Table of Content

10 August 2020, Volume 42 Issue 4

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GEOLOGY EXPLORATION

Reservoir Geomechanical Characteristics and the Influence on Development in Keshen Gas Field

JIANG Tongwen, ZHANG Hui, XU Ke, WANG Zhimin, WANG Haiying

2020, 42(4):  1-12.  DOI: 10.11885/j.issn.1674-5086.2020.04.09.01

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The fractured sandstone reservoir has experienced strong compression structure deformation in deep zone of Kelasu tectonic zone. Complex current in-situ stress field and natural fracture system lead to strong heterogeneity and anisotropy of reservoir. There were obvious differences in gas well productivity between different structures and at different locations of the same structure. In order to clarify the main controlling geological factors affecting the development of natural gas in this area, the research on reservoir geomechanical modeling of Keshen Gas Field was carried out based on the evaluation of 1 D geomechanical parameters and the construction of structural framework. The rock mechanics properties, present in-situ stress field and development characteristics of natural fractures of reservoirs in several structural belts of Keshen Gas Field are analyzed in depth. The geomechanical characteristics of reservoirs in different structural belts, different parts of the same structural belt and different horizons are summarized respectively. Combining with the development status of typical wells in Keshen Gas Field, the relationship between geomechanical characteristics and productivity is established. Finally, the matching well distribution principles are proposed for different types of gas reservoirs. It is shown that: (1) the distribution characteristics of in-situ stress field in different structural types of gas reservoirs are quite different, and the relationship between stress orientation and natural fracture occurrence is also distinctly different; (2) geomechanical properties of reservoirs in gas reservoirs show selfstratification characteristics, which directly affect the distribution of reservoir porosity and permeability; and (3) gas reservoirs are located in low stress value, small angle between fracture strike and horizontal principal stress orientation, good permeability and higher productivity of single well. The research not only provides a useful supplement for reservoir evaluation and gas reservoir description, but also promotes well location optimization of development plan.

Major Controlling Factors and a Method for Predicting Bioclastic Limestone Reservoirs in Da'anzhai, Northern Sichuan

WANG Weidong, PENG Jun, XIA Qingsong, DUAN Guanyi, SUN Enhui

2020, 42(4):  13-21.  DOI: 10.11885/j.issn.1674-5086.2019.03.04.06

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The aim of this study was to clarify the characteristics and major factors controlling the formation and development of bioclastic limestone reservoirs in the lake facies of the Da'anzhai Member in Northern Sichuan, and to search for favorable reservoir development zones. Through drilling core description, thin slice identification, scanning electron microscope observation and test analysis, we performed a study on the sedimentology and reservoir characteristics in the area. According to our findings, the Da'anzhai Member in Northern Sichuan Basin is a shallow-lake-semi-deep-lake facies deposit. In the shallow-lake subfacies develops the bioclastic beaches, inter-beach depressions, and shallow-lake mud micro-facies, whereas in the semi-deep lake subfacies develops the beachfront lake slope and semi-deep lake mud micro-facies. Dominated by bioclastic limestone the reservoir is poor overall physical properties and is characteristic of ultra-low porosity and ultra-low permeability with average porosity of 1.18%, permeability less than 1 mD. The types of reservoir space are mainly corrosion pores, holes, and cracks. The predominant reservoir type is pore-fractured, while fracture-porosity reservoirs and fracture-type reservoirs also developed in the study area. Based on the results and analyses, the factors controlling the development of lake-facies bioclastic limestone reservoirs are discussed. We believe that favorable sedimentary facies belts, constructive diagenesis, and the fracture system control the development of reservoirs in the Da'anzhai Member. Finally, we propose a targeted reservoir prediction method based on the stratigraphic characteristics of each layer in the Da'anzhai Member.

