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    10 June 2019, Volume 41 Issue 3
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    ACADEMICIAN THOUGHTS
    On the Energy Revolution and the Mission of Science and Technology
    ZOU Caineng, PAN Songqi, DANG Liushuan
    2019, 41(3):  1-12.  DOI: 10.11885/j.issn.1674-5086.2019.04.07.01
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    Energy is a country's driving force towards power and the cornerstone of national security. The world's energy development is currently entering the third stage of the transition from coal, oil, and gas to new energy sources. This stage is characterized by a new combination of energy supply worldwide:33% from petroleum, 24% from natural gas, 28% from coal, and 15% from new energy sources. However, China still has a coal-based energy, as its "coal-rich and oil-and-gas-lacking" energy endowment has led to an energy supply structure of "one leader with three followers":59% from coal, 19% from petroleum, 8% from natural gas, and 14% from new energy sources. It is therefore necessary to initiate a revolutionary process of transformation of the energy structure, in order to achieve a condition in which the energy supply is provided by a more balanced combination of coal (40%), oil and gas (31%), and new energy sources (29%). China's petroleum industry is undergoing a transformation from conventional to unconventional oil and gas resources; thus, it currently can be defined as a "mixed conventional-unconventional" oil and gas industry. At the same time, the industry is undergoing a "theoretical revolution" from the exploitation of single-entrapment oil and gas reservoirs to that of "sweet spot areas" on a large scale, a technological revolution from the use vertical natural wells to that of fractured horizontal well networks of "man-made reservoirs", a management revolution from manual operations to intelligent and low-cost development, and a strategic revolution from energy politics to reshaping the energy balance. China has chosen the strategies of "reducing coal, stabilizing petroleum, and increasing gas" and "vigorously developing new energy sources" as the two paths towards energy transformation. At the same time, China is facing "three major challenges":the need to achieve a clean coal utilization, the rising dependence on imported oil and gas, and the uncertainty about the future pillar industries of the new energy. In order to overcome these challenges, China needs to establish the "three major strategic areas" of coal, oil and gas, and new energy sources, by carrying out "four major revolutions" concerning the energy supply, consumption, technical aspects, and overall system; exploiting the "five major opportunities" presented by the current national policy (the "One Belt One Road" strategy); pursuing a new round of oil price recovery and a large-scale development of natural gas; and working in the direction of a technological revolution in the new energy resources so as to complete the historical mission of China's energy transformation. The development of social civilization and the progress of science and technology are two driving forces for energy transformation, with the former being the internal driving force and the latter the fundamental driving force. The transition from traditional fossil energy to non-fossil new energy sources is the inevitable trend and the inevitable choice of energy development.
    GEOLOGY EXPLORATION
    The Spatial Distribution of Elastic Parameters of Orthotropic Rocks
    GUI Junchuan, CHEN Ping, MA Tianshou
    2019, 41(3):  13-28.  DOI: 10.11885/j.issn.1674-5086.2018.09.21.02
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    The mechanical parameters of rocks are the basic parameters for studying the wellbore stability and fracturing reformation. Their values can be calculated based on the stiffness matrix. Currently, the models used for calculating the mechanical parameter of rocks based on the stiffness matrix consider the formation as a VTI medium. This approach failed to take into consideration of the significant amount of ORT features in the actual formation and the effect of observation coordinate systems on the mechanical properties of rock. In this study, the expression of the stiffness parameter used for calculating the rock mechanical parameters was derived based on the constitutive equation of rock and considering the ORT features of shale gas formations. First, the expression of the stiffness matrix used for calculating the rock mechanical parameters was derived from the constitutive relation of the rock. Next, by considering the intersection angle between the wellbore and the stratum, combining the definition of mechanical parameters for rock, and performing coordinate transformation, a method for calculating the mechanical parameters of rocks was established in the observation coordinate system. The mechanical parameters of rocks in different observation coordinate systems were also analyzed and compared. Finally, considering that the actual formation is composed of shale-sandstone interbeds, we analyzed the influence of the variation in sandstone content on the mechanical parameters of rock in the observation coordinate system.
