组合模式与地震图上的终止震相——兼论唐山地震的震源破裂过程

本文从成因上研究了组合模式与地震图上终止震相的联系。组合模式因积累单元端部有剪应力集中区,张应力让位区和弱介质让位区,故断层传播到积累单元端部要加速,然后急剧停止,这就导致了终止相的形成。这些端部因素是调整单元的存在引起的。地震图上的终止震相的发育程度与组合模式中的调整单元让位的充分程度有关,让位条件愈好,终止震相愈明显。最后本文以唐山地震为例进行了实际讨论。     

板内大断裂形成问题的讨论

本文讨论了大断裂形成的力源问题,分析了我国一些大地震的资料后认为大断裂形成的力源是板块水平挤压力和上地幔垂直力作用到地壳后引起的应力迭加的结果。综述了前人利用断裂力学理论与实验结果研究地壳中断裂传播时所持的不同观点。地壳中断裝的传播不只是受断裂力学规律本身的制约,外部附加的剪切应力对断裂的传播也起着重要作用。地壳下部大断裂蠕滑所产生的施加在地壳上层底部的分布剪切力在地壳上层中产生的附加剪切力可以增强原来断裂端部的剪切应力,使岩体首先超过抗剪强度因而断裂沿合成剪切力的方向快速错动,从而形成了地壳中长而直的断裂带。利用弹性体的半空间问题推导了分布剪切力在地壳上层产生的附加应力场和估算了附加剪切应力和附加张应力的大小。利用静力弹性位错理论分析了软弱区引起的像力对断裂扩展的影响。在实际地壳中介质並不是均匀的,在地壳上层还可能存在一些局部的破碎区、软弱区。积累单元断层面除受有效构造应力外还受到由于断层物质蠕变形成的附加剪切应力和由于软弱区、破碎区的存在形成的附加剪切应力的作用,这两种附加剪切应力都是时间的函数,随着时间的增加而增加,而且像力还和积累单元断层面到软弱区的距离成反比。断裂的传播要受到软弱区对它作用的像力,即相当于附加了一个剪切应力在断裂端部,增加了断裂端部的应力强度因子。最后讨论了震源断层面的下方有岩浆侵入时的防拐作用。当孕裳的脆性层底部有热物质侵入而形成直线凹槽时断裂沿其传播也不拐弯。     

在围压条件下切口岩石破裂过程的实验研究

本文根据地震的断层说观点在室温、围压600—1,200巴条件下研究了具切口的花岗闪长岩、辉长岩和大理岩试件的破裂发展过程。在连续增加的差应力作用下观测到:切口内部充填的软弱夹层首先发生剪切变形和破裂,接着在切口端部一侧扩展张性裂纹,然后在切口前缘方向扩展剪切裂纹,最后发生贯通试件的剪切和张裂-剪切主破坏。张裂纹扩展长度受到围压的强烈抑制。岩石的切口结构和岩性变化对破裂迹线的空间展布和主破坏机制有重要影响。讨论了实验结果在断层扩展型地震的形成过程及其在预报预测方面的意义     

震源区的断层构造与震源应力积累过程关系的实验研究

本实验研究了地壳内对压组合构造和对张组合构造中垂断层蠕滑,破裂错动时对主震断层(底断层)应力积累过程的影响,并结合实际地震活动中的一些现象进行了讨论。所得结论如下: 1.当垂断层蠕滑时,对压组合构造中垂直于底断层的压应力增大,它可以延迟主震发生但增大发震的能量;对张组合构造中垂直于底断层的压应力减小,剪应力略有增大,因而可以促使主震发生。2.如果垂断层某一部分为原来锁住的愈合断层或为完整介质,当其突然破裂错动时,可以使对张组合构造中的底断层的剪应力突然增大,同时压应力减小,因此前震序列中这类垂断层上的较大前震可看作底断层上主震即将来临的信号。3.由垂断层破裂前后单轴压力不变和位移不变的实验结果说明了地壳中主震断层应力集中的过程。4.底断层的主震破裂可以使处于引张状态的垂断层上余震发育甚至发生强余震。本文还应用实验结果对前震活动的条带现象进行了解释,这将有助于判定对压组合构造中主震的断层面。     

