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The effect of natural fracture on the fluid leak-off in hydraulic fracturing treatment

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Petroleum 2019年第1期5卷 85-89页

作者： Amir Ghaderi Jaber Taheri-Shakib Mohamad Amin Sharifnik National Iranian South Oil Company AhwazIran Research Institute of Petroleum Industry TehranIran

Fluid leak-off phenomenon plays a critical role in hydraulic fracturing *** phenomenon can be very impressive in successful operation of hydraulic *** operation is very complex in fractured reservoirs due to the reaction between induced fracture and natural *** this study with the cohesive element method,the effect of presence of natural fracture on the magnitude of hydraulic fracturing fluid leak-off is *** of all,cohesive element and extended finite element method methods are *** fluid flow inside hydraulic fracture and the affecting parameters on leak-off of this fluid on adjacent environment are ***,effects of natural fracture on hydraulic fracturing direction such as deviation,leak-off and the mutual influences(which includes the changes of stress regime around the natural fracture)and also changes in pore pressure are *** results indicate that presence of natural fracture will cause reduction in aperture of hydraulic *** decrease will lead to extension of fluid lag and eventually delaying of leak-off ***,this effect is negligible against the positive impact due to shear and normal displacement on increasing leak-off.

关键词： Hydraulic fracturing natural fracture Leak-off Interaction XFEM

natural fractures within unconventional reservoirs of Linxing Block,eastern Ordos Basin,central China

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Frontiers of Earth Science 2020年第4期14卷 770-782页

作者： Wei Ju Jian Shen Chao Li Kun Yu Hui Yang Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process Ministry of EducationChina University of Mining and TechnologyXuzhou221008China School of Resources and Geosciences China University of Mining and TechnologyXuzhou221116China Key Laboratory of Computational Geodynamics College of Earth and Planetary SciencesUniversity of Chinese Academy of SciencesBeijing100049China

Unconventional reservoirs are generally characterized by low matrix porosity and permeability,in which natural fractures are important factors for gas *** this study,we analyzed characteristics of natural fractures,and their influencing factors based on observations from outcrops,cores and image *** orientations of natural fractures were mainly in the∼N-S,WNW-ESE and NE-SW directions with relatively high fracture dip *** densities were calculated based on fracture measurements within cores,indicating that natural fractures were not well-developed in the Benxi-Upper Shihezi Formations of Linxing *** majority of natural fractures were open fractures and *** to the characteristics of fracture sets and tectonic evolution of the study area,natural fractures in the Linxing Block were mainly formed in the Yanshanian and Himalayan *** lithology and layer thickness influenced the development of natural fractures,and more natural fractures were generated in carbonate rocks and thin layers in the study *** addition,in the Linxing Block,natural fractures with∼N-S-trending strikes contributed little to the overall subsurface fluid flow under the present-day stress *** study results provide a geological basis for gas exploration and development in the Linxing unconventional reservoirs of Ordos Basin.

关键词： natural fracture unconventional reservoir Linxing region influencing factors Ordos Basin

Study on interaction between induced and natural fractures by extended finite element method

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Science China(Physics,Mechanics & Astronomy) 2017年第2期60卷 24-37页

作者： DanDan Xu ZhanLi Liu Zhuo Zhuang QingLei Zeng Tao Wang School of Aerospace Engineering Tsinghua University Beijing 100084 China

Fracking is one of the kernel technologies in the remarkable shale gas revolution. The extended finite element method is used in this paper to numerically investigate the interaction between hydraulic and natural fractures, which is an important issue of the enigmatic fracture network formation in fracking. The criteria which control the opening of natural fracture and crossing of hydraulic fracture are tentatively presented. Influence factors on the interaction process are systematically analyzed, which include the approach angle, anisotropy of in-situ stress and fluid pressure profile.