Formation Mechanism and Sedimentary Characteristics of Translational Point Bars

ZHAO Xiaoming, FENG Shenglun, TAN Chengpeng, FENG Mochen, TANG Chun

2020, 42(4):  22-36.  DOI: 10.11885/j.issn.1674-5086.2019.01.11.04

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Researches on translational point bars, which are the main structural units in meandering river sediment, is inadequate lagging. This paper summarizes the formation mechanism and sedimentary characteristics of translational point bars through literature analysis and modern sedimentary observation. Studies have shown that an incised valley in the lowstand period and the limiting conditions of synsedimentary faults are the basis for the development of translational point bars. According to the variations in plane shape, a translational point bar can be divided into two parts: the point bar body and the point bar tail. The point bar body is mainly composed of coarse-grained sediments, and along the direction of water flow, the sediment preservation increases while granularity gradually decreases. Two different modes of point bar tail deposition can be formed, depending on the angle at which the water flow hits the outer bank: counter-point-bar, mainly composed of fine-grained sediments, and eddyaccretion deposits, mainly composed of coarse-grained sediments. By establishing a three-dimensional (3D) lithofacies model, we further clarified the distribution range of the lateral mud interlayer and the thickness of the sand body in the translational point bar. The sand body in the point bar body was characterized by good connectivity and great thickness, whereas the sand body in the point bar tail was poorly connected and relatively thin.

Quantitative Characterization of the Reservoir Structural Stacking Relationship in the Deep-water Turbidite Channel

LI Chenxi, WANG Yaqing, YANG Xipu, BU Fanqing, DUAN Ruikai

2020, 42(4):  37-46.  DOI: 10.11885/j.issn.1674-5086.2019.01.31.01

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In order to accurately describe the superposition relationship between individual water channels within the sand body of deep-water turbidite composite channels, we made a quantitative study on Reservoir Z in the AKPO Oilfield in the Niger Basin. The study showed that the various stacking relationships between single sand bodies in deep-water turbidite reservoirs can be quantitatively characterized by the “stacking ratio” parameter. This parameter can be further divided into a vertical stacking ratio and a lateral stacking ratio. There is a certain correlation between the stacking ratio of sand bodies of an individual channel and the camber curvature of the composite channel. In addition, the channel curvature is highly correlated with geological factors such as the slope of the basin and material resource supply. The stacking ratio of sand bodies of an individual channel is correlated to the interior connectivity of the composite sand body, and can be used as a reference for judging the internal connectivity of the reservoir when combined with the ”connectivity coefficient”. This study found that the stacking ratio is an important link. It can be used to build a mathematical connection between the stacking pattern and the morphology of sand bodies, with reservoir connectivity and development effect. It is one of the most effective means of fine characterization and digitization research of deep-water turbidite sand bodies.

Structural and Model Analysis of the Multi-period Structural Superimposed in Fangzheng Fault Depression

WU Jingfeng, MENG Qi'an, FU Xiaofei

2020, 42(4):  47-54.  DOI: 10.11885/j.issn.1674-5086.2019.03.02.01

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In order to clarify the basin deformation caused by multi-period tectonic overlap in Fangzheng Fault Depression, the complex structural styles in the fault depression and the problems of multi-solution in structural analysis, we combine the analysis of seismic data, regional tectonic characteristics and Tanlu Fault evolution with the analysis of extensional, strike-slip pull-apart, strike-slip compression and later uplift-denudation of Fangzheng Fault Depression. New understanding and methods are put forward for structural analysis, and a three-dimensional stress model of extension-strike-slip-compression in Fangzheng fault depression is established. The study shows that the western part of the fault depression is weakly reformed and inherits the extension model of the Cretaceous basin in the early stage of the fault depression. The compression-nappe reformation in the eastern part of the fault depression is strong in the later stage, and the extension model is no longer applicable. The influence of thrust-nappe structure must be considered. The developed Yihantong Fault has obvious strike-slip characteristics and floral structure. The east and west sides of the Yihantong fault are characterized by asymmetric differential strike-slip fault depression. The strike-slip model is applied to the analysis of both sides of the Yihantong fault. Therefore, the extension model can not be used to analyze the multi-structural superimposed fault basin, but the later transformation model should be considered, and on this basis, a set of structural analysis method for complex faulted basins has been found.

