SHELL Well Summary Garn Central North

Cuttings samples: Norske Shell well 3/7 - 6

SILDRIL CONCENTRATION

MBT & LGS

VOLUMES Projected: 425 m 3 Used: 496 m 3

The combination of the packed bottomhole assembly and the gauge wellbore was the primary cause of the problems experienced during the 8.5" interval. The restricted annulus created a bottleneck, which prevented efficient cuttings transport. As a result the cutting were mechanically broken down into fine solids which was interpreted as inadequate inhibition and "bit balling."

The engineers offshore and onshore had not been properly briefed on the SILDRIL system. As a consequence the engineers were not able to satisfactorily deal with the fluid and drilling problems.

The fluid properties of the SILDRIL system were good during the entire interval. The displacement of the active system was not justified based on the fluid properties. The observation of the fine cuttings discharge was interpreted as inadequate inhibition, when in fact, it was a result of the mechanical breakdown of the drilled cuttings. This conclusion is based on the mud report data (rheology and MBT), analysis of the cuttings, the caliper, and the volume of fluid used during the interval.

Pre-well planning with the operator and all services to ensure that all details are properly communicated.

Use of Virtual Hydraulics during the planning and drilling phase to correlate ECD, hole cleaning, drilling performance.

Orientation of all M-I engineers (offshore and onshore) with the project prior to the drilling phase.

Use of concentrated premixes from onshore to minimize treatment during the drilling phase.

Use of under-gauge stabilizers or an alternative BHA assembly, especially for the 8.5" interval. Determine the necessity for the near- gauge stabilizer or an alternative to provide efficient cutting transport. Rheology and flow rate are ineffective to alleviate this problem.

Supplement the one-page program with a detailed mud program