Extended finite element-based cohesive zone method for modeling simultaneous hydraulic fracture height growth in layered reservoirs

In this study,a fully coupled hydromechanical model within the extended finite element method(XFEM)-based cohesive zone method(CZM)is employed to investigate the simultaneous height growth behavior of multi-cluster hydraulic fractures in layered porous reservoirs with modulus contrast.The coupled hydromechanical model is first verified against an analytical solution and a laboratory experiment.Then,the fracture geometry(e.g.height,aperture,and area)and fluid pressure evolutions of multiple hydraulic fractures placed in a porous reservoir interbedded with alternating stiff and soft layers are investigated using the model.The stress and pore pressure distributions within the layered reservoir during fluid injection are also presented.The simulation results reveal that stress umbrellas are easily to form among multiple hydraulic fractures’tips when propagating in soft layers,which impedes the simultaneous height growth.It is also observed that the impediment effect of soft layer is much more significant in the fractures suppressed by the preferential growth of adjoining fractures.After that,the combined effect of in situ stress ratio and fracturing spacing on the multi-fracture height growth is presented,and the results elucidate the influence of in situ stress ratio on the height growth behavior depending on the fracture spacing.Finally,it is found that the inclusion of soft layers changes the aperture distribution of outmost and interior hydraulic fractures.The results obtained from this study may provide some insights on the understanding of hydraulic fracture height containment observed in filed.

A method for predicting the water-flowing fractured zone height based on an improved key stratum theory

In the process of using the original key stratum theory to predict the height of a water-flowing fractured zone(WFZ),the influence of rock strata outside the calculation range on the rock strata within the calculation range as well as the fact that the shape of the overburden deformation area will change with the excavation length are ignored.In this paper,an improved key stratum theory(IKS theory)was proposed by fixing these two shortcomings.Then,a WFZ height prediction method based on IKS theory was established and applied.First,the range of overburden involved in the analysis was determined according to the tensile stress distribution range above the goaf.Second,the key stratum in the overburden involved in the analysis was identified through IKS theory.Finally,the tendency of the WFZ to develop upward was determined by judging whether or not the identified key stratum will break.The proposed method was applied and verified in a mining case study,and the reasons for the differences in the development patterns between the WFZs in coalfields in Northwest and East China were also fully explained by this method.

Formation mechanism and height calculation of the caved zone and water-conducting fracture zone in solid backfill mining

To study the heights of the caved zone and water-conducting fracture zone in backfill mining,the failure mechanism of strata during backfill mining was analyzed,and a method for determining the heights of the two zones was proposed based on key strata theory.The movement and failure regularity of the strata above the backfilling panel were revealed through numerical simulation.Considering the geologic conditions of the CT101 backfilling panel,the height of the fracture zone was determined using the proposed method along with empirical calculation,numerical simulation,and borehole detection.The results of the new calculation method were similar to in situ measurements.The traditional empirical formula,which is based on the equivalent mining height model,resulted in large errors during calculation.The findings indicate the reliability of the new method and demonstrate its significance for creating reference data for related studies.

Research of the electrical anisotropic characteristics of water-conducting fractured zones in coal seams

Water flooding disasters are one of the five natural coal-mining disasters that threaten the lives of coal miners. The main causes of this flooding are water-conducting fractured zones within coal seams. However, when resistivity methods are used to detect water-conducting fractured zones in coal seams, incorrect conclusions can be drawn because of electrical anisotropy within the water-conducting fractured zones. We present, in this paper, a new geo-electrical model based on the geology of water-conducting fractured zones in coal seams. Factors that influence electrical anisotropy were analyzed, including formation water resistivity, porosity, fracture density, and fracture surface roughness, pressure, and dip angle. Numerical simulation was used to evaluate the proposed electrical method. The results demonstrate a closed relationship between the shape of apparent resistivity and the strike and dip of a fracture. Hence, the findings of this paper provide a practical resistivity method for coal-mining production.

