Table of Content

10 October 2019, Volume 41 Issue 5

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The Characteristics of the Low Permeability Tight Reservoir in the Shenmu Gas Field and the Evaluation of Horizontal Well Development

WANG Guoting, SUN Jianwei, HUANG Jinxiu, HAN Jiangchen, ZHU Yujie

2019, 41(5):  1-9.  DOI: 10.11885/j.issn.1674-5086.2018.07.20.01

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The Shenmu Gas Field located in the east of the Ordos Basin is a major component of the reservoir and production of gas in the Changqing gas zone. A systematic analysis of the reservoir characteristics, the spatial superposition structure, and the applicability of horizontal well development is of significance in the scientific development of the gas field. The experimental analysis shows that the reservoir rocks in Shanxi and Taiyuan Formation in Shenmu Gas Field are mainly lithic quartz sandstone, lithic sandstone, and quartz sandstone. The pores in the rocks are mainly dissolution pores, intercrystalline pores, and intergranular pores. The porosity of the reservoir ranges from 20% to 10.0% with an average value of 6.6%, while the permeability of the reservoir ranges from 0.10 to 1.00 mD with an average value of 0.83 mD. The reservoir can be classified as a low-permeability and tight sandstone reservoir. The results from gas tests show that a porosity of 5%, a permeability of 0.10 mD, and a gas saturation level of 45% is the lower limit of the physical properties for effective reservoir. Based on the dissection of the close well spacing, the effective spatial structure of the sand body is classified into three types:the multi-layer isolated dispersed type, the vertical multi-stage superposition type, and the lateral multi-stage superposition type. The study shows that the Shenmu Gas Field is not suitable for large scale horizontal well development. Local horizontal wells can be deployed in certain regions.

A Fine Characterization Method of the Interbed in Shallow-water Braided Delta in the PL Oilfield

LIU Jianhua, WANG Libing, ZHAO Jingkang, ZHANG Jun, MENG Yuntao

2019, 41(5):  10-20.  DOI: 10.11885/j.issn.1674-5086.2018.08.06.01

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The fine characterization of the interbed in the reservoir can provide an important basis for exploring the distribution pattern of the residual oil and adjusting the development plan of the oil field. In this study, the interbed in the shallow-water braided delta in the PL Oilfield is re-classified from the perspective of the difference in the characterization method used for the interbed. A layer-by-layer quantitative characterization of the interbed is performed based on the principle of layered modeling. The study suggests that the interbed in the shallow-water braided delta in PL Oilfield can be divided into four types including the spacer interlayer, inter-sand interlayer, sand interlayer, and physical interlayer. These interlayers correspond to the level 6 to level 3 configuration interfaces in the reservoir architecture. Three different modeling methods are used to quantitatively characterize the four different interbeds layer by layer. Specifically, the spacer interlayer and sand interlayer are characterized by a borehole data-based deterministic three-dimensional sand drawing technology, the inter-sand interlayer is characterized using a self-adaptive river-based method with the single sand body controlling during the process, and the physical interlayer is characterized by an equivalent characterization method. The layered quantitative characterization method of the interbed is a simple and practical approach that reflects the reservoir structure and the interbed distribution characteristics in the shallowwater braided delta well.

Characteristics of High-quality Reservoirs in the Braided River Delta in Kenli-A Oilfield

ZHAO Hanqing, GUO Cheng, CHEN Xiaoming, LIU Chao, ZHANG Bo

2019, 41(5):  21-32.  DOI: 10.11885/j.issn.1674-5086.2018.09.02.03

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A clear understanding of the characteristics and genesis of high-quality reservoirs in Kenli A Oilfield in the Laizhou Bay Sag of the Bohai Bay Basin in Upper Es₃ of the Paleogene Shahejie Formation can provide a foundation for oil and gas exploration in the depression. Combining data from drilling, logging, thin section casting, scanning electron microscopy, physical properties, fluid inclusions, and other analytical testing methods, the regional tectonic background, burial history, and sedimentary systems were investigated. The upper reservoir of the Shahejie Formation exhibited characteristics of "high porosity and high permeability" and the reservoir space was shown to be dominated by intergranular pores with relatively welldeveloped micro-cracks. The pore throat can be classified as large-medium or medium-small throat. The reservoir diagenetic effect is generally observed in middle diagenetic stage A, which is characterized by "medium compaction, strong dissolution, and weak cementation". The formation of high-quality reservoirs is affected by four main aspects:Tectonic setting, sedimentary environment, diagenesis, and overpressure of the formation. Reservoir development in the southern slope of the Laizhou Bay Sag is zonal, where high-quality reservoirs develop on the inner side of the gravity slip fault (F₁), providing a favorable area for oil and gas accumulation.

