Impact of Mass Transport Deposits on Field Development on the Upper Slope of Sabah, Deepwater Northwest Borneo

Hongbo Lu, Craig Shipp, and Chris Hadley
Shell International Exploration and Production Inc, Houston, TX

The study area is located on the northwest Borneo continental slope with a water depth of 2800-4000 ft, adjacent to the Brunei border in the Malaysian state of Sabah. The most distinctive feature in this area is a dip-oriented (southeast to northwest) seafloor structure (bulge) with 400-500 ft of positive relief that dominates the mid to upper slope. A second distinctive feature is complex of mass transport deposits (MTDs) that occur in the near-surface interval northeast of the bulge with a thickness up to several hundred feet. The MTD complex displays a fan-like shape in map view and is exposed on the seafloor at distal end, while the proximal end near the shelf edge is overlain by 50-100 ft of hemipelagic drape. Steep slopes on the northeast flank of the bulge seem related to erosion caused by mass failure associated with the MTD complex.

A primary objective of this study was to generate a suite seafloor and near-surface maps to guide the design of subsea infrastructure. The geohazards assessment focused on characterizing seafloor and near-surface geological features, especially the geometry, process, and evolution of the MTD complex. A variety of techniques were used to differentiate seafloor textures and near-surface features on both conventional (3D) and high-resolution (2D and 3D) seismic data sets. Additionally, offset well logs were used to evaluate the internal character of the MTDs.