Determination of equivalent circulating density of drilling fluids in deepwater drilling

Evaluation of bottom-hole pressure is a critical concern for high-pressure/high temperature (HP/HT) and deepwater drilling operations. Accurate determination of drilling fluid temperature and pressure is a key step for the prediction of fluid density. A simulator was developed to calculate the wellbore temperature and pressure during circulation and static conditions. The simulation includes effects of various operational parameters, such as rate of penetration, fluid loss as well as pump rate schedules. The mathematical model of heat transfer was developed for a deviated offshore well profile to make the algorithm flexible for different applications. The upwind numerical discretization scheme is used for determination of temperature profile. The temperature prediction of the model was verified with available analytical models for a vertical onshore well. The hydraulic model employs the yield power-law rheology model. The local density of drilling fluid as a function of temperature and pressure is evaluated using the available PVT correlations. It is shown that when mud circulation stops, the equivalent static density slightly increases with time. The results of simulation also indicate that during circulation, a higher equivalent circulating density is expected as compared to the case of constant fluid density. The results of the developed method are compared with downhole temperature and pressure data in an offshore well. The comparison indicates that the developed model has a good accuracy to track the bottom-hole circulating temperature and pressure. The proposed method can be integrated into various parts of a drilling simulator such as hydraulic design, wellbore stability and well control.