The extra-low cyclic fracture problem of medium carbon steel under axial fatigue loading was investigated. Several problems, such as the relations of the cycle times to the depth and tip radius of the notch, loading f...The extra-low cyclic fracture problem of medium carbon steel under axial fatigue loading was investigated. Several problems, such as the relations of the cycle times to the depth and tip radius of the notch, loading frequency, loading range and the parameters of fracture design for medium carbon steel on condition of extra-low axial fatigue loading were discussed based on the experiments. Experimental results indicated that the tension-pressure fatigue loading mode was suitable for extra-low cyclic fatigue fracture design of medium carbon steel and it resulted in low energy consumption, fracture surface with high quality, low cycle times, and high efficiency. The appropriate parameters were as follows： loading frequency 3-5 Hz, notch tip radius r = （0.2-0.3） mm, opening angle α = 60°, and notch depth t = （0.14-0.17）D.展开更多
For extra-low permeability reservoirs, with a permeability of about 0.3×10?3 μm2, fluid flow and production performance in cores were studied. A long core holder with a multi-location piezometric measurement was...For extra-low permeability reservoirs, with a permeability of about 0.3×10?3 μm2, fluid flow and production performance in cores were studied. A long core holder with a multi-location piezometric measurement was specially designed. An artificial long core, about 700 mm long and with a cross section of 45mm×45mm, was used. In the experiment, pressure distribution along the core can be measured in real time. Single phase flow in the core was investigated. Different modes of production in long cores were also simulated including natural depletion, water flooding, and advanced water flooding. Through physical simulation, flow parameters were collected and production characteristics in extra-low permeability cores were studied. From experimental results, it can be seen that fluid flow in extra-low permeability cores is different from that in high permeability cores. Transmission of pressure in extra-low permeability cores is very slow, and it needs a long time for the pressure to become stable. The distribution curve of pressure along the core is nonlinear and the production rate in extra-low permeability reservoirs decreases sharply. The development effects of different production modes in extra-low permeability cores were compared with one another. Among the production modes, advanced water flooding has much potential for effective development of extra-low permeability reservoirs. Natural depletion and conventional water flooding can also be used in early production periods. In addition, the countermeasures and some ideas especially for the potential development of extra-low permeability reservoirs are suggested.展开更多
The influence of pore structure difference on rock electrical characteristics of reservoir and oil reservoir was analyzed taking Triassic Chang 6 reservoir in Block Yanwumao in the middle of Ordos Basin as an example....The influence of pore structure difference on rock electrical characteristics of reservoir and oil reservoir was analyzed taking Triassic Chang 6 reservoir in Block Yanwumao in the middle of Ordos Basin as an example. The relationship between the pore structure difference and the low resistivity oil layer was revealed and demonstrated through core observation, lab experiments, geological research, well log interpretation and trial production etc. The results show that there were two kinds of oil layers in Chang 6 oil layer set, normal oil layer and low resistivity oil layer in the region, corresponding to two types of pore structures, pore type mono-medium and micro-fracture-pore type double-medium; the development of micro-fracture changed greatly the micro-pore structure of the reservoir, and the pore structure difference had an important influence on the rock electrical characteristics of the extra-low permeability sandstone reservoir and oil reservoir; the normal oil layers had obvious characteristics of pore-type mono-medium, and were concentrated in Chang 61, Chang 6232 and Chang 62; the low resistivity oil layers had obvious characteristics of micro-fracture-pore type double-medium, which were mainly distributed in Chang 612 and Chang 63. The mud filtrate penetrated deep into the oil layers along the micro-cracks, leading to sharp reduction of resistivity, and thus low resistivity of the oil layer; the low resistivity oil layers had better storage capacity and higher productivity than the normal oil layers.展开更多
After analyzing many studies of fluid flow theory of multi-porous media in low and extra-low permeability reservoirs and the numerical simulation of non-Darcy flow, we found that a negative flow rate occurs in the exi...After analyzing many studies of fluid flow theory of multi-porous media in low and extra-low permeability reservoirs and the numerical simulation of non-Darcy flow, we found that a negative flow rate occurs in the existing non-Darcy flow equation, which is unreasonable. We believe that the existing equation can only be considered as a discriminant to judging Darcy flow or non-Darcy flow, and cannot be taken as a fluid flow governing equation of multi-porous media. Our analysis of the experimental results shows that the threshold pressure gradient(TPG) of low and extra-low permeability reservoirs is excessively high, and does not conform to fluid flow through multi-porous media in the actual reservoir situation. Therefore, we present a reasonable TPG ranging from 0.006 to 0.04 MPa/m at the well depth of 1500 m and oil drainage distance of 500 m. The results of our study also indicate that the non-Darcy flow phenomenon will disappear when the TPG reaches a certain value. In addition, the TPG or non-Darcy flow in low and extra-low permeability reservoirs does not need to be considered in the productivity prediction and reservoir numerical simulation. At present, the black oil model or dual-porous media is suitable for simulating low and extra-low permeability reservoirs.展开更多
