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Lankelma completes investigation in the Gulf of Guinea
Thursday, September 20th, 2012
Geotechnical specialist Lankelma has completed a field investigation and advanced Core Penetration Test (CPT) lead analysis for the positioning of an exploration platform in the Gulf of Guinea, Cameroon.
The investigation was commissioned by an independent oil and gas company. The works were on the critical path of exploration operations and required a rapid turnaround of fieldwork and subsequent analysis, with staff and equipment mobilised from both the UK and New Zealand to site at two weeks notice.
Investigation work was undertaken from an adjacent fixed platform to provide a high resolution soil profile plus strength data which was then used in predicting the eventual leg penetration depth of the exploration rig upon full loading. All the equipment was hand portable so it could be transferred from the platform’s top deck to a lower deck 25m above the sea bed.
The CPT equipment, along with rotary drilling kit, supplied by Webster Drilling from New Zealand, was mounted on a bespoke frame welded to the platform in order to provide a stable base for drilling, CPT and soil sampling.
Two CPT soundings, using a 10cm2 electric piezocone, were carried out to 60m below seabed, through a nested drill rod and casing arrangement. Casing was installed to the seabed to protect and support the CPT push rods, before an initial test was carried out to 30m below mudline. At this stage, casing was advanced to 29m to provide further support in the very soft clay before the CPT was continued to the full depth.
Lankelma used the data from the two CPTs to identify the depth at which thin walled tube samples were to be taken by a follow-on rotary wireline borehole drilled by the same crew. Samples were retrieved from between 20m and 50m below seabed.
Leg penetration analysis considered the interaction between the acquired ground profile, the structural loading and the leg/spudcan geometry and, within 48 hours of completion of fieldwork, a preliminary penetration depth of 47m was advised to the client. This prediction, refined by confirmatory laboratory testing, proved to be within 3% of the actual penetration.
Carlton Hall, Engineering Director at Lankelma, said: “We have worked hard to develop our specialist investigation skill base over recent years – both technically and geographically. When coupled with our ability to rapidly position experienced staff and high quality equipment around the world, it has enabled us to service particularly demanding projects such as this. It is an excellent example of Lankelma’s ability to deliver high quality work in a difficult environment”.