Drilling a sidetrack from a Gulf of Mexico HPHT well in the hard Smackover limestone required a steerable turbodrill and wireline steering tool. The excellent toolface control provided by the Neyrfor™ turbodrilling system enabled turning off the steering tool to prevent overheating downhole while successfully drilling on the first attempt, saving 19 rig days.

Find robust sidetracking assembly

After a conventional rotary assembly became stuck in a Gulf of Mexico deepwater well, the operator needed a sidetracking drilling assembly. Located just above the production zone, this HPHT long tangent well proved difficult to sidetrack because of its location in the very hard Upper Jurassic Smackover limestone, characterized by 50% to 90% limestone, 10% to 50% shale, and a compressive strength of 9,000 to 30,000 psi. Furthermore, the bottomhole static temperature exceeded 205 degC [400 degF], eliminating the potential for available MWD tools and a conventional positive displacement motor with a sidetrack bit, which wouldn't survive the trip to bottom.

The only way to sidetrack the well was with a steerable turbodrill and a wireline steering tool. Unfortunately, the steering tool had a limited downhole life of only approximately 4 hours before it would overheat (because of internal heat buildup while turned on). With numerous wireline trips required for the steering tool, this limitation would cause significant lost time and money, forcing the operator to find a new strategy.

Drill ahead with the same assembly to successfully sidetrack and save 19 rig days

In consideration of the high temperature and excessive downhole time planned, SLB supplied a 6 5/8-in T2 MK1 steerable Neyrfor turbodrilling system with a 1.0° bent housing to complete the sidetrack. The Neyrfor turbodrilling system is different from a conventional sidetrack assembly in that no special bit is required. The same long-gauge box connection bits used on all turbodrill systems are capable of performing the sidetracks, so bits are selected based on formation compatibility rather than the limitations of the motor.

For this sidetrack, the team chose a 9 1/2-in impregnated bit and drilled 874 ft on the first run and 281 ft to TD on the second run. The Neyrfor turbodrilling system was stabilized in the same configuration as it would be for normal drilling, meaning there was no need to make a trip after sidetracking—the same assembly drilled ahead. It also exhibited excellent toolface control associated with high speed and low torque, which allowed the wireline steering tool to be turned off to conserve heat buildup.

The Neyrfor turbodrilling system assembly was able to sidetrack and drill ahead on the first attempt at a higher ROP of 6.8 ft/h, resulting in 19 rig days saved. The operator also saw significant benefits with the ability to turn off the steering tool and continue sliding.