    Hydrocarbon Generation Potential and Pore Characteristics of Chang 7 Oil Shale in the Zhangjiawan Region
    TANG Jianyun, ZHANG Gang, FAN Hongwei, LIU Jiantong, CHEN Yubao
    2019, 41(3):  29-41.  DOI: 10.11885/j.issn.1674-5086.2018.03.12.01
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    Hydrocarbon generation potential and pore characteristics of Chang 7 oil shale from the Yanchang Formation in the Zhangjiawan Region of the Zhiluo Oilfield were examined in this study. We conducted petrological and organic geochemical analyses, and methods like scanning electron microscopy and argon ion milling were used to analyze the distribution, geochemical characteristics, and pore characteristics of the Chang 7 shale in the study area. The results reveal that the Chang 7 black lake shale from the Yanchang Formation in the study area is heterogeneous both horizontally and vertically. It is thick in the northwest, but thin in the southeast. The organic matter in the Chang 7 oil shale are primarily type I and Ⅱ1 and are highly mature. Therefore, the shale is a desirable hydrocarbon source rock. The shale reservoir is a type 1 enrichment reservoir. The pores of the reservoir are mainly intergranular pores, intercrystalline pores, dissolution pores, and organic pores, where the pore sizes are mostly <0.5 μm. The throat radius ranges from 100 to 750 nm. There is a relatively porosity range (0.5% to 1.9%) with an average of approximately 1.0%. It is believed that the "newly discovered" Chang 7 shale in the study area has relatively great hydrocarbon generation potential, with a relatively high content of movable oil.
    Sinian-Cambrian Natural Gas Reservoir Formation Shown by Segmented Capture of Oil and Gas
    LIU Huan, LI Minglong, JIANG Lin, XIA Jiwen, WANG Tingdong
    2019, 41(3):  42-50.  DOI: 10.11885/j.issn.1674-5086.2018.10.27.01
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    Hydrocarbon generation from source rocks follows specific temporal and spatial sequences while tectonic activities and trap formation have different stages. In addition, large volumes of pyrolysis gases resulting from enriched paleo-reservoirs and scattered residual crude oil will migrate and accumulate. Therefore, reservoir formation may undergo multiple stages. The principle of segmented capture of oil and gas was employed to analyze the Sinian-Cambrian natural gas reservoir formation processes and patterns of the three typical reservoir architecture types. The studied reservoirs are the Weiyuan, Ziyang, and Gaoshiti-Moxi in the southern part of the Sichuan Basin. The reservoir formation probabilities of other unknown areas can thereby be estimated. It is concluded that, the Sinian-Cambrian traps in the Gaoshiti-Moxi Area, being a succeeding paleouplift, captured oil and gas formed during nearly all stages. This occurred from the early hydrocarbon generation from source rocks to the late-stage gas generation from kerogen. Meanwhile, the Weiyuan and Ziyang areas only captured oil and gas resulting from some stages. For an unknown area, namely the Luzhou Uplift, it is possible to capture the natural gas resulting from the peak generation stage and the subsequent stages. These include the pyrolysis gases from scattered residual crude oil and late-stage kerogen. If the configurations of the reservoirs and traps are well determined, the area has a great potential for natural gas exploitation.
    Genetic Types and Distribution of Crude Oil in Weixi'nan Depression, Beibuwan Basin
    YANG Xibing, JIN Qiuyue, HU Lin, HU Desheng
    2019, 41(3):  51-60.  DOI: 10.11885/j.issn.1674-5086.2018.08.14.01
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    In this work, the characteristics of the source rocks in the Weixi'nan Sag are analyzed, based on a large amount of data from saturated hydrocarbon chromatography, mass spectrometry chromatography, and carbon isotope ratios, which were obtained from rock and crude oil samples. According to their geochemical characteristics, the source rocks are classified into three types (A, B, and C). Differences in the organic geochemical characteristics of the crude oils in the Weixi'nan Sag are also analyzed systematically, and their physical properties are analyzed statistically. Based on the genetic types according to the strontium, decane, and saturated hydrocarbon compositions, the crude oils are classified into five subgroups (A, B1, B2, C1, and C2). A detailed comparison of oil sources, and the analysis of the spatial distribution of the crude oil, show that type-A crude oil originates from type-A source rock, and is mainly distributed near fractures No. 1, 2, and 3, on the slopes in the southeast of the Weixi'nan Sag. Type-B1 and type-B2 crude oils originate from type-B source rock; type-B1 crude oil is mainly distributed near fracture No. 2, and type B2 crude oil is mainly concentrated near fracture No. 3. Type-C1 and type-C2 crude oils come from type-C source rock; type C1 crude oil is distributed in areas close to those of type-B2 crude oil, while type-C2 crude oil is mainly concentrated at the intersection between fracture No. 2 and fracture No. 3.