Height of fractured zone inside overlying strata under high-intensity mining in China

The height of fractured zone(HFZ) at the high-intensity longwall mining panel plays a vital role in the safety analysis of coal mining under bodies of water. This paper described definitions of the highintensity mining. The processes of overburden failure transfer(OFT) were analyzed, which were divided into the development stage and the termination stage. Through theoretical analysis, the limited suspension-distance and the limited overhanging distance were proposed to judge the damage of each stratum. Mechanical models of strata suspended integrity and overhanging stability were established.A theoretical method to predict the HFZ at the high-intensity longwall mining panel was put forward based on the processes of OFT. Taking a high-intensity longwall mining panel(No. 11915 panel) as an example, the theoretical method proposed, the engineering analogy and the empirical formulas in the Regulation were used to predict the HFZ. The results show that the theoretical result is consistent with the engineering analogies' result and empirical formulas' result. The rationality and reliability of the theoretical method proposed is verified.

Height prediction of water flowing fractured zones based on BP artificial neural network

Factures caused by deformation and destruction of bedrocks over coal seams can easily lead to water flooding(inrush)in mines,a threat to safety production.Fractures with high hydraulic conductivity are good watercourses as well as passages for inrush in mines and tunnels.An accurate height prediction of water flowing fractured zones is a key issue in today's mine water prevention and control.The theory of leveraging BP artificial neural network in height prediction of water flowing fractured zones is analysed and applied in Qianjiaying Mine as an example in this paper.Per the comparison with traditional calculation results,the BP artificial neural network better reflects the geological conditions of the research mine areas and produces more objective,accurate and reasonable results,which can be applied to predict the height of water flowing fractured zones.

Height Detection and Analysis of Water Flowing Fractured Zone of Coal Face

Taking 91105 working face as the research object, the observation method of water flowing fractured zone and the layout of mining holes were determined by analyzing the field geological structure. It was shown that the fractured zone height and the ratio given by the measured method were 52.33 and 12.46, respectively. By the numerical simulation method with the software of UDEC, the fractured zone height and the ratio were 42.5 and 10.12. By comparison of measured height data and UDEC numerical simulation, there were some differences between the measured height and the calculated results of UDEC numerical simulation method. The method of simulation can be used as the technical basis for the design of waterproof coal pillar in the future.

基于相似模拟试验的顶板导水裂隙带高度及发育形态研究

目的 为研究采动影响下顶板导水裂隙带高度及其发育形态,方法 以司马煤矿三采区1303工作面为研究对象,开展相似模拟试验,并以此为基础,对顶板的岩性组合加以改变,结合数字照相量测系统对不同岩性组合顶板导裂带高度和发育形态进行分析,并进行理论验证。结果 结果表明:(1)工作面推进长度为160 m时,硬岩岩性顶板模型、硬-软岩岩性组合顶板模型以及软岩岩性顶板模型的导水裂隙带最大发育高度分别为69.6,55.6,61.1 m;(2)3种模型的导水裂隙带发育形态分别为底角50°的正梯形、前底角62°后底角60°的近似正梯形、前底角50°后底角60°的梯形;(3)根据模型试验和数据统计结果,给出适用于长治二岗山断褶带以南井田导水裂隙带发育高度预测式;(4)运用材料力学方法分析垮落角形成规律,垮落角与导水裂隙带发育高度呈反正切函数关系,并计算得到3种模型导水裂隙带前底角发育角度,分别为49.24°,61.21°和51.12°。通过导高计算公式得到3种模型导水裂隙带发育高度分别为74.1,51.1,59 m,均与相似模拟试验结果吻合。结论 研究结果对各类岩性顶板煤矿导水裂隙带发育高度预测具有参考意义。

