Subsea Rock Installation Support

Client challenge

Following several days of adverse weather, ROV surveys identified significant seabed mobility and scour development around the bow leg spudcan of a Mobile Offshore Drilling Unit (MODU). Differential penetration of the spudcan indicated localised loss of seabed support, increasing the risk of continued scour and foundation instability.

To maintain safe operations, Ithaca Energy required rapid assessment of the seabed loss and support for a targeted Subsea Rock Installation (SRI) campaign to restore seabed levels and install a protective rock berm around the affected spudcan.

How we helped

Vysus Survey & GeoEngineering (S&G) used spudcan geometry, penetration measurements, and survey water depths to assess the extent of scour and estimate the volume of material lost around the foundation.

Using penetration measurements collected at 12 locations around the spudcan circumference, S&G developed a geometric scour model to calculate:

• volume of seabed material requiring replacement, and
• rock volume required to construct a stable protective berm.

The assessment incorporated engineering constraints, including rock grading, berm geometry, and allowable repose angles to support safe installation design.

Successful Planning & Results

S&G delivered a rapid and technically robust assessment that enabled SRI works to be completed efficiently.

Key outcomes included:

• Rapid estimation of scour and rock placement volumes under time-critical conditions.
• Development of a dynamic calculation tool to support real-time offshore installation decisions.
• A clear and defensible engineering methodology integrating survey data and geometric modelling.
• Recommendations for installation monitoring and post-placement verification to support ongoing foundation stability.

The work provided Ithaca with a practical and risk-informed solution that stabilised the affected spudcan, reduced further scour risk, and supported the continued safe operation of the MODU.