Fine-grained Sedimentary Rock Lithofacies Assemblage Characteristics in Dongying Depression

NING Fangxing, WANG Xuejun, HAO Xuefeng, YANG Wanqin, DING Juhong

2020, 42(4):  55-65.  DOI: 10.11885/j.issn.1674-5086.2018.11.07.01

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According to many core observation, thin section identification and X-ray diffraction, lithofacies of fine-grained sedimentary rocks in upper Es4 to lower Es3 in Dongying Depression can be divided into 8 main lithofacies based on rock constituents, sedimentary structure, TOC and carbonate crystal structure: organic-rich laminated cryptocrystalline argillaceous limestone facies, organic-rich laminated microcrystalline argillaceous limestone facies, organic-rich laminated calcareous mudstone facies, organic-rich layered argillaceous limestone facies, organic-rich layered calcareous mudstone facies, organic-rich massive calcareous mudstone facies, organic layered calcareous mudstone facies, organic layered gypsum mudstone facies. We first reconstructed of the ancient environment of climant, salinity, water depth and oxidation and reduction of water bodies on the basis of geochemical elements, then fine-grained sedimentary rock lithofacies assemblage characteristics and origin of different depositional environment was determined. On this basis, fine-grained sedimentary rock sedimentary model of upper Es4 to lower Es3 in Dongying Depression was built. The study is of guideance value for shale oil exploration.

Accumulation Conditions of CO₂ and Its Influence to Pre-salt Oilfields, Santos Basin

JIA Huaicun, KANG Hongquan, LI Minggang, CHENG Tao, HOU Bo

2020, 42(4):  66-72.  DOI: 10.11885/j.issn.1674-5086.2018.12.04.01

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In recent years, the pre-salt sequence of Santos Basin is the focused exploration area, but CO₂ is generally found in the pre-salt oil fields. After analysis of CO₂ content, carbon isotope and helium isotope, the generation type of CO₂ in Santos basin pre-salt layers is inorganic mantel. Based on generation type and the comprehensive analysis of the correlation of CO₂ content with basement faults distribution, we found that fields closed to faults are generally high in CO₂ content. Meanwhile, the analysis of generation factors and accumulation elements of CO₂ in the typical fields displays that volcano activities and basement faults are the controlling factors for the accumulated CO₂ gas cap. And the volcano provides CO₂ source, faults acting as migration pathways. Affected by a large amount of inflow of continuous CO₂, evaporation and diffluence occurred in oil and gas composition and generated gas cap of high CO₂ content.

An Analysis of the Oil Enrichment Factors and Accumulation Models of the Upper Wilcox Formation of Perdido Belt, Mexico

LI Dong, HUANG Xingwen

2020, 42(4):  73-82.  DOI: 10.11885/j.issn.1674-5086.2019.03.11.02

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To determine the controlling factors of oil enrichment in the Upper Wilcox Formation of Perdido Belt, the commercial and non-commercial fields of the Upper Wilcox are taken as the research objects. This study integrates the analysis of effective hydrocarbon supply range, oil and gas transmission mode, matching relationship between trap formation and hydrocarbon generation and expulsion period and preservation conditions. The study discusses the controlling factors of oil and gas enrichment in Wilcox Formation and petroleum accumulation model. The study shows that the scale of hydrocarbon supply area has obvious control effect on field scale; there are three vertical migration modes in the Upper Wilcox Formation, i.e. along-source, toward-source and back-source. Among them, along-source and toward-source migration modes are advantageous. Trap formation and hydrocarbon generation-expulsion period match well, hydrocarbon supply is sufficient and reservoir scale is large; It is a necessary condition for oil enrichment and a small scale of seriously damaged reservoirs. Three accumulation models of Upper Wilcox Formation in Perdido Belt are established, among which“ double supply along-source” and“ single supply toward-source” are favorable for oil enrichment and are favorable models for searching large size fields in Perdido Belt.

