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01 December 2022, Volume 18 Issue 4

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OIL AND GAS EXPLORATION

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Application of Air-Foam Drilling in Well Chaitan1

SUN Lanjiang , ZHANG Shuxia , LI Baoqing , XING Chao , LIU Wan , ZHONG Ninglong

2022, 18(4):  1-6.  DOI: 10.12388/j.issn.1673-2677.2022.04.001

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In many areas of Qaidam Basin，such as Yingxiongling，Ganchaigou and Xiandong，the shallow strata have poor lithology， loose cementation，fracture development，and frequently-occurred loss-return leakage in the process of drilling，which have seriously restricted the speed of drilling and affected the safety of drilling. This is a regional problem that needs to be solved urgently. Well Chaitan1 is a risk exploratory well located in Xiandong area. Conventional drilling fluid was used for the drilling of the surface section hole with a diameter of 660.4 mm. Leakage during the drilling was huge，and the plugging effect was not satisfactory. Therefore，it no longer possessed conditions to continue with the drilling. By using air-foam drilling technique and selecting the most suitable foaming agent and inhibitor for this well，the problem of frequently-occurred loss-return leakage in shallow strata has been solved，and the drilling cycle has been greatly shortened. By using the technique of sand cleaning-casing running，safe casing running has been realized in the well section with instable borehole and irregular hole diameters. The successful application of air-foam drilling technique in the Φ660.4 mm hole of Well Chaitan1 provides an approach and technical reserve for solving the problems of low pressure and likelihood for leakage and collapse in shallow strata during drilling in Qaidam Basin.

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Quality Control Technology of S-Wave Seismic Acquisition in Piedmont Zone and Its Application

KONG Dezheng, Wang Yanfeng, WEN Zhongtao, CHEN Jianguo, WANG Jianbing, WU Yonghui

2022, 18(4):  7-11.  DOI: 10.12388/j.issn.1673-2677.2022.04.002

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S-wave seismic exploration has many natural advantages，such as micro-fracture prediction and gas cloud area imaging. In recent years，the attention and research of geophysical circles on S-wave exploration are rapidly heating up. S-wave seismic acquisition，however，is obviously different from the P-wave seismic acquisition that we are familiar with regarding excitation，reception，and other aspects，and has more restrictive factors and stricter requirements for construction quality. In this paper，the piedmont S-wave seismic acquisition test line in the Tarim Basin is used as an example to expound in detail the construction process and quality control technology of the key links such as the embedding and angle correction of the 3-component geophone，as well as the excitation azimuth control of the S-wave source. The processing and analysis results of S-wave data show that in order to improve the imaging effect of Swave seismic acquisition data，an observation system with higher coverage times and larger S-wave source driving amplitude should be adopted in terms of S-wave seismic acquisition method，high，steep and complex structural areas should be avoided where possible in terms of deep seismic geological conditions，and the control of environmental noise should be strengthened in terms of the signal-tonoise ratio of original data. Field tests have provided technical reference for the quality control，popularization and application of Swave seismic acquisition technology.

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Evaluation of Uncertainty in Quality Testing of Grade G Oil Well Cement 

DI Xinye , MA Jiang , QI Jing , LI Liangbing , ZHANG Wei

2022, 18(4):  12-19.  DOI: 10.12388/j.issn.1673-2677.2022.04.003

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With the development of metrology，measurement uncertainty has been widely applied to many fields，which reflects the testing level of a laboratory and the reliability of testing results. In order to improve the accuracy of the quality testing data of grade G oil well cement，the testing processes of all physical parameters were investigated and analyzed in respect of testing repeatability，sample weighing，and cement slurry preparation by building a mathematical model. A typical method to evaluate the uncertainty in testing the thickening time，free liquid content and compressive strength of grade G oil well cement was established. The evaluation results show that when the inclusion factor K is 2，and the thickening time of grade G oil well cement is 103.3 min，its spread uncertainty is 1.09 min； when the free fluid content is 3.71%，its spread uncertainty is 0.71%；when the compressive strength at 38 ℃ is 5.44 MPa，its spread uncertainty is 1.23 MPa. The factors affecting the uncertainty in the testing process were determined，which are mainly the testing repeatability of samples，and followed by the mass weighing of samples. In actual testing，the testing error should be minimized by improving the weighing process of the mixed materials and increasing the number of repeated testing of samples. 

