18 March 2014, Volume 32 Issue 8

    

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Articles
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  Extraction of Remote Sensing Information of Lakes in Badan Jaran Desert and Trend of Their Dynamic Changes

  JIN Xiaomei, GAO Mengmeng, KE Ke, GONG Peng

  journal1. 2014, 32(8): 15-21. https://doi.org/10.3981/j.issn.1000-7857.2014.08.001

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  Based on analysis of the spectral characteristics of ground objects in Badan Jaran Desert, modified index for desert lake water identification was put forward in this paper. This new water index effectively increased the discrimination of water body from the information of vegetation and dry lakes, improving the extraction efficiency and precision. Using TM/ETM+ remote sensing images (eight remote sensing image totally), this study analyzed the variation of lake area in summer and autumn from 1990 to 2010 using the method of MDLWI. The results showed that the average lake area is 19.11 km² in summer and 17.74 km² in autumn, which is significantly smaller than that in summer. The lake area has been slowly decreasing in the 20 years, while in summer the lake area shows a decrease-increase-decrease trend and the change is relatively large. Combined with changes of precipitation and evaporation, the analysis showed that underground water recharge is the main source for desert lake recharge instead of precipitation, the amount of which is more in summer than in autumn.
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  Attribute Synthetic Evaluation Model for Rockburst Disaster Prediction in Underground Engineering

  WANG Liguan, PEI Anlei, PENG Ping'an

  journal1. 2014, 32(8): 22-26. https://doi.org/10.3981/j.issn.1000-7857.2014.08.002

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  According to the present situation of the limitation and low accuracy of rockburst disaster prediction in underground engineering, based on the attribute mathematics theory, the ratio of maximum tangential stress to uniaxial compressive strength of rock, brittleness coefficient and elastic energy index are chosen as the discriminant indexes to build an attribute synthetic evaluation model for predicting the rockburst probability and intensity. The attribute measurement functions of each index are constructed based on the attribute mathematics theory, while the synthetic attributive measurement is calculated by the similar weight. Finally, the probability and intensity of rockburst samples are recognized by the confidence criterion. Taking 10 groups of underground engineering projects at home and abroad for example, the model is validated. Results show that the evaluation by this attribute synthetic model has a good consistency with the actual situation, which validates the feasibility and effectiveness of the proposed model for rockburst prediction. The methodology presented in the paper provides a reference for some similar engineering involving rockburst.
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  Prediction of Water Breakthrough Time of Horizontal Wells in Gas Reservoirs with Bottom Water

  ZHU Weiyao, HUANG Xiaohe, YUE Ming

  journal1. 2014, 32(8): 27-31. https://doi.org/10.3981/j.issn.1000-7857.2014.08.003

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  Development of the horizontal well technology offers a new approach to exploitation of gas reservoirs with bottom water. The most important problem for a horizontal well in gas reservoir is water cresting which restricts the horizontal well to be developed effectively. Based on the imaging theory and potential energy superposition principle, a study on prediction of water breakthrough time of horizontal wells in gas reservoir with bottom water is presented. This paper derives the water breakthrough time formula and productivity of horizontal well in a reservoir with bottom water. In the process of derivation, factors, such as impermeable boundary on the top of the reservoir, equal pressure interface, anisotropy, height of water avoidance, all have influences on the potential distribution in the gas reservoirs with bottom water. The case study indicates that for a horizontal gas well with a constant production rate, the water breakthrough time is proportional to the height of water avoidance, and that the productivity of a horizontal well in gas reservoir with bottom water is affected by horizontal well location and formation anisotropy. The productivity of the horizontal well increases with the height of water avoidance but decreases with the vertical permeability. The results and the method are useful for gas reservoir engineering design and the theoretical study of horizontal well.
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  Fracturing Damage of Coal Bed Methane Caused by Surfactants

  XIA Yongjiang, GUAN Baoshan, LIANG Li, LIU Ping

  journal1. 2014, 32(8): 32-38. https://doi.org/10.3981/j.issn.1000-7857.2014.08.004

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  The coal expansibility, wettability, adsorption, surface tension, damage, adsorption and desorption experiments of cationic surfactant, nonionic surfactant and anionic surfactant were performed to investigate the effect of surfactants on hydraulic fracturing in coal bed methane (CBM) reservoir. The expansion height, contact angle, adsorption forms and absorbance, the surface tension and permeability of coal samples before and after damage, adsorption and desorption of different surfactants and compounded systems were compared and analyzed to identify the optimal system. The investigation shows that the surfactants and water have little effect on coal expansibility. The cationic surfactant increases the coal sample's hydrophobicity, the nonionic surfactant maintains the coal wettability, and the anionic surfactant increases the coal hydrophilia. The nonionic surfactant enlarges coal porosity and accelerates coal gas desorption. The GM is dot adsorption, OP is tile adsorption, and 1831 is conjoined structure adsorption. The GMOP-4 compounded system with low surface tension significantly decreases the GM adsorption volume and accelerates coal gas desorption. The GMOP-4 compounded system realizes the low-cost and high-performance application of cationic surfactants in CBM hydraulic fracturing.
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  Integrated Hydrocyclone and Flotation Separation Technology for Water Preseparation and Wastewater Treatment

