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 th...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 k Pa） is larger than that in case of the conventional drilling（115 k Pa） 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.展开更多
To ensure safe drilling with narrow pressure margins in deepwater, a new deepwater dual-gradient drilling method based on downhole separation was designed. A laboratory experiment was conducted to verify the effective...To ensure safe drilling with narrow pressure margins in deepwater, a new deepwater dual-gradient drilling method based on downhole separation was designed. A laboratory experiment was conducted to verify the effectiveness of downhole separation and the feasibility of realizing dual-gradient in wellbore. The calculation of dynamic wellbore pressure during drilling was conducted. Then, an optimization model for drilling parameters was established for this drilling method, including separator position, separation efficiency, injection volume fraction, density of drilling fluid, wellhead back pressure and displacement. The optimization of drilling parameters under different control parameters and different narrow safe pressure margins is analyzed by case study. The optimization results indicate that the wellbore pressure profile can be optimized to adapt to the narrow pressure margins and achieve greater drilling depth. By using the optimization model, a smaller bottom-hole pressure difference can be obtained, which can increase the rate of penetration(ROP) and protect reservoirs. The dynamic wellbore pressure has been kept within safe pressure margins during optimization process, effectively avoiding the complicated underground situations caused by improper wellbore pressure.展开更多
基金Project supported by the National Natural Science Foundation-Outstanding Youth Foundation(Grant No.51622405)the Natural Science Foundation of Shandong Province(Grant No.JQ201716)the Construction Project of Taishan Scholars
文摘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 k Pa） is larger than that in case of the conventional drilling（115 k Pa） 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.
基金Supported by the Key Program of National Natural Science Foundation of China(51734010)
文摘To ensure safe drilling with narrow pressure margins in deepwater, a new deepwater dual-gradient drilling method based on downhole separation was designed. A laboratory experiment was conducted to verify the effectiveness of downhole separation and the feasibility of realizing dual-gradient in wellbore. The calculation of dynamic wellbore pressure during drilling was conducted. Then, an optimization model for drilling parameters was established for this drilling method, including separator position, separation efficiency, injection volume fraction, density of drilling fluid, wellhead back pressure and displacement. The optimization of drilling parameters under different control parameters and different narrow safe pressure margins is analyzed by case study. The optimization results indicate that the wellbore pressure profile can be optimized to adapt to the narrow pressure margins and achieve greater drilling depth. By using the optimization model, a smaller bottom-hole pressure difference can be obtained, which can increase the rate of penetration(ROP) and protect reservoirs. The dynamic wellbore pressure has been kept within safe pressure margins during optimization process, effectively avoiding the complicated underground situations caused by improper wellbore pressure.