Ordovician Fractured-vuggy Diagenetic Trap and Its Genesis in Hanikatam Formation

MIN Huajun, JIA Xiangjin, TIAN Jianjun, CAI Quan, ZHAO Shaoze

2019, 41(5):  33-44.  DOI: 10.11885/j.issn.1674-5086.2018.06.06.02

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This study focuses on the analysis of Ordovician fractured-vuggy carbonate diagenetic trap of the Halahatang oil reservoir in the north of Tarim Basin. By combining static and dynamic information such as regional geology, drilling time log, acid fracturing, pressure testing, and production dynamics, we discuss the dynamic identification method, characteristics, and genesis of traps. We hold that the wellhead oil pressure drop can be used to replace the formation pressure drop for plotting the N_p-△p diagram due to the high permeability of fractured-vuggy carbonate oil reservoir. The diagram can be further used to determine if the oil reservoir is an open reservoir or a closed diagenetic trap reservoir. The total number of fractured-vuggy diagenetic traps is relatively small in the area. Cave reservoir being the major type of reservoir. Combinations of multiple other trap elements developed with various lithology of trap cover, reservoir cover combination, and diverse occlusion conditions. The multi-stage filling and stacking is found to be the fundamental cause of the closure of fractured-vuggy diagenetic trap. The diagenetic filling caused by large-scale rapid settlement since the Neogene may be the direct cause of the closure of most fractured-vuggy diagenetic traps. These settlements simultaneously result in abnormal formation pressure in some parts of the reservoir.

An Investigation of the Genesis of Hydrogen Sulfide in Permian and Triassic Gas Reservoirs in Southeast of Sichuan Basin

QIN Hua, PAN Lei, XU Zuxin, MEI Qinghua

2019, 41(5):  45-55.  DOI: 10.11885/j.issn.1674-5086.2018.12.27.02

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In this study, by analyzing natural gas components, hydrocarbon isotopic compositions, flakes, inclusions, and other geochemical features, we investigated the genesis of hydrogen sulfide (H₂S) in the gas reservoirs of the Changxing, Feixianguang, and Maokou Formations of the Permian and the Triassic in the southeast of the Sichuan Basin. The results indicated that the natural gas in these formations is mainly constituted by alkane gas, with an average ratio of non-hydrocarbon of 24.68%. The alkane gas of the analyzed samples was consistently dry. The ethane content of some samples was too low to be detected. Among the samples with a detectable content of ethane, the concentration of ethane ranged from 0.03% to 0.39% (0.15% in average). In contrast, the content of δ¹³C₁ was high across the samples, ranged from -28.3‰ to -35.2‰ (-31.1‰ in average); some samples showed a δ¹³C₁ > δ¹³C₂ inversion. The non-hydrocarbon component was mainly constituted by CO₂ and H₂S, with the concentration of H₂S ranging from 1.0% to 21.7% (5.3% in average). Bitumen of various types, which would suggest histories of oil filling, and cracking of paleo-reservoirs was uncommon in the reservoirs. The hydrocarbon inclusions in calcite veins were predominantly in gaseous state, whereas oil inclusions were rare. By combining our results with published ones, we concluded that the fractured vuggy gas reservoirs of the Maokou Formation in the southeast of the Sichuan Basin (occurring in north Fulin and Qijiang), which barely contained any H₂S, showed no signs of thermal sulfate reduction (TSR) alteration. The geneses of the H₂S contained in the reservoirs of the Feixianguang Formation (in north Fulin), the reservoirs of the Changxing Formation (mainly in north and central Fulin), and the hydrothermal dolomite reservoirs of the Maokou Formation (mainly in central and south Fulin) all showed TSR. Some of the gas reservoirs altered by TSR showed a low H₂S content, which is likely due to recent reduction.In the reservoirs of the Feixianguan Formation, the hydrocarbons participating in the TSR reaction were predominantly in liquid state. However, in reservoirs at other horizons, hydrocarbons were mainly gaseous (methane). This probably depends on the amount of liquid hydrocarbons present in the reservoir when the TSR occurred. In addition, it was found that the TSR reactions took place independently in each reservoir other than being affected by those occurring in the Feixianguan Formation. The source of sulfur for the TSR reaction in the Changxing Formation could have come from the lateral brine discharge of the Feixianguang Formation during the deposition period, while that required in the Maokou Formation could have come from the fluid of the adjacent horizon rich in SO₄^2-.

