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Multistage volume fracturing in horizontal Wells is the main means to improve the productivity of tight reservoirs. Complex fracture networks with various shapes are generated around the wellbore after volume fracturing. However, most of the current seepage models only consider a single main fracture, which results in a large error in reservoir analysis and evaluation. To this end, a discrete fracture seepage model for tight gas fractured horizontal wells with complex fracture networks was established. Three shapes of complex fracture networks were considered, namely, rectangular fracture networks, elliptic fracture networks and hyperbolic fracture networks. The finite element method with hybrid elements was used to solve the model, and well test log-log type curves of three fracture network shapes were obtained. The characteristics of the well test log-log type curves were analyzed, and the results were compared with those of the conventional single fracture model. The results show that the well test log-log type curves of the fracture networks model include four main flow stages, i.e. pseudo-radial flow stage of the stimulated reservoirs region, transition flow or radial flow stage of the unstimulated reservoirs region, linear flow stage and system radial flow. The biggest difference of well test log-log type curves between the fracture networks model and the conventional single fracture model is that the first linear flow stage of the single fracture model is replaced by the pseudo-radial flow stage of the fracture networks model. The end time of the pseudo-radial flow stage is mainly determined by the size and shape of the stimulated area. Through the well test analysis of a tight gas fractured horizontal well in the Changqing oilfield, it is proved that the new model is reliable and practical, and the effective stimulated reservoir volume and the conductivity of fracture networks can be obtained.

In recent decades, with the vigorous development of shipping and transportation logistics industry, a large number of portal cranes have been installed in the ports of our country for production, and some of the equipment has approached or even exceeded its designed service life, and there is a great hidden danger of safety in the continued use of the equipment. This paper discusses a safety performance evaluation method of portal crane based on analytic hierarchy process (AHP). Through the determination and measurement of evaluation index, the safety condition of equipment can be obtained. according to the value of equipment safety condition, the safety performance can be classified, and the user and management organization can respond effectively according to the safety performance level of equipment, and the risk caused by long-term service of equipment can be effectively eliminated.

15NiCuMoNb has good mechanical properties, which is widely used in high-end equipment. However, the performance of existing material standards has been conservative in the past. In this paper the mechanical properties of 15NiCuMoNb at different temperatures are systematically studied. It is shown that the yield strength of the material decreases with the increase of temperature. The decrease tends would be slown after 200 °C, and the tensile strength of the material has similar characteristics. The least square method is used to obtain the prediction formula of the material in the range of 20~350 °C, which could be effectively predicted the mechanical properties of material. It could be useful to improve the accuracy of analytical design results, and provide a data basis for the revision of subsequent material standards.

20MnMoNb alloy steel is a structural steel for forgings with good mechanical properties, which is typically used in the manufacture of pressure vessel tube sheets. The mechanical properties of 20MnMoNb at different temperatures were systematically studied. It is shown that the 20MnMoNb material has the good high temperature resistance. With the increase of temperature, the yield strength and tensile strength of the material have little difference. The tensile strength is nearly 800MPa at high temperature, and the yield strength is about 643MPa, which could meet the complex working environment of the high pressure heaters. It is helpful to improve the accuracy of analytical design results and provide a data base for the revision of subsequent material standards.

9Ni steel has good toughness and high strength. This paper focuses on the influence of vertical hole defects on the ultrasonic propagation characteristics, which are studied from two aspects of the propagation characteristics of the base metal and the ultrasonic waves of the weld, respectively. The acoustic reflection characteristics of the reflector are compared with the acoustic reflection characteristics of the two different welding processes, (manual welding and automatic welding). It is shown that the gain compensation of the weld is larger than the gain of the same diameter and the same position of the vertical hole in the base metal. The gain compensation of the automatic welding is larger than that of the manual welding. The ultrasonic attenuation in the automatic welding is larger than that of the manual welding. The results of the study contribute to improving the application of ultrasonic testing in 9Ni weld joints.

Finite element technology provides the basis for the complex structural analysis and calculation, which has been widely used in the design and evaluation of large-scale equipment. However, the time and cost of calculations are getting larger and larger due to complexity of the structure. How to improve the economics and rationality of calculations as much as possible under the premise of ensuring accuracy has become the focus of research. In this paper, the simplified high-pressure heater is taken as the research object, and the influence of different grid size on the calculation accuracy is shown. It is shown that the mesh size could be appropriately increased under the premise of the certain calculation accuracy, which could improve the calculation process and shorten the calculation time.

This paper focuses on the influence of vertical hole defects on the ultrasonic propagation characteristics, which are studied from two aspects of the propagation characteristics of the base metal and the ultrasonic waves of the weld, respectively. The acoustic reflection characteristics of the reflector are compared with the acoustic reflection characteristics of the two different welding processes, manual welding and automatic welding, and the properties of the base material. It is shown that the cross-slot of the weld is different from the cross-slot in the base metal, and the attenuation of the ultrasonic wave in the base metal and the weld is different. The gain compensation is too large, and the automatic welding gain compensation ratio of the upper groove of the weld is lower. The automatic welding gain compensation of the cross-slot is large, and the manual welding gain compensation of the lower cross-slot is higher than that of the automatic welding, and the cross-slot gain compensation of the automatic welding upper surface weld is higher than that of the manual welding.

Cloud computing raises new challenges for how to protect user privacy. Fully homomorphic encryption is one way to solve the problem. In this paper, we show a useful property of Dual-LWE assumption to construct Key-Switching procedure compared with LWE assumption without extra error term. Hence, we propose to construct "Errorless Key Switching" fully homomorphic encryption (FHE) scheme based on dual learning with errors (Dual-LWE) assumption. Specifically, we compile the Dual-LWE problem proposed by Gentry et.al. at STOC2008 and First-is-errorless LWE (Ferr.LWE) problem proposed by Brakerski et al. at STOC2013 into Dual-First-is-errorless LWE (Dual-Ferr.LWE) problem. Then, utilizing Dual-Ferr.LWE assumption to construct a various GPV(vGPV) scheme, and we use vGPV scheme as the fundamental building block to construct FHE with errorless key switching scheme. Lastly, under the assumption of decisional learning with errors(DLWE), we prove that our scheme is CPA secure.