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Case Study • Leg Penetration Assessment for Production Platform in Gulf of Guinea, West Africa • Lankelma

Production Platform Positioning
Leg Penetration Assessment
Geotechnical Contractor
May 2012 – December 2013
Gulf of Guinea, West Africa
The safe positioning of production platform depends on balanced penetration of legs until a stable founding depth has been achieved.

The very soft clays in the Gulf of Guinea can result in leg penetration reaching between 40m and 50m - the practical limit of many production platforms. At the mouth of the River Congo however, highly variable ground conditions lead to unpredictable soil strengths and hence leg penetrations.

The client was concerned about achieving leg stability at depth and engaged Lankelma to provide Leg Penetration Assessment (LPA) services, comprising fieldwork and reporting, to enable location approval and warranty surveyor certification.

To date, four campaigns have been carried out. Our initial team, plus our Heli/hand portable drilling and CPT equipment, were mobilised within two weeks to address the most urgent concerns.

Clear technical, operational and safety procedures were developed with the client before work began, to identify risks. Briefing documents managed the Lankelma/client operational safety interface and key emergency protocols were agreed.

The Lankelma team grew to 15, including field laboratory and geotechnical analysts, providing realtime preliminary assessments.

Work was carried out 24/7 using third party vessels and rigs, in water depths up to 25m, with testing to 80m. Each campaign satisfied warranty officers of the viability of the rig location and operation.
Related Case Studies
Lankelma carried out multi-disciplinary geotechnical and geophysical investigations for a jetty extension, construction of a new bauxite-handling jetty and dredging of an approach channel at a Container Terminal in Guinea. The jetty was being extended by 500m and a new berthing pocket dredged, to allow barges to offload bauxite. The new 500m long Jetty ... Moreis due to be built to the south of the existing Jetty. Investigations also covered the 17km approach channel being dredged in the estuary.

Lankelma used its Combifloat C5 Jack-Up Platform "Sandpiper" to carry out cone penetration tests (CPTs) up to 23m deep and drill geotechnical boreholes to 50m through the underlying clays, silts, gravels, laterites and into the underlying sandstone.

Along with offshore piston sampling and thin-wall push sampling, the investigation included nearshore CPT and drilling, geotechnical laboratory testing, data interpretation and correlation, and geotechnical reporting.

Lankelma's former sister companies – Gardline Geosurvey and Alpine Ocean Seismic Surveys – undertook bathymetric and geophysical surveys, metocean surveys, tide gauge installation and monitoring. Vibrocores were also carried out using a client-chartered vessel along the approach channel to ground truth the results of the geophysical survey.

The team had to overcome major logistical and health challenges (including the outbreak of the Ebola Virus) and maintained good communications and relations with the client and its engineering consultant throughout.
Cone Penetration TestingCPTDrillingEngineeringGeotechnicalJack-Up PlatformLaboratory TestingLeg Penetration AssessmentLPAOffshore
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