Relationship Between Densification and Hydrocarbon Filling of the Gaotaizi Oil Layer in the Qijia Area

SI Shanghua, REN Xiang, ZHAO Yutao, WU Weitao, LI Xu

2019, 41(5):  56-66.  DOI: 10.11885/j.issn.1674-5086.2018.12.10.01

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To determine the relationships between the densification and hydrocarbon filling of the Gaotaizi reservoir in the Qijia Area, Songliao Basin, this study employed various methods, such as casting thin sections, scanning electron microscopy, nanoCT, mercury intrusion experiments, fluid inclusion analysis, and the compaction-recovery curve, to examine the microscopic characteristics of the Gaotaizi tight reservoir in detail. And fine description of the formation period of the tight reservoir was made. The findings were integrated with the evolutionary characteristics of reservoir pores to discuss the relationship between the densification processes and hydrocarbon filling in the region. The results indicate that the Gaotaizi tight reservoir in the Qijia Area is dominated by lithic feldspar-bearing sandstones followed by feldspar-bearing lithic sandstones. The reservoir pores are mainly residual intergranular and dissolution pores and they are mostly submicron-nano in size, with good pore and throat connectivity. Reservoir densification occurred in the Lower Mingshui Formation. There are two phases of hydrocarbon filling in the Gaotaizi oil layer in the region. The first occurred during the period 79~75 Ma, corresponding to the formation of the Upper Nenjiang Formation. The second phase occurred during the period 69~65 Ma, when the Lower Mingshui Formation formed. The Gaotaizi reservoir in the Qijia Area, Songliao Basin has undergone multiple formation periods which were accompanied by densification.

A Method for Calculating Reservoir Fracture Porosity Based on the Porous Media Model

LU Yunlong, CUI Yunjiang, LI Ruijuan, WANG Peichun

2019, 41(5):  67-74.  DOI: 10.11885/j.issn.1674-5086.2018.08.12.02

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To address the difficulty of calculating the fracture porosity of fractured reservoirs, a calculation method based on the porous media model is proposed. The pore aspect ratio spectrum function is defined to characterize the distribution of rock fractures and its effect on the macroscopic petrophysical characteristics of rocks. This function is added to the porous media model to account for the fractures. Theoretical calculations show a correlation between the distribution of the pore aspect ratio spectrum and the change in the bulk modulus of rocks. An inverse function of the rock modulus is also defined, and the array of acoustic logging data obtained from field measurements is utilized for the inverse calculation of the pore aspect ratio spectrum. Finally, this result is used to calculate the fracture porosity. Results obtained from actual data demonstrate that the calculation fracture porosity can better reflect the fracture development of the reservoirs and is in good agreement with the calculation results of electrical imaging logs. The fracture porosity calculated by the method proposed in this paper is consistent with the actual production of the reservoirs. Therefore, the method is considered suitable for the calculation of fracture porosity and expands the applications of array acoustic logging.

Smart Prediction of the Three-dimensional Stress Field of Block Yi 176 of the Bonan Oilfield

