Galaxy clusters present unique advantages for cosmological study.Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters.The redshifts of the lensing clu...Galaxy clusters present unique advantages for cosmological study.Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters.The redshifts of the lensing clusters lie between 0.1 and 0.6,and the redshift range of their arcs is from 0.4 to 4.9.These clusters are selected carefully from strong gravitational lensing systems which have both X-ray satellite observations and optical giant luminous arcs with known redshifts.Giant arcs usually appear in the central region of clusters,where mass can be traced with luminosity quite well.Based on gravitational lensing theory and a cluster mass distribution model,we can derive a ratio using two angular diameter distances.One is the distance between lensing sources and the other is that between the deflector and the source. Since angular diameter distance relies heavily on cosmological geometry,we can use these ratios to constrain cosmological models.Moreover,X-ray gas fractions of galaxy clusters can also be a cosmological probe.Because there are a dozen parameters to be fitted,we introduce a new analytic algorithm,Powell＇s UOBYQA（Unconstrained Optimization By Quadratic Approximation） ,to accelerate our calculation.Our result demonstrates that this algorithm is an effective fitting method for such a continuous multi-parameter constraint.We find an interesting fact that these two approaches are separately sensitive toΩΛandΩM.By combining them,we can get reasonable fitting values of basic cosmological parameters：ΩM=0.26 ＋0.04 -0.04,andΩΛ=0.82 ＋0.14 -0.16.展开更多
Multi-cluster perforation and multi-staged fracturing of horizontal well is one of the main technologies in volumetric fracturing stimulation of unconventional oil and gas reservoirs,but unconventional reservoirs in C...Multi-cluster perforation and multi-staged fracturing of horizontal well is one of the main technologies in volumetric fracturing stimulation of unconventional oil and gas reservoirs,but unconventional reservoirs in China are generally of strong heterogeneity,which causes different fracture initiation pressures in different positions of lateral,making it difficult to ensure the balanced fracture initiation and propagation between clusters in multi-cluster perforating.It is in urgent need to precisely evaluate the difference in rock strength in lateral and determine the well section with similar rock strength to deploy fractures,so as to reach the goal of balanced stimulation.Based on the drilling and logging data,this paper establishes an unsupervised clustering model of mechanical specific energy of bit at the bottomhole the lateral.Then,the influence of drill string friction,composite drilling and jet-assisted rock breaking on the mechanical specific energy is analyzed,and the distribution and clustering categories of bottomhole mechanical specific energy with decimeter spatial resolution are obtained.Finally,a fracture deployment optimization method for horizontal well volumetric fracturing aiming balanced stimulation is developed by comprehensively considering inter-fracture interference,casing collar position,plug position,and clustering result of bottomhole mechanical specific energy.The following results are obtained.First,compared with brittleness index,Poisson's ratioandstressdifference,perforation erosion area isina strongercorrelationwith themechanical specific energy,andthemechanical specific energy can effectively characterize the difference in the amount of proppant injected into the perforation clusters in the lateral,so it can be served as one of the important indicators for the selection of fracture deployment position.Second,the drilling and logging data cleaning and smoothing and the clustering number selection by the elbow method are the key steps to obtain the clustering results of bottomhole mechanical specific energy,which can tell the difference in the mechanical specific energy with decimeter-level resolution.Third,the interval with mechanical specific energy within 10%of the averagevalue in the section is selected for deploying perforation clusters,and the compiled computer algorithm can automatically determine the optimal position of fracturing section and cluster,so as to realize the differential design of stage spacing and cluster spacing.In conclusion,the research results can further improve the fractures deployment efficiency and balanced stimulation of volumetric fracturing in unconventional oil andgasreservoirs,and this technology is expected to provide ideas andnew methods forthe fracturedeployment optimization of horizontal well volumetric fracturing in unconventional oil and gas reservoirs.展开更多
We study the statistics of large-separation multiply-imaged quasars lensed by clusters of galaxies. In particular, we examine how the observed brightest cluster galaxies （BCGs） affect the predicted numbers of wide-s...We study the statistics of large-separation multiply-imaged quasars lensed by clusters of galaxies. In particular, we examine how the observed brightest cluster galaxies （BCGs） affect the predicted numbers of wide-separation lenses. We model the lens as an NFW-profiled dark matter halo with a truncated singular isothermal sphere to represent the BCG in its center. We mainly make predictions for the Sloan Digital Sky Survey Quasar Lens Search （SQLS） sample from the Data Release 5 （DRS） in two standard ACDM cosmological models： a model with matter density ΩM = 0.3 and δ8 = 0.9, as is usually adopted in the literature （ACDM1）, and a model suggested by the WMAP seven-year （WMAPT） data with ΩM = 0.266 and δ8 = 0.801. We also study the lensing properties for the WMAP3 cosmology in order to compare with the previous work. We find that BCGs in the centers of clusters significantly enhance the lensing efficiency by a factor of 2 - 3 compared with that of NFW-profiled pure dark matter halos. In addition, the dependence of mass ratios of BCGs to their host halos on the host halo masses reduces the lensing rate by - 20% from assuming a constant ratio as in previous studies, but considering the evolution of this ratio with redshift out to z - 1 would reduce it by - 3%. Moreover, we predict that the numbers of lensed quasars with image separations larger than 10″ in the statistical sample of SQLS from DR5 are 1.22 and 0.47, respectively for ACDM1 and WMAP7 and 0.73 and 0.33 for separations between 10″ and 20″, which are consistent with the only observed cluster lens with such a large separation in the complete SQLS sample.展开更多
基金Supported by the National Natural Science Foundation of Chinasupported by the National Science Foundation of China under the Distinguished Young Scholar Grant 10825313by the Ministry of Science and Technology's National Basic Science Program(Project 973)under grant No.2007CB815401
文摘Galaxy clusters present unique advantages for cosmological study.Here we collect a new sample of 10 lensing galaxy clusters with X-ray observations to constrain cosmological parameters.The redshifts of the lensing clusters lie between 0.1 and 0.6,and the redshift range of their arcs is from 0.4 to 4.9.These clusters are selected carefully from strong gravitational lensing systems which have both X-ray satellite observations and optical giant luminous arcs with known redshifts.Giant arcs usually appear in the central region of clusters,where mass can be traced with luminosity quite well.Based on gravitational lensing theory and a cluster mass distribution model,we can derive a ratio using two angular diameter distances.One is the distance between lensing sources and the other is that between the deflector and the source. Since angular diameter distance relies heavily on cosmological geometry,we can use these ratios to constrain cosmological models.Moreover,X-ray gas fractions of galaxy clusters can also be a cosmological probe.Because there are a dozen parameters to be fitted,we introduce a new analytic algorithm,Powell＇s UOBYQA（Unconstrained Optimization By Quadratic Approximation） ,to accelerate our calculation.Our result demonstrates that this algorithm is an effective fitting method for such a continuous multi-parameter constraint.We find an interesting fact that these two approaches are separately sensitive toΩΛandΩM.By combining them,we can get reasonable fitting values of basic cosmological parameters：ΩM=0.26 ＋0.04 -0.04,andΩΛ=0.82 ＋0.14 -0.16.
