Hazards in the Ocean

22 June 2005 Australasia Branch Evening Meeting

Chairman Andy Lane, Chief Geohazard Analyst, Woodside Energy Ltd

Overview

The ocean is inherently dangerous and a hard task master with conspicuous natural hazards: tsunami, landslides, hurricanes/cyclones, icebergs, etc. In the latter half of the 20th century the potential exposure to hazards increased significantly as operations moved to deeper water, encountering gas hydrates, seafloor instability on local and regional scales, shallow gas, faults, could temperatures and high pressures. The management of ocean hazards is a core HSE activity.

Presentations

Australian Seabed Change and Submarine Pipeline Risk Evaluation

Fangjun Li, Research Scientist, CSIRO Petroleum

Australia's increasing offshore oil and gas exploration has demanded more accurate and reliable methods to evaluate and forecast the stability and trend of seabed change. As part of the Wealth from Oceans Flagship programme CSIRO Petroleum is involved in a new five-year study to investigate and predict the effect of possible climate change on the Australian seabed over the next 50 years.

Under this programme a large quantity of Australian seabed sampling data has been collected, as well as a variety of long-term environmental observation data for wave height, tidal speed and ocean currents. The novelty of the Sedpipe programme lies in the combination of large-scale seabed change evaluation and local pipeline interaction under a changing climate. Where the sediment layer is unstable, it cannot be assumed that a pipeline which is buried one year will still be buried next year, especially when active sand waves are a possible hazard.

Why the 2005 Sumatran Earthquake Did Not Generate a Damaging Tsunami: Comparison between 26 December 2004 (M9.15) and 28 March 2005 (M8.7) Earthquakes Off Northern Sumatra

Elio Novello, Principal, URS Australia Pty Ltd

URS Seismologists have developed earthquake slip maps of the 26 December 2004 and 28 March 2005 earthquakes in Asia, using them to calculate the tsunamis from the two earthquakes. Fault slips refers to the relative displacement of formerly adjacent points on opposite sides of a fault, measured on the fault surface. A slip map describes the amount, distribution and timing of slip associated with an earthquake. Two earthquakes with the same magnitude can produce very different tsunamis, depending on the depth and distribution of fault slip.

Results of the slip map are present and help explain why the March 2005 earthquake registering 8.7 in magnitude only generated a small local tsunami, compared to the devastating tsunami in December 2004.

Deepwater Geohazard Identification—Reducing the Engineering Risk Profile

Ian Hobbs, Geotechnical Engineer, Fugro Survey Pty Ltd

This presentation summarised deepwater geohazards and their potential significance on exploration and development operations. Survey technology over the past 10 years has been developed to meet the deepwater challenges and now datasets can be acquired, which provide the quality and resolution that was previously only achievable in shallow water depths. The key survey tools were reviewed along the importance of integrating different datasets to understand the big picture and the importance of involving key stakeholders from an early project stage.

By conducting a detailed geohazard investigation engineers have gained invaluable knowledge of the challenges for which they should plan ahead. A geohazard assessment is not simply a question of technical adequacy of the planned development, but also the financial and HSE risks.