XU Ke, WANG Bifeng, FU Xiaolong, SHI Da

2019, 41(5):  75-84.  DOI: 10.11885/j.issn.1674-5086.2018.06.24.02

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In this study, an intelligent prediction of the three-dimensional stress field of block Yi 176 of Bonan Oilfield is performed by combining the modeling technology of Petrel and ANSYS and using the construction technology of a threedimensional heterogeneous rock mechanics field. To improve the computational efficiency of the numerical simulation of the stress field, the boundary condition, which is traditionally set manually, is now set automatically using the self-adaptive boundary program developed by the APDL program in ANSYS. The results show that the self-adaptive boundary program can greatly reduce the time taken to set the correct boundary conditions by repetitive manual trials. This approach can improve the efficiency of stress field simulation while ensuring prediction accuracy. The maximum horizontal principal stress of block Yi 176 follows an EW-SEE direction in general. The boundary fault has a significant impact to the stress direction, causing a deflection of around 5°~10°. The in-situ current stress value varies substantially with a high level of discreteness and a belt-like distribution in the plane. Furthermore, the stress is found to be higher in the north region and smaller in the south region. In the current formation, the stress belongs to the type I_a in-situ stress. The heterogeneity of the rock is the main cause of the difference in stress values. In general, a belt-like distribution of "stress dessert" is found in the central part of block Yi 176, which can be used as an advantageous area for well location deployment and fracturing operations.

Improving the Recovery Efficiency and Sensitivity of Tight Oil Reservoirs by Dissolved Gas Reinjection

WEI Bing, SONG Tao, ZHAO Jinzhou, VALERIY Kadet, PU Wanfen

2019, 41(5):  85-95.  DOI: 10.11885/j.issn.1674-5086.2019.07.06.01

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To address the rapid decline in production of horizontal wells in tight oil reservoirs and low recovery of the depletion development mode, a method for improving oil recovery by reinjected dissolved gas in the late stage of depletion development is proposed. Based on the geological reservoir characteristics of the Baikouquan Formation in the Manas Lake Depression, Xinjiang, a multi-stage fracturing bilevel well mechanism model for tight oil reservoirs was established. The production characteristics and sensitivity of the above methods in tight oil reservoirs were systematically studied. The results show that dissolved gas reinjection can effectively improve the recovery efficiency of tight oil reservoirs and alleviate the rate of decline in horizontal-well production. The degree of recovery increases with the injection volume, injection speed, and huff-n-puff rounds. The diffusion of gas molecules can increase the scope of the matrix response and increase the action radius of the gas. Using dissolved gas for a weak heterogeneous reservoir (variation coefficient of 0.2) to enhance oil recovery can achieve the best effect. Sensitivity analysis demonstrates that the number of huff-n-puff rounds is the most important factor in increasing recovery with dissolved gas reinjection, followed by injection time, injection speed, diffusion coefficient, and soak time. In addition, the proposed model can accurately predict and optimize the oil recovery from tight oil reservoirs by dissolved gas reinjection.

An Experimental Study on Enhanced Foam Anti-gas Channeling in the Yumen H Low Permeability Fractured Reservoir

HU Lingzhi, ZHAO Jinzhou, WEI Peng, ZHANG Yiwen

2019, 41(5):  96-104.  DOI: 10.11885/j.issn.1674-5086.2019.06.19.02

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In a pilot test of the oxygen-poor air drive in the Yumen Oilfield, the three production wells had premature gas channeling, which caused a substantial drop in the liquid and oil production and affected normal production. The foam properties of different formulations with a salinity of 8.3×10⁴ mg/L and a temperature of 114℃, were determined with the Waring Blender method. The optimal formulation was determined:0.2%WP4 + 0.3% NS enhanced foam system. The stability at high-temperature and high-pressure, the plugging of low permeability cracks, and the EOR effect of oxygen-poor air foam injection after gas drive studied. The results show that the stability of the enhanced foam is improved under high-pressure. It can also increase the resistance of the fluid flowing in the matrix and the cracks and can control the fluidity. The resistance factor is between 5.09~38.66. Enhanced foam profile control and displacement after oxygen-poor air drive can increase the recovery efficiency of core by 16.70%~38.11%.

Channeling Characteristics and Profile Modification Measures for Polymer Flooding in Conglomerate Reservoirs in Xinjiang Oilfield

TANG Ke, JI Ping, WANG Xuehua, LUO Qiang

2019, 41(5):  105-111.  DOI: 10.11885/j.issn.1674-5086.2018.07.11.01

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Polymer flooding channeling is an important factor affecting polymer flooding. Targeting the complex mode pore structure, which is special to the conglomerate reservoirs in Qidong-1 Area, crossflow characteristics and profile modification measures of polymer flooding were studied through physical simulation experiments conducted indoors in parallel with those at the rock cores. The study shows that, when the permeability variation coefficient of the conglomerate reservoirs is less than 0.3, no crossflow occurs in polymer flooding; when it is larger than 0.5, the effect of profile improvement by the polymer is limited, and channeling occur, which lead to a rapid rebound in water content of highly permeable cores after polymer flooding takes effect. As the permeability variation coefficient increases, the time taken for the polymer to break through the highly permeable layer is shortened, channeling occur earlier and more severely, and subsequently, the percentage of liquid absorption in the highly permeable layer is increased from 52% to 75%. With timely profile modification after channeling, channeling can be effectively controlled while polymer flooding takes effect, increasing the recovery rate by 28.75%.

