Geotechnical and geophysical investigations

The CarbonNet Project is planning for its next field activity, the drilling of an offshore appraisal well (OAW) at the Pelican site in Commonwealth waters in late 2019.

Standard geophysical and geotechnical investigations have been undertaken to confirm that the proposed location is suitable to support a drill rig.

Investigation methods and equipment

Geophysical investigations involve seabed imaging, assessing water depths, profiling underwater topography and identifying seabed obstructions (such as unmarked shipwrecks and buried pipelines). The investigations were conducted using a small, locally-based vessel.

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

All work was undertaken in Commonwealth waters. Both activities took less than one week each to complete.

The investigations 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 NOPSEMA.

Table 1 describes the investigation methods.

Table 1: Geophysical investigations – Commonwealth waters

EquipmentPurposeDuration Potential impact and mitigation
Multi-beam echo sounder (MBES) Undertakes detailed measurements of water depth (bathymetry) in the project area. About 4 days.

Potential minor and temporary impacts on sound sensitive fauna, if present. To be risk assessed in Environment Plan, informed by habitat assessments.

In accordance with the EPBC Act Policy Statement 3.1, a 500-m shutdown zone will be maintained during equipment operation minimise impacts.

Side-scan sonar Detects hazards such as existing pipelines, lost shipping containers, boulders, debris, unmarked wrecks, reefs and craters. Operated at the same time as the MBES. As above.
Sub-bottom profiler Investigates the layering and thickness of the uppermost seabed sediments, typically imaging to a minimum depth of 30 m below the seabed. Operated at the same time as the MBES. As above.
Shallow seismic Provides near-surface geological structural information and detects geohazards. Around 24 hours at less than 5% intensity of that used for the marine seismic survey. As above.
Magnetometer Detects metallic objects on or immediately below the seabed (e.g. shipwreck debris, anchors, etc) that may not be identified by acoustic means. Operated at the same time as the MBES. The source will be kept to the lowest level required. Potential impacts to be risk assessed in Environment Plan.

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.

Table 2: Geotechnical investigations – Commonwealth waters

EquipmentPurposeDurationImpact
Seabed grab sampling (SGS) Provides samples of unconsolidated sediments (e.g. sands, silts and clays for analysis). A few hours in total. Temporary and localised seabed disturbance and turbidity. Impacts to be risk assessed in Environment Plan, informed by habitat assessments.
Seabed coring (SC) Provides samples for geophysical analysis of formations below the seabed. 5–7 days. As above.
Piezo Cone Penetrometer Test (PCPT) Determines soil strength and helps to delineate soil stratigraphy. Takes place at same time as coring ops. As above.

Note: The above information was preliminary as of July 2018.

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

Contact us

If you have any feedback or questions about the geotechnical and geophysical investigations please contact AGR (Australia) Pty Ltd

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Page last updated: 22 Oct 2019