Prediction method for equivalent circulating density of deepwater drilling when subsea pressurization is considered

Considering the shortcomings in ECD prediction and control of deepwater wellhole presently, the ECD prediction model of deepwater drilling has been established, with the temperature and rock debris effects are considered and the lift system of subsea pressurization pipeline is provided. The ECD changes are calculated and analyzed based on the living examples, when the lift system of subsea pressurization pipeline is provided in the deepwater drilling. According to the results, when the displacement in the drilling string is constant, the larger the augmented injection displacement, the smaller the ECD value; when the lift system of subsea pressurization pipeline is provided, the ECD value under such calculation conditions does not exceed the loss pressure, so it should be safe under such parameter conditions; when no subsea pressurization exists, as the displacement decreases, the annular ECD gradually increases, and the ECD added value is relatively greater; when the displacement is less than a constant value, the ECD increase will lead to the stratum loss during the drilling. Therefore, during the deepwater drilling, special attention should be paid to the borehole cleaning at the riser section. In addition to the control over mechanical drilling rate, pumping of cleaning fluid and other measures, the displacement should be appropriately increased to clear the drilling cuttings in time, which is in order to keep the borehole clean. Finally, the model validity has been compared and analyzed. Under such calculation conditions, the maximum deviation from actually-measured value of PWD is 1.36%. This method has certain reference significances for the optimization design of hydraulic parameter on deepwater drilling and well control.