水库地震成因的新看法——弱化象力模式

以前的水库地震成因学说大多是认为地下断层积累了较高的应力,难以错动,当水库蓄水后,水通过裂隙渗透到断层面上,从而降低了断层面上的有效正压力或摩擦系数,导致断层的快速错动形成地震。然而这个学说对解释极浅源地震是有困难的。根据模拟实验,产生粘滑要有一定的正应力,否则仅能产生稳滑。在地下几公里的深度上围压比较小,因之在这样的深度是否存在粘滑条件还值得商榷。在这种情况下,用水去帮助断层错动更没有必要了。本文作者认为水库地区坚硬介质中大量小裂缝的接通是某些水库发生大量小震的原因。水进入裂缝后可加强裂纹的蠕滑,它使裂纹端部形成应力集中,有利于诸裂纹间的接通,而不是水进入断层后使断层本身发生错动而形成地震。当大量小裂缝互相接通时,即大量水库小震发生后,水又进一步渗透到小震活动区,使这一软弱区的范围(面积和深度)进一步扩大,形成应力调整区。如果在库区下方较深处有隐伏的蠕滑断层(走滑或倾滑),这可成为水库区另一个调整单元。它们之间相对完整的介质区即为应力积累区——震源区。在区域应力场的作用下,隐伏的蠕滑断层端部有剪应力集中,另外水库弱化区下方也有应力集中,这就使两个调整单元有接通的趋势,当积累单元的应力达到极限值时,这种接通就必然产生,并形成较大水库地震。另外,水库弱化区的下界面对蠕滑断层端部还有象力作用,它也有使该断层向弱化区传播的趋势,从而导致较大的水库地震。本模式说明,如果建水库前对未来诱发的地震进行预测时,应注意库区更深部是否有隐伏断层存在。     

某些构造部位上地震的震源机制和应力场特点

研究了发生在一条断层的端部,且靠近引张区一侧的地震,或发生在右(左)旋向右(在)错开的两条雁列型断层的交错部位的地震的震源机制的特点,发现走滑型地震和倾滑型地震兼而有之,但是总的看来它们比发生在主断层上的地震具有较大的倾滑分量。用在无限大平板中含有一条裂纹的平面应力模型,计算了一条二维裂纹附近的应力场,结果表明,局部最大主应力相对远场主应力旋转了5～15°。估计了次生剪切裂纹可能出现的范围,表明它们主要集中在裂纹端部表现为引张的区域内,其取向或者和主裂纹大致平行,或者接近分叉张裂纹的方向。这些裂纹面上的附加正应力为张应力,并且当它们的取向接近张裂纹取向时数值较大,所以,如果地震是由接近张裂纹的剪切裂纹引起的,其震源机制应具有较大的倾滑分量,反之,如果地震与大致平行于主裂纹的剪切裂纹有关时,震源机制的走滑分量应占优势。     

基于连续-离散单元法的汶川地震动力学二维自发破裂全周期模拟研究

首先利用地震地质调查、地震剖面探测结果对汶川地震的发震断层几何形态及周边块体介质参数进行约束,建立了3个包含有不同主断层的龙门山断裂带二维黏弹性有限元模型;然后基于连续-离散单元法对汶川地震的孕育与发生进行了全周期模拟,包括震间应力积累阶段、同震应力释放阶段及震后恢复调整阶段。模型对比研究结果表明,龙门山断裂带中由于断层几何结构及断层面剪切应力与正应力的综合作用,使得最先达到断层破裂准则阈值的灌县-江油断层率先破裂,初始破裂在深度15~20km处,破裂进一步传导至映秀-北川断层;同时由于灌县-江油断层与映秀-北川断层的破裂导致系统内应力大幅度降低,使得灌县-江油断层不具备产生同震破裂的应力条件。然而,尽管汶川-茂汶断层上的应力水平与汶川地震前相比有所减弱,但仍积累了较高的震间应力,可能预示其在汶川地震后具有较高的地震危险性。模拟结果还表明,铲型逆冲断层系统的深部断层破裂能够推动浅部高倾角区域发生被动破裂,因而其发震断层的倾角上限很可能比传统认识的大。     