    Characteristics and Identification of Seismic Reflection in Heterogeneous Beach Reservoirs
    DAI Ruixue, RAN Qi, GUAN Xu, LIANG Han, LAI Qiang
    2019, 41(3):  61-70.  DOI: 10.11885/j.issn.1674-5086.2018.01.11.02
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    The Longwangmiao Formation Reservoir in the middle of the Sichuan Basin is highly heterogeneous, leading to diversified seismic reflection characteristics. Hence, based on in-depth analyses of actual drilling data and forward modeling, the seismic reflection modes in the Longwangmiao Formation Reservoir are summarized in order to delineate which distribution favors beach reservoirs. Beach reservoir variations in the Longwangmiao Formation are examined based on actual drilling data. It is believed that the main body of the Moxi Reservoir is more developed, and the reservoir in the peripheral areas is generally thinner with higher heterogeneity. There are five seismic reflection modes in the Longwangmiao Formation in the middle Sichuan area. In particular, reflection characteristics such as troughs at upper boundaries, strong internal peaks, and double peaks are characteristics of favorable seismic responses in the Longwangmiao Formation. A beach reservoir can be effectively identified based on the idea that lower reservoir boundaries correspond to highlight crests and that reservoir development influences reflection from the upper boundaries in the Longwangmiao Formation. In particular, contiguous beach reservoirs develop along the main body of the Moxi Reservoir, while northeast-striking banded point beaches develop in the peripheral areas.
    A Study on Fracture Modelling of the Bedrock Reservoir in Dongping Gas Field, Qaidam Basin
    ZHAN Diao, SHAO Zhenpeng, ZENG Li, WANG Yingjun, TONG Lin
    2019, 41(3):  71-79.  DOI: 10.11885/j.issn.1674-5086.2018.09.09.03
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    The bedrock gas reservoir in the Dongping Gas Field is a rare and unconventional fractured gas reservoir, and it is challenging to model the development and distribution of the naturally occurring fractures in the area. We aimed to solve this problem by establishing a Discrete Fracture Network (DFN) model of the bedrock reservoir based on the spatial characteristics of the reservoir in the Dongping gas field. We first divided these natural fractures in the Dongping Gas Field into two roughly perpendicular groups based on fracture characteristics measured in image logs, such as the inclination angle and azimuth, and we modelled the density distribution of each group. A DFN model was then built using a fracture density curve as the target curve and seismic attributes as constraints. By extracting attribute parameters such as fracture density, porosity, and permeability, we studied the distribution characteristics of the fractures in the Dongping bedrock reservoir. The results showed that these fractures are generally controlled by faults, and there is strong non-uniform development along both horizontal and vertical axes. Finally, this paper validates that the DFN model is suitable for bedrock reservoirs by demonstrating fitting between the dynamic characteristics of production in the Dongping bedrock reservoir and the modelled production of the gas reservoir.
    OIL AND GAS ENGINEERING
    Effects of Morphology of Hydraulic Fractures on Acid Etching Behaviors and Fluid Diversion Capacity
    GOU Bo, LI Xiao, MA Huiyun, ZHOU Changlin
    2019, 41(3):  80-90.  DOI: 10.11885/j.issn.1674-5086.2018.10.28.01
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    At present, most simulations of hydraulic fractures are conduced based on the assumption of smooth parallel plates, ignoring the effects of the morphology of the fractures on acid etching behaviors and fluid diversion capacity. A self-developed device named "acid pressure test system for fracture fluid diversion" was used to simulate smooth and rough fractures, respectively, with smooth and rough plates to study the characteristics of acid etching behaviors and diversion capacity of the two types of fracture morphology with different acid injection volumes and periods. The results show that the tortuosity of the fracture profile increased after acid etching for smooth fractures, whereas the opposite was observed for rough fractures, as acid etching reduced the peaks and deepened the troughs. Increasing the acid injection volume or period led to significantly larger change in elevation, fracture width, acid dissolution amount, and diversion capacity for rough fractures than for smooth fractures, whereas the former had not only better retention ability of fluid diversion, but also higher sensitivity to changes in acid injection parameters. In conclusion, the assumption of rough plates is beneficial for realistically evaluating the diversion capacity of acid pressure fractures under reservoirs, thus improving the targetedness of the acid pressure scheme design and the acid pressure effect.
