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Propagation and sealing efficiency of chemical grouting in a two-dimensional fracture network with flowing water

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International Journal of Mining Science and Technology 2023年第7期33卷 903-917页

作者： Guosheng Zheng Wanghua Sui Gailing Zhang Jiaxing Chen Dingyang Zhang School of Resources and Geosciences Institute of Mine Water Hazards Prevention and Controlling TechnologyChina University of Mining and TechnologyXuzhou 221116China Shandong Provincial Communications Planning and Design Institute Group CO. Ltd.Jinan 250031China National Coal Mine Water Hazard Prevention Engineering Technology Research Center Suzhou 234000China School of Geology and Geomatics Tianjin Chengjian UniversityTianjin 300380China

In this study, an orthogonal array experiment is conducted by using a transparent fracture network replica. Image processing and theoretical analysis are performed to investigate the model sealing efficiency(SE), factors influencing SE, and the effect of flowing water on propagation. The results show that grout propagation can be classified into three patterns in the fracture network: sealing off, partial sealing,and major erosion. The factors controlling the SE in a descending order of the amount of influence are the initial water flow speed, fracture aperture, grout take, and gel time. An optimal value for the combination of the gel time and grout take(artificial factors) can result in a good SE. The grouting and seepage pressures are measured, and the results reveal that their variations can indicate the SE to some extent. The SE is good when the seepage pressure at each point increases overall;the frequent fluctuations in the seepage pressure indicate a moderately poor SE, and an overall decline in the seepage pressure indicates a major erosion type. The deflection effect of grouting shows an approximately elliptical propagation with the long axis expanding along the wider fracture opening, demonstrating further application in grouting design.

关键词： fracture network Grouting Propagation Sealing efficiency Physical modeling Deflection effect of grouting

Graph theoretical analysis of limestone fracture network damage patterns based on uniaxial compression test

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第9期16卷 3485-3510页

作者： Mingyang Wang Congcong Wang Enzhi Wang Xiaoli Liu Xiao Li State Key Laboratory of Hydro-science and Engineering Tsinghua UniversityBeijing100084China Department of Automation Tsinghua UniversityBeijing100084China Beijing Huairou Laboratory Beijing101400China Institute of Geology and Geophysics Chinese Academy of ScienceBeijing100029China

The topological attributes of fracture networks in limestone,subject to intense hydrodynamics and intricate geological discontinuities,substantially influence the mechanical and hydraulic characteristics of the rock *** dynamical evolution of fracture networks under stress is crucial for unveiling the interaction patterns among ***,existing models are undirected graphs focused on stationary topology,which need optimization to depict fractures'dynamic development and rupture *** compensate for the time and destruction terms,we propose the damage network model,which defines the physical interpretation of fractures through the ternary *** focus primarily on the evolution of node types,topological attributes,and motifs of the fracture network in limestone under uniaxial *** expose the varying behavior of the nodes'self-dynamics and neighbors'adjacent dynamics in the fracture *** approach elucidates the impact of micro-crack behaviors on large brittle shear fractures from a topological perspective and further subdivides the progressive failure stage into four distinct phases(isolated crack growth phase,crack splay phase,damage coalescence phase,and mechanical failure phase)based on the significance profile of the *** analysis reveals a positive linear and negative power correlation between fracture network density and branch number to the rock damage resistance,*** damage network model introduces a novel methodology for depicting the interaction of two-dimensional(2D)projected fractures,considering the dynamic spatiotemporal development characteristics and fracture geometric *** helps dynamically characterize properties such as connectivity,permeability,and damage factors while comprehensively assessing damage in rock mass fracture networks.

关键词： Motif fracture network Topological property Damage resistance Limestone

Earthquake-induced fracture displacements and transmissivity changes in a 3D fracture network of crystalline rock for spent nuclear fuel disposal

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第9期15卷 2313-2329页

作者： Wenbo Pan Zixin Zhang Shuaifeng Wang Qinghua Lei Department of Geotechnical Engineering College of Civil EngineeringTongji UniversityShanghaiChina Key Laboratory of Geotechnical and Underground Engineering Ministry of EducationTongji UniversityShanghaiChina Department of Earth Sciences ETH ZürichZürichSwitzerland Department of Earth Sciences Uppsala UniversityUppsalaSweden

During the long service period of a nuclear waste repository in crystalline rock,large earthquake(s)may occur nearby the repository site and coseismically alter the local stress field around pre-existing fractures within the geological *** resulting fracture normal/shear displacements may lead to fracture opening and further promote the transport of leaked radionuclides into the groundwater ***,it is of central importance to analyze the consequences of potential future earthquake(s)on the hydrogeological properties of a repository site for spent nuclear fuel *** on the detailed site characterization data of the repository site at Forsmark,Sweden,we conduct a three-dimensional(3D)seismo-hydro-mechanical simulation using the 3Dimensional Distinct Element Code(3DEC).We explicitly represent a primary seismogenic fault zone and its surrounding secondary fracture network associated with a power-law size scaling and a Fisher orientation *** earthquake with a magnitude of M_(w)=5.6 caused by the reactivation of the primary fault zone is modeled by simulating its transient rupture propagating radially outwards from a predefined hypocenter at a specified rupture speed,with the faulting dynamics controlled by a strength weakening *** model the coseismic response of the off-fault fracture network subject to both static and dynamic triggering *** further diagnose the distribution of fracture hydro-mechanical properties(***/hydraulic aperture,hydraulic transmissivity)before and after the earthquake in order to quantify earthquakeinduced hydraulic changes in the fracture *** is found that earthquake-induced fracture transmissivity changes tend to follow a power-law decay with the distance to the earthquake *** simulation results and insights obtained have important implications for the long-term performance assessment of nuclear waste repositories in fractured crystalline rocks.