河流下多煤层开采安全性及保护技术

我国新疆地区干旱缺水,艾维尔沟河作为新疆一条具有重要地理特征和环境影响的河流,其对于流经区域的经济、生态都具有重要意义,因此在艾维尔沟河下进行煤炭开采时,既要保证矿井安全也要保证河流的正常使用。采用理论分析、数值模拟等方法对河流下多煤层开采安全性及河流保护技术进行研究,通过理论计算得到多煤层开采条件下,覆岩导水裂隙带发育高度(11401工作面为41.9 m、1502工作面为110 m、11401工作面为113.8 m)并绘制剖面示意图;同时,采用数值模拟方法对覆岩导水裂缝发育形态及高度进行确定,最终基于导水裂隙带高度(117.8 m)与最小煤层埋藏深度(191.5 m)的相互关系,确定河流下开采是安全的可行的。在保证河流下煤层安全开采的前提下,通过分析离层注浆原理,并结合采动影响特征参数及工程现场,提出了以离层注浆为主,河道防渗及优化开采设计为辅的多手段对采动影响范围内地表特定目标的精准保护技术。根据实际采矿地质条件,采用概率积分法计算试采工作面开采前后河道位置处地表移动变形,计算结果显示:采用离层注浆精准保护技术后,河道的最大水平变形值(2 mm/m)未超出允许坝体的极限变形值(2.5 mm/m),所以采用离层注浆精准保护技术可以实现,井下安全开采的同时,保证河道的正常使用。通过对河流下多煤层开采的安全性及保护技术的分析研究,为矿山绿色开采提供参考和借鉴。

坚硬覆岩预裂弱化改性效应及导水裂缝带控制机理

针对深部煤层开采坚硬覆岩条件下导水裂缝带控制问题,充分借鉴坚硬顶板预裂弱化技术,提出预裂弱化坚硬主控覆岩控制导水裂缝带高度的新方法。综合采用实验室试验、理论分析、数值模拟等方法,研究了坚硬主控覆岩预裂弱化改性效应,详细阐述了不同弱化层位对导水裂缝带的控制机理,并进行了实测验证。研究结果表明:预制裂缝可以使坚硬岩石往强度低的方向进行转变,并将完整岩样的劈裂破坏特征转变为以预制裂缝为主控的张拉剪切破坏,坚硬岩石的破坏程度由剧烈趋于缓和;揭示了预制裂缝对坚硬岩体的弱化改性效应,计算得到应力与裂缝耦合的损伤变量,定性的分析了弱化程度与岩性转变的关系,改性后岩体能量存储能力降低,耗散能力增强;数值模拟了不同弱化层位对导水裂缝带的控制效果,综合对比覆岩破坏形态、裂隙数量及破坏高度动态演化规律,发现“马鞍形”破坏形态随着弱化层位的升高而逐渐减弱,覆岩裂隙数量演化基本呈现“缓增−突增”的演化趋势,未弱化以及中、高位弱化覆岩破坏高度动态演化近似呈现“S”形,而中位弱化呈“半抛形”,综合分析得出低位弱化对导水裂缝带的控制效果最好;在分析高、中、低位坚硬岩层破坏特征的基础上,揭示了不同预裂弱化层位控制导水裂缝带发育机理;钻孔实测孟村矿顶板压裂条件下的“两带”发育高度,对比发现预裂弱化条件下裂采比降低,初步验证了顶板预裂弱化对导水裂缝带发育的抑制性。研究成果将为深部矿区耦合灾害防控、水资源及生态保护等领域提供理论和科学依据。

基于LDA-RBF及综合赋权法的顶板突水危险性评价

为了解决龙凤煤矿9号煤层开采过程中顶板突水危险性问题,采用线性判别分析法(LDA)构建1种LDA-RBF神经网络导水裂隙带发育高度预测模型,并基于改进CRITIC评价法结合层次分析法(AHP)建立了CRITIC-AHP综合赋权法,分别评价矿区顶板采裂危险性及含水层富水性等级;通过ArcGis地理信息处理技术,将采裂危险性分区与富水性分区叠加,得到9号煤层顶板突水危险性综合分区图。结果表明:LDA-RBF神经网络预测模型结构简单且拟合精度更高,9号煤层导水裂隙带发育预测高度为50.4 m,已超过区域内大部分含水层底界标高,表明大部分区域存在较高的采裂危险性;而改进后的综合赋权法避免了评价结果主客观性过强的问题,其富水性分区结果与钻孔实际涌水量相符;突水危险区主要在矿区中北部呈条状分布,这是该区域含水层富水性较强和采裂危险性较高共同作用的结果,因此,在实际开采中应对以上区域予以重视。