    Evaluation Method for Development of Gas Condensate Reservoir Based on Fuzzy Mathematics
    ZHAO Kunshan, WANG Yong, DING Lijuan, CUI Can, HE Haibo
    2019, 41(3):  91-99.  DOI: 10.11885/j.issn.1674-5086.2018.11.22.01
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    At present, gas condensate reservoirs commonly adopt the depletion development mode. However, only a few evaluation methods are suitable for the depletion assessment of gas condensate reservoirs. Targeting this problem, a study on the evaluation method for the depletion effect of gas condensate reservoirs was performed. Key parameters affecting the depletion effect of gas condensate reservoirs were selected to establish a production index system reflecting the development degree. Fuzzy mathematics was used to analyze to which extent key parameters affect the development degree, and a theoretical chart for the evaluation of the development effect was developed. The goodness of fit between the curves from actual data and the theoretical chart was used as the scoring criterion to establish a new method suitable for assessing the development of gas condensate reservoirs through depletion. Analysis using real examples shows that this method can comprehensively evaluate the development of gas condensate reservoirs through depletion from five aspects:production capacity, formation energy, degree of water flooding, recovery, and composition of well. The results are comprehensive, accurate, and reliable, capable of providing guidance for production on site.
    An Assessment of the Profile Control Capability of an Active Polymer for Offshore Q Oilfield Applications
    WU Binbin, CHEN Bin, WANG Chengsheng, WU Xiaoyan, ZUO Qingquan
    2019, 41(3):  100-106.  DOI: 10.11885/j.issn.1674-5086.2017.11.07.20
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    The profile control capability of an active polymer was studied to address the issues of high heterogeneity and overall high water content with offshore Q Oilfields. The viscosity-improvement capacity and interfacial activity of the active polymer were examined by a rheometer and an interfacial tensiometer, respectively. An indoor physical simulation experiment was then performed to examine the active polymer for its injection properties, oil displacement capability, and displacement efficiency using various methods of injection. The experimental results showed that, compared to common polymers, the active polymer showed better viscosity-improvement capacity, with low concentration but high-viscosity. At a concentration of above 400 mg/L, it resulted in an oil-water interfacial tension of below 11 mN/m. It was capable of in-depth profile control, as demonstrated by the evident pressure increase at the end of the rock core into which it was injected. Its oil displacement efficiency was 8.66% higher than that of common polymers of the same viscosity. In addition, it could improve the recovery rate by up to 22.34% when used along with water for alternative injection.
    Prediction of Gas-liquid Two-phase Flow Patterns in Horizontal Gas Wells
    LIU Yonghui, LUO Chengcheng, LIU Tong, REN Guirong, WANG Zhongwu
    2019, 41(3):  107-112.  DOI: 10.11885/j.issn.1674-5086.2018.06.11.01
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    An accurate estimation of the flow pattern of a horizontal gas well that produces water is the key to predicating the pressure drop of the wellbore and establishing a sensible water-drainage production plan. The angle of a horizontal well constantly varies from 90 ° to 0 according to the flow direction. A unified flow pattern map that describes the two-phase flow of horizontal wells has not yet been discovered. Therefore, three separate flow pattern maps are used to describe the horizontal, slanted, and vertical pipes individually. These maps are obtained under extremely different experimental conditions. In addition, the gas wells may produce extremely low water output. In such cases, the gas-liquid ratio may exceed the valid coordinate range of the commonly used gas-liquid two-phase flow pattern map leading to significant errors in the prediction results. Considering all these drawbacks, this study has developed an air-water two-phase flow simulation experimental device for horizontal, slanted, and vertical pipes. Provided the extremely high gas-liquid ratio of the gas well with water production, this study has conducted a gas-water two-phase flow pattern experiment using 7 slanted pipes and 641 horizontal pipes. It has summarized five flow patterns and the typical characteristics of horizontal gas wells. This work has used the dimensionless gas velocity number defined by Duns and Ros and the pipe inclination angle as the X-axis. A three-dimensional flow pattern map has been constructed to describe the gas-liquid two-phase pipe flow in the horizontal gas well. This study has also proposed a method to predict the flow pattern based on the back propagation neural network model. The pressure measurement results from 20 horizontal gas wells in the gas fields at Western Sichuan indicate that the flow map demonstrates an accuracy of 90% in prediction.
