A joint industry project was established to study barite sag mechanisms and
to develop field guidelines to manage the consequences. A simple empirical
model was developed to compare sag potential for a wide range of fluid typ
es. In the study, physical properties of the mud, wellbore conditions, and
characteristics of the weighting material were shown to have a large influe
nce on sag behavior. The study also included direct measurements of the pro
perties of settled weight-material beds. These results provide new insight
into the mechanisms of barite sag and how best to manage problems in the fi
eld.
Data from the tests clearly demonstrate that the parameters affecting sag a
re interrelated and seldom act in isolation. For all muds tested, the highe
st sag occurred at low annular velocities over angles from 60 to 75 degrees
. Drillpipe rotation was particularly beneficial in minimizing barite settl
ement. Rotation also assisted in re-distributing barite deposits formed on
the low side of the hole.
The improved understanding of the mechanisms of barite sag enabled developm
ent of practical field guidelines. Case history studies presented in the pa
per demonstrate how the results of the work together with better field moni
toring have been successfully applied to manage the effects of barite sag i
n high-pressure/high-temperature and extended-reach drilling operations.