煤矿导水裂隙带影响因素敏感性及高度预测研究

研究导水裂隙带高度是含水层修复和地表生态保护的重要基础,明确其影响因素的敏感性排序,有利于抓住主要矛盾,安全高效地实现矿井水预防。本文采用现场实测、数值模拟和数学统计方法,分析了导水裂隙带高度与岩层硬度、工作面长度、采高和埋深的内在联系,得到了导水裂隙带高度计算公式,并在现场得到应用。通过研究可知:导水裂隙带高度在硬岩中传导更快,而软岩可以抑制导水裂隙带高度。软岩与硬岩组合(下软上硬)导水裂隙带高度大于硬岩与软岩组合(下硬上软)导水裂隙带高度。开采方法会影响导水裂隙带高度,综放开采导水裂隙带高度大于厚煤层分层开采、单一薄煤层开采、单一中厚煤层开采。各因素影响导水裂隙带高度的程度为:采高>硬岩岩性比例系数>采深>工作面长度。与“三下”规程经验公式相比,利用多因素拟合公式可以较好地实现乌兰木伦煤矿12403工作面导水裂隙带高度预测,误差仅为−2.54%,研究成果为地下水资源保护和水害治理提供指导依据。

高家堡井田二盘区导水裂隙带高度实测研究

为了查明煤层顶板导水裂隙发育规律,采用地面钻孔分段注水测试和钻孔窥视方法实测了高家堡井田204工作面和205工作面煤层顶板导水裂隙带发育高度。研究结果表明:(1)205工作面DT1钻孔位置煤层顶板导水裂隙带发育高度为327.75 m,裂采比25.81。(2)204工作面DT2钻孔位置煤层顶板导水裂隙带发育高度为197.85 m,裂采比35.33。(3)高家堡井田二盘区导水裂隙带实测结果丰富了黄陇煤田综放采煤覆岩破坏规律。

金谷煤矿充水因素分析评价及涌水量预测

本文对山西古县金谷煤业有限公司的地质与水文地质条件进行分析研究,查明矿井主要充水因素,包括大气降水及地表水、含水层水、采空区积水等。通过现场实测和数据分析,确定了各含水层的水文特征及其与矿井充水的关系,计算了垮落带和导水裂隙带高度以及奥灰水突水系数。在此基础上,采用面积比拟法对矿井涌水量进行了预测,得出矿井正常涌水量为54.58 m^(3)/h,最大涌水量为81.87 m^(3)/h。这一研究为金谷煤业矿井水害防治提供了科学依据,有助于提高矿井的安全生产水平,对于类似地质条件下的煤矿充水因素评价与涌水量预测具有重要的参考价值。

多煤层开采顶板导水裂隙带发育高度模拟分析研究

针对由顶板覆岩破坏而导致的矿井水害问题,以A煤矿一、二水平工作面为工程背景,采用力学理论分析与数值模拟等方法,分析了该煤矿多煤层开采条件下导水裂隙带发育高度特征,探讨了9号煤层回采不同距离时覆岩运移特征。结果表明:在4+5号及8号煤层回采结束后的重复采动过程中,9号煤层导水裂隙带与8号煤层贯通;9号煤层斜长200 m,工作面割煤回采引起导水裂隙带发育高度约为144.95 m,对8号煤层导水裂隙带发育高度影响不明显,对4+5号煤层导水裂隙带发育高度造成一定影响。对复杂开采条件下顶板导水裂隙带发育高度的研究,对指导矿井安全生产,防治矿井水害有着重要的现实意义。

地表水体下大采高工作面重复采动安全性评价

为了确定地表水体下大采高工作面重复采动的可行性和安全性,采用FLAC3D数值模型,对宁东煤田红石湾煤矿五煤和八煤重复采动后的覆岩破坏规律进行研究,五煤和八煤工作面均为大采高工作面,采高分别为4.6 m和4.8 m,根据数值模拟结果,五煤和八煤工作面回采后的冒落带高度分别为13.8 m和15.0 m,八煤工作面的导水裂隙带高度为242.0 m,保护带厚度为56.4 m,八煤工作面最浅处距离地表水体353.0 m,大于需要留设的防隔水煤(岩)柱高度(298.4 m),结合研究区的构造发育条件和隔水层隔水性能特征,确定地表水体下五煤和八煤的大采高工作面重复开采的安全性较高。结果表明,可以采用数值模型对大采高工作面重复开采后的覆岩破坏规律进行分析,通过实例分析,地表水体下大采高工作面重复采动安全性评价符合实际情况,可以作为井田未来评价工作面受地表水体威胁程度的依据。