  HU Changchao, DANG Wei, TAN Wenjie, WANG Lili, TANG Zhiwei

  journal1. 2014, 32(8): 39-43. https://doi.org/10.3981/j.issn.1000-7857.2014.08.005

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  In view of the disadvantages of the current water preseparation facilities in a high water-cut oilfield, a high efficient integrated technology of the hydrocyclone, the self-dissolved gas flotation, the second stage flotation and the inclined plate coalescence for the water preseparation and the wastewater treatment is proposed, and the laboratory equipment is developed. With this equipment for the water preseparation and the wastewater treatment, 38% of the wastewater can be preseparated, and the outlet content of oil and suspended solids can be controlled under 15 mg/L and 5 mg/L, respectively, when the inlet water-cut is more than 80% and the concentration of suspended solids is less than 300 mg/L. With its high efficiency, the short process flow, the small size and the low investment, the equipment can be used for the water preseparation and the wastewater treatment at transfer stations of gathering systems and marginal oilfields, to bring about great economic benefits.
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  Planning Craft Surface Modeling Based on NURBS with Surface Features

  YOU Dandan, SUN Liping, LIU Ning, SUN Hanbing

  journal1. 2014, 32(8): 44-48. https://doi.org/10.3981/j.issn.1000-7857.2014.08.006

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  The section curves of rigid inflatable planning boat are constructed by free curves and analytic curves based on NURBS curves combination algorithm. The feature extraction and optimization have been launched in the characteristics of the complex section points and improved skinning has also been applied in smoothing surface to precisely construct the planning hull form with knuckle line and broadside airbag. The above methods provide a good solution for constructing complex hull surfaces. It can be a great technical support for automatic partition of hull surface bin, surface block dividing by using CAD/CAM, statics calculation and the generation of constructed mesh in CFD.
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  Test of Effective Tension of High-strength Wire in PC Bridge Based on Transverse Tensioning Method

  HOU Wei, HE Chuanhai, HAN Zhiqiang, LUAN Juan

  journal1. 2014, 32(8): 49-52. https://doi.org/10.3981/j.issn.1000-7857.2014.08.007

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  To test the effective tension of high-strength steel wire of PC bridge, experiments were carried out on a WED electronic universal testing machine using a tensioned tension tester (LCZL-50) that is developed independently. First, the high-strength steel wire was stretched to different tension values using a testing machine, then the effective tension of it was tested by transverse tensioning method, and the experimental data were analyzed based on the least squares method. The above method was used in practical bridge test and calculation. The results of comparative analysis of the theoretical value and measured value of PC bridge show that when the ø5mm high-strength steel wire was under relatively small transverse tension, the variation of transverse tension and transverse displacement had a linear relationship, and conditions of small deformation were satisfied. The error between the measured value and theoretical value was smaller than 5%, indicating the test precision of this method meets the demands for practical engineering, and may provide technical basis for the maintenance, strengthening or modification of PC bridges.
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  Rapid Analysis of Electrolyzer’s Temperature Stress Based on ABAQUS

  QIN Zhongguo, WEI Yulu, LIU Cong, LI Quanhai

  journal1. 2014, 32(8): 53-57. https://doi.org/10.3981/j.issn.1000-7857.2014.08.008

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  For the problem of the electrolytic tank cracks caused by thermal stress appearing in the operation process, a finite element pre-treatment procedure written in VB is developed to analyze the three-dimensional temperature field and temperature stress of the electrolytic tank. The model input files to be imported to ABAQUS to analyze the electrolytic tank's temperature field and thermal stress problem can be quickly generated, with different sizes, different materials, different climates and different liquid level heights according to a few parameters form the interface. This procedure is simple to operate and suitable for batch size, batch condition of electrolytic cell rapid analysis. By means of the distribution law of temperature field and thermal stress, the main factors affecting the change are analyzed to provide a theoretical guidance for the design of the electrolytic cell and prolong its service life.
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  Oil-sand Phases Flow Detection Based on Acoustic Emission Technology

  CHEN Chao, YU Qiling, QIAN Yuxiang, LIU Pengtao

  journal1. 2014, 32(8): 58-63. https://doi.org/10.3981/j.issn.1000-7857.2014.08.009