Overcooling causes thermal discomfort and wastes energy.Effectiveness of a novel dedicated outdoor air system(DOAS)consisting of a multi-stage direct expansion coil to generate extra-low temperature(XT)outdoor air to ...Overcooling causes thermal discomfort and wastes energy.Effectiveness of a novel dedicated outdoor air system(DOAS)consisting of a multi-stage direct expansion coil to generate extra-low temperature(XT)outdoor air to handle the entire space cooling demand for better energy and humidity control has been confirmed in previous studies.In these studies,the terminal system was assumed using variable air volume(VAV)without reheating.The conventional VAV system without reheating has overcooling problem.This is associated with uncertain fluctuations of operating characteristics.However,virtually no study has been done to investigate its overcooling risk,and how it is compared with XT-DOAS.In this study,a rigorous probabilistic approach is proposed to account for the uncertain fluctuations of operating characteristics to assess their overcooling risks.Monte Carlo simulations with 10,000 interactions was used for risk analysis.A morphing method was employed to develop 10,000 weather files that could give an accurate prediction of future variations in yearly weather conditions.Reliable datasets were used to develop the probability distribution functions to account for the daily variations in use patterns.The most probable operating characteristics were input to EnergyPlus for hour-by-hour simulations.The annual cooling load profile formulated by the probabilistic approach was successfully validated by in-situ measurements.The probabilistic assessment results show that XT-DOAS has far less overcooling hours and lower long-term percentage of dissatisfied than the conventional VAV system.The results also indicate that the proposed probabilistic approach is useful for a robust system performance evaluation.展开更多
This article proposes a novel approach combining exponential-reaching-law-based equivalent control law with radial basis function (RBF) network-based switching law to strengthen the sliding mode control (SMC) tracking...This article proposes a novel approach combining exponential-reaching-law-based equivalent control law with radial basis function (RBF) network-based switching law to strengthen the sliding mode control (SMC) tracking capacity for systems with uncertainties and disturbances. First, SMC discrete equivalent control law is designed on the basis of the nominal model of the system and the adaptive exponential reaching law, and subsequently, stability of the algorithm is analyzed. Second, RBF network is used to f...展开更多
基金supported by the Ministry of Education of China(No.208152)Gansu Natural Science Foundation(No.3ZS061-A52-47).
文摘The extra-low cyclic fracture problem of medium carbon steel under axial fatigue loading was investigated. Several problems, such as the relations of the cycle times to the depth and tip radius of the notch, loading frequency, loading range and the parameters of fracture design for medium carbon steel on condition of extra-low axial fatigue loading were discussed based on the experiments. Experimental results indicated that the tension-pressure fatigue loading mode was suitable for extra-low cyclic fatigue fracture design of medium carbon steel and it resulted in low energy consumption, fracture surface with high quality, low cycle times, and high efficiency. The appropriate parameters were as follows： loading frequency 3-5 Hz, notch tip radius r = （0.2-0.3） mm, opening angle α = 60°, and notch depth t = （0.14-0.17）D.
基金supported by China National Program on Key Basic Research Project (973 Program) (Grant No. 2006CB705805)National Key Scientific and Technological Project (Grant No. 2008ZX05009-004)
文摘For extra-low permeability reservoirs, with a permeability of about 0.3×10?3 μm2, fluid flow and production performance in cores were studied. A long core holder with a multi-location piezometric measurement was specially designed. An artificial long core, about 700 mm long and with a cross section of 45mm×45mm, was used. In the experiment, pressure distribution along the core can be measured in real time. Single phase flow in the core was investigated. Different modes of production in long cores were also simulated including natural depletion, water flooding, and advanced water flooding. Through physical simulation, flow parameters were collected and production characteristics in extra-low permeability cores were studied. From experimental results, it can be seen that fluid flow in extra-low permeability cores is different from that in high permeability cores. Transmission of pressure in extra-low permeability cores is very slow, and it needs a long time for the pressure to become stable. The distribution curve of pressure along the core is nonlinear and the production rate in extra-low permeability reservoirs decreases sharply. The development effects of different production modes in extra-low permeability cores were compared with one another. Among the production modes, advanced water flooding has much potential for effective development of extra-low permeability reservoirs. Natural depletion and conventional water flooding can also be used in early production periods. In addition, the countermeasures and some ideas especially for the potential development of extra-low permeability reservoirs are suggested.
