Delineation of Debris and Turbidity Flows Through Integration of UHR Engineering Geophysical Systems, Geologic/Geotechnical Sampling and 3-D Seismic – Greater Gorgon Development, Northwest Shelf of Australia

K.R. McPhail
ExxonMobil Exploration Company, Houston, TX

The Greater Gorgon Development is a coordinated effort between ExxonMobil and Chevron to exploit resources once thought stranded. Initial development and production of this 12 Billion Dollar (USD) project will originate from the combined 40+ TCF Gorgon and Jansz fields.

A multi-phase survey was developed to advance the project design phase while reducing overall acquisition cycle time. Phase 1a acquired hull-mounted Multi-Beam Echo Sounder (MBES), Sub Bottom Profiler (SBP) and Side Scan Sonar (SSS) data to refine initial pipeline/umbilical routes. Phase 1b obtained Large Gravity Piston Cores (LGPC) and box cores to increase the overall understanding of local stratigraphy and calibrate UHR data types. The cores were then processed for detailed stratigraphic and x-ray analysis in conjunction with paleontologic sub-sampling. Phase 2 utilized a co-located sensor package, the DeepTow 2 (DT2), to acquire more resolute MBES, SBP and SSS data to tighten proposed pipeline corridors and broaden general understandings of near surface geology and geomorophologic processes.

High resolution DT2 chirp-SBP data provided more detail to for the identification of seismically resolvable debris flows in the near surface sediments. With this knowledge, an additional coring program was designed to target flows in an attempt to constrain and estimate frequency of these events. Early C14 analysis of foraminifera and pteropods indicate flow events as recent as ~5500 years ago along the Northern Routes and ~38000 years ago along the Southern Route. In addition, SSS analysis along the N1C route illustrates dendritic drainage patterns indicative of erosional scour generated from turbidity flows.