关于发震断层与静止断层交遇的讨论

发震断层在其传播过程中与静止断层的交遇是地震时带有普遍性的现象,本文把交遇问题分为四种基本类型;建立各自相应的力学模型;通过物理力学分析和数学模拟,并结合地震实例讨论了各类交遇可能产生的后果: 1.发震断层终止于交遇处。2.发震断层被静止断层所截,而后,交遇区域发生强余震。3.发震断层穿越静止断层向前传播,而后,可能发生共轭地震。这些讨论可能对预测未来大震的震级及强余震的发生有一定的意义。     

近断层应力变化快速计算方法及对强余震空间分布的指示意义:以M_w7.9汶川地震为例

构造地震一般由断层摩擦失稳所致.断层内部及周边所累积的剪切形变则通过同震滑动位移得到局部释放.因此,震后断层内部及近断层周边的静态剪切应力变化量的空间分布可通过断层面上的滑动位移分布计算得到.本文采用傅氏变换方法(FTM)计算单一有限断层同震滑移场所形成的静态剪切应力变化分布,近断层两侧的应力变化计算可由波数域内应力近似算法获得.结果表明,FTM快速有效、易于实现,有效地避免了常规应力计算中奇异值的出现.以2008年Mw7.9中国汶川大地震为例,采用前人所得有限断层滑动位移模型,得到了断层面和近断层周边准3D剪切应力分布解,并同主震后中强余震的空间分布特征作了比较.结果表明,大部分的中强余震震源位置处于剪切应力变化值为正的区域,由同震位移所产生的局部应力降峰值和均值大小同应力变化的正值大致相当,从而表明了快速且有效地计算断层内部及近断层附近的应力变化分布可以为主震后强余震发生的潜在区域提供指示意义.需要强调的是,应力变化空间分布特征的获取强烈地依赖于有限断层滑移模型解.有关滑动位移反演解的多解性对应力变化计算结果的影响,本文作了必要的讨论.     

2014年8月云南鲁甸MS 6.5地震典型地表破裂特征

北京时间2014年8月3日16时30分,云南省鲁甸县发生了M_S 6.5地震,本次地震的发震构造为包谷垴-小河断裂。野外调查发现,王家坡不稳定斜坡上的地表破裂在整个破裂带中比较具有代表性,其地表破裂带整体走向N45°W-N50°W,并且由剪切破裂、张剪切破裂、压剪切破裂、张性破裂以及鼓包等典型地表破裂组成。其中左、右地表破裂边界与发震断层的出露位置一致,由断层错动造成;而部分地表破裂与断层的位置不重合,其成因分为2种,一种是发震断层导致的一些次级地表破裂,另一种是地震引发的滑坡后缘破裂。地表破裂类型和基本组合特征显示出王家坡潜在不稳定斜坡上的地表破裂带具有左旋走滑的性质。     

Cohesive Crack Analysis of Toughness Increase Due to Confining Pressure

Apparent fracture toughness in Mode I of microcracking materials such as rocks under confining pressure is analyzed based on a cohesive crack model. In rocks, the apparent fracture toughness for crack propagation varies with the confining pressure. This study provides analytical solutions for the apparent fracture toughness using a cohesive crack model, which is a model for the fracture process zone. The problem analyzed in this study is a fluid-driven fracture of a two-dimensional crack with a cohesive zone under confining pressure. The size of the cohesive zone is assumed to be negligibly small in comparison to the crack length. The analyses are performed for two types of cohesive stress distribution, namely the constant cohesive stress (Dugdale model) and the linearly decreasing cohesive stress. Furthermore, the problem for a more general cohesive stress distribution is analyzed based on the fracture energy concept. The analytical solutions are confirmed by comparing them with the results of numerical computations performed using the body force method. The analytical solution suggests a substantial increase in the apparent fracture toughness due to increased confining pressures, even if the size of the fracture process zone is small.     