Oil Displacement Performance of Rhamnolipid Fermentation Broths

DING Mingshan, WANG Jing, LIN Junzhang, WANG Weidong

2019, 41(5):  112-119.  DOI: 10.11885/j.issn.1674-5086.2018.08.30.01

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In view of the unvaried nature of current oil displacement systems and uncertainty about the action of rhamnolipids in oil displacement and oil field development, the mechanisms and performance of rhamnolipids in oil displacement were investigated in the present study. Fermentation broths consisting primarily of two types of biosurfactants, viz. mono-rhamnolipids and di-rhamnolipids, were obtained via indoor fermentation, and the interfacial performance, wettability, oil washing efficiency, and oil displacement efficiency of the fermentation broths were assessed. The rhamnolipid fermentation broths were highly resistant to heat and salt, and the interfacial tensions between the 1% fermentation broths and crude oil were 0.2~0.5 mN/m. Assessments of the wettability and oil washing efficiency of the fermentation broths showed that di-rhamnolipids resulted in a greater improvement in wettability and achieved an oil washing efficiency of 90.1%, an increase of 15% compared to that of the mono-rhamnolipids. It was found that rhamnolipids could reduce the work of adhesion between crude oil and the substrate from 30.2 mN/m to a minimum of 0.059 8 mN/m (achieved with di-rhamnolipids), and that this was a key factor in the enhancement of oil washing efficiency by the fermentation broths. Assessment of oil displacement efficiency revealed that the di-rhamnolipid fermentation broth increased the oil displacement efficiency by 12.3% based on a water-oil displacement efficiency of 42.16%, thereby exhibiting great potential for field applications.

An Experimental Study on the Optimization of Converting Time of Binary Combination Flooding Systems

ZHANG Xiaoqin, ZHU Shijie, SHI Leiting

2019, 41(5):  120-126.  DOI: 10.11885/j.issn.1674-5086.2018.12.07.03

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Polymer flooding exacerbates the heterogeneity of the reservoir and the difficulty of starting the sweep of the remaining oil. The use of combination flooding to reduce the synergy between interfacial tension and fluidity control can further enhance oil recovery. Indoor flooding experiments and converting time studies were carried out using combination systems with different performances. The results show that the ratio of fluidity control and the reduction in interfacial tension to the oil displacement effect in the combination system is 1.2:1.0. Using the difference between the water flooding characteristics and the subsequent water flooding characteristic formulas of different nodes, a quick determination of optimal converting time for polymer flooding was established; i.e., the effect is best when the converting time occurs at the end of the polymer flooding and the beginning of the subsequent water flooding phase. The optimized compound system under the experimental conditions is primarily based on fluidity control, and the interfacial tension is reduced to 10^-1~10^-2 mN/m. The best converting time for compound flooding is at the beginning of the subsequent water flooding 0.14 PV after the end of the polymer flooding, which is suitable for excavating the oil remaining after polymer flooding.

Calculation Model of Shale Gas Adsorption Capacity Under Supercritical Conditions

ZHAO Jun, LIU Kai, YANG Lin, HE Yufei

2019, 41(5):  127-133.  DOI: 10.11885/j.issn.1674-5086.2018.08.28.02

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Shale gas adsorption capacity is a key parameter in determining the development value and life of shale gas wells. The existing Langmuir isotherm adsorption model for the adsorption of monolayers is not suitable for the reservoir conditions of shale gas in China. Therefore, the main factors affecting shale gas adsorption capacity were studied by isothermal adsorption experiments at different temperatures and fitting of the isothermal adsorption curves. The analysis shows that the main factors are formation temperature and pressure, porosity, organic matter content and maturity, and mineral composition and content (including clay minerals as direct factors). Based on the Polanyi adsorption theory, a quantitative calculation model of shale gas adsorption that considers temperature, pressure, porosity, organic matter content and maturity, and mineral composition and content was constructed. The calculation results are consistent with the results of the analysis of gas content from on-site core sampling. The new model considers supercritical adsorption, which compensates for the shortcomings of the monolayer adsorption model that is currently in use, and has important practical significance for shale gas adsorption capacity calculation.