基金supported by the Science Fund for Excellent Youth of the National Natural Science Foundation of China"Well hydrodynamics and engineering"(No.52122401).
文摘Multi-cluster perforation and multi-staged fracturing of horizontal well is one of the main technologies in volumetric fracturing stimulation of unconventional oil and gas reservoirs,but unconventional reservoirs in China are generally of strong heterogeneity,which causes different fracture initiation pressures in different positions of lateral,making it difficult to ensure the balanced fracture initiation and propagation between clusters in multi-cluster perforating.It is in urgent need to precisely evaluate the difference in rock strength in lateral and determine the well section with similar rock strength to deploy fractures,so as to reach the goal of balanced stimulation.Based on the drilling and logging data,this paper establishes an unsupervised clustering model of mechanical specific energy of bit at the bottomhole the lateral.Then,the influence of drill string friction,composite drilling and jet-assisted rock breaking on the mechanical specific energy is analyzed,and the distribution and clustering categories of bottomhole mechanical specific energy with decimeter spatial resolution are obtained.Finally,a fracture deployment optimization method for horizontal well volumetric fracturing aiming balanced stimulation is developed by comprehensively considering inter-fracture interference,casing collar position,plug position,and clustering result of bottomhole mechanical specific energy.The following results are obtained.First,compared with brittleness index,Poisson's ratioandstressdifference,perforation erosion area isina strongercorrelationwith themechanical specific energy,andthemechanical specific energy can effectively characterize the difference in the amount of proppant injected into the perforation clusters in the lateral,so it can be served as one of the important indicators for the selection of fracture deployment position.Second,the drilling and logging data cleaning and smoothing and the clustering number selection by the elbow method are the key steps to obtain the clustering results of bottomhole mechanical specific energy,which can tell the difference in the mechanical specific energy with decimeter-level resolution.Third,the interval with mechanical specific energy within 10%of the averagevalue in the section is selected for deploying perforation clusters,and the compiled computer algorithm can automatically determine the optimal position of fracturing section and cluster,so as to realize the differential design of stage spacing and cluster spacing.In conclusion,the research results can further improve the fractures deployment efficiency and balanced stimulation of volumetric fracturing in unconventional oil andgasreservoirs,and this technology is expected to provide ideas andnew methods forthe fracturedeployment optimization of horizontal well volumetric fracturing in unconventional oil and gas reservoirs.
基金supported by the National Natural Science Foundation of China(Grant No. 11073023)the National Basic Research Program of China (973 ProgramGrant No.2009CB24901)
文摘We study the statistics of large-separation multiply-imaged quasars lensed by clusters of galaxies. In particular, we examine how the observed brightest cluster galaxies （BCGs） affect the predicted numbers of wide-separation lenses. We model the lens as an NFW-profiled dark matter halo with a truncated singular isothermal sphere to represent the BCG in its center. We mainly make predictions for the Sloan Digital Sky Survey Quasar Lens Search （SQLS） sample from the Data Release 5 （DRS） in two standard ACDM cosmological models： a model with matter density ΩM = 0.3 and δ8 = 0.9, as is usually adopted in the literature （ACDM1）, and a model suggested by the WMAP seven-year （WMAPT） data with ΩM = 0.266 and δ8 = 0.801. We also study the lensing properties for the WMAP3 cosmology in order to compare with the previous work. We find that BCGs in the centers of clusters significantly enhance the lensing efficiency by a factor of 2 - 3 compared with that of NFW-profiled pure dark matter halos. In addition, the dependence of mass ratios of BCGs to their host halos on the host halo masses reduces the lensing rate by - 20% from assuming a constant ratio as in previous studies, but considering the evolution of this ratio with redshift out to z - 1 would reduce it by - 3%. Moreover, we predict that the numbers of lensed quasars with image separations larger than 10″ in the statistical sample of SQLS from DR5 are 1.22 and 0.47, respectively for ACDM1 and WMAP7 and 0.73 and 0.33 for separations between 10″ and 20″, which are consistent with the only observed cluster lens with such a large separation in the complete SQLS sample.