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  The sand production problem in unconsolidated sandstone reservoir development has become increasingly prominent. To decrease the difficulty of oil well sand production management, moderate sanding techniques are usually used to maximize the benefit of oil and gas wells. Therefore, it is significant to develop oil-sand flow detection technology for timely and effective prediction and control of oil and gas well sand production. This paper proposes a method of flow detection in oil-sand phases based on acoustic emission technology. The method uses ultrasonic to measure the oil phase flow, also uses acoustic emission sensors to detect sand signal in oil flow, and build the experimental device of oil-sand flow detection, then analyzes the signal characteristics through specialized collection software. The results show that with other conditions remaining unchanged, acoustic emission power increases with the increase of sand mass and oil velocity, and decreases with increasing sand size; finally the acoustic emission power model of sand mass, sand size and oil velocity is established to obtain the sand flow information.
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  A Magnetic Resonance Image De-noising Approach Based on Improved K-SVD

  JIANG Xingguo, QIN Yang, WEI Baolin

  journal1. 2014, 32(8): 64-69. https://doi.org/10.3981/j.issn.1000-7857.2014.08.010

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  Magnetic resonance image is an important research field in medical image processing. Because it can degrade the image quality, the signal noises have a negative impact on clinical diagnosis. The K-SVD algorithm can obtain better de-noising results, but the time-consuming problem of the dictionary training still exists. A medical image denoising algorithm based on improved K-SVD is studied to solve this problem. First of all, an efficient and flexible dictionary structure is proposed based on a sparsity model of the dictionary atoms over a know dictionary. The sparse dictionary provides efficient forward and adjoint operators, has a compact representation, and can be effectively trained from given example data. Then the basic framework of the existing K-SVD algorithm, combined with the dictionary sparse representation, can improve K-SVD training algorithm, and the improved K-SVD algorithm can be trained for greater dictionary, especially for high-dimensional data. Therefore, it can be used to remove the noise of magnetic resonance images. The experimental results show that the algorithm, in comparison with the discrete cosine transform dictionary and conventional K-SVD algorithm, can effectively filter Gaussian white noise of the image to retain image details, and reduce the time of dictionary training. It is found that the peak signal-to-noise ratio is increased by about 1~3db with the proposed method.
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  A Delay-sensitive Broadcasting Retransmission Algorithm Based on Significance of Packets

  XU Zhuo, YAO Fuqiang, GUAN Shengyong, XU Ba

  journal1. 2014, 32(8): 70-75. https://doi.org/10.3981/j.issn.1000-7857.2014.08.011

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  Because of noise and multipath fading in wireless channels, the performance of wireless broadcasting is unsatisfactory. Conventional wireless broadcasting retransmission technology takes retransmission efficiency into consideration, while the significance of lost packets is neglected, making it difficult to meet the demand of applications sensitive to packet significance. To improve the performance of wireless broadcasting and meet the demand for packet- significance- sensitive applications, a delay- sensitive broadcasting retransmission algorithm based on significance of packets (DBRA) is proposed on the basis of the conventional broadcasting retransmission technique. According to the significance level of lost packets, the algorithm gives priority to timesensitive lost packets and terminals with significant lost packets, and finds the maximum number of coding opportunities in opportunistic network coding (ONC), thus the transmission efficiency is improved, and the transfer delay of packets is decreased and terminals need less time to get significant lost packets. Simulations show that this algorithm has a probability with better efficiency than other classical algorithms and significant packets have priorities in transmission under classical wireless channel conditions.
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  Progress and Revelation of Exploration of Large Oil and Gas Fields Around the Globe

  JIA Huaicun

  journal1. 2014, 32(8): 76-83. https://doi.org/10.3981/j.issn.1000-7857.2014.08.012

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  More than 250 years of petroleum exploration indicated that reserves of oil and gas are centralized in a minority of large oil and gas fields. In 2010, some world-class fields have been discovered, such as Leviathan and Franco, enhancing the confidence in discovering large fields. Research of new large fields in terms of distribution and accumulation potential may provide guidance for exploring potential large fields. Databases have been built for the 57 large fields discovered from 2007 to 2012. Based on analysis of the distribution, accumulation conditions and patterns of new large fields, this paper summarizes their accumulation characteristics and revelation to future exploration through instance analysis of typical fields. A majority of new large oil and gas fields are mainly distributed in 21 key basins. The Upper Jurassic-Lower Cretaceous is the major hydrocarbon source rocks, though a majority of reserves are distributed in Lower Cretaceous. Turbidite sandstones of subsea fans and slope channels are the further potential reservoirs for discovering large fields. Mesozoic of pan-Tethyan basins and Lower Cretaceous basins located in both sides of the south Atlantic ocean are the next areas for exploring potential large fields.