Performance Report: North Sea, Norway - SILDRIL System


An effective drilling fluid was required to drill the 17½-in interval. The objective was to use the fluid to drill the soft, reactive clays and shales in the lower part of the Naust formation and Kai formation in the Nordland Group and the upper part of the Hordaland Group.


Silicate water base fluids are recognized in the industry as an effective water base fluid for chemical wellbore stability. Silicate fluids require the potassium ion in the form of an organic or inorganic salt for optimal performance.

A SILDRIL L / KCl system was used to provide an effective, efficient solution to drill the 17½-in interval through the problematic Naust, Nordland, and Hordaland formations.


The 17½-in interval was drilled with the silicate-potassium system from 1,205 m to 2,415 m in 5 d. The initial ROP for the interval was 24.5 m/h, and the final ROP was 5.9 m/h (average ROP = 29.3 m/h for the whole section). The mud gave excellent cuttings integrity, with defined edges and no sign of mud intrusion. Dry hard cuttings (up to 10 cm) with excellent integrity were observed throughout the entire interval. Coarse mesh screens (60&84 mesh) were used at the start of the section to avoid blinding the screens. As the flowline temperature increased and polymers were conditioned, finer mesh screens were used to effectively control the mud weight and viscosity. The only maintenance volume required was for the hole volume drilled.

Cavings were observed at the shakers at 4330 meters and excessive torque was experienced. Increasing the density to 1.53 SG cured the problem. As the mud weight was increased, the rheology showed a distinct increasing trend and the mud had to be diluted with low viscosity premixes. Bit runs were reduced; no bit-change was required.

The hole was in gauge with no shale sloughing, bit or BHA balling, or screen blinding typical of previous wells.

Well Information
Location 6406/1-2, Haltenbanken North Sea
Spud / Completion June 26, 2003
Intervals Drilled 17½” from 1205m to 2415m (1210 meters)
Formations Drilled Gumbo, clay, shale, sandstone
Maximum Density 1.53 SG / 12.74 ppg
Maximum Deviation
Total days on interval 5 days
Problems none

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