关键词： Earthquake fracture network Aperture fracture transmissivity Shear dilation Nuclear waste disposal

Simulation of the Pressure-Sensitive Seepage fracture network in Oil Reservoirs with Multi-Group fractures

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Fluid Dynamics & Materials Processing 2022年第2期18卷 395-415页

作者： Yueli Feng Yuetian Liu Jian Chen Xiaolong Mao State Key Laboratory of Petroleum Resources and Prospecting China University of Petroleum(Beijing)Beijing102249China College of Petroleum Engineering China University of Petroleum(Beijing)Beijing102249China

Stress sensitivity is a very important index to understand the seepage characteristics of a *** this study,dedicated experiments and theoretical arguments based on the visualization of porous media are used to assess the effects of the fracture angle,spacing,and relevant elastic parameters on the principal value of the permeability *** fracture apertures at different angles show different change rates,which influence the relative permeability for different sets of ***,under the same pressure condition,the fractures with different angles show different degrees of deformation so that the principal value direction of permeability *** phenomenon leads to a variation in the water seepage direction in typical water-injection applications,thereby hindering the expected exploitation effect of the original well ***,the research findings in this paper can be used as guidance to improve the effectiveness of water injection exploitation in the oil field industry.

关键词： Pressure sensitive fracture network physical simulation seepage laws

The fracture network model of Shen 229 block buried hill:A case study from Liaohe Basin,China

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2006年第11期7卷 1904-1910页

作者： XING Yu-zhong FAN Tai-liang ZHENG Li-hui Energy Sources Department China University of Geosciences. Beijing 100083 China Exploration ＆ Exploitation Research Institute of Liaohe Oil Field Company Petrochina. Panjin 124010. China

High oil production from the Proterozoic formation of Shen 229 block in Damingtun Depression, Liaohe Basin, China, indicates the presence of natural fractured reservoir whose production potential is dominated by the structural fracture. A con- sistent structural model and good knowledge of the fracture systems are therefore of key importance in reducing risk in the de- velopment strategies. So data from cores and image logs have been collected to account for the basic characteristics of fracture, and then the analyzed results were integrated with the structural model in order to restrict the fracture network development during the structural evolvement. The structural evolution of the Proterozoic reservoir with time forms the basis for understanding the de- velopment of the 3D fracture system. Seismic interpretation and formation correlation were used to build a 3D geological model. The fault blocks that compose the Proterozoic formation reservoir were subsequently restored to their pre-deformation. From here, the structures were kinematically modeled to simulate the structural evolution of the reservoirs. At each time step, the dilatational and cumulative strain was calculated throughout the modelling history. The total strain which records the total spatial variation in the reservoir due to its structural history, together with core data, well data and the lithology distribution, was used to simulate geologically realistic discrete fracture networks. The benefit of this technique over traditional curvature analysis is that the structural evolution is taken into account, a factor that mostly dominates fracture formation.

关键词： Buried hill fracture network In-situ stress Structural fracture

Pump-stopping pressure drop model considering transient leak-off of fracture network

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Petroleum Exploration and Development 2023年第2期50卷 473-483页

作者： WANG Fei XU Jiaxin ZHOU Tong ZHANG Shicheng State Key Laboratory of Petroleum Resources and Prospecting China University of Petroleum(Beijing)Beijing 102249China Chongqing Fuling Shale Gas Exploration and Development Co. Ltd.SinopecChongqing 408014China Petroleum Exploration and Production Research Institute SinopecBeijing 102206China

By introducing the coupling flow expressions of main fracture-matrix, secondary fracture-matrix and main fracture-secondary fracture into the traditional main fracture material balance equation, the “main fracture-secondary fracture-matrix” leak-off coupling flow model is established. The pressure-dependent fracture width equation and the wellbore injection volume equation are coupled to solve the pressure-rate continuity problem. The simulation and calculation of the bottomhole pressure drop and fracture network closure after the pump stopping in slickwater volumetric fracturing treatment are realized. The research results show that the log-log curve of pump-stopping bottomhole pressure drop derivative presents five characteristic slope segments, reflecting four dominant stages, i.e. inter-fracture crossflow, fracture network leak-off, fracture network closure and residual leak-off, after pump shutdown. At the initial time of pump shutdown for volumetric fracturing treatment of horizontal well, the crossflow between main and secondary fractures is obvious, and then the leak-off becomes dominant. The leak-off of main and secondary fractures shows a non-uniform decreasing trend. Specifically, the leak-off of main fractures is slow, while that of secondary fractures is fast;the fracture network as a whole presents the leak-off law of fast first, then slow, until close to zero. The influence of fracture network conductivity on the shape of pressure decline curve is relatively weaker than that of fracture network size. The fracture network conductivity is positively correlated with leak-off volume and fracture closure. The secondary fracture size is positively correlated with leakoff volume and closure of the secondary fracture, but negatively correlated with closure of the main fracture. Field data validation proves that the proposed model and simulation results can effectively reflect the closure characteristics of the fracture network, and the interpretation results

