Detecting rupture precursors and determining the main fracture spread direction of rock with dynamic rock resistivity change anisotropy

In the past, domestic and abroad scientific workers have done a large number of experiment researches on a great number of researches of experiment for the relationship between electrical resistivity change and the load stress on rock (Geoelectric Testing Group, Department of Geophysics, Peking University and Research Division, Seismological Brigade of Lanzhou, 1978; Zhang, 1981; Chen, et al, 1983; Zhao, et al, 1983; Zhang, Lu, 1983; Zhang, et al, 1985; Brace, Orange, 1968; Kurite, 1986; Teisseyre, 1989), such as imitating dynamic fracture of rock, frictional sliding course, and observing its resistivity change shape with a lot of experimental workssuch as simulating the dynamic course of crustal rocks fracturing and frictional slipping along the fracture surface, and observing its resistivity change shape with experiment. They found that, in the fracture process of rock under loading, not only its resistivity shape change notably, and its direction changes also very clearly, and therefore many scientific workers have shown strong interest in anisotropy of resistivity change, and have done some researches onfor it.     

用动态岩石电阻率变化各向异性探测岩石破裂前兆和确定主破裂扩展方向

用实验模拟动态岩石的破裂和摩擦滑动过程 ,观测其电阻率变化形态 ,研究电阻率变化与岩石受力的关系 ,国内外的学者曾做过大量实验研究工作 (北京大学地球物理教研室地电组 ,兰州地震大队报室 ,1 978;张同俊 ,1 981 ;陈大元等 ,1 983;赵玉林等 ,1 983;张金铸 ,陆阳泉 ,1 983;张天中等 ,1 985;Brace,Orange,1 968;Kurite,1 986;Teisseyre,1 989) .在实验中 ,学者们发现岩石在受力破裂过程中 ,不光其电阻率形态变化显著 ,而且其方向变化也很明显 .不少学者对电阻率变化的方向性产生了浓厚的兴趣 ,开展了一些这方面的研究工作 . 80年代初 ,陈…     

岩石电阻率图像及各向异性变化的实验研究

在两组人工样品自由表面以中心点为基准对称布设3条辐射状测线,对样品实施单轴应力加载和卸载后,利用电阻率层析成像方法构建了相应的视电阻率相对变化图像,并计算和绘制了表征裂隙产生和发展速率的视电阻率各向异性系数λ*以及表征裂隙产生和发展方位的各向异性主轴方位角α随应力和深度的变化曲线.结果表明:所有测线所对应的RRC图像均随着应力的变化呈现出相同的变化趋势,即在加载阶段,随着应力的增加,视电阻率相对变化图像中电阻率降低区域逐渐收缩,而电阻率升高区域逐渐扩张,在卸载阶段,随着应力的减小,电阻率降低区域继续收缩,电阻率升高区域继续扩张;样品中的高阻体对其所在部位及附近区域的电阻率增幅有较大影响,而对横越高阻体测线的视电阻率相对变化图像的趋势性变化无影响;对于原始电性为各向异性的样品,随着应力的增加,其各向异性程度降低;裂隙主要在岩样的浅部产生和发展,而在较深部位的裂隙产生和发展的速率相对较低.上述结果有助于解释和理解地震、火山活动和大型地质构造运动引起的视电阻率及其各向异性的变化特征,电阻率层析成像方法可能成为目前地震电阻率观测方法的有益补充.      

Research on dependence of resistivity changing anisotropy on microcracks extending in rock with experiment

Intr0ducti0nTheproblemsaboutcrustalrocksfracturingandfricti0nalslippingalongthefracturesurfaCearecloselyrelatedtotheresearchesofearthquakemechanismandgeol0gichazards,andalsoareoneofthosebeinggivenmoreconcernbyscientistsinearthscience-Discussingab0utthegenera-tionanddevelopmentprocess0fintraPlateearthquakes,Wang,etal(l999)proPOsedthatearth-quake'spregnant,mechanicspropertyandgeometricstructureofmatterinearthquake'sgestatingareaaredifferinthousandswaysf0rdifferentplaceinsideslab-Thus,thepregna…     

Modelling frequency-dependent seismic anisotropy in fluid-saturated rock with aligned fractures: implication of fracture size estimation from anisotropic measurements