关键词： hydraulic fracturing natural fracture interaction criterion fluid pressure extended finite element method

Characterization of natural fractures in deep-marine shales: a case study of the Wufeng and Longmaxi shale in the Luzhou Block Sichuan Basin, China

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Frontiers of Earth Science 2023年第1期17卷 337-350页

作者： Shasha SUN Saipeng HUANG Enrique GOMEZ-RIVAS Albert GRIERA ΒοLIU Lulu XU Yaru WEN Dazhong DONG Zhensheng SHI Yan CHANG Yin XING PetroChina Research Institute of Petroleum Exploration&Development Beijing 100083China Key Laboratory of Continental Shale Hydrocarbon Accumulation and Efficient Development Ministry of EducationNortheast Petroleum UniversityDaqing 163318China Departament de Mineralogia Petrologia i Geologia AplicadaFacultat de Ciències de la TerraUniversitat de Barcelona(UB)c/Martíi Franquès s/nBarcelona 08028Spain Departament de Geologia Universitat Autònoma de BarcelonaBellaterra 08193Cerdanyola del VallèsSpain Hubei Geological Survey Wuhan 430034China School of Geography Science and Geomatics Engineering Suzhou University of Science and TechnologySuzhou 215009China

natural fractures are of crucial importance for oil and gas reservoirs,especially for those with ultralow permeability and *** deep-marine shale gas reservoirs of the Wufeng and Longmaxi Formations are typical targets for the study of natural fracture *** descriptions of full-diameter shale drill core,together with 3D Computed Tomography scans and Formation MicroScanner Image data acquisition,were carried out to characterize microfracture morphology in order to obtain the key parameters of natural fractures in such *** fracture type,orientation,and their macroscopic and microscopic distribution features are *** results show that the natural fracture density appears to remarkably decrease in the Wufeng and Longmaxi Formations with increasing the burial *** trends have been observed for fracture length and ***,the natural fracture density diminishes as the formation thickness *** are three main types of natural fractures,which we interpret as(I)mineral-filled fractures(by pyrite and calcite),i.e.,veins,(II)those induced by tectonic stress,and(III)those formed by other processes(including diagenetic shrinkage and fluid overpressure).natural fracture orientations estimated from the studied natural fractures in the Luzhou block are not consistent with the present-day stress *** difference in tortuosity between horizontally and vertically oriented fractures reveals their morphological *** addition,natural fracture density,host rock formation thickness,average total organic carbon and effective porosity are found to be important factors for evaluating shale gas *** study also reveals that the high density of natural fractures is decisive to evaluate the shale gas *** results may have significant implications for evaluating favorable exploration areas of shale gas reservoirs and can be applied to optimize hydraulic fracturing for permeability enhancement.

关键词： marine shale natural fracture filled fracture tortuosity

Evaluating the mechanical properties of anisotropic shale containing bedding and natural fractures with discrete element modeling

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International Journal of Coal Science & Technology 2022年第2期9卷 91-106页

作者： Yingjie Li Lihong Song Yuanjun Tang Jianping Zuo Dongjie Xue School of Mechanics and Civil Engineering China University of Mining and Technology(Beijing)Beijing 100083China

natural fracture data from one of the Carboniferous shale masses in the eastern Qaidam Basin were used to establish a stochastic model of a discrete fracture network and to perform discrete element simulation research on the size efect and mechanical parameters of *** solutions of fctitious joints in transversely isotropic media were derived,which made it possible for the proposed numerical model to simulate the bedding and natural fractures in shale *** results indicate that there are two main factors infuencing the representative elementary volume(REV)size of a shale *** frst and most decisive factor is the presence of natural fractures in the block *** second is the anisotropy ratio:the greater the anisotropy is,the larger the *** bedding angle has little infuence on the REV size,whereas it has a certain infuence on the mechanical parameters of the rock *** the bedding angle approaches the average orientation of the natural fractures,the mechanical parameters of the shale blocks decrease *** REV representing the mechanical properties of the Carboniferous shale masses in the eastern Qaidam Basin were comprehensively identifed by considering the infuence of bedding and natural *** the numerical model size is larger than the REV,the fractured rock mass discontinuities can be transformed into equivalent continuities,which provides a method for simulating shale with natural fractures and bedding to analyze the stability of a borehole wall in shale.

