Negative Bit LL with DNO

Gomez (2/5-15) – Surface section

What happened:

Drilled 12 ¼” hole with Smith XZ616 AxeBlade PDC bit from 1613 m to 2895 m in a vertical hole. Drilled Hordaland group with frequent Limestone stringers form 0,3 m to 1,3 m thick. Limestone stringers (Dolomitic) were hard to very hard. Approximately 170 Limestone stringers were drilled. Achieved ROP of 20-60 m/hr drilling Claystone between stringers. Stringers were drilled with 0,5- 5 m/hr. Started section with moderate WOB 5-10 t. As Claystone got more compact WOB was increased up to 24 t WOB. Stringers were drilled with high WOB 15-24 t. Alternated drilling parameters but high weight and 100-160 RPM seems to give best ROP. At 2815 m drilled into the Horda formation which was more “plastic”. Observed a gradual decrease in ROP and at 2895 m it was drilled 0,3 m over 1 hour. POOH and found bit badly worn / damaged. No PDC cutters remaining. 2 x lost nozzles. Matrix material worn and broken off in places. 1/8″ under gauge.
Total bit hours: 110,7. ROP run 11,6 m/hr.

What was planned:

Drill 12 1/4″ hole vertical from 1613 m to casing point at 3112 m using OBM. Bit selection: AxeBlade XZ616, TFA 1,27.

What was learned:

Hard and frequent limestone stringers caused excessive wear on the bit. WOB run up to 24 t was necessary to achieve some progress. The high WOB most likely shorten the bit life.

What actions are required:

Look into bit selection for the combination of hard limestone stringers, claystone and “plastic” claystone in Horda formation. Consider planning to drill this section in two bit runs.

What Was Done

POOH and changed to new bit: StingBlade Z616, TFA 1,27.