    Productivity Model and its Influencing Factors for Multistage Fractured Horizontal Wells in Low Permeability Reservoirs
    BAI Hui, TIAN Min, FENG Min, LIU Pengcheng, WANG Haitao
    2019, 41(3):  113-120.  DOI: 10.11885/j.issn.1674-5086.2018.03.24.01
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    Multistage fractured horizontal wells (MFHWs) can greatly improve single well productivity in low permeability reservoirs and improve their development benefits. The accurate calculation of gas well productivity and analysis of related influencing factors are the basis for fracturing optimization and scientific development of gas reservoirs. Herein, a rigorous mathematical model was established for the calculation of MFHW productivity in low permeability reservoirs. Laplace transforms, the superposition principle, boundary discretization method of integral equations, matrix theory, and other mathematical methods were used to successfully solve the proposed model and to perform quantitative calculations and analysis of the production capacity with various influencing factors. The effects on gas well productivity due to the effective thickness of the gas layer, gas reservoir permeability, number of fractures, fracture half-length, and flow conductivity of the fractures were analyzed. The difference in the inflow rate from the stratum to each fracture was also determined. When the effective thickness of the gas layer or the permeability of the gas reservoir increases, the gas well production capacity increases almost linearly. When the number of fractures, fracture half-length, and flow conductivity of the fracture increase, the output increases with an initially higher rate of increase which slows during the later stage. The inflow rate from the stratum to each fracture remains largely unchanged during the early stages, but the difference in the later stage is clear, where the flow rate is greater at the ends compared to that observed in the middle.
    Experimental Study on Adaptive Water Control and Gravel Packing in Horizontal Wells
    ZHAO Xu
    2019, 41(3):  121-128.  DOI: 10.11885/j.issn.1674-5086.2018.12.06.01
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    In the development of horizontal wells for easy production of sand, it is difficult to achieve good sand control effect by using adaptive flow-regulating water-control screen alone. It is necessary to study a new completion technology combining adaptive flow control and gravel packing. To this end, design and optimization were performed for experimental process parameters affecting the displacement, sand ratio, flushing ratio, loss of the transported gravel, and viscosity of the sand carrying fluid. According to the design results of the test process parameters, a ground-based simulation experimental device was independently designed and built for adaptive flow control and gravel packing in horizontal wells, based on which the experiment was performed twice. The test results show that the optimized low-density gravel solves the problem of limited packing displacement. Under the optimized packing parameters, the packing efficiency reached 100%. The axial seepage resistance of the packed gravel is much larger than its radial seepage resistance, realizing the function of an annulus packer, and the function of water control and oil stabilization of this flow-regulating water-control device is fully exerted. Eventually, reasonable ranges of construction parameters are obtained to provide effective guidance for field applications.
    Comparative Selection of Optimal Timing and Strategy for Secondary Supercharging in Daniudi Gas Field
    WAN Wei, LIAN Zhanghua, PENG Xingyu, LIU Lisheng, LIU Chang
    2019, 41(3):  129-136.  DOI: 10.11885/j.issn.1674-5086.2018.07.02.01
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    The process of primary centralized supercharging is unable to fulfill the requirements of the Daniudi gas field due to its continuous development. In addition, the gas well pressure attains only approximately 40% of the pipe network pressure after the first centralized supercharging. Therefore, it is vital to perform a secondary supercharging process. Following the analysis of the changing pattern of oil pressure in gas wells, this study has determined the timing for the secondary supercharging and proposed the following four secondary supercharging modes according to the characteristics of the gas field:(1) single-well supercharging plan; (2) decentralized supercharging plan in gas gathering stations; (3) regional centralized supercharging plan; and (4) regional concentrated supercharging and single gas gathering station supercharging plan. Furthermore, this study has compared the four plans from the technological and economic point of view. The results show that the regional concentrated supercharging together with the single gas gathering station supercharging mode appears to be the most sensible strategy to fulfill the requirements of the external transmission of pipe network and achieve the economic benefits as well.