基于HHO-ELM模型的导水裂隙带高度预测方法

为了精确预测滨湖煤矿16煤开采导水裂隙带发育高度,收集华北煤田31个下组煤开采工作面实测数据,选取采高、采深、煤层倾角、倾向长度、硬岩比例系数5个因素进行综合分析。运用哈里斯鹰算法(HHO)优化ELM神经网络,构建了HHO-ELM导水裂隙带高度预测模型,将其应用于滨湖煤矿导水裂隙带高度预计,并将预测结果与规范公式计算结果和实测结果进行对比。结果表明:HHO-ELM模型预测滨湖煤矿21603工作面导水裂隙带发育高度为24.17 m,规范公式计算结果为18.58~29.78 m,实测结果为21.45~22.98 m。可见,采用HHO-ELM模型预计导水裂隙带高度,计算简单,针对性强,预测精度可靠,为滨湖煤矿及相似地质条件下的华北型煤田下组煤开采顶板水害治理决策提供了依据。

麦捷煤矿回采期间顶板裂隙发育规律及瓦斯治理应用研究

为有效改善软弱煤层工作面瓦斯治理情况,以麦捷煤矿150508采煤工作面为研究对象,采用数值模拟、理论计算和现场实践相结合的方法,对工作面回采期间的围岩裂隙发育和瓦斯治理模式进行研究,提出了“高抽巷-顶板裂隙孔-风排瓦斯”的治理模式。利用数值模拟方法,对顶板裂隙钻孔施工参数和高抽巷布置层位进行了优化设计,并进行现场应用考察。结果表明:煤层冒落带发育高度为16.8 m,裂隙带发育高度为54.5 m;高抽巷最佳布置层位为16.8~35.6 m,顶板裂隙孔布置层位为20~40 m。在“高抽巷-顶板裂隙孔-风排瓦斯”的治理模式下,上隅角瓦斯体积分数平均为0.26%,工作面瓦斯抽排率平均为64%,瓦斯治理达到预期目标,保障了工作面安全回采。

矿井煤层综放开采导水裂隙带发育高度研究

针对马道头煤业存在煤层开采导水裂隙带与地下含水层连通,突水事故风险高的问题,该矿进行了导水裂隙带发育高度预测研究。分别采用经验公式计算法、关键层理论分析法、数值模拟法预测3号煤层8404采区的导水裂隙带高度为183~200 m。为验证理论预测的准确性,进行现场两个钻孔冲洗液漏失量、岩芯完整性实测,确定导水裂隙带发育高度为196~216 m,证明了理论分析法的准确性和实用性。

袁大滩煤矿超长工作面覆岩两带发育规律研究

针对超长工作面采动影响下覆岩两带发育规律,以袁大滩煤矿工作面为背景,采用理论分析与离散元的3DEC数值计算软件相结合的方法,研究该条件下覆岩裂隙的分布特征与两带发育规律。结果表明,根据理论计算,得到2号煤层工作面不同采高下2种经验公式的两带发育高度,得出随着工作面采高的增加,工作面采后的导水裂隙带高度逐渐增加,但其裂隙高度的递增幅度逐渐减小的规律;通过3DEC数值模拟,11207超长工作面采高每增加0.2 m所得导水裂隙带高度约增加2.01~3.05 m,超长工作面采高越大,开采高度增加引起裂隙发育高度增幅越小。数值模拟与理论计算基本一致且相互印证。工作面实际开采过程中工作面的开采高度逐渐减小,裂隙带发育高度逐渐降低,覆岩位移量逐渐减小,集中应力逐渐减弱,开采初期需要加强监测,增强防护措施。