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The impact of cleats on hydraulic fracture initiation and propagation in coal seams

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Petroleum Science 2014年第4期11卷 532-539页

作者： Fan Tiegang zhang guangqing Cui Jinbang College of Mechanical and Transportation Engineering China University of Petroleum College of Petroleum Engineering China University of Petroleum Beijing CBM Branch Company Huabei Oilfield Company

Cleats are systematic, natural fractures in coal seams. They account for most of the permeability and much of the porosity of coalbed methane reservoirs and can have a significant effect on the success of hydraulic fracturing stimulation. Laboratory hydraulic fracturing experiments were conducted on coal blocks under true tri-axial stress to simulate fracturing stimulation of coal seams. Fractures were initiated by injecting a water gel with luminous yellow fluorescent dye into an open hole section of a wellbore. The impact of cleats on initiation and propagation of hydraulic fractures in coal seams is discussed. Three types of hydraulic fracture initiation and propagation pattern were observed in this study： 1） The hydraulic fracture initiated and then grew along the cleat. 2） The hydraulic fracture initiated along a butt cleat or a fracture （natural or induced by drilling） oriented roughly in the minimum horizontal stress direction, then turned to propagate along the first face cleat that it encountered or gradually turned towards the maximum horizontal stress direction. 3） The hydraulic fracture initiated perpendicular to the minimum stress and, when it encountered a face cleat, tended to propagate along the cleats if the extension direction does not deviate greatly （〈20° as determined in this paper） from the maximum horizontal stress direction. When a coal seam is hydraulically fractured, the resulting fracture network is controlled by the combined effect of several factors： cleats determine the initiation and extension path of the fracture, the in-situ stress state dominates the main direction of the fracture zone and bedding planes impede fracture height growth.

关键词： Cleats coalbed methane hydraulic fracturing coal seam simulation experiment

Effective stress law for anisotropic double porous media

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Chinese Science Bulletin 2004年第21期49卷 2327-2331页

作者： ZHAO Ying CHEN Mian zhang guangqing School of Oil&Gas Engineering University of PetroleumBeijing102249China

An effective stress law is derived analytically to describe the effect of pore (fracture pore and matrix-block pore) fluid pressure on the linearly elastic response of ani- sotropic saturated dual-porous rocks, which exhibit anisot- ropy. For general anisotropy the difference between the ef- fective stress and the applied stress is not hydrostatic simply multiplied by Biot coefficient. The effective stress law in- volves four constants for transversely isotropic response; these constants can be expressed in terms of the moduli of the single porous material, double porous material and of the solid material. These expressions are simplified considerably when the anisotropy is structural rather than intrinsic, i.e. in the case of an isotropic solid material with an anisotropic pore structure. In this case the effective stress law involves grain bulk modulus, four moduli and two compliances of the porous material for transverse isotropy. The law reduces, in the case of isotropic response, to that suggested by Li Shuiquan (2001). And reduction to the single-porosity (de- rived analytically by Carroll (1979)) is presented to demon- strate the conceptual consistency of the proposed law.

关键词： anisotropy single porous media double porous media pore fracture effective stress

Deformation Mechanisms and Safe Drilling Fluids Density in Extremely Thick Salt Formations

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Petroleum Science 2007年第4期4卷 56-61页

作者： Yang Henglin Chen Mian zhang guangqing Drilling Research Institute CNPC Beijing 100097 China School of Petroleum Engineering China University of Petroleum Beijing 102249 China

Hydrocarbons are very often associated with salt structures. The oil and gas industry is often required to drill along and through long salt sections to reach and recover hydrocarbons. The unique physical properties of salt require special techniques to ensure borehole stability and adequate casing design. This paper assumed that the mechanical behavior of salt is regulated by the magnitude of mean stress and octahedral shear stress and under the influence of different stress conditions the deformation of rock salt can be represented by three domains, i.e. compression domain, volume unchanged domain, and dilatancy domain, which are separated by a stress dependent boundary. In the compression domain, the volume of salt decreases until all microcracks are closed, with only elastic deformation and pure creep; in the volume unchanged domain the deformation is considered steady incompressible flow controlled by pure creep; and in the dilatancy domain the volume of salt increases during deformation due to micro-cracking, causing damage and accelerating ＂creep＂ until failure. This paper presents a hypothesis that the borehole is stable only when the magnitude of octahedral shear stress is below the dilatancy boundary. It gives the design method for determining drilling fluids density, and calculates the closure rate ofborehole with the recommended drilling fluids density. If the closure rate of the borehole is less than 0.1%, the drilling fluids density window can be used during drilling through extremely thick salt formations.