常规测井资料识别裂缝性储层流体类型方法研究

裂缝性储层流体类型识别一直是测井界亟待解决的难题．一方面裂缝性储层具有岩性复杂、储集类型多样、物性变化大和非均质性强等特点,因而其测井解释和流体类型识别要复杂和困难得多．另一方面,复杂岩性油气藏越来越得到人们的重视．本次研究中,通过对流体类型影响因素的分析,认识到不同流体类型与电阻率比值的高低、粘土含量的多少以及孔隙度的大小密切相关．提出了综合考虑上述三项因素的流体类型识别参数FTI．该方法应用于辽河盆地大民屯凹陷变质岩和碳酸盐岩潜山地层流体类型识别,效果良好．     

Development of a new semi-analytical model for cross-borehole flow experiments in fractured media

Analysis of borehole flow logs is a valuable technique for identifying the presence of fractures in the subsurface and estimating properties such as fracture connectivity, transmissivity and storativity. However, such estimation requires the development of analytical and/or numerical modeling tools that are well adapted to the complexity of the problem. In this paper, we present a new semi-analytical formulation for cross-borehole flow in fractured media that links transient vertical-flow velocities measured in one or a series of observation wells during hydraulic forcing to the transmissivity and storativity of the fractures intersected by these wells. In comparison with existing models, our approach presents major improvements in terms of computational expense and potential adaptation to a variety of fracture and experimental configurations. After derivation of the formulation, we demonstrate its application in the context of sensitivity analysis for a relatively simple two-fracture synthetic problem, as well as for field-data analysis to investigate fracture connectivity and estimate fracture hydraulic properties. These applications provide important insights regarding (i) the strong sensitivity of fracture property estimates to the overall connectivity of the system; and (ii) the non-uniqueness of the corresponding inverse problem for realistic fracture configurations.     

基于GA-BP理论的储层视裂缝密度地震非线性反演方法

基于GA-BP理论,将自适应遗传算法与人工神经网络技术(BP算法)有机地相结合,形成了一种储层裂缝自适应遗传-神经网络反演方法.这种新的方法是由编码、适应度函数、遗传操作及混合智能学习等组成,即在成像测井裂缝密度数据约束下,通过对目标问题进行编码(称染色体),然后对染色体进行选择、交叉和变异等遗传操作,使染色体不断进化,从而快速获得全局最优解.在反演执行过程中,利用地震数据和成像测井裂缝密度数据之间的非线性映射关系建立训练样本,将GA算法与BP算法有机地结合,优化三层前向网络参数;或将GA与ANFIS相结合,优化ANFIS网络参数.并采用GA算法与TS算法(Tabu Search)相结合的自适应混合学习算法,该学习算法自始至终将GA和BP两种算法按一定的概率比例进行,其概率自适应变化,以达到混合算法的均衡.这种混合算法提高了网络的收敛速度和精度.我们分别利用两个研究地区的6井和1井成像测井裂缝密度数据与地震数据之间的非线性映射关系建立训练样本,对过这两口井的测线的地震数据进行反演,获得了视裂缝密度剖面,视裂缝密度剖面上裂缝分布特征符合沉积相分布特征和岩石力学性质的变化特征.这种视裂缝密度剖面含有储层裂缝的定量信息,其误差可为油气勘探开发实际要求所允许.因此,这种新的方法优于只能作裂缝定性分析的常规裂缝地震预测方法,具有广阔的应用前景.     

Characterization of fractured reservoirs using a consistent stiffness‐permeability model: focus on the effects of fracture aperture

In this paper we propose a method for the characterization of naturally fractured reservoirs by quantitative integration of seismic and production data. The method is based on a consistent theoretical frame work to model both effective hydraulic and elastic properties of fractured porous media and a (non‐linear) Bayesian method of inversion that provides information about uncertainties as well as mean (or maximum likelihood) values. We model a fractured reservoir as a porous medium containing a single set of vertical fractures characterized by an unknown fracture density, azimuthal orientation and aperture. We then look at the problem of fracture parameter estimation as a non‐linear inverse problem and try to estimate the unknown fracture parameters by joint inversion of seismic amplitude versus angle and azimuth data and dynamic production data. Once the fracture parameters have been estimated the corresponding effective stiffness and permeability tensors can be estimated using consistent models. A synthetic example is provided to clearly explain and test the workflow. It shows that seismic and production data complement each other, in the sense that the seismic data resolve a non‐uniqueness in the fracture orientation and the production data help to recover the true fracture aperture and permeability, because production data are more sensitive to the fracture aperture than the seismic data.     

