Currently, horizontal well fracturing is indispensable for shale gas development. Due to the variable reservoir formation morphology, the drilling trajectory often deviates from the high-quality reservoir,which increa...Currently, horizontal well fracturing is indispensable for shale gas development. Due to the variable reservoir formation morphology, the drilling trajectory often deviates from the high-quality reservoir,which increases the risk of fracturing. Accurately recognizing low-amplitude structures plays a crucial role in guiding horizontal wells. However, existing methods have low recognition accuracy, and are difficult to meet actual production demand. In order to improve the drilling encounter rate of high-quality reservoirs, we propose a method for fine recognition of low-amplitude structures based on the non-subsampled contourlet transform(NSCT). Firstly, the seismic structural data are analyzed at multiple scales and directions using the NSCT and decomposed into low-frequency and high-frequency structural components. Then, the signal of each component is reconstructed to eliminate the low-frequency background of the structure, highlight the structure and texture information, and recognize the low-amplitude structure from it. Finally, we combined the drilled horizontal wells to verify the low-amplitude structural recognition results. Taking a study area in the west Sichuan Basin block as an example, we demonstrate the fine identification of low-amplitude structures based on NSCT. By combining the variation characteristics of logging curves, such as organic carbon content(TOC), natural gamma value(GR), etc., the real structure type is verified and determined, and the false structures in the recognition results are checked. The proposed method can provide reliable information on low-amplitude structures for optimizing the trajectory of horizontal wells. Compared with identification methods based on traditional wavelet transform and curvelet transform, NSCT enhances the local features of low-amplitude structures and achieves finer mapping of low-amplitude structures, showing promise for application.展开更多
Fast radio bursts(FRBs)are bright,millisecond-duration radio emissions originating from cosmological distances.In this study,we report multi-year polarization measurements of four repeating FRBs initially discovered b...Fast radio bursts(FRBs)are bright,millisecond-duration radio emissions originating from cosmological distances.In this study,we report multi-year polarization measurements of four repeating FRBs initially discovered by the Canadian Hydrogen Intensity Mapping Experiment(CHIME):FRBs 20190117A,20190208A,20190303A,and 20190417A.We observed the four repeating FRBs with the Five-hundred-meter Aperture Spherical Radio Telescope(FAST),detecting a total of 66 bursts.Two bursts from FRB 20190417A exhibit a circular polarization signal-to-noise ratio greater than 7,with the highest circular polarization fraction recorded at 35.7%.While the bursts from FRBs 20190208A and 20190303A are highly linearly polarized,those from FRBs 20190117A and 20190417A show depolarization due to multi-path propagation,with σ_(RM)=2.78±0.05and 5.19±0.09 rad m^(-2),respectively.The linear polarization distributions among five repeating FRBs—FRBs 20190208A,20190303A,20201124A,20220912A,and 20240114A—are nearly identical but show distinct differences from those of nonrepeating FRBs.FRBs 20190117A,20190303A,and 20190417A exhibit substantial rotation measure(RM)variations between bursts,joining other repeating FRBs in this behavior.Combining these findings with published results,64% of repeating FRBs show RM variations greater than 50 rad m^(-2),and 21% exhibit RM reversals.A significant proportion of repeating FRBs reside in a dynamic magneto-ionic environment.The structure function of RM variations shows a power-law index of γ~(0-0.8),corresponding to a shallow power spectrum α=-(γ+2)~-(2.0-2.8)of turbulence,if the RM variations are attributed to turbulence.This suggests that the variations are dominated by small-scale RM density fluctuations.We perform K-S tests to compare the RMs of repeating and non-repeating FRBs,which reveal a marginal dichotomy in the distribution of their RMs.We caution that the observed dichotomy may be due to the small sample size and selection biases.展开更多
The variability in multi-pulse gamma-ray bursts(GRBs)may help to reveal the mechanism of underlying processes from the central engine.To investigate whether the self-organized criticality(SOC)phenomena exist in the pr...The variability in multi-pulse gamma-ray bursts(GRBs)may help to reveal the mechanism of underlying processes from the central engine.To investigate whether the self-organized criticality(SOC)phenomena exist in the prompt phase of GRBs,we statistically study the proper ties of GRBs with more than 3 pulses in each burst by fitting the distributions of several observed physical variables with a Markov Chain Monte Carlo approach,including the isotropic energy E_(iso),the duration time T,and the peak count rate P of each pulse.Our sample consists of 454 pulses in 93 GRBs observed by the CGRO/BATSE satellite.The best-fitting values and uncertainties for these power-law indices of the differential frequency distributions are:α_(E)^(d)=1.54±0.09,α_(T)^(d)=1.82_(-0.15)^(+0.14)andα_(P)^(d)=2.09_(-0.19)^(0.18),while the power-law indices in the cumulative frequency distributions are:α_(E)^(c)=1.44_(-0.10)^(+0.08),α_(T)^(c)=1.75_(-0.13)^(0.11)andα_(P)^(c)=1.99_(-0.19)^(+0.16).We find that these distributions are roughly consistent with the physical framework of a Fractal-Diffusive,Self^Organized Criticality(FD-SOC)system with the spatial dimension S=3 and the classical diffusionβ=1.Our results support that the jet responsible for the GRBs should be magnetically dominated and magnetic instabilities(e.g.,kink model,or tearing-model instability)lead the GRB emission region into the SOC state.展开更多