OIL AND GAS DEVELOPMENT

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Study on Main Controlling Factors of Water Production in Tight Gas Wells 

LI JingSong, LIU Zixiong, KOU Shuangyan, ZHANG Xiuming, LIU Rumin, WANG Jinwei

2022, 18(4):  20-25.  DOI: 10.12388/j.issn.1673-2677.2022.04.004

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It is well known that water production is the main factor leading to low production and low efficiency of gas wells. However， due to the lack of understanding of the main controlling factors of water production，applying the conventional drainage gas production method is always of low efficiency. In order to comprehensively study the main controlling factors of water production，the cocoon stripping optimization algorithm by big data analysis is introduced to firstly establish a big data sample library for factors that may affect water production，including geological，engineering，drainage and production factors；secondly，all the data is cleaned to eliminate invalid data. After that，the single factor analysis is carried out to determine the positive and negative relationship of each factor；then，multifactor analysis is conducted to find out the main controlling factors affecting water production in tight gas wells. Finally，39 main controlling factors are found out by using elimination method and the main control equation of water production is established to define the effect of each factor on water production. The study shows that：the main factors that greatly affect water production are producible porosity and total porosity identified by logging，gas testing and production casing pressure，clay content，etc. In order to avoid the impact of water production on gas production in the later stage，the reservoir sections with larger producible porosity，larger total porosity and lower clay content are preferred for fracturing. Meanwhile，the production scheme shall be implemented in the production process to avoid excessive pressure difference which can aggravate formation water production，so as to provide a basis for taking effective treatment measures for water-producing gas well in the later stage. 

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Practices of Zipper Fracturing for Tight Reservoir Development with Small Well Spacing

WAN Tao , QIN Jianhua , ZHANG Jing

2022, 18(4):  26-32.  DOI: 10.12388/j.issn.1673-2677.2022.04.005

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A fully coupled hydrodynamic model and field monitoring data are used to reveal the changes in in-situ stress during zipper fracturing in tight conglomerate reservoir under the volumetric development pattern of small well spacing，and the corresponding propagation pattern of fracture network. In the case that horizontal well adopts mono-interval and multi-cluster，staggered fracture arrangement and zipper fracturing，there exist stress interferences between wells and fractures at the same time. A large amount of fluid is injected into the wells fractured first to increase the pore pressure and induce the change in in-situ stress field. The mass and pressure transfer effect of fracturing improves the minimum horizontal principal stress，and reduces the two-way stress difference，which preactively creates geomechanical conditions more conducive to the formation of complex fracture network. The development effect of Mahu volumetric development demonstration zone in Junggar Basin with small well spacing shows that the stimulation effect of intervals subjected to centralized batch fracturing is much better，primary well pattern is more advantageous for the deployment of centralized fracturing and putting into production，and the wells to be fractured later have a more complex fracture network. By reducing the well spacing and conducting zipper fracturing，the horizontal stress difference is reduced continually，and the interferences between artificial fractures are mitigated，which is conducive to the formation of complex fracture network，and can effectively improve the production and recovery factor. 

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Design of One-Trip PDM for the Ultra-Shallow Horizontal Well in Block Chepaizi and Its Application

DONG Zhihui, YANG Zening

2022, 18(4):  33-37.  DOI: 10.12388/j.issn.1673-2677.2022.04.006

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Because the ultra-shallow horizontal well in Block Chepaizi of Xinjiang has shallowly-buried target layer, poor diagenesis, large difference in drillability, and very low and unstable angle-building rate, large-degree progressive displacement motor (PDM) is needed to control the trajectory of the angle-building section. A large-degree PDM has large torque during compound drilling, and is very likely to have screw failure, which is not conducive to safe drilling. For the drilling of horizontal section, it is necessary to trip out and replace the large-degree PDM with a small-degree one. A large-degree PDM can neither achieve trajectory control for the secondspud vertical section, the deviated section and the horizontal section in one trip nor satisfy the demand for safe drilling. The analysis shows the one-trip drilling technique for the ultra-shallow horizontal well in Block Chepaizi requires that the PDM should not only have a high angle-building rate, but also be able to reduce the torsional force produced by compound drilling, so as to prevent the screw from twisting off or breaking off. Based on this, short-bend point PDM that meets the requirements is optimized and designed, which has the distance from the bend point of a conventional one to the bottom of bit adjusted to 1.3 m from 1.8 m. After such adjustment, anglebuilding ability of the screw is basically unchanged, but the screw offset value is reduced from 0.056 m to 0.038 m, which further reduces the torsional force acting on the PDM enclosure under compound drilling conditions from 3.7 kN·m to 1.5 kN·m. The newly-designed PDM can effectively control the trajectory by way of slide drilling combined with compound drilling, and complete the directional drilling operation of the ultra-shallow horizontal well in Block Chepaizi in one trip.

