Barite sag: Measurement, modeling, and management

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.