There are some similarities between bursts of repeating fast radio bursts(FRBs)and giant pulses(GPs)of pulsars.To explore possible relations between them,we study the cumulative energy distributions of these two pheno...There are some similarities between bursts of repeating fast radio bursts(FRBs)and giant pulses(GPs)of pulsars.To explore possible relations between them,we study the cumulative energy distributions of these two phenomena using the observations of repeating FRB 121102 and the GPs of Crab pulsar.We find that the power-law slope of GPs(with fuence≥130 Jy.ms)is 2.85±0.10.The energy distribution of FRB 121102 can be well fitted by a smooth broken power-law function.For the bursts of FRB 121102 above the break energy(1.22×10^(37)erg),the best-ftting slope is 2.90^(+0.55)_(-0344),similar to the index of GPs at the same observing frequency(~1.4 GHz).We further discuss the physical origin of the repeating FRB 121102 in the framework of the super GPs model.And we find that the super GPs model involving a millisecond pulsar is workable and favored for explaining FRB 121102 despite that the magnetar burst model is more popular.展开更多
基金supported by Sichuan Science and Technology Program under Grant 2024NSFSC1984 and Grant 2024NSFSC1990。
文摘Currently, horizontal well fracturing is indispensable for shale gas development. Due to the variable reservoir formation morphology, the drilling trajectory often deviates from the high-quality reservoir,which increases the risk of fracturing. Accurately recognizing low-amplitude structures plays a crucial role in guiding horizontal wells. However, existing methods have low recognition accuracy, and are difficult to meet actual production demand. In order to improve the drilling encounter rate of high-quality reservoirs, we propose a method for fine recognition of low-amplitude structures based on the non-subsampled contourlet transform(NSCT). Firstly, the seismic structural data are analyzed at multiple scales and directions using the NSCT and decomposed into low-frequency and high-frequency structural components. Then, the signal of each component is reconstructed to eliminate the low-frequency background of the structure, highlight the structure and texture information, and recognize the low-amplitude structure from it. Finally, we combined the drilled horizontal wells to verify the low-amplitude structural recognition results. Taking a study area in the west Sichuan Basin block as an example, we demonstrate the fine identification of low-amplitude structures based on NSCT. By combining the variation characteristics of logging curves, such as organic carbon content(TOC), natural gamma value(GR), etc., the real structure type is verified and determined, and the false structures in the recognition results are checked. The proposed method can provide reliable information on low-amplitude structures for optimizing the trajectory of horizontal wells. Compared with identification methods based on traditional wavelet transform and curvelet transform, NSCT enhances the local features of low-amplitude structures and achieves finer mapping of low-amplitude structures, showing promise for application.
基金supported by the National Natural Science Foundation of China(Grant Nos.12588202,12203045,12233002,12403100,12103069,and 12403042)the Leading Innovation and Entrepreneurship Team of Zhejiang Province of China(Grant No.2023R01008)+3 种基金the Key R&D Program of Zhejiang(Grant No.2024SSYS0012)supported by the National Natural Science Foundation of China(Grant No.12473047)the National SKA Program of China(Grant No.2022SKA0130100)the support from the Xinjiang Tianchi Program。
文摘Fast radio bursts(FRBs)are bright,millisecond-duration radio emissions originating from cosmological distances.In this study,we report multi-year polarization measurements of four repeating FRBs initially discovered by the Canadian Hydrogen Intensity Mapping Experiment(CHIME):FRBs 20190117A,20190208A,20190303A,and 20190417A.We observed the four repeating FRBs with the Five-hundred-meter Aperture Spherical Radio Telescope(FAST),detecting a total of 66 bursts.Two bursts from FRB 20190417A exhibit a circular polarization signal-to-noise ratio greater than 7,with the highest circular polarization fraction recorded at 35.7%.While the bursts from FRBs 20190208A and 20190303A are highly linearly polarized,those from FRBs 20190117A and 20190417A show depolarization due to multi-path propagation,with σ_(RM)=2.78±0.05and 5.19±0.09 rad m^(-2),respectively.The linear polarization distributions among five repeating FRBs—FRBs 20190208A,20190303A,20201124A,20220912A,and 20240114A—are nearly identical but show distinct differences from those of nonrepeating FRBs.FRBs 20190117A,20190303A,and 20190417A exhibit substantial rotation measure(RM)variations between bursts,joining other repeating FRBs in this behavior.Combining these findings with published results,64% of repeating FRBs show RM variations greater than 50 rad m^(-2),and 21% exhibit RM reversals.A significant proportion of repeating FRBs reside in a dynamic magneto-ionic environment.The structure function of RM variations shows a power-law index of γ~(0-0.8),corresponding to a shallow power spectrum α=-(γ+2)~-(2.0-2.8)of turbulence,if the RM variations are attributed to turbulence.This suggests that the variations are dominated by small-scale RM density fluctuations.We perform K-S tests to compare the RMs of repeating and non-repeating FRBs,which reveal a marginal dichotomy in the distribution of their RMs.We caution that the observed dichotomy may be due to the small sample size and selection biases.
