Research on the Change Law of the Annular Pressure for the Deepwater Riserless Mud Recovery System during Drilling Operations

The precise control of the annular pressure involves drilling safety and drilling cost, which have always been the focus of drilling engineering. In this paper, combined with the characteristics of the Riserless Mud Recovery (RMR) System, the calculation method of equivalent circulating density (ECD) and annulus pressure of the RMR system is proposed. According to the characteristics of the heat exchange of the RMR system, a mathematical model of the thermal field in the annular is established. The variation law of thermal field in the annular of some well sections was simulated by computational fluid dynamics (CFD) software. Comparing the CFD analysis results with the calculation results of mathematical models, the feasibility of the mathematical model is verified, and the temperature variation curve in the annulus is obtained. Based on the drilling data of a vertical well in the South China Sea, this paper analyzes the effects of seawater depth, equivalent static density (ESD) of drilling fluid, cuttings concentration, and discharge capacity on the annular pressure and ECD of the RMR system.