    Rheological Properties of Wet Crude Oil in the Huizhou Oilfield
    CHEN Xiaoyu, CHEN Sijia, ZHANG Jie, CHEN Yunxian, LIU Lihao
    2019, 41(3):  137-142.  DOI: 10.11885/j.issn.1674-5086.2018.09.03.01
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    To study the effects of temperature and water content on the apparent viscosity of crude oil in the Huizhou oilfield, the rheological characteristics of wet crude oil were tested using a MCR302 high-temperature and high-pressure rheometer. The experimental results revealed an exponential relationship between the apparent viscosity and temperature with constant water content in wet crude oil. With a fixed temperature, the apparent viscosity and water content were found to follow a cubic polynomial distribution. By combining these findings with dimensional analysis, we proposed a comprehensive correlation describing the relationships among the apparent viscosity, temperature, and water content. The coefficients of the correlations were obtained by fitting the experimental data with the proposed expression. A three-dimensional surface map was plotted to show the change in the apparent viscosity with different temperature and water-content conditions. The accuracy of the empirical fitting was also analyzed in this study. As demonstrated in this study, the comprehensive correlation fundamentally reflects the effect of temperature and water content on the apparent viscosity of wet crude oil. This correlation can provide valuable guidance in calculating pressure drop during the collection and transportation of high water-content crude oil.
    Numerical Simulation of Temperature Field and Temperature Stress of Hydrothermal Spallation
    WANG Guohua, TAN jun, XIONG Jiyou, HAN Jinqiang, KUANG Shengping
    2019, 41(3):  143-150.  DOI: 10.11885/j.issn.1674-5086.2019.03.15.01
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    Hydrothermal spallation drilling technology uses a high-temperature medium such as supercritical water for rapid heating of the rock locally to break the rock. The rock matrix has a very low thermal conductivity. Consequently, temperature stresses are formed on the rock surface. When the temperature stresses exceed the rock's strength, micro-cracks are formed inside the rock, and the crack will continue to expand and eventually cause thermal cracking on the rock surface, which causes the rock surface to fall off from the body, leading to breaking of the rock. Based on the thermo-solid coupling theory, a thermal cracking drilling model was established, and the distribution laws of temperature field and temperature stresses of the rock at the well bottom were obtained using the Crank-Nicolson differential method. The results show that, during the thermal cracking drilling process, the temperature of the heated part of the rock increases rapidly, and temperature gradients are generated in the radial and axial directions. The volume expansion of the heated part is subjected to compressive stress in the radial direction, and shear stress in the axial direction under buckling.
    Method for Reconstructing Relative Permeability Curves Based on Flooding Effect
    LI Jinyi, DUAN Yu, ZHOU Fengjun, ZHU Wensen, XIN Zhaoling
    2019, 41(3):  151-159.  DOI: 10.11885/j.issn.1674-5086.2018.11.16.01
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    Targeting the problem of difficulty in summarizing the influence of reservoir flooding on the laws of formation fluid seepage, a study on the influence of the flooding effect on oil-water relative permeability curve was conducted. The study used core samples from confined coring wells in Oilfield LD, which is an unconsolidated sand reservoir of thin oil rims, typically found in the Bohai Sea, and in Oilfield Q of heavy oil rims. Based on the influence of flooding effect on relative permeability, parameters characterizing the infiltration curves under different degrees of flooding were extracted and regrouped to construct the "full life cycle" oil-water relative permeability curves of the two types of reservoirs by considering the flooding effect. Experimental results show that, compared with the oil-water relative permeability curves of unflooded and weakly flooded samples, oil-water relative permeability curves obtained from layers that underwent medium to heavy flooding had higher saturation of the bound water and lower saturation of the residual oil with higher oil displacement efficiency, and their points of equivalent permeability were closer to the right. Reconstructed relative permeability curves that consider the flooding effect had lower saturation of residual oil and bound water than those that do not. When they both had the same water saturation, their two-phase relative permeability showed an overall downward trend with an enhanced oil displacement efficiency at the end. Applying the reconstructed relative permeability that considered the flooding effect into numerical simulation for Oilfield Q led to an improvement in the recovery percentage of almost 1% at 98% water content.