基金Supported by the Natural Science Foundation of Shaanxi Province,China(2010JM5003)
文摘The influence of pore structure difference on rock electrical characteristics of reservoir and oil reservoir was analyzed taking Triassic Chang 6 reservoir in Block Yanwumao in the middle of Ordos Basin as an example. The relationship between the pore structure difference and the low resistivity oil layer was revealed and demonstrated through core observation, lab experiments, geological research, well log interpretation and trial production etc. The results show that there were two kinds of oil layers in Chang 6 oil layer set, normal oil layer and low resistivity oil layer in the region, corresponding to two types of pore structures, pore type mono-medium and micro-fracture-pore type double-medium; the development of micro-fracture changed greatly the micro-pore structure of the reservoir, and the pore structure difference had an important influence on the rock electrical characteristics of the extra-low permeability sandstone reservoir and oil reservoir; the normal oil layers had obvious characteristics of pore-type mono-medium, and were concentrated in Chang 61, Chang 6232 and Chang 62; the low resistivity oil layers had obvious characteristics of micro-fracture-pore type double-medium, which were mainly distributed in Chang 612 and Chang 63. The mud filtrate penetrated deep into the oil layers along the micro-cracks, leading to sharp reduction of resistivity, and thus low resistivity of the oil layer; the low resistivity oil layers had better storage capacity and higher productivity than the normal oil layers.
基金sponsored by National Key Project of Science and Technology of the Ministry of Science and Technology(MOST)(Grant No.2011ZX05043-002)
文摘After analyzing many studies of fluid flow theory of multi-porous media in low and extra-low permeability reservoirs and the numerical simulation of non-Darcy flow, we found that a negative flow rate occurs in the existing non-Darcy flow equation, which is unreasonable. We believe that the existing equation can only be considered as a discriminant to judging Darcy flow or non-Darcy flow, and cannot be taken as a fluid flow governing equation of multi-porous media. Our analysis of the experimental results shows that the threshold pressure gradient(TPG) of low and extra-low permeability reservoirs is excessively high, and does not conform to fluid flow through multi-porous media in the actual reservoir situation. Therefore, we present a reasonable TPG ranging from 0.006 to 0.04 MPa/m at the well depth of 1500 m and oil drainage distance of 500 m. The results of our study also indicate that the non-Darcy flow phenomenon will disappear when the TPG reaches a certain value. In addition, the TPG or non-Darcy flow in low and extra-low permeability reservoirs does not need to be considered in the productivity prediction and reservoir numerical simulation. At present, the black oil model or dual-porous media is suitable for simulating low and extra-low permeability reservoirs.
文摘Overcooling causes thermal discomfort and wastes energy.Effectiveness of a novel dedicated outdoor air system(DOAS)consisting of a multi-stage direct expansion coil to generate extra-low temperature(XT)outdoor air to handle the entire space cooling demand for better energy and humidity control has been confirmed in previous studies.In these studies,the terminal system was assumed using variable air volume(VAV)without reheating.The conventional VAV system without reheating has overcooling problem.This is associated with uncertain fluctuations of operating characteristics.However,virtually no study has been done to investigate its overcooling risk,and how it is compared with XT-DOAS.In this study,a rigorous probabilistic approach is proposed to account for the uncertain fluctuations of operating characteristics to assess their overcooling risks.Monte Carlo simulations with 10,000 interactions was used for risk analysis.A morphing method was employed to develop 10,000 weather files that could give an accurate prediction of future variations in yearly weather conditions.Reliable datasets were used to develop the probability distribution functions to account for the daily variations in use patterns.The most probable operating characteristics were input to EnergyPlus for hour-by-hour simulations.The annual cooling load profile formulated by the probabilistic approach was successfully validated by in-situ measurements.The probabilistic assessment results show that XT-DOAS has far less overcooling hours and lower long-term percentage of dissatisfied than the conventional VAV system.The results also indicate that the proposed probabilistic approach is useful for a robust system performance evaluation.
文摘This article proposes a novel approach combining exponential-reaching-law-based equivalent control law with radial basis function (RBF) network-based switching law to strengthen the sliding mode control (SMC) tracking capacity for systems with uncertainties and disturbances. First, SMC discrete equivalent control law is designed on the basis of the nominal model of the system and the adaptive exponential reaching law, and subsequently, stability of the algorithm is analyzed. Second, RBF network is used to f...
