Recognizing a technology gap in offshore site investigations, PanGeo Subsea developed the Acoustic Corer™. The Acoustic Corer™ provides very high-resolution data of the sub-seabed layers and buried objects through large volume acoustic cores (Figure 1).
The Acoustic Corer™ is a seabed deployed unit with dual subsurface scanning sonar heads attached to a 12m rotating boom (Figure 2). The Acoustic Corer™ 3D technology uses acoustic intensity imaging to delineate sub-seabed stratigraphy and buried geohazards. The Acoustic Corer™ delivers high-resolution, high-definition, multi-aspect 12m diameter volumetric images to a depth of 30m to 40m below seafloor depending on geological complexity of the site.
Figure 2: Acoustic Corer™ is a seabed deployed unit with dual subsurface scanning sonar heads attached to a 12m boom rotating to cover 360 degrees.
The image below (Figure 3) shows how the acquired 3D sub-bottom image is sectioned and interpreted by geoscientists to yield very detailed information of sub-seabed geological layers and anomalous responses within the sub-seabed interpreted in terms of geohazards or inhomogeneous soil conditions.
Figure 3: The acoustic core image yields detailed structural information about the sub-bottom and enables geohazard position and size to be determined.
A wide variety of analyses can be performed on the data. For example, by contouring reflection data from bed rock underlying overburden we can determine if cavities and pinnacles exist within the rock that could pose a threat to the secure placement of jack-up rigs (Figure 4)
Figure 4: Acoustic Corer™ data analysis to provide bedrock surface map, which would identify bedrock cavity and pinnacle hazards.
PanGeo Subsea uses the Acoustic Corer™ to investigate the sub-seabed condition prior to the placement of offshore infrastructure through the acquisition and analysis of 3D sub-seabed acoustic images. These images are interpreted to provide information about geohazards:
- Buried boulder identification, location and sizing
- Dense cobble/gravel layer delineation
- Gassy soils identification, location and sizing
- Unexploded ordnance (UXO) location and sizing in support of magnetic survey
The Acoustic Corer™ can be used to identify hazards prior to placing offshore structures such as jack-up rigs. The following hazards can be imaged and identified using the technology:
- Location and extent of old buried spudcan impressions
- Hard ground delineation
- Identification of thinning layers that present the risk of punch through
- Identification of buried cavities and rock pinnacles
- Identification of dipping slippage planes/beds
The Acoustic Corer™ can be used as a preliminary site investigation tool, prior to traditional geotechnical site investigations. In this instance, the interpreted acoustic core results are used to direct borings and cone penetration tests (CPT) to regions that are competent, free of geohazards and homogeneous thereby avoiding costly re-work of borehole and CPT’s. The acoustic cores can also resolve any conflict between physical cores and CPT data in complex seabeds, because they provide a greater lateral coverage and show the continuity of geological layers.
The Acoustic Corer™ provides several benefits to the customer. These are:
- Reduced risk by sampling full site volume
- Reduces the number of physical cores required
- Mitigates against cost overruns and schedule delays
- Improved survey data reduces overall project risk.
Stable, protected and working seabed platforms are critical to ongoing operational success of any subsea infrastructure. Permanent seabed based infrastructure requires piling to reduce the risk of movement over time.
The Acoustic Corer™ provides data during risk evaluation and site selection, pre-installation, and to reduce the potential for a failure in pile driving.
Jack-up placement requires an understanding of the geotechnical properties of the seabed.
The Acoustic Corer™ technology adds confidence to platform foundation surveys and is complementary to conventional geophysical/geotechnical site investigation methods.
Windturbine placement requires robust foundation installation to provide stability of the turbine under loads and vibration generated while operating.
The Acoustic Corer™ technology provides increased confidence in the placement of the foundation by providing a complete image of the sub-seabed within the foundations footprint. This complements conventional site investigation methods.
Excavated Drilling Centers (Glory Holes) protect seabed installations by lowering the profile of installed infrastructure below the natural seafloor.
The Acoustic Corer™ technology can locate major geotechnical hazards pre-excavation to assist in the correct placement of glory holes and facilitate informed selection of template and piling locations.
Decommissioning of subsea infrastructure can require a pre or post verification of the installation site.
The Acoustic Corer™ technology provides accurate reconnaissance prior to or after removal of buried infrastructure or debris.