Well Location Optimization Technology of Strong Heterogeneity Gas Reservoir in Shuang 110 Well Block of Shenmu Gas Field

ZHU Jinli

2020, 42(4):  83-94.  DOI: 10.11885/j.issn.1674-5086.2019.12.05.01

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The geological conditions of Shuang 110 Well Block are complex with strong heterogeneity, and it is difficult to predict, and to deploy the well location for tracking adjustment. From 2017 to 2019, Great Wall Drilling Company has been working together with Changqing Oilfield Company on an innovative basis, aiming to complete the construction of 1 billion cubic meters of production capacity in Shuang 110 Well Block of Shenmu Gas Field. Though integration of geology and engineering, fine geological research, and well location deployment optimization, we have the goal. In order to ensure development effect, we carried out researches on structural characteristics, sedimentary faces characteristics, sand body and effective reservoir distribution using seismic data, well logging and logging data and core and gas testing data, and a three-dimensional geological model has been established to optimize the gas bearing enrichment area. Based on the demonstration of well pattern, the well location is optimized. Finally the goal of fewer wells and higher yield is realized. Finally, 208 vertical / directional wells have been drilled, with 37 wells less than original plan. The proportion of static first and second level wells is up to 84.0%. The 15 horizontal wells have been deployed and completed. The average length of horizontal wells is 1 433.5 m, and the drilling rate of sandstone is 83.3%, which proves to be a good development results.

OIL AND GAS ENGINEERING

Measurement and Effecting Factors of Nitrogen Diffusion Coefficient in Vug-fracture Reservoir

SONG Chuanzhen, ZHU Guiliang, LIU Zhongchun

2020, 42(4):  95-103.  DOI: 10.11885/j.issn.1674-5086.2019.09.18.02

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Diffusion coefficient is an important parameter for studying the mechanism of enhanced recovery by gas injection and numerical simulation. In this paper, pressure decay method is utilized to determine the N₂ diffusion coefficient under the condition of high temperature and high pressure in Tahe Oilfield. Not only the effects of oil viscosity and gas composition on N₂ diffusion coefficient in the bulk oil phase are analyzed, but the determination and comparison of N₂ diffusion coefficient in different filling model of fracture-cave carbonate reservoirs of Tahe Oilfield are studied. The solubility and diffusion coefficient of nitrogen in heavy oil are lower than in light oil, but more sensitive to pressure variation than in light oil. The mixing of CO₂ contributes the diffusion process. Diffusion results of nitrogen in the breccia, silt and tight media show that the tighter the filling model is, the more difficult it is for nitrogen to diffuse into the filling medium. The diffusion coefficient of nitrogen in the tight medium reaches the order of magnitude of solid diffusion coefficient (×10^-11 m²/s). Besides, the rise of water saturation in the filling medium also retards the diffusion process of nitrogen in the filling medium. This paper presents the N₂ diffusion coefficient in bulk oil phase and filling model of fracture-cave carbonate reservoirs under condition of high temperature and high pressure conditions (temperature >100 ℃, pressure >20 MPa) for the first time, and analyzes the related influencing factors. The results furthers understanding of EOR mechanism of gas injection, and offers strategic insights for field application of nitrogen injection.

Tectonic Stress is Not the Main Driving Force for Primary Migration of Oil and Gas

LUO Chuan, YANG Hu

2020, 42(4):  104-110.  DOI: 10.11885/j.issn.1674-5086.2019.06.10.02

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The primary migration of oil and gas is an unsolved academic problem. In the field of petroleum geology, structural stress is considered to be one of the main driving forces for the primary migration of oil and gas. According to the theory of effective stress and elastic mechanics, the influence of structural stress on pore pressure is analyzed. The calculation model of pore pressure increment and the calculation model of oil-gas migration scale driven by pore pressure release are established. Theoretical analysis and quantitative calculation results show that under the same structural stress condition, the increment of pore pressure of source rock is mainly affected by Young's modulus. The larger the Young's modulus is, the smaller the increment of pore pressure is; the increment of pore pressure caused by structural stress is generally not more than 60 MPa; the release of pore pressure only needs to discharge a small amount of formation fluid, and the distance to drive oil and gas migration is very short, relatively because the thickness of source rock is negligible, and the influence of structural stress on the primary migration of oil and gas is very weak, which can not be the main driving force of the primary migration.