关键词： Rock salt borehole stability deformation mechanisms constitutive equations equivalent viscosity drilling fluids density

On the Stability of the Defocusing Mass-Critical Nonlinear Schrödinger Equation

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International Journal of Modern Nonlinear Theory and Application 2016年第3期5卷 115-121页

作者： guangqing zhang College of Science Hohai University Nanjing China

We consider the defocusing mass-critical nonlinear Schr?dinger equation in the exterior domain in (). By analyzing Strichartz estimate and utilizing the inductive hypothesis method, we prove the stability for all init... 详细信息

关键词： Mass-Critical Stability Nonlinear Schrödinger Equation

Time-sensitivity of the Kaiser effect of acoustic emission in limestone and its application to measurements of in-situ stress

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Petroleum Science 2009年第2期6卷 176-180页

作者： Jin Yan Qi Zili Chen Mian zhang guangqing Xu Guangqiang Key Laboratory of Petroleum Engineering Ministry of Education China University of Petroleum Beijing 102249 China

Measuring in-situ stress by using the Kaiser effect in rocks has such advantages as timeefficiency, low cost and little limitation, but the precision of the method is dependent on rock properties and delay time of the measurement. In this paper, experiments on the Kaiser effect in limestones were performed, and it was found that the limestones had good ability to retain a memory of their recent stress history and high time-sensitivity. The longer the experiment was delayed from the extraction of the stone, the larger the Felicity ratio was. As the Felicity ratio approached l, significant Kaiser effect was observed. In-situ stress should be determined by the limestone measurements when the delay time was 40-120 days. Finally, the in-situ stress in a limestone formation could be successfully measured in practice.

关键词： In-situ stress Kaiser effect limestone time sensitivity

Identifying the real fracture hidden in rock microcrack zone by acoustic emission energy

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International Journal of Mining Science and Technology 2024年第6期34卷 731-746页

作者： Yuekun Xing Bingxiang Huang guangqing zhang Binghong Li Hang Xu Xuejie Jiao Yang Yu Taisen Han Jinlong Chen State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources China University of Mining and TechnologyXuzhou 221116China State Key Laboratory of Petroleum Resources and Engineering China University of Petroleum-BeijingBeijing 102249China

Identifying the real fracture of rock hidden in acoustic emission(AE)source clusters(AE-depicted microcrack zone)remains challenging and *** we revealed the AE energy(representing dissipated energy)distribution rule in the rock microcrack zone and proposed an AE-energy-based method for identifying the real fracture.(1)A set of fracture experiments were performed on granite using wedgeloading,and the fracture process was detected and recorded by *** microcrack zone associated with the energy dissipation was characterized by AE sources and energy distribution,utilizing our selfdeveloped AE analysis program(RockAE).(2)The accumulated AE energy,an index representing energy dissipation,across the AE-depicted microcrack zone followed the normal distribution model(the mean and variance relate to the real fracture path and the microcrack zone width).This result implies that the nucleation and coalescence of massive cracks(i.e.,real fracture generation process)are supposed to follow a normal distribution.(3)Then,we obtained the real fracture extension path by joining the peak positions of the AE energy normal distribution curve at different cross-sections of the microcrack ***,we distinguished between the microcrack zone and the concealed real fracture within *** deviation was validated as slight as 1–3 mm.

关键词： GeoEnergy exploitation Rock fracture Fracture identification Acoustic emission AE energy analysis

预后营养指数对腹膜透析患者心血管疾病死亡的影响:一项多中心回顾性队列研究

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中国全科医学 2025年第5期28卷 568-574页

作者：朱露艾军廖生武黄淑婷龚妮容孔耀中刘德慧窦献蕊张广清南方医科大学南方医院肾内科广东省广州市510515 南方医科大学护理学院广东省广州市510515 南方医科大学南方医院医技片区党总支广东省广州市510515 广东省佛山市第一人民医院肾内科 528000 江西省赣州市人民医院肾内科 341000 南方医科大学顺德医院(顺德区第一人民医院)肾内科广东省佛山市528300 南方医科大学南方医院院办公室广东省广州市510515

背景心血管疾病(CVD)是腹膜透析(PD)患者死亡的主要原因,而营养不良是PD患者发生CVD及死亡的重要危险因素之一。预后营养指数(PNI)作为一种综合评估患者免疫、炎症和营养状态的指标,因其具有便利性与可靠性等优点,在肿瘤等多种疾病的预... 详细信息

