Transient Temperature and Pressure Calculation Model of a Wellbore for Dual Gradient Drilling

During deep-water oil and gas explorations, the dual gradient drilling (DGD) technology provides solutions to problems caused by the narrow density window and the shallow gas by controlling the pressure profile in the wellbore. A transient temperature calculation model is established with consideration of the heat generated by the pump in the specific processes of the DGD systems. Besides, the momentum equation is modified by considering the lift force of the pump on the drilling mud in the pressure calculation. An iterative scheme for the coupled temperature and pressure calculations is developed. Besides, the transient temperature and pressure are analyzed for a deep-water well in South Sea. It is shown that the bottom-hole pressure varies significantly with the transient temperature in the wellbore, and the change of the bottom-hole pressure in the case of the DGD (626 kPa) is larger than that in case of the conventional drilling (115 kPa) due to the constant inlet pressure of the subsea pump. With this fact in mind, an adequate safety margin is strongly recommended to be considered during the hydraulic parameter design of the DGD. Our results further show that the DGD can significantly extend the operation range of the drilling fluid density, and the advantage becomes more obvious in a deep water.