. The findings emphasise the critical role of seismic data analyses in identifying geohazards and guiding safe and cost-effective drilling strategies. By providing insights into seabed morphology and shallow subsurface geology, this study contributes to mitigating risks and enhancing the safety of offshore petroleum exploration within Tano Basin.