In-situ stress is a critical factor influencing the permeability of coal reservoirs and the production capacity of coalbed methane(CBM)wells.Accurate prediction of in-situ stress and investigation of its influence on ...In-situ stress is a critical factor influencing the permeability of coal reservoirs and the production capacity of coalbed methane(CBM)wells.Accurate prediction of in-situ stress and investigation of its influence on coal reservoir permeability and production capacity are significant for CBM development.This study investigated the CBM development zone in the Zhengzhuang area of the Qinshui Basin.According to the low mechanical strength of coal reservoirs,this study derived a calculation model of the in-situ stress of coal reservoirs based on the multi-loop hydraulic fracturing method and analyzed the impacts of initial fractures on the calculated results.Moreover,by combining the data such as the in-situ stress,permeability,and drainage and recovery data of CBM wells,this study revealed the spatial distribution patterns of the current in-situ stress of the coal reservoirs and discussed the impacts of the insitu stress on the permeability and production capacity.The results are as follows.(1)Under given fracturing pressure,longer initial fractures are associated with higher calculated maximum horizontal principal stress values.Therefore,ignoring the effects of the initial fractures will cause the calculated values of the in-situ stress to be less than the actual values.(2)As the burial depth increases,the fracturing pressure,closure pressure,and the maximum and minimum horizontal principal stress of the coal reservoirs in the Zhengzhuang area constantly increase.The average gradients of the maximum and minimum horizontal principal stress are 3.17 MPa/100 m and 2.05 MPa/100 m,respectively.(3)Coal reservoir permeability is significantly controlled by the magnitude and state of the current in-situ stress.The coal reservoir permeability decreases exponentially with an increase in the effective principal stress.Moreover,a low lateral pressure coefficient(less than 1)is associated with minor horizontal compressive effects and high coal reservoir permeability.(4)Under similar conditions,such as resource endowments,CBM we展开更多
Parameter calculation is the key problem in analysing the AC machines with armatureasymmetries. The multi-loop method, which is effective on this subject, uses such parametersas the self-inductances of and the mutual-...Parameter calculation is the key problem in analysing the AC machines with armatureasymmetries. The multi-loop method, which is effective on this subject, uses such parametersas the self-inductances of and the mutual-inductances between every stator branch, every dam-per loop and the field circuit. They are different from those used in Park’s equations.The parameters of the stator branch are composed of those of related coils according to itscomposition. Two methods, the air-gap permeance analysis method and the field numericalanalysis method, are proposed to calculate the saturated parameters. And the methods arethen verified and compared with each other by application to a generator.展开更多
The increase in the capacity and the improvement in the structure of large generatorsrequire better performance of their protection systems against armature faults. Therefore, itis desirous to further the study on the...The increase in the capacity and the improvement in the structure of large generatorsrequire better performance of their protection systems against armature faults. Therefore, itis desirous to further the study on the operation of synchronous machines with internal faultsin stator windings. For this purpose, the armature asymmetry of synchronous generatorsconnected to the power system and operating on load condition is analysed for the first timeby using the multi-loop method. In consideration of the power source a mathematical modelfor asymmetrical generators is established and its solution is proposed. Compared withexperimental results at rated voltage, the new approach is justified.展开更多
基金sponsored by the National Natural Science Foundation of China(42002181)projecta public bidding project of 2020 Shanxi Provincial Science and Technology Program(20201101002-03).
文摘In-situ stress is a critical factor influencing the permeability of coal reservoirs and the production capacity of coalbed methane(CBM)wells.Accurate prediction of in-situ stress and investigation of its influence on coal reservoir permeability and production capacity are significant for CBM development.This study investigated the CBM development zone in the Zhengzhuang area of the Qinshui Basin.According to the low mechanical strength of coal reservoirs,this study derived a calculation model of the in-situ stress of coal reservoirs based on the multi-loop hydraulic fracturing method and analyzed the impacts of initial fractures on the calculated results.Moreover,by combining the data such as the in-situ stress,permeability,and drainage and recovery data of CBM wells,this study revealed the spatial distribution patterns of the current in-situ stress of the coal reservoirs and discussed the impacts of the insitu stress on the permeability and production capacity.The results are as follows.(1)Under given fracturing pressure,longer initial fractures are associated with higher calculated maximum horizontal principal stress values.Therefore,ignoring the effects of the initial fractures will cause the calculated values of the in-situ stress to be less than the actual values.(2)As the burial depth increases,the fracturing pressure,closure pressure,and the maximum and minimum horizontal principal stress of the coal reservoirs in the Zhengzhuang area constantly increase.The average gradients of the maximum and minimum horizontal principal stress are 3.17 MPa/100 m and 2.05 MPa/100 m,respectively.(3)Coal reservoir permeability is significantly controlled by the magnitude and state of the current in-situ stress.The coal reservoir permeability decreases exponentially with an increase in the effective principal stress.Moreover,a low lateral pressure coefficient(less than 1)is associated with minor horizontal compressive effects and high coal reservoir permeability.(4)Under similar conditions,such as resource endowments,CBM we
文摘Parameter calculation is the key problem in analysing the AC machines with armatureasymmetries. The multi-loop method, which is effective on this subject, uses such parametersas the self-inductances of and the mutual-inductances between every stator branch, every dam-per loop and the field circuit. They are different from those used in Park’s equations.The parameters of the stator branch are composed of those of related coils according to itscomposition. Two methods, the air-gap permeance analysis method and the field numericalanalysis method, are proposed to calculate the saturated parameters. And the methods arethen verified and compared with each other by application to a generator.
文摘The increase in the capacity and the improvement in the structure of large generatorsrequire better performance of their protection systems against armature faults. Therefore, itis desirous to further the study on the operation of synchronous machines with internal faultsin stator windings. For this purpose, the armature asymmetry of synchronous generatorsconnected to the power system and operating on load condition is analysed for the first timeby using the multi-loop method. In consideration of the power source a mathematical modelfor asymmetrical generators is established and its solution is proposed. Compared withexperimental results at rated voltage, the new approach is justified.