关键词： Shale Discrete fracture network natural fracture Anisotropy Discrete element modeling

A 3D analysis of the occurrence of fractures in hot dry rock reservoirs based on the spatial distribution of natural fractures

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Energy Geoscience 2023年第4期4卷 95-107页

作者： Siqing He Bo Feng Jinshou Zhu Xiyao Liu Shuantong ShangGuan Xiaofei Qi Jiulong Liu College of New Energy and Environment Jilin UniversityChangchun130021China Qinghai Bureau of Geological Survey Xining810001China The Second Exploration Team Hebei Bureau of Coal Geological ExplorationHebei Provincial Hot Dry Rock Research CenterXingtaiHebei054001China Center for Hydrogeology and Environmental Geology Survey China Geology SurveyTianjin300304China

Hot dry rock(HDR)geothermal energy is a kind of widely distributed clean energy with huge ***,its commercial development has been constrained by reservoir *** the early stage of HDR geothermal energy development,properly determining spatial distribution patterns of natural fractures in HDR reservoirs can effectively guide reservoir *** study analyzes the spatial distribution of natural fractures by using FracMan software based on the actual geological data and log data of well M-2 in the Matouying Uplift area,Hebei *** fracture parameters are counted and Monte Carlo simulation technique is introduced to optimize the parameters,which makes the natural fracture model more accurate and ***,this study simulates hydraulic fracturing using the model combined with the actual in-situ stress parameters and the construction *** verified by fitting the changes in simulated wellhead pressure during hydraulic fracturing with the actual wellhead pressure data detected during construction,the methods for natural fracture modeling used in this study are scientific and *** preliminary prediction results show that the displacement design scheme with a pump displacement of 2.0-3.0 m^(3)/min,4.0-5.5 m^(3)/min and 6-7 m^(3)/min in the early,middle and late stages,respectively,has good fracturing *** results of this study can be utilized as a reference for preparing development schemes for HDR reservoirs.

关键词： natural fracture Hot dry rock Reservoir modeling

Visualization of hydraulic fracture interacting with pre-existing fracture

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Petroleum Science 2023年第6期20卷 3723-3735页

作者： Zi-Xiao Xie Xiao-Guang Wu Teng-Da Long Zhong-Wei Huang Gen-Sheng Li Wen-Chao Zou Zhao-Wei Sun State Key Laboratory of Petroleum Resources and Prospecting China University of Petroleum-BeijingBeijing102249China

Hydraulic fracturing is considered the main stimulation method to develop shale gas reservoirs. Due to its strong heterogeneity, the shale gas formation is typically embedded with geological discontinuities such as bedding planes and natural fractures. Many researchers realized that the interaction between natural fractures and hydraulic fractures plays a crucial role in generating a complex fracture network. In this paper, true tri-axial hydraulic fracturing tests were performed on polymethyl methacrylate (PMMA), on which pre-existing fracture was pre-manufactured to simulate natural fracture. A cohesive model has been developed to verify the results of the experimental tests. The key findings demonstrate that the experimental results agreed well with the numerical simulation outcomes where three main interaction modes were observed: crossing;being arrested by opening the pre-existing fracture;being arrested without dilating the pre-existing fracture. Crossing behavior is more likely to occur with the approaching angle, horizontal stress difference, and injection rate increase. Furthermore, the higher flow rate might assist in reactivating the natural fractures where both sides of the pre-existing fractures were reactivated as the injection rate increased from 5 to 20 mL/min. Additionally, hydraulic fractures show a tendency to extend vertically rather than along the direction of maximum horizontal stress when they are first terminated at the interface. This research may contribute to the field application of hydraulic fracturing in shale gas formation.

