Abstract
Laboratory and field experiences record
that sagging of weighting agents such as
barite in drilling fluids is often worse in
dynamic conditions, e.g. pumping, tripping
or drill pipe rotation, than in static conditions.
Barite sag has resulted in problematic
wellbore issues including loss of wellbore
control, lost circulation, stuck pipe and high
torque. Till date, the prediction of barite sag
in dynamic condition is still a challenge in the
industry. An indirect measurement protocol
to examine the effects of shear rate and
viscosity on dynamic barite sag of drilling
fluids is proposed. This study presents an
experimental analysis of dynamic barite sag
phenomenon on a typical oil-based drilling
fluid sample. All rheometry and dynamic
barite sag tests were conducted at 50o
C using
an advanced Anton Paar rheometer MCR
102/302 with either the smooth or grooved
bob-in-cup measuring system. The
viscoelastic properties which are related to
the microstructural building/breakdown of
the fluid sample were investigated under
oscillatory amplitude and frequency sweeps.
The dynamic sag was measured under steady
and oscillatory low to ultra-low shear rates
from 5.11 to 0.001 !"# to closely compare to
sag-prone conditions during drilling
operation. Preliminary results indicate a
strong dependence of barite sag on shear rate
above a critical shear rate value of 0.1 !"#.
Furthermore, with higher viscosity, less
dynamic sag is observed.
that sagging of weighting agents such as
barite in drilling fluids is often worse in
dynamic conditions, e.g. pumping, tripping
or drill pipe rotation, than in static conditions.
Barite sag has resulted in problematic
wellbore issues including loss of wellbore
control, lost circulation, stuck pipe and high
torque. Till date, the prediction of barite sag
in dynamic condition is still a challenge in the
industry. An indirect measurement protocol
to examine the effects of shear rate and
viscosity on dynamic barite sag of drilling
fluids is proposed. This study presents an
experimental analysis of dynamic barite sag
phenomenon on a typical oil-based drilling
fluid sample. All rheometry and dynamic
barite sag tests were conducted at 50o
C using
an advanced Anton Paar rheometer MCR
102/302 with either the smooth or grooved
bob-in-cup measuring system. The
viscoelastic properties which are related to
the microstructural building/breakdown of
the fluid sample were investigated under
oscillatory amplitude and frequency sweeps.
The dynamic sag was measured under steady
and oscillatory low to ultra-low shear rates
from 5.11 to 0.001 !"# to closely compare to
sag-prone conditions during drilling
operation. Preliminary results indicate a
strong dependence of barite sag on shear rate
above a critical shear rate value of 0.1 !"#.
Furthermore, with higher viscosity, less
dynamic sag is observed.