Quantitative Characterization Method and Application of Reservoir Flow Field

LU Fengming, WU Xi, ZHU Hongyun, ZHANG Yang, WANG Rui

2020, 42(4):  111-120.  DOI: 10.11885/j.issn.1674-5086.2019.10.25.03

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Due to long term washing of water injection in the complex fault block reservoirs, the distribution of reservoir flow field would be more and more complicated and it results in forming different types of reservoir flow field with different intensities. In regions of high intensity of reservoir flow field, invalid water injection is very serious. But water injection cannot reached the regions of low intensity easily. It results in a poor efficiency of reservoir development and makes it hard to adjust reservoir development. Due to the above reasons, taking a case Block Zao Z of the first member of the Kongnan, Cangdong Sag, south of Huanghua Depression, the simulation model was modeled to study quantitatively reservoir flow field at high water cut stage. According to the influence on reservoir flow field, the primary characterization parameters were selected from some static and dynamic parameters, including permeability, pressure gradient, oil saturation and surface flux. A calculation model of intensity of reservoir flow field was proposed by the theory of fuzzy mathematics. The ranges of different types of reservoir flow field were determined on the study reservoir. And then technical strategies of reservoir flow field adjustment were given in different types of reservoir flow field. The implement results of flow field adjustment of the study reservoir show that the characterization method of reservoir flow field could be applied to a correct understanding of the characteristic of reservoir flow filed at high water cut stage. It is helpful to guide to adjust layer series and well groups and to improve effect of reservoir development.

Improvement and Solution Binomial Production Equation of High Pressure and Low Permeability Gas Wells

MA Shuai, ZHANG Fengbo, WANG Wenjuan, ZHA Yuqiang, WANG Yanli

2020, 42(4):  121-126.  DOI: 10.11885/j.issn.1674-5086.2019.03.21.02

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The gas reservoir pressure in Ledong X Area of the western South China Sea is up to 100 MPa and permeability is as low as 0.1 mD. The binomial productivity equation slope obtained from the productivity test regression of such high pressure and low permeability gas wells is often negative, and the real productivity cannot be obtained. The production binomial's slope of high pressure and low permeability is always negative which results in failure to get real capacity. The gas well testing process is analyzed and the material balance model within the effective supply range is established and solved. It is considered that except the first level system, the formation pressure changes with the output and time, and the lower the permeability of the formation, the greater the pressure change. The traditional binomial method does not consider the formation pressure change is the main reason for the negative slope of regression. Taking into account the formation pressure drop in the effective supply range during the test, the new binomial equation of deliverability and the expression of unobstructed flow are obtained by regression. It is considered that the unobstructed flow in the gas well is related to the original formation pressure, test conditions and formation physical properties. The correction of the binomial production equation of six high pressure and low permeability wells, such as LDX-5-A, has successfully solved the production capacity anomalies in this type of wells, provided a basis for rational development of gas fields in the next step and a solution to the abnormal capacity correction of such high pressure and low permeability gas wells.