基金supported by the National Natural Science Foundation of China(Grant Nos.11673068,11725314,U1831122,11703064,11903019,U1938116)the Shanghai Sailing Program(No.17YF1422600)+2 种基金the Youth Innovation Promotion Association(2017366)the Key Research Program of Frontier Sciences(Grant Nos.QYZDB-SSW-SYS005,ZDBS-LY-7014)the Strategic Priority Research Program uMulti-waveband gravitational wave Universe”(Grant No.XDB23000000)of the Chinese Academy of Sciences.
文摘The variability in multi-pulse gamma-ray bursts(GRBs)may help to reveal the mechanism of underlying processes from the central engine.To investigate whether the self-organized criticality(SOC)phenomena exist in the prompt phase of GRBs,we statistically study the proper ties of GRBs with more than 3 pulses in each burst by fitting the distributions of several observed physical variables with a Markov Chain Monte Carlo approach,including the isotropic energy E_(iso),the duration time T,and the peak count rate P of each pulse.Our sample consists of 454 pulses in 93 GRBs observed by the CGRO/BATSE satellite.The best-fitting values and uncertainties for these power-law indices of the differential frequency distributions are:α_(E)^(d)=1.54±0.09,α_(T)^(d)=1.82_(-0.15)^(+0.14)andα_(P)^(d)=2.09_(-0.19)^(0.18),while the power-law indices in the cumulative frequency distributions are:α_(E)^(c)=1.44_(-0.10)^(+0.08),α_(T)^(c)=1.75_(-0.13)^(0.11)andα_(P)^(c)=1.99_(-0.19)^(+0.16).We find that these distributions are roughly consistent with the physical framework of a Fractal-Diffusive,Self^Organized Criticality(FD-SOC)system with the spatial dimension S=3 and the classical diffusionβ=1.Our results support that the jet responsible for the GRBs should be magnetically dominated and magnetic instabilities(e.g.,kink model,or tearing-model instability)lead the GRB emission region into the SOC state.
基金This work was partially supported by the National Natural Science Foundation of China(Grant Nos.11673068,11725314,U1831122,11903019,11533003,and 11703002)the Youth Innovation Promotion Association(2017366)+4 种基金the Key Research Program of Frontier Sciences(Grant Nos.QYZDB-SSW-SYS005 and ZDBS-LY-7014)the Strategic Priority Research Program"Multi-waveband gravita-tional wave universe"(Grant No.XDB23000000)the Chinese Academy of Sciences,the China Post-doctoral Science Foundation(Nos.2018M631242 and 2020M671876)the Fundamental Research Funds for the Central Universitiesthe National Postdoctoral Program for Innovative Talents(Grant No.BX20200164).
文摘There are some similarities between bursts of repeating fast radio bursts(FRBs)and giant pulses(GPs)of pulsars.To explore possible relations between them,we study the cumulative energy distributions of these two phenomena using the observations of repeating FRB 121102 and the GPs of Crab pulsar.We find that the power-law slope of GPs(with fuence≥130 Jy.ms)is 2.85±0.10.The energy distribution of FRB 121102 can be well fitted by a smooth broken power-law function.For the bursts of FRB 121102 above the break energy(1.22×10^(37)erg),the best-ftting slope is 2.90^(+0.55)_(-0344),similar to the index of GPs at the same observing frequency(~1.4 GHz).We further discuss the physical origin of the repeating FRB 121102 in the framework of the super GPs model.And we find that the super GPs model involving a millisecond pulsar is workable and favored for explaining FRB 121102 despite that the magnetar burst model is more popular.
