3D Seismic and AUV Data Integration for Deepwater Geohazard Assessment: Application to Offshore Northwest Borneo, Brunei

A 3D seismic and AUV data integration has been performed for geohazard assessment at an early stage of a field development. The study area is located on the South China Sea, approximately 100 km northwest of the coast of Brunei Darussalam margin characterized by a delta toe fold-thrust belt. Elongated mini-basins are separated by shale-cored ridges created by basin-directed thrusting. The continental slope is characterized steep slopes and affected by large channels, and mass transport deposits (MTD). A regional geohazard assessment was performed on the 3D exploration seismic data highlighting the presence of numerous seabed an sub-seabed features potentially affecting E&P activity. In order to better assess the possible impact of these geohazards on the field development, a detailed AUV survey has been performed on target areas. The study area ranges from 830 m to 2050 m of water depth and is characterized by seabed gradient up to 45°. Several events of buried MTD including more cohesive blocks which result in the hummocky signature on the present-day seabed are observed. The presence of such MTDs may induce vertical and lateral soil variability that may impact both drilling operations or pile/anchor installation and flowlines installation passing through the hummocky seabed. In addition, the slopes are affected by recent instability processes covering 2 km² to 10 km². Larger slide scarps with an amphitheatre-like source area are observed and appear to be created by various retrogressive events. The slides initiate on various slope angles, from 2° to 16°, and measured run-out distances show a large range of values, from hundreds to thousands of metres. Evidences of seafloor expulsion features (craters, pockmarks), shallow gas, gas hydrates are also observed within the study area. The 3D seismic dataset has been used to identify at a regional scale particular geohazards areas requiring a more detailed investigation via AUV at an engineering scale. Such engineering scale allows producing favorability maps created from selection criteria and allowing mitigation strategies for safe E&P activities.