Method of Improved Parameters for PR-EOS in CO₂-crude Oil System

XIE Dan, QU Liming, CHI Jianping, TAO Wulong, XIONG Weili

2020, 42(4):  127-134.  DOI: 10.11885/j.issn.1674-5086.2019.08.16.01

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For imperfect CO₂-crude oil system at high temperature and high pressure, the existing state equation cannot give consideration to the requirement of accuracy and simplicity of calculation simultaneously. In order to obtain practical state equation for CO₂-crude oil system, influence factors such as temperature, pressure and the interaction of non-hydrocarbons components have been taken into account, Based on the principle of thermodynamics and flash calculation, parameters of PR EOS have been corrected, and the dimensionless coefficient has been changed from previous constant coefficient to function item which is associated with reduced temperature, thus prediction for density of liquid and characteristics of heavy components have been improved. Based on the data of components measured on site, the calculation accuracy of oil and gas components before and after PR EOS correction have been compared under condition of reservoir temperature and pressure. The results show that without sacrificing the simplicity of calculation, the new state equation has been improved significantly with calculation accuracy, and relative error of parameter has been reduced to less than 5%, which meets the requirements of engineering application and has better practical value in simulating and predicting fluid phase states under reservoir conditions and provides support for numerical simulation of CO₂ flooding.

The Dynamics Characteristics and Strength Check of Drilling String in Ultra-deep Horizontal Well

ZHONG Wenjian, LI Shuanggui, XIONG Yulou, FU Jianhong, SU Yu

2020, 42(4):  135-143.  DOI: 10.11885/j.issn.1674-5086.2019.11.18.02

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Drilling tools failure of occurs frequently in the process of ultra-deep well drilling. Therefore, the research on the dynamic characteristics of drilling string plays an important role in the safety of drilling tools. Considering the influence of the real well trajectory, the interaction between bit and formation, the contact between drilling string and borehole wall and the viscous effect of drilling fluid, a simulation model of the whole well drilling string with dynamic characteristics is established. Under different WOB and rotation speed, the changes of axial force, torque, displacement and equivalent stress over time are simulated. The fourth strength theory is used to calculate the assurance coefficient of the wellhead drilling tools and check the strength of the drilling tools in ultra-deep horizontal wells. The results show that the wellhead axial force and equivalent stress display a characteristics of low-frequency change, while the equivalent stress and acceleration at MWD are high-frequency vibration, and the lateral vibration is more severe than the axial vibration; when WOB and rotation speed are small, WOB and rotation speed have little influence on the wellhead axial load, torque, equivalent stress and assurance coefficient; the equivalent stress at MWD increases with the increase of WOB, and the amplitude of lateral acceleration increases significantly with the increase of rotation speed. When the well depth is more than 8 000 m, the hole size is φ120.65mm, and G105 φ114.3 mm drill pipe is used at the wellhead, the wellhead assurance coefficient obtained from dynamic analysis will fluctuate around 1.2, so generally the drilling tool is safe.

The Agent Technologies for Efficient Development of Moxi T₂l₁¹ Gas Reservoir

HE Xiaochuan, OU Jiaqiang

2020, 42(4):  144-154.  DOI: 10.11885/j.issn.1674-5086.2020.02.23.01

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In view of the problems of thin effective thickness, poor permeability and natural gas sulfur content in the Moxi T₂l₁¹ gas reservoir, the related researches on the description of fine gas reservoirs and the safe production of downhole pipelines are carried out. In order to confirm the effective thickness and physical properties of reservoirs in Moxi T₂l₁¹ gas reservoir, a combination of logging data and seismic information is adopted to form the integrated 3D geological modeling-reservoir simulation process.Accurate division of layers and identification of sweet spots in reservoirs have resulted in the development of high efficiency gas reservoir technology, such as open hole multistage acidizing technology, horizontal wells and well pattern optimization technology. In view of the serious corrosion and blockage of downhole pipes, the life evaluation of downhole tubing and FRP tubing has been carried out, and the preventive replacement of tubing has been adopted, formed the workover (to extent eroded wells life span) and surface system optimization technology. Development practice has indicated that T₂l₁¹ gas reservoir maintains stable production of more than 25 years by successful application of efficient development technologies described above, setting an example as an efficiently developed low-permeability gas reservoir. This field has a gas production of 11 billion cubic meters, showing a good development effect.