Method to Predict the Self-supporting Fracture Conductivity of Shale

CAO Haitao, GUAN Xiaoxu, LI Xiaoping, ZHAO Yong, YU Xiaoqun

2019, 41(5):  134-141.  DOI: 10.11885/j.issn.1674-5086.2019.03.27.05

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The production capacity of shale gas wells primarily depends on the conductivity of the proppant filling layer fracture and the self-supporting fracture formed by the shear slip of the reservoir. Currently, our understanding of the variation law and mechanism that influences the self-supporting fracture conductivity of shale is insufficient. The fractal theory method was used to introduce the fractal dimensions of fracture aperture and tortuosity to characterize the fracture space quantitatively, and a mathematical model of self-supporting fracture conductivity was established that considers the effect of closure stress. An experiment of self-supporting fracture conductivity was conducted. The results show that the initial fracture conductivity reached 30~50 D·cm and could be maintained above 1 D·cm under a closure pressure of 40 MPa. The theoretical model prediction results agree well with the experimental test results. The sensitivity analysis shows that the fractal dimension of fracture aperture is positively correlated with the conductivity, while the fractal dimension of tortuosity is negatively correlated with the conductivity. The proposed method can quickly and accurately predict the self-supporting fracture conductivity of shale and provide support for rational prediction of gas well productivity.

New Optimization Design Method for Perforation Parameter Based on Optimal Perforation Depth Analysis

LI Jin, XU Jie, WANG Kunjian, HAN Yaotu, QI Yanlai

2019, 41(5):  142-149.  DOI: 10.11885/j.issn.1674-5086.2018.09.12.02

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As one of the main completion methods, perforated completion is especially important for the connection between reservoirs in cased wells, removal of the near-wellbore pollution, and maximization of production capacity. As such, design of the perforation parameter is the key to the effect of perforation. Existing design methods for perforation parameter mainly perform sensitivity analysis of the perforation parameter through surface calculations, and undertake parameter design according to curve shape, distribution density, and changing trend. As the calculation model for perforated surface does not effectively consider the influence of the flow friction of perforation tunnels, it is impossible to describe the accepted understanding of the relationship between the perforation depth and the production capacity accurately. Thus, the optimal perforation depth cannot be determined based on the results of parameter sensitivity analysis of the surface. From the perspective of fluid mechanics, the perforation tunnel can be viewed as equivalent to the horizontal well at microscale, and a coupled mathematical model of the flow between the reservoir and the perforation is established, which fully considers the influence of the flow friction of the perforation tunnels. Based on the Dikken optimization principle, a determination method for the optimal perforation depth is established, yielding a new design method for the perforation parameter based on optimal perforation depth analysis.

Optimization of Steady Operation of Large Scale Natural Gas Pipelines

LIU Enbin, KUANG Jianchao, Lü Liuxin, LIU Yuan, ZHANG Lu

2019, 41(5):  150-160.  DOI: 10.11885/j.issn.1674-5086.2018.12.12.01

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To address the high energy consumption of the compressor station of natural gas long-distance pipelines, a pipeline operation optimization model was established based on the dynamic programming method. The optimization variables are the compressor starting quantity and the outbound pressure. The objective function is the lowest total energy consumption of largescale natural gas pipeline compressor stations. Using this model and using the pipelines of the West-East Gas Pipeline I as an example, the operation optimization results of the 22 compressor stations and 32 compressors for the entire line were solved within 60 s, which demonstrates that the dynamic programming method is fast and effective. An analysis of the optimization results indicates that the optimized operation scheme has two more compressors compared with the actual operation scheme. The total pressure drop of the pipeline is reduced by 3.40 MPa, the average efficiency of the gas turbine unit is increased by 4.23%, and the average efficiency of the electric drive unit is increased by 4.88%. The total compressor power is reduced by 18 720.38 kW, and the production unit consumption is reduced by 16.24 kgce/(10⁷ Nm³·km). The optimized operation scheme can greatly reduce the total energy consumption of the West-East Gas Pipeline I, thus verifying the correctness and feasibility of the optimized model.

