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 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
|Equipment||Purpose||Duration||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.|
Table 2: Geotechnical investigations – Commonwealth waters
|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.
The investigations were carried out in Commonwealth waters approximately 6 km to 11 km offshore (Figure 3).
The geophysical investigations were completed in March 2019.
The geotechnical investigations were completed in July 2019.
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Page last updated: 18 Mar 2020