Study on Formation Mechanism of Trailing Oil in Product Oil Pipeline

LIU Enbin, LI Wensheng, CAI Hongjun, XIE Ping, SHANG Chen

2020, 42(4):  155-164.  DOI: 10.11885/j.issn.1674-5086.2019.01.03.01

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Trailing oil is the tail section of contamination in oil pipelines. It is generated in batch transportation, and it has an effect on the quality of oil. In the dead-leg section, the main reasons for the formation of trailing oil contamination is the outflow of the preceding batch that remains in the dead-legs. The traditional calculation formula of oil mixing does not consider the influence of trailing oil. The Reynolds time-averaged method is used to simulate turbulence. To obtain contamination-related experimental data, Computational Fluid Dynamics (CFD) software is used to simulate different flow rates and bypass lengths. The oil replacement rate in a dead-leg is exponentially related to the flow speed and the length of the dead-leg is exponentially related to the replacement time of the oil. To reduce the amount of contamination, the main flow speed should be kept at about 1.6 m/s, and the length of the dead-leg should be less than five times the diameter of the main pipe. The MATLAB software was used to perform multi-nonlinear regression for the oil substitution time, the length of the dead-leg, and the flow speed to calculate the contamination length. A modified equation for calculating the length of the contamination was obtained by combining the Austin-Palfery equation with new factors. Using engineering data, the contamination predicted by the corrected equation is closer to the actual contamination than that predicted by other equations.

PETROLEUM MACHINERY AND OILFIELD CHEMISTRY

A Simulation Study on Buckling Friction Resistance of Casing Uplift and Flushing in Three-dimensional Complex Well

LIN Tiejun, LI Zhaoyang, WANG Xuegang, DENG Yuanzhou, SONG Lin

2020, 42(4):  165-172.  DOI: 10.11885/j.issn.1674-5086.2019.07.05.01

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In the casing lowering process, it is difficult or even unable to reach the expected well depth due to complex wellbore structures, complex wellbore trajectories and well diameter changes. Intending to solve this problem, a simulation study on buckling friction resistance of casing uplift and flushing in three-dimensional complex well is carried out. Based on the theory of additional friction in helical buckling sleeves, a three-dimensional finite element model of the“ up-and-push” operation of a complex wellbore casing was established based on the actual operating parameters of Well H by ABAQUS. The model was used to analyze the casing stress and buckling deformation of the whole well section. The results of analysis show that the axial force of the casing in the vertical well section of Well H at the moment of flushing and releasing and after free stabilization is greater than its helical buckling critical load, there was severe helical buckling deformation in the section between the well depth of 2 000 m and the deflection point, the lower casing is unable to transmit power and has difficulty in lowering. It reveals the mechanism of this kind of three-dimensional complex wellbore casing down-diffusion, which is of great significance for the research on buckling morphological damage and failure of complex wellbore casing strings.

Synthesis and Performance Evaluation of Phosphate-modified Furan Resin Aqueous Sand Consolidation

SONG Jinbo, ZHAO Yizhong, JIA Peifeng, ZHANG Yuchen, CHEN Xue

2020, 42(4):  173-180.  DOI: 10.11885/j.issn.1674-5086.2019.04.29.01

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The study aimed at the contradiction between the strength of sand consolidation and the retention rate of formation permeability. Phosphate modified furan resin sand consolidation agent was prepared by hydroxyl polycondensation with phosphate, polyether (L35) and furan resin as main raw materials, and it was used as sand consolidation agent after dilution with water on ratio 1： 3. On the one hand, water was used as natural pore increasing agent, on the other hand, sand consolidation agent film was formed and solidified in water environment, which guaranteed compressive strength and high formation permeability. It effectively solves the difficult problem that puzzles the sand consolidation effect of chemical method for a long time. The results show that the phosphate modified furan resin can be consolidated at 60 ℃ for 48 h after dilute with water for 3 times. The compressive strength is above 4 MPa. It is suitable for sand consolidation in underwater environment of oil field. By March 2019, phosphate modified furan resin sand consolidation agent had been used in 10 wells in oilfield, with a 100% success rate of sand control and acumulative oil increase of 13 000 t. It has obtained the good effect in the practical application.