Measurements of seismic anisotropy in fractured rock are used at present to deduce information about the fracture orientation and the spatial distribution of fracture intensity. Analysis of the data is based upon equivalent-medium theories that describe the elastic response of a rock containing cracks or fractures in the long-wavelength limit. Conventional models assume frequency independence and cannot distinguish between microcracks and macrofractures. The latter, however, control the fluid flow in many subsurface reservoirs. Therefore, the fracture size is essential information for reservoir engineers. In this study we apply a new equivalent-medium theory that models frequency-dependent anisotropy and is sensitive to the length scale of fractures. The model considers velocity dispersion and attenuation due to a squirt-flow mechanism at two different scales: the grain scale (microcracks and equant matrix porosity) and formation-scale fractures. The theory is first tested and calibrated against published laboratory data. Then we present the analysis and modelling of frequency-dependent shear-wave splitting in multicomponent VSP data from a tight gas reservoir. We invert for fracture density and fracture size from the frequency dependence of the time delay between split shear waves. The derived fracture length matches independent observations from borehole data.     

各向异性层状介质中视电阻率与磁场响应研究

针对任意各向异性地层,利用极向型和环向型标量位函数,导出相应的直流电视电阻率和磁电阻率的磁场响应关系.计算了各向异性地层的直流电视电阻率和磁电阻率响应特征,重点分析了电阻率测深方法与磁电阻率探测方法对地下各向异性介质的探测能力.文中采用状态矩阵的分析方法,首先采用极向型和环向型标量位构造了各向异性层状介质电场与磁场的通解,利用各层界面电场、磁场的连续性及地面激励源的耦合条件,推导了不同层之间电磁场的状态矩阵,建立了空间电场与磁场的递归计算关系.其次,针对递归计算中指数项数值计算的不稳定性,借用状态矩阵的性质,导出了将不稳定指数计算项转化为稳定的指数项的转换关系.针对横向各向同性(TI)介质中极向位与环向位解耦的特点,导出了电磁场的直接积分解.最后,采用解析解验证了算法的正确性,给出了多层各向异性地层模型的视电阻率和磁场响应曲线,分析了直流电法探测裂缝性地层、估计裂缝分布性状的可能性.     

Dynamic evolution patterns of the degree of ground resistivity anisotropy and the seismogenic process

Following a new train of thinking, this paper has explored first the potential information in the ground resistivity data observed by the existing geoelectric observation system, investigated and proposed a new dimensionless geoelectric precursor factor, the degree of ground resistivity anisotropy, S, and studied the characteristics of dynamic evolution pattern of S during the seismogenic process. The results show that, during the seismogenic process, the degree of ground resistivity anisotropy (S) displays a process of 'normal' →'abnormal strengthening (amplitude, range)' →abnormal weakening' → 'earthquake occurrence'→ 'normal'. The earthquake would occur at the time when the S value has entered the late stage of strengthening and turns to weaken and in the gradient belt on the margin of S anomaly region. The dynamic evolution pattern of S reflects the changes of the tectonic stress field during the seismogenic process. Therefore, it would be possible to trace the process of earthquake generation and occurrence from the dynamic evolution pattern of S so as to service earthquake prediction.     

地电阻率EW/NS比值变化与地震的关系

主要对河北省4个台站的两个方向(EW、NS)的电阻率比值进行了大量计算,结果发现比值的变化能够很好地对应近年来河北省内发生的较大地震,尤其是作为中长期地震异常有着很好的映震能力,这对于预测和预报未来地震有着十分重要的意义。     

Calculation of the parameters of georesistivi－ty anisotropy and case history of earthquake precursors

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Application of scaling-rule theory in crustal rock fracture to studying characteristics of seismological precursors associated with M=6.1 Shandan-Minle earthquake

In the paper, we introduce Allegre＇s scaling-rule theory of rock fracture and the probability to develop a method for predicting earthquake occurrence time on its basis. As an example, we study the characteristics of seismological precursors （seismic spatial correlation length and coda Qc） associated with the earthquake （M=6.1） occurred in Shandan-Minle, Gansu Province. The results show an increasing trend of seismic spatial correlation length and coda Qc before the earthquake. And a power exponent relation is used to fit the increasing variation form of these two parameters. The study has provided a basis for creating a method and finding indexes to predict the earthquake occurrence time by using the monitored seismic spatial correlation length and coda Qc.     

