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
Vanadium flow battery(VFB)is one of the most promising energy storage technologies because of its superior safety,reliability and cycle life,but the poor electrochemical performance at high cur-rent density limits its...Vanadium flow battery(VFB)is one of the most promising energy storage technologies because of its superior safety,reliability and cycle life,but the poor electrochemical performance at high cur-rent density limits its commercial application.Herein,an advanced design of the dual-gradient carbon nanofibers/graphite felt(DG-CNFs/GF)composite electrode is firstly proposed for the next-generation VFB with high power density.Specifically,there is a macro gradient distribution of CNFs along the thickness direction of the electrode,meanwhile a micro gradient distribution of CNFs is also existed along the ra-dial direction of a single fiber,and both the macro and micro gradient structure are verified through the physicochemical characterizations.In addition,the DG-CNFs/GF with a dual-gradient structure exhibits an excellent electrocatalytic activity and a fast mass transfer characteristic.It is worth noting that the energy conversion efficiencies,cycling stability in addition to power density of VFB with DG-CNFs/GF are much better than those with commercial GF,which make the dual-gradient DG-CNFs/GF to be a promis-ing alternative.Most importantly,the accomplishment of this work will provide a promising development direction of the highly efficient electrode for the next-generation VFB with high power density.展开更多
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.
基金This work was financially supported by the National Natural Science Foundation of China Youth Fund(No.21703263)Open project of State Key Laboratory of Heavy Oil Processing in China University of Petroleum(No.Y7F1911191).
文摘Vanadium flow battery(VFB)is one of the most promising energy storage technologies because of its superior safety,reliability and cycle life,but the poor electrochemical performance at high cur-rent density limits its commercial application.Herein,an advanced design of the dual-gradient carbon nanofibers/graphite felt(DG-CNFs/GF)composite electrode is firstly proposed for the next-generation VFB with high power density.Specifically,there is a macro gradient distribution of CNFs along the thickness direction of the electrode,meanwhile a micro gradient distribution of CNFs is also existed along the ra-dial direction of a single fiber,and both the macro and micro gradient structure are verified through the physicochemical characterizations.In addition,the DG-CNFs/GF with a dual-gradient structure exhibits an excellent electrocatalytic activity and a fast mass transfer characteristic.It is worth noting that the energy conversion efficiencies,cycling stability in addition to power density of VFB with DG-CNFs/GF are much better than those with commercial GF,which make the dual-gradient DG-CNFs/GF to be a promis-ing alternative.Most importantly,the accomplishment of this work will provide a promising development direction of the highly efficient electrode for the next-generation VFB with high power density.