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Formation Mechanism of Hydrogen Sulfide in Thermal Recovery Wells of Bohai Offshore Heavy Oilfield

XIAO Sa, LIU Yaqiong, CAI Jun, SUN Yubao, WANG Shaohua, CAI Yina

2022, 18(4):  38-43.  DOI: 10.12388/j.issn.1673-2677.2022.04.007

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Formation of H2S will bring great potential hazard to the safety of personnel and equipment in offshore oil fields. In order to determine the source of H2S in offshore heavy oil thermal recovery wells，the formation mechanism of H2S during thermal recovery development was investigated by conducting experiments. Simulated experimental study on the formation of H2S at different temperatures was carried out for the three reactions systems of heavy oil，heavy oil + distilled water，and heavy oil + water + core + methane. Besides， experiment was also conducted on the formation of H2S at high temperatures for sulfonate surfactant. The results show that for the heavy oil of Bohai S Oilfield，the concentration of H2S produced by the cracking and aquathermolysis of heavy oil increases with the increase in reaction temperature，and the organic gas produced is mostly the gas of light hydrocarbons below C5，with a small amount of C6+ gas. The aquathermolysis of heavy oil has caused the change in heavy oil composition. The contents of resin and asphaltene in heavy oil decrease，while the contents of saturated and aromatic components increase. This phenomenon becomes more obvious with the increase in reaction temperature. For the mixed system under study，at 200 ~ 300 ℃，aquathermolysis and TSR are dominant，which are the main sources of H2S；when the temperature reaches 350 ℃，cracking and TSR become dominant. At the same time，it is also found that it is very easy for sulfonate surfactant to produce H2S at high temperatures due to its instability at high temperatures. It is recommended that the use of sulfonate surfactant in the presence of steam be minimized in thermal recovery. 

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Technology to Stimulate Xinjiang Fengcheng Super-Heavy Oil Reservoir Containing Muddy Interlayers by Drilling Multilateral Wells 

DU Binghui , LIN Botao, , ZHANG Runxue , HUANG Yong

2022, 18(4):  44-51.  DOI: 10.12388/j.issn.1673-2677.2022.04.008

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Muddy interlayers are developed in Fengcheng super-heavy oil reservoir in Xinjiang，featuring extensive distribution，large thickness and poor permeability. As a result，the steam chamber fails to effectively affect the reservoir near the interlayers during conventional SAGD and vertical well-assisted SAGD. Aiming at the engineering problem that muddy interlayers seriously impede the flow through reservoir，this paper takes a SAGD well group in Fengcheng Oilfield as the research object. By way of drilling multilateral wells through its upper interlayers from the steam injection well，water was injected stage by stage to increase the pressure and expand the capacity，so as to achieve the purpose of reservoir stimulation. In addition，a finite element calculation model of reservoir stimulation by increasing the pressure stage by stage for the SAGD of multilateral wells containing interlayers was also established. The calculation results show that the formation pore pressure increases significantly in the areas near the multilateral wells. The capacity expanding area starts from the intersection of the lateral well and the steam injection well，and gradually extends outward. Finally，the effective capacity expansion covers reservoir in the vertical direction of 10 m and the horizontal direction of 5 m. In this scope，the increase range of porosity increases with the increase in the viscosity of the injected fluid. On this basis，the curve of construction flow rate versus wellhead pressure was established to provide basis for the design of field construction parameters. After multilateral wells were drilled in the field，the well group was subjected to micro-fracturing for capacity expansion. Compared with other well groups in the same block，the preheating period of this well group was shortened by 60 days，the average daily production increased by 5.6 t/d after 300 days of normal production，and the oil/steam ratio increased by 0.05. This shows that the stimulation effect of super-heavy oil reservoir containing muddy interlayers by drilling multilateral wells is satisfactory.