关键词： volume fracturing stop-pumping pressure drop fracture network characteristic curve transient leak-off frac-ture closure stimulation performance

Nonlinear fluid flow through three-dimensional rough fracture networks:Insights from 3D-printing,CT-scanning,and high-resolution numerical simulations

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第5期13卷 1020-1032页

作者： Bo Li Jiafei Wang Richeng Liu Yujing Jiang Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province Shaoxing UniversityShaoxing312000China State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou221116China School of Engineering Nagasaki UniversityNagasaki852-8521Japan

Nonlinear flow behavior of fluids through three-dimensional(3D)discrete fracture networks(DFNs)considering effects of fracture number,surface roughness and fracture aperture was experimentally and numerically *** physical models of DFNs were 3D-printed and then computed tomography(CT)-scanned to obtain the specific geometry of *** validity of numerically simulating the fluid flow through DFNs was verified via comparison with flow tests on the 3D-printed models.A parametric study was then implemented to establish quantitative relations between the coefficients/parameters in Forchheimer’s law and geometrical *** results showed that the 3D-printing technique can well reproduce the geometry of single fractures with less precision when preparing complex fracture networks,numerical modeling precision of which can be improved via CT-scanning as evidenced by the well fitted results between fluid flow tests and numerical simulations using CT-scanned digital *** in DFNs become increasingly tortuous as the fracture number and roughness increase,resulting in stronger inertial effects and greater curvatures of hydraulic pressure-low rate relations,which can be well characterized by the Forchheimer’s *** critical hydraulic gradient for the onset of nonlinear flow decreases with the increasing aperture,fracture number and roughness,following a power *** increases in fracture aperture and number provide more paths for fluid flow,increasing both the viscous and inertial *** value of the inertial permeability is approximately four orders of magnitude greater than the viscous permeability,following a power function with an exponent a of 3,and a proportional coefficient b mathematically correlated with the geometrical parameters.

关键词： Nonlinear flow 3D-printing CT-scanning fracture network Permeability Fluid flow test

An optimization model for conductivity of hydraulic fracture networks in the Longmaxi shale,Sichuan basin,Southwest China

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Energy Geoscience 2020年第1期1卷 47-54页

作者： Zhihong Zhao Kaidi Wu Yu Fan Jianchun Guo Bo Zeng Wenhan Yue State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChenduSichuanChina Shale Gas Research Institute PetroChina Southwest Oil and Gas Field CompanyChenduSichuanChina

Shale gas is an important unconventional *** economic recovery of shale gas is only possible when a fracture network with sufficient conductivity is created by hydraulic fracturing,that,if effectively propped,connects fracturing fractures and natural *** on the Longmaxi shale in the Sichuan Basin,Southwest China,we built an optimization model for conductivity of multi-grade fractures based on equivalent seepage *** then experimentally analyzed the conductivity of self-propped and sand-propped fractures,and optimized the propping patterns of multi-grade hydraulic fractures in shale gas *** concluded that the propping effectiveness of fracture networks could be improved by using low concentrations of small-sized sands and by focusing on creating a large number of self-propped *** applying this understanding to the optimization of fracturing designs for the Longmaxi shale,we successfully created networks of well-propped fractures.

关键词： fracture network Conductivity optimization Propped fracture Self-propped fracture Shale gas

A new variational inequality formulation for unconfined seepage flow through fracture networks

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Science China(Technological Sciences) 2012年第11期55卷 3090-3101页

作者： JIANG QingHui YE ZuYang YAO Chi ZHOU ChuangBing School of Civil Engineering Wuhan UniversityWuhan 430072China State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan 430072China

Darcy's law only applying to the flow domain is extended to the entire fracture network domain including the dry *** partial differential equation(PDE) formulation for unconfined seepage flow problems for discrete fracture network is established,in which a boundary condition of Signorini's type is prescribed over the potential seepage *** order to reduce the difficulty in selecting trial functions,a new variational inequality formulation is presented and mathematically proved to be equivalent to the PDE *** numerical procedure based on the VI formulation is proposed and the corresponding algorithm has been *** a continuous penalized Heaviside function is introduced to replace a jump function in finite element analysis,oscillation of numerical integration for facture elements cut by the free surface is eliminated and stability of numerical solution is *** numerical results from two typical examples demonstrate,on the one hand the effectiveness and robustness of the proposed method,and on the other hand the capability of predicting main seepage pathways in fractured rocks and flow rates out of the drainage system,which is very important for performance assessments and design optimization of complex drainage system.

关键词： fracture network seepage flow free surface variational inequality condition of Signorini's type

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