Dynamic evolution patterns of the degree of ground resistivity anisotropy and the sets mogenic process

IntroductionTothefinalanalysis,earthquakepredictionisstillamarginalscienceofextremedifficultyintheworld.Tomakesomebreakthroughorpromoteearthquakeprediction,itisnecessarytostrengthentheresearchonnewtrainofthinking,newtheoryandnewmethods.Theresearchontheanisotropyofcrustalmediaduringtheseismogenicprocesshasbeentakenmoreandmoreseriouslybyseismologists.Inthepast,manyscholarsoftenmadestudiesonthefeaturesofmediainresponsetoseismicwavesandachievedsomeprogress(Teng,etal,1992).Thispaperstudiestheelect…     

含裂缝地层的过套管电阻率测井响应特征研究

由于石油压裂开采等开发措施的实施,会使在套管周围存在着许多被油气等高阻流体填充的微裂缝.尽管这些裂缝或孔隙可能很小,但对套管井电阻率测量会有非常大的影响,甚至会改变原地层的电阻率测井特征,因此裂缝测井响应的计算及考察对过套管电阻率测井十分重要.为解决裂缝测井响应的计算问题,本文提出了计算等效电阻的电流通量管模型,利用该电流通量管模型给出了含垂直裂缝地层横向电阻的计算方法,基于传输线方程法及地层电阻的过套管测量方法实现了含裂缝地层的过套管电阻率测井响应的数值计算,通过计算实例考察了地层裂缝对过套管电阻率测井响应的影响.算例表明：裂缝中的高阻流体对地层视电阻率测量结果会有较大的影响;环形裂隙比垂直裂缝有更大的电阻率测井响应.本文的研究为解决微裂缝过套管电阻率测井响应的计算这一关键技术问题提供了一种可行的计算与考察方法.

     

Seismic characterization of reservoirs with multiple fracture sets using velocity and attenuation anisotropy data

Knowledge about the spatial distribution of the fracture density and the azimuthal fracture orientation can greatly help in optimizing production from fractured reservoirs. Frequency-dependent seismic velocity and attenuation anisotropy data contain information about the fractures present in the reservoir. In this study, we use the measurements of velocity and attenuation anisotropy data corresponding to different seismic frequencies and azimuths to infer information about the multiple fracture sets present in the reservoir. We consider a reservoir model with two sets of vertical fractures characterized by unknown azimuthal fracture orientations and fracture densities. Frequency-dependent seismic velocity and attenuation anisotropy data is computed using the effective viscoelastic stiffness tensor and solving the Christoffel equation. A Bayesian inversion method is then applied to measurements of velocity and attenuation anisotropy data corresponding to different seismic frequencies and azimuth to estimate the azimuthal fracture orientations and the fracture densities, as well as their uncertainties. Our numerical examples suggest that velocity anisotropy data alone cannot recover the unknown fracture parameters. However, an improved estimation of the unknown fracture parameters can be obtained by joint inversion of velocity and attenuation anisotropy data.     

The nature of the high values of the anisotropy of magnetic susceptibility of rock samples with polydomain ferromagnetics

Samples of different rocks, which possess high values of the anisotropy of magnetic susceptibility, were studied by the magneto-mineralogical and optical methods and by microprobe analysis. It was established that for the samples, which contain the pseudo-single-domain ferromagnetite elongated particles, the source of the anisotropy of magnetic susceptibility is the distribution anisotropy of not only ferromagnetic grains themselves, but also ferromagnetic patterns in the heterogeneous accessory minerals. For samples with multidomain ferromagnetic materials, the nature of the anisotropy of magnetic susceptibility is caused by the orientation of the ilmenite lamellar phase in the structures of disintegration of titanomagnetites or by the orientation of the ferromagnetic structures of disintegration in iron sulfides.     