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Perforation Adjustment Modes of Oil & Water Wells for Water Flooding in Thick Reservoirs 

TIAN Hongzhao

2022, 18(4):  52-55.  DOI: 10.12388/j.issn.1673-2677.2022.04.009

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Targeted at the problems of uneven vertical water flooding and gradual deterioration of development effect in the reservoirs of block B in G Oilfield with thick oil layers during water flooding，and combined with the actual geological parameters，a waterflood mechanism model for thick reservoirs is established. The influence of different perforation adjustment modes and adjustment timing of oil and water wells on the effect of water flooding is simulated and analyzed，and the optimal mode for next step of adjustment is given. Study results show that all oil and water wells should be perforated for production in the waterflood process of reservoirs，and high water-cut layers should be sealed off in time so that production can return to upward layers one by one after oil wells have water breakthrough. The effect of oil-water gravity differentiation should be fully utilized，which not only prevents the rapid formation of preferential channels after oil wells are waterflooded，but also reduces water cut. In addition，large production thickness of oil wells is beneficial to maintain higher oil production rate and better economic benefits，which is worth being applied and popularized. 

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Numerical Simulation Study of Hole Erosion under Directional Perforating Conditions

GUO Xiaodong , CHENG Leiming , ZHANG Jingchen , LI Heng , LI Yan

2022, 18(4):  56-61.  DOI: 10.12388/j.issn.1673-2677.2022.04.010

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Long-interval multi-cluster fracturing is to achieve uniform and effective fracture opening and propagation for each cluster by increasing the interval length and controlling the number of perforation holes. In the process of fracturing，the phenomenon of hole erosion can cause imbalanced fluid feed among clusters，resulting in the failure of uniform fracture propagation. Directional perforating technology can mitigate the impact of hole erosion to a certain extent，but the pattern of hole erosion rate versus perforating angle is still unclear. In this paper，the hole erosion rate under directional perforating conditions is studied using the approach of numerical simulation to investigate the hole erosion pattern for different perforating angles by gradually analyzing from a single cluster to multiple clusters. The results show that the hole erosion rate is the minimum when the perforating angle is 90°，and the difference in hole erosion rates between different clusters is the minimum when the perforating angle is 80°，which can alleviate the negative impact of uneven fluid distribution due to hole erosion. The study findings are of significant reference for field fracturing jobs. 

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Optimization Technology of Water Injection System for Low-Permeability Reservoir in Wellblock S 

LI Benshuang , SI Yuanzheng , LI Lianqun , HE Fengqing , HE Ming , YUAN Peng

2022, 18(4):  62-66.  DOI: 10.12388/j.issn.1673-2677.2022.04.011

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The existing water injection system in Wellblock S mainly had such problems as insufficient equipment capacity，great pressure loss of main pipeline，seriously insufficient injection of injectors，tremendous equipment maintenance volume and cost，and polluted water in the station area. Later，the system was optimized by using the technologies of partial pressure injection，equipment configuration optimization，simulation，non-metallic pipeline for corrosion protection，and closed water injection. After optimization，the increase of daily injection in Wellblock S is 2 115 m3 /d，injection satisfaction rate of injectors is increased by 20.7%，the natural decline rate of reservoir production is decreased by 4.8%，and the efficiency of injection system is increased by 4.1%. Old injectors that failed to satisfy water injection requirements can now meet injection allocation requirements，the corresponding well group has a daily oil increase of 33.4 t，and the annual increase in earnings is CNY 26.75 million. The effect on improving quality and increasing earnings is remarkable. 

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Well Selection Conditions of Velocity String Fluid Drainage and Gas Production Technology

CHEN Rui

2022, 18(4):  67-73.  DOI: 10.12388/j.issn.1673-2677.2022.04.012

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For gas field with high condensate oil content in its produced fluid and unsuitable for foam carrier technology，velocity string fluid drainage and gas production technology is selected. Because the technology has strict requirements for well selection conditions， the well selection conditions for the fluid drainage gas production technology of velocity string have been determined by analyzing such factors as critical liquid-carrying flow rate，liquid production，gas production，gas-liquid ratio，formation pressure，bottom hole flow pressure and remaining recoverable reserves of gas well. After Well P2 was subjected to an application analysis，the optimal size of velocity string，favorable gas-liquid ratio，unflowing pressure and unflowing recoverable reserves have been obtained. It solves the problem that the gas well maintains the production status through external and internal drainage，reduces the loss of natural gas blowout， and eliminates the risk of killing the gas well without timely drainage，which lays a solid foundation for the well selection conditions of this technology in the future.