A new upscaling method for fractured porous media

We present a method to determine equivalent permeability of fractured porous media. Inspired by the previous flow-based upscaling methods, we use a multi-boundary integration approach to compute flow rates within fractures. We apply a recently developed multi-point flux approximation Finite Volume method for discrete fracture model simulation. The method is verified by upscaling an arbitrarily oriented fracture which is crossing a Cartesian grid. We demonstrate the method by applying it to a long fracture, a fracture network and the fracture network with different matrix permeabilities. The equivalent permeability tensors of a long fracture crossing Cartesian grids are symmetric, and have identical values. The application to the fracture network case with increasing matrix permeabilities shows that the matrix permeability influences more the diagonal terms of the equivalent permeability tensor than the off-diagonal terms, but the off-diagonal terms remain important to correctly assess the flow field.     

A numerical method for two-phase flow in fractured porous media with non-matching grids

We propose a novel computational method for the efficient simulation of two-phase flow in fractured porous media. Instead of refining the grid to capture the flow along the faults or fractures, we represent the latter as immersed interfaces, using a reduced model for the flow and suitable coupling conditions. We allow for non matching grids between the porous matrix and the fractures to increase the flexibility of the method in realistic cases. We employ the extended finite element method for the Darcy problem and a finite volume method that is able to handle cut cells and matrix-fracture interactions for the saturation equation. Moreover, we address through numerical experiments the problem of the choice of a suitable numerical flux in the case of a discontinuous flux function at the interface between the fracture and the porous matrix. A wrong approximate solution of the Riemann problem can yield unphysical solutions even in simple cases.     

储层构造裂缝预测方法及其应用

根据构造裂缝的力学成因,对储层构造裂缝系发育强度及方向进行了估计,通过实例对该方法进行了检验。结果表明：（１）用有效张应力描述张裂缝和张剪裂缝发育程度是一个切实有效的方法;（２）在储层的同一层位上,影响张裂缝和张剪裂缝的主要因素是古构造面的曲率和扭率及断层运动性质（逆冲、正断或平推）,自古隆起顶部向坡底,裂缝由张性向张剪性和剪切性裂缝发展;（３）自储层顶界面（古隆起构造面）往下,随深度增加,张裂缝和张剪裂缝发育程度降低;（４）裂缝预测的不同模型和方法,反映不同方面的特征和优势,根据储层占有资料和目的要求选择合适的裂缝预测模型和方法比较有效     

A two－dimensional earthquake fault modeling with fractal structure strength distribution

Ａｔｗｏ┐ｄｉｍｅｎｓｉｏｎａｌｅａｒｔｈｑｕａｋｅｆａｕｌｔｍｏｄｅｌｉｎｇｗｉｔｈｆｒａｃｔａｌｓｔｒｕｃｔｕｒｅｓｔｒｅｎｇｔｈｄｉｓｔｒｉｂｕｔｉｏｎＸＩＡＮＧ－ＸＩＯＮＧＣＨＥＮ（陈祥熊）ＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕｏｆＦｕｊｉ...     

Seismic prediction method of multiscale fractured reservoir

Common prestack fracture prediction methods cannot clearly distinguish multiplescale fractures. In this study, we propose a prediction method for macro- and mesoscale fractures based on fracture density distribution in reservoirs. First, we detect the macroscale fractures (larger than 1/4 wavelength) using the multidirectional coherence technique that is based on the curvelet transform and the mesoscale fractures (1/4–1/100 wavelength) using the seismic azimuthal anisotropy technique and prestack attenuation attributes, e.g., frequency attenuation gradient. Then, we combine the obtained fracture density distributions into a map and evaluate the variably scaled fractures. Application of the method to a seismic physical model of a fractured reservoir shows that the method overcomes the problem of discontinuous fracture density distribution generated by the prestack seismic azimuthal anisotropy method, distinguishes the fracture scales, and identifies the fractured zones accurately.