中国南海蚀变火成岩导电机理研究与低阻成因分析

近年来, 随着油气资源勘探开发的不断发展, 火成岩储层越来越受到关注.岩性矿物和孔隙结构的复杂程度造成了蚀变火成岩储层测井评价困难的问题.蚀变程度、润湿性、蚀变矿物种类、孔隙结构以及复杂的流体分布形式对其导电机理的影响尚不明确, 这也制约了蚀变火成岩导电和饱和度模型的研究.本文基于多组分数字岩心, 利用有限元和数学形态法进行岩石电性模拟, 并依据地质客观规律合理构造变蚀变程度、变孔隙度和混合润湿性的数字岩心, 有效分析了上述因素对蚀变火成岩导电机理的影响机制.多组分数字岩心构建和蚀变火成岩储层的低阻成因分析, 为蚀变火成岩储层测井评价提供了理论基础, 也为蚀变火成岩数字岩心数值模拟提供了技术支撑.

     

Features and physical process of the dynamic evolution pattern of ground resistivity precursor front

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青藏高原东北缘地壳各向异性及其动力学意义

利用中国地震科学探测台阵项目二期（ChinaArray Ⅱ）81个台站的地震数据,使用时间域反褶积方法提取接收函数,挑选满足要求的高质量Ps震相,通过改进的剪切波分裂计算方法获取了53个台站共130对高质量各向异性参数对.地壳各向异性分析指出,研究区东南部地区地壳各向异性方向为NWW向,与XKS各向异性方向、GPS速度场三者近平行关系,说明该地区在青藏高原向欧亚大陆增生的过程中是一个耦合的连贯变形过程;位于研究区中、北部地区的地壳各向异性方向表现为NEE-SWW或E-W方向,与GPS速度场方向一致,而与XKS结果的偏振方向大角度相交,说明该地区受到青藏高原下地壳塑性管道流的影响,可能存在壳幔解耦作用.

     

中国东北地区北部上地幔各向异性及其动力学意义

中国东北地区广泛发育新生代板内火山,晚中生代以来岩石圈遭受过多期拉张作用.作为中国唯一的深震孕育区,中国东北地区受到太平洋板块的西向俯冲,使得其成为研究岩石圈变形、板块俯冲和板内火山成因及其相互作用关系的天然实验室.通过分析架设在中国东北地区北部的147个流动和固定台站的SKS波形数据,共计得到了377对各向异性参数和251个无效分裂结果.结果表明,中国东北地区东西两侧具有不同的各向异性分布:西部地区各向异性方向变化范围为N143-199°E,平均N169°E,与晚中生代岩石圈伸展方向一致;其各向异性延迟时间平均值约为0.8s,说明来自地幔的各向异性比较微弱,主要由残留在岩石圈中的古老变形所引起.同时,在松辽盆地和佳木斯地块部分区域,观测到延迟时间较小的各向异性(~0.4s),可能是由于岩石圈的拆沉和热地幔物质的上涌侵蚀了保留在岩石圈的古老形变所致.在研究区东部,NNW-SSE朝向的各向异性被观测到,并伴随较大的延迟时间(大于1.0s),可能与太平洋板块撕裂回撤而产生的地幔流动有关.此外,近W-E方向的各向异性只在佳木斯地块被观测到,而太平洋板块在地幔过渡带中的俯冲可能是其产生的主要成因.     

The influencing factors and mechanisms of the electromagnetic radiation during rock fracture

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不同土壤中含油污水污染区的电性变化研究及污染区探测

本文利用室内电阻率测试的方法研究了研究了饱和土和不饱和土两类土中含油污水的侵入量对其导电性的影响.测试结果表明,对于不饱和土,含油污水的侵入会改变土的饱和度从而引起其电阻率的降低,侵入量越大其电阻率越低;而饱和土的电阻率随含油污水侵入量的增大而增大直到趋于稳定.基于此,通过室内模拟土层污染和野外实地观测污染土层的方式研究了含油污水污染不同饱和度土层的电剖面异常特征,在不饱和土层中污染区域表现为相对低阻异常区而在饱和土层中表现为相对高阻异常区.通过对比不同时期的监测结果显示异常区的范围随污染区的变化而变化,并可反映出污染区的实际分布.文章分析了利用电阻率法进行含油污水污染地下介质调查的几个模糊点,对提高探测效果具有指导意义.