True triaxial rockburst experiments with four different unloading rates were performed on four prism specimens of granite sampled from Beishan, China. The damage evolution in the rockburst test was investigated from t...True triaxial rockburst experiments with four different unloading rates were performed on four prism specimens of granite sampled from Beishan, China. The damage evolution in the rockburst test was investigated from two aspects including fracture surface crack and fragment characteristics. The scanning electron microscopy was used to observe the micro crack information on fragment surface. Combing binarization and box counting dimensions, the fractal dimensions of cracks were obtained. Meanwhile,the fragments were collected and a sieving experiment was conducted. We weighed the fragments qualities, counted the amount of fragments and measured the fragments length, width and thickness.Utilizing four methods to calculate damage fractal dimensions of fragments, the trend of fractal value changing with unloading rates can be roughly described. It can be concluded from these experiments that the fractal dimension either for crack or for fragment holds a decreasing trend with the decreasing unloading rate, indicating a reduction of damage level.展开更多
he numbers and distribution of cracks in bulk beryllium which was loaded by intense electron beam were observed by optical image analysis, where the crack characteristic measurement and analysis were performed. The re...he numbers and distribution of cracks in bulk beryllium which was loaded by intense electron beam were observed by optical image analysis, where the crack characteristic measurement and analysis were performed. The results show that: 1) The crack numbers in TR30 of beryllium with fine grain size and relatively high BeO content (no more than 3%) are about 2～4 times more than that in DShG200 of beryllium, whose grain size is larger but BeO content is less than 0.8%, under the same electron beam loading conditions, the ceramic phase of BeO in beryllium makes beryllium more brittle. 2) The successive electron pulse irradiation results in the wider cracks since the cracks formed by the former shot might be enlarged by following shots. The reason might be that there was a stress concentration at original cracks when the second shot came and so that thermal stress raised. DShG200 exhibit the better thermal shock resistance than that of TR30.展开更多
High-amplitude events in seismic reflection profiles of oil and gas reservoirs are the exploration“bright spot”target,as have also been observed in recent borehole acoustic reflection imaging applications.This paper...High-amplitude events in seismic reflection profiles of oil and gas reservoirs are the exploration“bright spot”target,as have also been observed in recent borehole acoustic reflection imaging applications.This paper uses the cracked porousmedium elastic wave theory to analyze the cause of this phenomenon.We model the reservoir as layered cracked porous media and analyze the effect of wave-induced squirt flow in a multi-crack system on acoustic reflection.The propagator matrix method can generally be used to calculate wave reflection and transmission through the layered reservoir model.In particular,for a single fracture layer,assuming that the layer thickness is small compared with the wavelength,the linear slip interface theory can be used to solve the problem.The insight gained from this analysis is that,in addition to acoustic impedance,crack abundance(i.e.,crack density)and fluid properties(water,oil,or gas)significantly affect the wave reflection amplitude.Higher crack density and lighter fluid(i.e.,gas)will substantially increase the reflection intensity,generating“bright spots”in reflection surveys.The theoretical result has been verified by a deep well acoustic reflection imaging case study.The results can be used to provide a“bright spot”exploration technology for fractured oil and gas reservoirs.展开更多
基金supported by the National Key Basic Research Program (No. 2010CB226800)the Innovation Team Development Program of the Ministry of Education (No. IRT0656)the Fundamental Research Funds for the Central Universities (No. 2010YL14)
文摘True triaxial rockburst experiments with four different unloading rates were performed on four prism specimens of granite sampled from Beishan, China. The damage evolution in the rockburst test was investigated from two aspects including fracture surface crack and fragment characteristics. The scanning electron microscopy was used to observe the micro crack information on fragment surface. Combing binarization and box counting dimensions, the fractal dimensions of cracks were obtained. Meanwhile,the fragments were collected and a sieving experiment was conducted. We weighed the fragments qualities, counted the amount of fragments and measured the fragments length, width and thickness.Utilizing four methods to calculate damage fractal dimensions of fragments, the trend of fractal value changing with unloading rates can be roughly described. It can be concluded from these experiments that the fractal dimension either for crack or for fragment holds a decreasing trend with the decreasing unloading rate, indicating a reduction of damage level.
文摘he numbers and distribution of cracks in bulk beryllium which was loaded by intense electron beam were observed by optical image analysis, where the crack characteristic measurement and analysis were performed. The results show that: 1) The crack numbers in TR30 of beryllium with fine grain size and relatively high BeO content (no more than 3%) are about 2～4 times more than that in DShG200 of beryllium, whose grain size is larger but BeO content is less than 0.8%, under the same electron beam loading conditions, the ceramic phase of BeO in beryllium makes beryllium more brittle. 2) The successive electron pulse irradiation results in the wider cracks since the cracks formed by the former shot might be enlarged by following shots. The reason might be that there was a stress concentration at original cracks when the second shot came and so that thermal stress raised. DShG200 exhibit the better thermal shock resistance than that of TR30.
基金supported by the National Natural Science Foundation of China(Grant Nos.U21B2064,42174145&41821002)。
文摘High-amplitude events in seismic reflection profiles of oil and gas reservoirs are the exploration“bright spot”target,as have also been observed in recent borehole acoustic reflection imaging applications.This paper uses the cracked porousmedium elastic wave theory to analyze the cause of this phenomenon.We model the reservoir as layered cracked porous media and analyze the effect of wave-induced squirt flow in a multi-crack system on acoustic reflection.The propagator matrix method can generally be used to calculate wave reflection and transmission through the layered reservoir model.In particular,for a single fracture layer,assuming that the layer thickness is small compared with the wavelength,the linear slip interface theory can be used to solve the problem.The insight gained from this analysis is that,in addition to acoustic impedance,crack abundance(i.e.,crack density)and fluid properties(water,oil,or gas)significantly affect the wave reflection amplitude.Higher crack density and lighter fluid(i.e.,gas)will substantially increase the reflection intensity,generating“bright spots”in reflection surveys.The theoretical result has been verified by a deep well acoustic reflection imaging case study.The results can be used to provide a“bright spot”exploration technology for fractured oil and gas reservoirs.
