Reduce shock and vibration in high-DLS well profile
An operator on the remote island of Sakhalin offshore Russia's eastern
coast targeted a formation comprising an interbedded lithology of sandstone and
clay. Prior to performing hole opening operations, hole exposure lasted more
than 24 days over the course of 10 coring and 4 drilling runs.
In seeking a solution that would open an 8 1/2-in hole to 12 1/4 in, the
operator required technology that could achieve this uncommon enlargement step
increase. The section to be opened was from 2,041 m [6,696 ft] to 2,651 m
[8,698 ft]. The well profile consisted of tangent zones in the cored section
combined with directionally drilled zones—inclination decreased from
40° to 19° at 3°/30 m. The directional profile created zones of
high bending stress, which can initiate shock and vibration, leading to
fatigue-induced drillstring failure.
The BHA selected for the operation would need to mitigate shock and
vibration, reduce differential sticking in the highly permeable reservoir
section, maintain the desired ROP, and avoid twistoff. To achieve steady
torque, low vibration, and a clean deviated wellbore, the operator aimed to
maintain 100 to 130 rpm and a WOB of 5,423 to 8,135 N.m [4,000 to 6,000 lbf] at
an ROP of 30 m/h [98 ft/h] with flow rates of 3,875 L/min [1,050
Customize BHA and drilling plan to run with continuous monitoring
Schlumberger engineers used the IDEAS platform to model BHAs that would
provide stability, reduce shock and vibration, and withstand bending stresses
while enlarging a hole after drilling. In total, 24 BHA designs were modeled
before finding one that met these criteria. Additional BHA modeling was
performed using Drilling Office software to minimize collar contact with the
borehole through optimal secondary stabilizer placement between drill collars.
The BHA selected comprised an 8 1/2-in × 12 1/4-in SHO and bullnose from
Smith Bits, a Schlumberger company.