Equation Derivation and Verification for Hoop Stress and Load of C-ring

LIAN Zhanghua, LIANG Jiankun, WANG Yuhai, ZHANG Qiang, MOU Yisheng

2019, 41(5):  161-168.  DOI: 10.11885/j.issn.1674-5086.2018.08.03.01

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Based on the structural dimensions and mechanical relation of an arbitrary C-ring specimen, a mechanical model for an arbitrary cross section within a C-ring was established. According to the fundamental theories of mechanics of materials, a theoretical equation was derived to describe the relation between the hoop stress at any point on the outer and inner walls and the loading displacement and load of a C-ring specimen. To verify the equation derived in this study, a mechanical model of C-ring specimen based on finite element method was established. The C-ring specimen test required the largest hoop tensile stress to be 650 MPa. The results of the finite element method and theoretical equation were compared for a C-ring specimen with tubing outer diameter of 88.9 mm. The error of load and displacement obtained by using the finite element method and the theoretical equation were -1.82% and 1.25%, respectively. The results verify the theoretical equation, which provides a simple calculation method for determining the experimental loading parameters of sulfide stress corrosion cracking and stress corrosion cracking tests on C-ring.

Structural Dynamic Characteristics of Sidewall Contact System in Logging Instrument

REN Tao, FENG Bin, SUN Wen, ZHANG Chunlin, TANG Daolin

2019, 41(5):  169-180.  DOI: 10.11885/j.issn.1674-5086.2018.07.10.02

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To accurately understand the wall contact characteristics of microsphere plate during logging operation and to ensure stable and efficient microsphere focusing logging, a kinematic model of the primary transmission mechanism of the sidewall contact system was established. The model carried out kinematic computations by adopting the closed-loop vector chain method. Based on the above, static dynamic analysis was carried out for each bar member in the sidewall contact system. Motion and dynamic constraint equations governing all the transmission members of the microsphere sidewall contact system under different constraints were derived. The motion pattern of the higher pair mechanism of two pin chutes on the microsphere plate and the link arm were studied extensively; Further, the dynamic performance parameters of the sidewall contact plate and arm were also studied. Through ADAMS, a kinematic and dynamic simulation model of multi-rigid body was established for the microsphere sidewall contact system, and the kinematic and dynamic performances of the sidewall contact system were analyzed. By comparing the simulation results with those from the mathematical model of the microsphere sidewall contact system, the model was verified. Furthermore, the dynamic parameter curve and motion pattern of each transmission member of the microsphere sidewall contact system were obtained.

Influence of Applied Potential on Stress Corrosion Cracking of X80 Steel in Manchurian Soil

ZHANG Wenjian, ZHU Zongxiang, XIAO Peng, CHEN Yuzhong, DONG Shuai

2019, 41(5):  181-188.  DOI: 10.11885/j.issn.1674-5086.2018.10.12.02

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Stress corrosion cracking (SCC) of X80 pipeline steel (X80 steel) in a simulated Manchurian soil solution was studied, with the aim of providing data to support the design of methods to prevent SCC in X80 steel used for manufacturing buried pipelines. By means of an AC impedance technique, a potentiodynamic polarization technique, and slow strain rate tensile tests, the SCC behavior of X80 steel in simulated Manchurian soil solution was investigated under different applied potentials, and the microscopic morphologies of the fracture surfaces were observed using a scanning electron microscope. The results indicated that the self-corrosion potential led to the initiation of cracks at corrosion pits in X80 steel, with anodic dissolution (AD) being the mechanism underlying SCC. Applied potentials of -850 mV and -930 mV provided inhibitory effects against SCC in X80 steel, and reduced sensitivity to SCC; in particular, -850 mV was determined to be the optimal cathodic protection potential. Under these two potentials, SCC in X80 steel occurred via a combination of AD and hydrogen-induced cracking (HIC), with HIC being the dominant mechanism of SCC under the applied potential of -930 mV. Under applied potentials of -1 000 mV and -1 200 mV, X80 steel exhibited higher sensitivity to SCC, with SCC occurring via HIC through the synergistic effects of hydrogen and stress.