背景心血管疾病(CVD)是腹膜透析(PD)患者死亡的主要原因,而营养不良是PD患者发生CVD及死亡的重要危险因素之一。预后营养指数(PNI)作为一种综合评估患者免疫、炎症和营养状态的指标,因其具有便利性与可靠性等优点,在肿瘤等多种疾病的预后评估中得到了广泛应用。然而,不同时间点的营养状态与PD患者预后之间的关系仍有待进一步探究。目的探讨PD患者首年PNI与CVD死亡之间的关系。方法本研究为多中心、回顾性观察性队列研究,纳入2000-01-01—2019-07-01在南方医科大学南方医院、南方医科大学顺德医院、佛山市第一人民医院以及赣州市人民医院4所中心置管并开始接受PD治疗的1640例PD患者作为研究对象。对患者进行随访,随访截止时间为2021-07-01,终点事件为CVD死亡并记录患者生存时间及具体死亡原因。应用限制性立方条图(RCS)分析PNI与PD患者CVD死亡风险之间的非线性关联;采用Kaplan-Meier法绘制PD患者的生存曲线,绘制PNI预测PD患者CVD死亡的受试者工作特征(ROC)曲线,并根据最佳截断值(cut-off=40.46)将患者分为低PNI组703例与高PNI组937例;采用Log-rank检验和Cox风险回归模型分析探讨PNI对PD患者CVD死亡的影响。结果本研究中位随访时间为30个月,随访期间共148例患者死亡,其中CVD死亡73例(49.32%)。RCS结果表明,PNI与CVD死亡事件呈线性关联(P for Nonlinear=0.655)。ROC曲线显示,PNI预测PD患者CVD死亡的曲线下面积(AUC)为0.717(95%CI=0.659~0.775,P<0.001),灵敏度为74.0%,特异度为58.6%。Kaplan-Meier生存分析结果显示,低PNI组CVD生存率低于高PNI组(χ^(2)=26.685,P<0.001)。多因素Cox风险回归模型分析,校正性别、年龄及CVD病史等混杂因素后,低PNI组仍是CVD死亡的独立预测因素(HR=7.76,95%CI=1.72~35.06,P=0.008),亚组分析结果仍稳健,无明显交互作用。结论PNI降低是PD患者CVD死亡的独立影响因素,PD首年PNI评分在评估PD患者预后有一定的指导意义。

关键词：慢性肾脏病腹膜透析预后营养指数心血管死亡预后队列研究回顾性研究影响因素分析

LABORATORY INTERPRETATION OF ROCK FRACTURE TOUGHNESS MEASUREMENT AT GREAT DEPTH

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LABORATORY INTERPRETATION OF ROCK FRACTURE TOUGHNESS MEASURE...

碳酸盐岩储层酸压后测试伤害的复合力学模型及其应用

The 2nd International Conference on New Development in Rock Mechanics and Rock Engineering

作者： guangqing zhang MIAN CHEN University of Petroleum China

＜正＞In this paper,finite element analysis（FEA） and empirical methods are employed to determine the fracture *** is proven experimentally that the analytic procedures are usable to calculate the fracture toughness only when fracture tip radius is a *** it is required that the failure pressure as an input of calculation correspond to the real magnitude of fracture tip

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岩石力学与工程学报 2009年第A02期28卷 3458-3463页

作者：张广清陈勉中国石油大学石油天然气工程学院北京102249

基于碳酸盐岩储层酸压的特点,考虑到固体变形和流体流动的相互作用关系,建立包含未酸蚀区、酸蚀区和支撑裂缝的复合力学试油模型。不同区域中的渗流参数随应力的改变不同。根据弹性力学,针对未酸蚀区和酸蚀区地层,建立孔隙度变化模型;... 详细信息

基于碳酸盐岩储层酸压的特点,考虑到固体变形和流体流动的相互作用关系,建立包含未酸蚀区、酸蚀区和支撑裂缝的复合力学试油模型。不同区域中的渗流参数随应力的改变不同。根据弹性力学,针对未酸蚀区和酸蚀区地层,建立孔隙度变化模型;针对支撑裂缝通过裂缝导流能力试验建立支撑裂缝的渗透率变化模型,发现对于特定支撑剂,作用于酸蚀区地层上闭合压力超过酸蚀岩石的抗压强度时,支撑裂缝的渗透率的变化模式改变,支撑剂嵌入造成不可恢复的伤害。考虑到不同区域的差别,采用固液耦合的算法计算有效应力的分布规律。现场应用表明,模型预测结果与实测数据基本吻合。

关键词：石油工程碳酸盐岩储层试油复合力学模型酸化压裂