Underbalanced drilling with coiled tubing in Oman

Results from the first five wells drilled with coiled tubing (CT) in the Yi bal field have shown that through-tubing underbalanced-CT-drilling (CTD) te chnology can be applied safely and successfully. A CT unit can compete succ essfully with a conventional drilling rig in drilling ultraslim wells targe ted at relatively small oil pockets, where well success depends on the accu racy of the reservoir model and geological knowledge of the target zone. Pr eliminary trials made it clear that this technology should be considered on ly for niche applications. Underbalanced drilling enables CTD to achieve ra tes of penetration (ROP's) as great as 80 m/h and 1000-m horizontal stepout s.