关键词： Hydraulic fracturing natural fracture fracture propagation Interaction mode PMMA

A method to experimentally investigate injection-induced activation of fractures

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第6期12卷 1326-1332页

作者： Changdong Ding Yang Zhang Qi Teng Dawei Hu Hui Zhou Jianfu Shao Chuanqing Zhang State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China University of Chinese Academy of Sciences Beijing100049China CNPC Engineering Technology R&D Company Limited Beijing102206China PetroChina Tarim Oilfield Company Korla841000China University of Lille LaMcubeCNRS FRE 201659000LilleFrance

natural fractures are generally well developed in most hydrocarbon and geothermal reservoirs,which can produce complex fracture networks due to the activation of fractures during hydraulic *** present paper is devoted to developing a method to investigate the activation characteristics of fracture under injection-shearing coupled condition at laboratory *** fluid is injected into the single-fractured granite until the fracture is activated based on the triaxial direct shear *** results show that injection process can significantly influence the shear stress distribution field,resulting in release of shear stress and relative slip between the opposite sides of the fractured *** injectioninduced activation of fracture is strongly dependent on the stress *** the normal stress increases,the injection-induced activation pressure increases,and the comparatively high normal stress can restrain the fracture *** fracture deformation mechanisms during fluid injection are also discussed preliminarily with the experimental *** sensitivity of shear stress to fluid injection increases with increase of shear stress level,while it decreases under high normal *** results can facilitate our understanding of the natural fracture activation behavior during fluid pressure stimulation.

关键词： natural fracture Fluid injection Induced activation Triaxial direct shear test Hydraulic fracturing

Mechanisms of fracture propagation from multi-cluster using a phase field based HMD coupling model in fractured reservoir

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Petroleum Science 2024年第3期21卷 1829-1851页

作者： Yun-Jin Wang Bo Wang Hang Su Tu Chang Ren-Cheng Dong Li-Zhe Li Wei-Yu Tang Ting-Xue Jiang Fu-Jian Zhou State Key Laboratory of Petroleum Resources and Engineering China University of Petroleum-BeijingBejing2249China China University of Petroleum-Beijing at Karamay Karamay834000XinjiangChina China National Oil and Gas Exploration and Development Corporation Ltd. Beijing100034China University of Texas at Austin United States SINOPEC Research Institute of Petroleum Engineering Beijing100101China

natural fractures(NFs)are common in shale and tight reservoirs,where staged multi-cluster fracturing of horizontal wells is a prevalent technique for reservoir *** NFs and stress interference are recognized as significant factors affecting hydraulic fracture(HF)propagation,the combined influence of these factors remains poorly *** address this knowledge gap,a novel coupled hydromechanical-damage(HMD)model based on the phase field method is developed to investigate the propagation of multi-cluster HFs in fractured *** comprehensive energy functional and control functions are established,while incorporating dynamic fluid distribution between multiple perforation clusters and refined changes in rock mechanical parameters during hydraulic *** HMD coupled multi-cluster HF propagation model investigates various scenarios,including single HF and single NF,reservoir heterogeneity,single HF and NF clusters,and multi-cluster HFs with NF *** results show that the HMD coupling model can accurately capture the impact of approach angle(θ),stress difference and cementation strength on the interaction of HF and *** criterion of the open and cross zones is not *** NF angle(a)is not a decisive parameter to discriminate the *** to the relationship between approach angle(θ)and NF angle(a),the contact relationship of HF can be divided into three categories(θ=a,θa).The connected NF can increase the complexity of HF by inducing it to form branch fracture,resulting in a fractal dimension of HF as high as2.1280 at angles of±45°.Inter-fracture interference from the heel to the toe of HF shows the phenomenon of no,strong and weak ***,under the influence of NFs,distant HFs from the injection can become dominant ***,as a gradually increases,inter-fracture stress interference becomes the primary factor influencing HF propagation,gradually superseding the dominance of NF

关键词： HMD coupling Phase field natural fracture Flow distribution Hydraulic fracturing Inter-fracture interference