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Cause Analysis and Countermeasures for Water Flooded Horizontal Wells during Fractur⁃ ing in Z211 Volumetric Development Zone 

LIU Jin , QIN Deqiang , GUO Lin , LIU Kesheng , WANG Yu

2022, 18(4):  74-78.  DOI: 10.12388/j.issn.1673-2677.2022.04.013

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The development of multi-layer reservoirs using horizontal wells for primary well pattern often leads to the failure of effective production of a large number of high-quality reservoirs in the vertical direction. Volumetric development with horizontal wells can realize the effective production of potential layers vertically，offering a solution to this problem. However，in the case of volumetric development with horizontal wells，old wells often get flooded by fracturing fluid during fracturing because the well spacing between new and old wells is too small，resulting in greater productivity loss. In this paper，water flooded wells during fracturing in Z211 Volumetric Development Zone are studied to analyze the mechanism for old wells to get water flooded because of the fracturing of new horizontal wells， and to define the decisive factors causing the water flooded wells. The safety and environmental risks that may arise during the fracturing of new wells，as well as their monitoring techniques and means are elaborated. The countermeasures for mitigating safety and environmental risks and minimizing productivity loss are explained. The patterns of productivity loss and recovery after getting water flooded during fracturing are summarized，and the treatment countermeasures are put forward. The above work provides a basis for mitigating the safety and environmental risks during the execution of the same type of horizontal wells in the later stage in Z211 Volumetric Development Zone，minimizing the productivity loss of old wells，and improving the recovery degree of water flooded wells. 

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Evaluate the Temporary Plugging Effectivity for Fractured Horizontal Wells Through Pump-off Pressure Drop Analysis Method

XU Peng, XIANG Yuankai, LIU Ruining, LU Ming, CHEN Shengen

2022, 18(4):  79-83.  DOI: 10.12388/j.issn.1673-2677.2022.04.014

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In Jimsar，the method of dense cutting+large section and multi-cluster is applied to most of the horizontal shale oil wells that have been subjected to volume fracturing for stimulation. In order to further improve the stimulation effectivity，the method of temporary plugging is used in field to promote even fracture initiation. To evaluate the effectivity of temporary plugging，this paper interprets the reservoir and engineering parameters before and after temporary plugging based on pump-off pressure drop data using fracturing software. According to the comparison and verification made by well testing software，the interpretation results are similar，and the conclusions are reliable and effective. This method is simple，easy to operate，and cost-effective，and provides powerful guidance for field test of temporary plugging. The study results show that after temporary plugging，the closure time of fractures is prolonged，the efficiency of fracturing fluid is improved，and the treatment zone permeability is reduced，which prove that the temporary plugging agent is effective in satisfactorily plugging areas with good physical properties.

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Design Optimization of Downhole Throttling for Gas Wells in Xinjiang Oilfield and Its Application 

DU Junjun , CHI Ming , Xieraili·MAIMAITI , WANG Gang , WANG Wenwen , LIANG Haibo

2022, 18(4):  84-88.  DOI: 10.12388/j.issn.1673-2677.2022.04.015

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In order to meet the requirements of gathering and transportation pressure，and prevent wellhead hydrate freeze bloking，design optimization has been made for the downhole throttling process of high-pressure and medium/low-pressure gathering and transportation regarding well selection conditions，gas nozzle diameter，setting depth，and other key technical parameters based on the technological principle of downhole throttling，and wellbore temperature and pressure profiles have been simulated. The results show that the downhole throttling process can meet the pressure requirements of high-pressure and medium/low-pressure gathering and transportation，and effectively solve the problem of wellhead hydrate freeze bloking. 

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Brief Analysis of the Application of Energy-Conserving Technology for Improving the Pow⁃ er Factor of Oilfield Power Grid

AI Qiang , LI Yong , CHEN Lei , LIU Jiangtao

2022, 18(4):  89-94.  DOI: 10.12388/j.issn.1673-2677.2022.04.016

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With the development of social economy and the improvement of awareness for energy conservation and emission reduction， upholding the philosophy of green development is a scientific reflection of the development law，as well as a positive response to the changes in the global ecological environment. Currently，the issues of industrial power consumption，power conservation，and improving the efficiency of power distribution network have aroused extensive attention of the whole society. This paper analyzes the impact on the power factor of the energy efficiency indicator of the power distribution network during actual production based on the load change and the distribution characteristics of main equipment in the mechanical recovery process of heavy oil fields，and makes discussions in close combination with the power consumption characteristics of oil fields. By applying such technologies as 3-phase equilibrium，inactive compensation and harmonic control，rational planning is made，compensation measures are taken，and effect is validated to ensure the effective improvement in power factor. Thus，a solution that combines the power consumption demand，energy efficiency management and smart grid technology of oil field together is formed to realize the production goal of energy conservation and consumption reduction by optimizing the distribution network environment，obtain satisfactory power conservation and emission reduction effect by improving the efficiency of distribution network，and practice the green development philosophy of energy and power conservation.