While drilling in the offshore Hasbah field, a polymer mud with conventional lost
circulation material was used to drill the 16-in. hole section on the HSBH-49. The
initial mud weight was 72 pcf and increased to 76 pcf while drilling to 8,760 feet
(Lower Fadhili formation). The circulation rate was 900-925 gpm with an average
ROP of 60 ft/hr. The transition zone to the Dhruma shale (at 9,160’) consists of
interbedded layers of dolomite and limestone, with possible fractures. While
drilling through this section, lost circulation was encountered and the rig was
unable to regain circulation. The decision was made to drill ahead with the mud
cap, with no returns to surface. Stuck pipe was encountered at 9,031 feet. Fishing
operations were unsuccessful and the BHA could not be retrieved. The decision
was made to sidetrack the well.
The polymer mud formulated for the new sidetrack and included an addition of
5 lb/bbl of FLC 2000 wellbore stabilizer. The mud weight was maintained at
72 pcf and drilling rate was controlled at 30 to 40 ft/hr with a circulation rate of
about 800 gpm. The mud system was later converted to a Hydroguard system
with the addition of shale inhibitors added from +/- 9,000 feet before entering
Dhruma shale. The change in drilling parameters and enhanced mud formulation
with the addition of 5 ppb FLC 2000 resulted in no drilling fluid related issues
while drilling to 9,268-ft. (16’-in. hole) as well as the 83⁄8-in. pilot hole to a depth of 9,873-ft.
FLC 2000 helped to mitigate induced fractures on the new sidetrack. Drilling of
the transition zone from the base of Lower Fadhili Reservoir to Dhruma shale
continued while maintaining 35-40 lb/bbl of conventional LCM/bridging material
and 5 lb/bbl of FLC 2000. The use of 80 API screens on the shakers avoided excessive
stripping of bridging material from the drilling fluid. Mud weight held steady
at 72 pcf and the controlled drilling rate allowed the wellbore to be properly
cleaned and minimized risk of solids loading in the annulus while controlling ECD.
The 83⁄8-in. pilot hole was drilled and after logging operations opened to 16-in.
without incident. Casing was run to total depth and cemented with no problems.