Drill vertical well in faulted shale formation
As part of a gas exploration program in South Australia, an operator was
drilling vertical wells in a faulted formation with a high dip angle.
Maintaining verticality of the wellbores was critical for conducting extensive
coring, wireline logging, and downhole testing. Natural walk and faults in the
formation had prevented the operator from achieving verticality in offset wells
using positive displacement mud motors and traditional rotary BHAs.
The first offset well was drilled to 2,585-m MD using a BHA with a mud
motor, and the well deviated to an inclination of 10° and departed 94.3 m
from the surface location at 2,585-m MD. The second offset well, which was
drilled using a rotary steerable BHA, deviated as much as 20° and departed
225 m from the surface location at 2,680-m MD.
Hold inclination with vertical drilling RSS
Schlumberger recommended using the PowerV RSS optimized with a SHARC
high-abrasion-resistance PDC drill bit to drill the 12¼-in section from
500-m MD to 2,400-m MD. The RSS was fitted with an another SHARC drill bit to
drill the 8½-in section from 2,400 m to TD at 4,400 m. Using automatic
inclination hold mode, the PowerV RSS maintains precise directional control.
The fully rotating design of the RSS also decreases the risk of differential
sticking and improves hole cleaning.
Maintain verticality to support wireline and coring operations
Using the PowerV RSS, the operator was able to maintain verticality with
a maximum of 0.75° inclination despite high dip faults in the critical
12¼-in section; a maximum of 0.26° was achieved in the 8½-in
section. The PowerV RSS paired with a SHARC drill bit drilled 1,863.5 m at 58.2
m/h, reaching section TD 2 days faster than was achieved in an offset well
drilled with a mud motor BHA. The wellbore also met the tight tolerances
required by the operator, which allowed for the successful conclusion of the
extensive well evaluation program.