Case study: Maari

Excellent sample recovery in soft clays and sand

The Project

Location: New Zealand
Date: December 2005 – January 2006
Vessel: 53m DP1 ROV Supplier
Geology: Soft clayey SILTS overlaying medium dense SANDS
Description: Multiple borings to a max. depth of ML-34m with continuous sampling and continuous CPTs

Overview

Benthic Geotech recently completed safe and successful drilling, sampling and insitu testing at the Maari field, Cook Strait, New Zealand for OMV New Zealand Ltd. The project was completed with negligible equipment down-time due to breakdown or maintenance. 

The investigation provided geotechnical data for foundation design to support a new well head platform. Sampling and CPT testing was undertaken at 24 locations to represent an area appropriate for the gravity based foundation. 

Significant achievements at Maari using PROD 

PROD provided a number of extra benefits to the client. These included: 

  • Detailed and accurate characterisation of surface soft soil layers. Supported on its broad skirted footings, PROD imparted negligible disturbance to the soft seabed enabling accurate definition of the thickness of the soft silt layer at seabed, and good depth control of the drilling operations. 
  • PROD’s piston sampling system recovered near continuous 2.75m long samples. Exceptional sample recovery was achieved in all materials, including clean sands. The high quality samples enabled the layered nature of the materials to be clearly observed. 

Excellent productivity was achieved. The 24 investigative holes were carried out in only 8 deployments of PROD. CPT testing at 17 locations delivered 180m of 18-bit CPTu data. Sampling at 7 locations, using the unique combination of controlled piston and the newly designed core catcher, resulted in 114m of silt and sand samples being obtained, with full recovery in both silts and sands. All work was completed in five days total operating time.