Geotechnical and geophysical investigations

In preparation for drilling the Offshore Appraisal Well, standard geotechnical and geophysical investigations were undertaken to confirm that the proposed location was able to support a drill rig.

Investigation methods and equipment

Geophysical investigations involve:

  • seabed imaging
  • assessing water depths
  • profiling underwater topography
  • identifying seabed obstructions (such as unmarked shipwrecks and buried pipelines).

The investigations were conducted in March 2019 using a small, locally-based vessel and took one week to complete.

Table 1 describes the investigation methods.

Table 1: Geophysical investigations – Commonwealth waters

EquipmentPurpose
Multi-beam echo sounder (MBES) Undertakes detailed measurements of water depth (bathymetry) in the project area.
Side-scan sonar Detects hazards such as existing pipelines, lost shipping containers, boulders, debris, unmarked wrecks, reefs and craters.
Sub-bottom profiler Investigates the layering and thickness of the uppermost seabed sediments, typically imaging to a minimum depth of 30m below the seabed.
Shallow seismic Provides near-surface geological structural information and detects geohazards.
Magnetometer Detects metallic objects on or immediately below the seabed (e.g. shipwreck debris, anchors, etc) that may not be identified by acoustic means.

Illustration showing a boat and types of geophysical equipment including a multi-beam echo sounder, side-scan sonar, sub-bottom profiler, shallow seismic and magnetometer.

The Geotechnical investigations involved taking shallow cores of seabed sediment and underlying rock to establish geological conditions at the potential drill rig location. The geotechnical investigations were performed using a medium sized vessel capable of transporting and deploying the larger equipment required for this task.

Fugro Mariner vessel

The investigations were conducted in July 2019 and took one week to complete.

Offshore activities were managed by AGR (Australia) Pty Ltd as the Drilling Management Contractor for CarbonNet. AGR has drilled over 40 offshore wells in Australia.

The Environment Plan for this activity was approved by the regulator, National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA), in late 2018. To view the Environment Plan Summary, visit the NOPSEMA website.

Table 2: Geotechnical investigations – Commonwealth waters

EquipmentPurpose
Seabed grab sampling (SGS) Provides samples of unconsolidated sediments (e.g. sands, silts and clays for analysis).
Seabed coring (SC) Provides samples for geophysical analysis of formations below the seabed.
Piezo Cone Penetrometer Test (PCPT) Determines soil strength and helps to delineate soil stratigraphy.

Illustration showing a boat and types of geotechnical equipment including seabed grab sampling, seabed coring and piezo cone penetrometer test.

Location

The investigations were carried out in Commonwealth waters approximately 6 km to 11 km offshore (Figure 3).

Image of Bass Strait offshore from Golden Beach and Paradise Beach Victoria showing the location of the CarbonNet Project geophysical and geotechnical investigations. The investigations will be in Commonwealth waters.

Timeframe

The geophysical investigations were completed in March 2019.

The geotechnical investigations were completed in July 2019.

More information

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Page last updated: 25 Nov 2020