Analysis of fluid movement along faults and shale diapirs in deep water settings, Bonga North Field, OML-118, offshore, Niger Delta.

Seismic data around the crest of the Bonga North Field is only of questionable quality because of recent shale flows, uplift and faulting. A 3D seismic data was reprocessed to improve seismic resolution across the diapirs. A well in the field encountered several gas flows which were neither predicted nor fully understood. Better knowledge of potential fluid pathways in the shallow section at Bonga North field is therefore required to help de-risk future drilling operations. The information derived from the 3D high resolution seismic data, well logs and end of well reports were used for this project. The shallow faults and other potential fluid migration pathways in and around the crest of the structures were mapped to better predict and mitigate potential hazards above the reservoir section. Eight stratigraphic units were mapped and analyzed for potential geohazards. Semblance slices, seafloor topography maps, dip/traverse sections and sub-volume sculpturing were created to capture the study intervals and observe structural and amplitude variations. The results showed that the Bonga North Field is highly faulted with fault density increasing towards the crest of the shale-induced structure where the BN3 well is situated. Faults are partially sealing and extend to the seafloor. The seafloor and near-surface assessment revealed potential hazards, including pockmarks (fluid escape features), shale intrusions, gas chimneys and near-surface faulting. In the subsurface; faults, shallow water flow (SWF), expulsion chimneys and seismic amplitude anomalies which may be indicative of shallow gas-filled sands were identified as the main geohazards. The BN1 and BN2 wells were drilled without problems but the BN3 well is closest to all these hazards. It is therefore recommended that; (1) the drill centers be moved farther to the northwest where there is lower risk of encountering hazards, (2) a high resolution seabed survey be conducted, (3) a working gas sensor, ROV and camera monitor be incorporated into the well drilling operations, (4) a kill-weight mud be made available to ensure well control and prevent blow-out in future wells.