Case Study

Finding new hydrocarbons for Chrysaor

Oil exploration well drilling in difficult operating conditions


Chrysaor NS Limited


Drilling an oil exploration well, West of Shetland, North Sea


non-productive time


under the authority for expenditures Zero accidents, incident or environmental impact

Client Challenge

Established in 2007, Chrysaor is a private company with a focus on generating superior equity returns through developing and commercialising oil and gas discoveries in the North Sea. Our client asked us to drill an oil exploration well, West of Shetland, where there was a ‘limited’ operational weather window.

The project was planned and executed in a short timeframe to ensure that the well could be drilled and tested in the summer and autumn months. In a tight rig market, the client assigned the mobile offshore drilling unit (MODU) Transocean Sedco 712 to the project, which was mobilised from Invergordon to the Mustard prospect.

How we helped

Working to tight timings, we created a bespoke rig intake plan, ensuring crew and equipment were ready.

During the initial drilling phase, we encountered boulders and igneous pebbles during the spud and 17½” intervals. This resulted in hole problems, while tripping drilling assemblies and running casing strings. On encountering the hole problems in the surface holes, a casing drive system was mobilised to the rig at short notice. This improved the successful running of the 13.3/8" casing.

A small influx was incurred in the 8½" interval of the wellbore, due to a small faulted zone of high pressure. Well control operations were undertaken and the pressure released from the system in a controlled manner, prior to resuming drilling operations.

A core run was successfully performed in the reservoir sequence, recovering 100% of the core. The well was then drilled to total depth (TD) before wireline evaluation; the mainbore was abandoned and a sidetrack interval drilled to explore the reservoir extent. The well was then suspended for future use.

Business Benefit

Overall non-productive time (NPT) was 11.8% of total operational time and the project was delivered 20% under the authority for expenditures (AFE). Hydrocarbons were discovered in both the mainbore and sidetrack reservoir intervals.

In my view, the Lloyd’s Register 'one team' philosophy was instrumental in contributing to attaining our primary goals on the project which were: 'drill the well in a safe and efficient manner without undue environmental effect and within AFE'. This was fully achieved with the project recording a zero-incident status for the well with no accidents, incidents or environmental impact.

Wells Director, Chrysaor

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