It is difficult to determine the optimal weight on bit (WOB) of the double-driven bottomhole assembly (DD-BHA, with double stabilizers and a bent housing positive displacement motor (PDM)) which is employed during ver...It is difficult to determine the optimal weight on bit (WOB) of the double-driven bottomhole assembly (DD-BHA, with double stabilizers and a bent housing positive displacement motor (PDM)) which is employed during vertical and fast drilling. High WOB leads to well deviation out of control, and low WOB leads to low rate of penetration (ROP). So considering the rock physical properties, the anisotropy index function of polycrystalline diamond compact (PDC) bit was derived with the structure and cutting performance parameters of the bit, and the effect of natural hole deviation tendencies on the performance of DD-BHA resisting deviation was represented. The concept of elliptic deformation ratio was used to characterize the performance of DD-BHA resisting deviation. Eventually, a model calculating the critical WOB was established. By comparing the model predictions with the measured hole angle changes in the field, the results show that the model predictions are accurate with error less than 5.8%, which can meet the operational requirements in the projects. Furthermore, the model was adopted to justify and guide the operating conditions and parameters during drilling, which shows that the optimum WOB predicted by the model can not only control deviation but also improve ROP effectively. The model is independent on the formation characteristics of blocks, so it can be expanded widely to other oilfields.展开更多
Ferromagnetic quantum critical points were predicted to be prohibited in clean itinerant ferromagnetic systems,yet such a phenomenon was recently revealed in CeRh_(6)Ge_(4),where the Curie temperature can be continuou...Ferromagnetic quantum critical points were predicted to be prohibited in clean itinerant ferromagnetic systems,yet such a phenomenon was recently revealed in CeRh_(6)Ge_(4),where the Curie temperature can be continuously suppressed to zero under a moderate hydrostatic pressure.Here we report the observation of quantum oscillations in CeRh_(6)Ge_(4)from measurements using the cantilever and tunnel-diode oscillator methods in fields up to 45 T,clearly demonstrating that the ferromagnetic quantum criticality occurs in a clean system.In order to map the Fermi surface of CeRh_(6)Ge_(4),we performed angle-dependent measurements of quantum oscillations at ambient pressure,and compared the results to density functional theory calculations.The results are consistent with the Ce 4f electrons remaining localized and not contributing to the Fermi surface,suggesting that localized ferromagnetism is a key factor for the occurrence of a ferromagnetic quantum critical point in CeRh_(6)Ge_(4).展开更多
Thermodynamics of phase transition for a black hole in 5D Einstein-Gauss-Bonnet gravity with a negative cosmological constant is studied.As the Bekenstein-Hawking entropy is adopted,we find the heat capacity,volume ex...Thermodynamics of phase transition for a black hole in 5D Einstein-Gauss-Bonnet gravity with a negative cosmological constant is studied.As the Bekenstein-Hawking entropy is adopted,we find the heat capacity,volume expansion coefficient and isothermal compressibility are divergent at the critical points,which implies the existence of phase transitions.The fact that the phase transitions are indeed second order is revealed by studying the Ehrenfest's equations and the Prigogine-Defay ratio.Furthermore near the critical points,we also explicitly calculate the critical exponents of the relevant thermodynamic quantities at fixed charge or fixed temperature.It is shown that the corresponding critical exponents satisfy the thermodynamic scaling law.The Generalized Homogeneous Function hypothesis is also checked by studying the Helmholtz free energy,which is shown to be consistent with the thermodynamic scaling law.展开更多
基金Projects(50804040,51004082)supported by the National Natural Science Foundation of China
文摘It is difficult to determine the optimal weight on bit (WOB) of the double-driven bottomhole assembly (DD-BHA, with double stabilizers and a bent housing positive displacement motor (PDM)) which is employed during vertical and fast drilling. High WOB leads to well deviation out of control, and low WOB leads to low rate of penetration (ROP). So considering the rock physical properties, the anisotropy index function of polycrystalline diamond compact (PDC) bit was derived with the structure and cutting performance parameters of the bit, and the effect of natural hole deviation tendencies on the performance of DD-BHA resisting deviation was represented. The concept of elliptic deformation ratio was used to characterize the performance of DD-BHA resisting deviation. Eventually, a model calculating the critical WOB was established. By comparing the model predictions with the measured hole angle changes in the field, the results show that the model predictions are accurate with error less than 5.8%, which can meet the operational requirements in the projects. Furthermore, the model was adopted to justify and guide the operating conditions and parameters during drilling, which shows that the optimum WOB predicted by the model can not only control deviation but also improve ROP effectively. The model is independent on the formation characteristics of blocks, so it can be expanded widely to other oilfields.
基金the National Key R&D Program of China(2017YFA0303100,and 2016YFA0300202)the National Natural Science Foundation of China(12034017,U1632275,and 11974306)+2 种基金the Science Challenge Project of China(TZ2016004)the Key R&D Program of Zhejiang Province(2021C01002)supported by the National Science Foundation Cooperative Agreement No.DMR-1644779 and the State of Florida。
文摘Ferromagnetic quantum critical points were predicted to be prohibited in clean itinerant ferromagnetic systems,yet such a phenomenon was recently revealed in CeRh_(6)Ge_(4),where the Curie temperature can be continuously suppressed to zero under a moderate hydrostatic pressure.Here we report the observation of quantum oscillations in CeRh_(6)Ge_(4)from measurements using the cantilever and tunnel-diode oscillator methods in fields up to 45 T,clearly demonstrating that the ferromagnetic quantum criticality occurs in a clean system.In order to map the Fermi surface of CeRh_(6)Ge_(4),we performed angle-dependent measurements of quantum oscillations at ambient pressure,and compared the results to density functional theory calculations.The results are consistent with the Ce 4f electrons remaining localized and not contributing to the Fermi surface,suggesting that localized ferromagnetism is a key factor for the occurrence of a ferromagnetic quantum critical point in CeRh_(6)Ge_(4).
基金supported by the National Natural Science Foundation of China (Grant Nos.11147012 and 11263003)supported by the Research Funds of Hubei University for Nationalities (Grant No.MY2012B007)the Natural Science Fund of Education Department of Hubei Province (Grant No.Q20131901)
文摘Thermodynamics of phase transition for a black hole in 5D Einstein-Gauss-Bonnet gravity with a negative cosmological constant is studied.As the Bekenstein-Hawking entropy is adopted,we find the heat capacity,volume expansion coefficient and isothermal compressibility are divergent at the critical points,which implies the existence of phase transitions.The fact that the phase transitions are indeed second order is revealed by studying the Ehrenfest's equations and the Prigogine-Defay ratio.Furthermore near the critical points,we also explicitly calculate the critical exponents of the relevant thermodynamic quantities at fixed charge or fixed temperature.It is shown that the corresponding critical exponents satisfy the thermodynamic scaling law.The Generalized Homogeneous Function hypothesis is also checked by studying the Helmholtz free energy,which is shown to be consistent with the thermodynamic scaling law.
