A Prediction Model for Drilling Fluid ECD in High Temperature Deep Wells.

A significant error will be generated in calculating the equivalent circulation density (ECD) of high temperature deep wells if drilling fluid rheology measured at surface was used. For wells with small differences between pore pressure and fracturing pressure, this error may lead to kick, blowout and/or mud losses. A model was established to predict the HTHP drilling fluid density, equivalent static density, rheology and ECD, based on the downhole temperature fields of wells in circulation. The model gave prediction that was highly consistent to measured values (with correlation coefficient being greater than 0.99). this model can be used in well pressure management and control, and is helpful in the prevention of downhole troubles.