    PETROLEUM MACHINERY AND OILFIELD CHEMISTRY
    Connectors for an Underwater Production System and Key Techniques
    TANG Yang, ZHANG Zhonggen, YI Dianxue, LIU Peisong, AN Jiawei
    2019, 41(3):  160-168.  DOI: 10.11885/j.issn.1674-5086.2018.02.08.01
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    Underwater production systems are widely used in developing deep-water and marginal oil fields. Connectors for an underwater production system are devices that connect subsea wellheads, manifold systems, and underwater control systems in an underwater production system. Therefore, they are key devices in the construction of a complete underwater production system. To further promote the localization of connectors for underwater production systems, both Chinese and international studies related to this topic are reviewed in this study. Based on the research, this study offers a brief overview of the characteristics of the structures, functions, and principles of three main connectors, namely, claw coupling, a clamp connector, and a bolted flange. Moreover, the properties of these connectors are compared and analyzed. In addition, through the analysis of typical products of these three types of connectors, the study summarizes the commonalities of related techniques for these products and describes the development trends of the techniques. Finally, based on the aforementioned analysis, the key techniques for utilizing connectors in underwater production systems, including positioning, alignment, locking, and sealing, are summarized. The difficulties of research and development are clearly highlighted in this study. The analysis of different types of connectors used in existing underwater production systems and relevant key techniques can act as a reference and provide a clear direction for overcoming technical barriers and achieving localization.
    Study on the Local Buckling Behavior of Buried Pipelines Under Reverse Faults
    ZHANG Jie, CHEN Xiaohua, LU Xin, PENG Yunfei
    2019, 41(3):  169-176.  DOI: 10.11885/j.issn.1674-5086.2018.06.20.02
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    To investigate the local crushing and winkling behaviors of buried pipelines under reverse faults, this study has analyzed the buried pipelines in the loess layers and established a numerical calculation model for pipe-soil coupling. Furthermore, it has examined the process of deformation and local buckling in buried pipelines under reverse faults and evaluated the influence of internal pressure, diameter-to-thickness ratio, and the number of dislocations in the local buckling of the pipelines. Research results show that with an increase in the number of dislocations, stress concentration can be observed on the pipelines on both sides of the fault layer gradually leading to local buckling. The deformation curve of the buried pipeline changes from the S-shape to Z-shape. Moreover, the deformation of the pipeline on both sides of the fault plane is neither symmetrical nor anti-symmetric. The upper panel has experienced more serious pipe buckling than the lower panel. When the number of dislocations is three times higher than the diameter of the pipe, the axial strain of the pipeline increases rapidly. Pipelines with no pressure and low pressure have experienced crushing. As the internal pressure increases, crushing will further develop into wrinkling, and the wrinkle width of the pipe increases with the internal pressure. The distance between the buckling part of the upper panel and the fault plane is less affected by the internal pressure and the diameter-to-thickness ratio, while that between the buckling part of the lower panel and the fault plane reduces with the increase of the internal pressure under crushing and increases with the increase of internal pressure under wrinkling. The maximum axial strain of the pipeline demonstrates different patterns according to the variations in the diameter-to-thickness ratio and the number of dislocations.
    Influence of Multivalent Metal Ions on Organic Borate-crosslinked Guanidine Gum Fracturing Gluids: Analysis and Countermeasures
    WANG Zhichen, LÜ Zhenhu, DONG Jingfeng, ZHANG Fengjuan, ZHOU Peiyao
    2019, 41(3):  177-184.  DOI: 10.11885/j.issn.1674-5086.2018.08.12.03
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    In this study, we investigate the influence of multivalent metal ions (such as Ca2+, Mg2+, Fe3+, and Fe2+) present in shallow groundwater, heavy oil thermal recovery-produced water, and fracturing flowback fluids in the periphery of the Mahu oilfield in Xinjiang, on the performance of organic borate-crosslinked guanidine gum fracturing fluids. Through the simulations of aqueous solutions containing different types and concentrations of multivalent metal ions, the influence patterns of multivalent metal ions on the swelling, crosslinking, thermal resistance, and shear resistance properties of organic boratecrosslinked guanidine gum fracturing fluids were analyzed. Furthermore, the shielding effects of three complexing agents (NSA, EDTA, and CA) toward various multivalent metal ions were investigated. The results indicated that the order of influence of the various multivalent metal ions on organic borate-crosslinked guanidine gum fracturing fluids is Fe2+ > Fe3+ > Mg2+ > Ca2+, and the order of shielding ability of the three complexing agents toward Mg2+, Ca2+, and Fe3+ are CA > NSA > EDTA, NSA > EDTA > CA, and EDTA>NSA, respectively.