Importance of fracturing during retro-metamorphism of eclogites

Presented textural and petrological data show that the deep to intermediate continental crust may fracture and that microfractures are the locus of fluid and mass transfer necessary for retrograde metamorphism. Kyanite eclogites from Ulsteinvik, Norway, underwent partial retrogression to granulite and amphibolite facies assemblages during near-isothermal exhumation from depths equivalent to more than 2.0 GPa at temperatures of 700–800 °C. Plagioclase-bearing assemblages, rich in hydrous phases, formed along margins of eclogite lenses and along mesoscopic fracture systems. Hydrated zones are from 1–50 cm thick, with adjacent wall-rock eclogite replaced by symplectites. At a low degree of reaction, the secondary minerals in the wall-rock are found along intra- and intergranular microfractures (typically 50–100 μm wide). Minerals filling the microfractures include orthopyroxene–plagioclase–spinel in garnet; plagioclase–sapphirine, plagioclase–corundum and plagioclase–spinel in kyanite; and diopside–plagioclase in omphacite. The microfractures are often arranged en echelon and are connected through microfaults. Releasing bends filled with amphibole and spinel form along microfaults in garnet. The faulting and fracturing caused localized chemical change in garnet: the damage zones close to faults are enriched in FeO and MnO with steep compositional gradients (8 wt% FeO over <20 μm). These FeO- and MnO-enriched zones form wedge-like structures around the tip of the faults (horsetail structures) and rose- or flame-like structures at sticking points along faults. They may represent examples of stress-induced chemical transport during fracture propagation. The change from dry to amphibole-bearing assemblages at the tip of the fracture, and fractures ending in splays of fluid inclusions trails, reflect the involvement of a fluid phase during fracture propagation. This suggests that the ‘dry’ granulite facies retrogression was also driven by fluid infiltration and that metamorphism at depth in collision zones may not be controlled by pressure and temperature alone.     

CONSEQUENCES OF FLUID LAG IN THREE-DIMENSIONAL HYDRAULIC FRACTURES

Research investigations on three-dimensional (3-D) rectangular hydraulic fracture configurations with varying degrees of fluid lag are reported. This paper demonstrates that a 3-D fracture model coupled with fluid lag (a small region of reduced pressure) at the fracture tip can predict very large excess pressure measurements for hydraulic fracture processes. Predictions of fracture propagation based on critical stress intensity factors are extremely sensitive to the pressure profile at the tip of a propagating fracture. This strong sensitivity to the pressure profile at the tip of a hydraulic fracture is more strongly pronounced in 3-D models versus 2-D models because 3-D fractures are clamped at the top and bottom, and pressures in the 3-D fractures that are far removed from the fracture tip have little effect on the stress intensity factor at the fracture tip. This rationale for the excess pressure mechanism is in marked contrast to the crack tip process damage zone assumptions and attendant high rock fracture toughness value hypotheses advanced in the literature. A comparison with field data is presented to illustrate the proposed fracture fluid pressure sensitivity phenomenon. This paper does not attempt to calculate the length of the fluid lag region in a propagating fracture but instead attempts to show that the pressure profile at the tip of the propagating fracture plays a major role in fracture propagation, and this role is magnified in 3-D models. © 1997 by John Wiley & Sons, Ltd. Int. J. Numer. Anal. Meth. Geomech., vol. 21, 229–240 (1997).     

Numerical models of hydraulic fracturing and the interpretation of syntectonic veins

The hydraulic fracture is modelled as an ellipse in an infinite elastic medium with an internal fluid pressure and loaded under biaxial stresses at infinity. The available stress function for this model has been evaluated numerically, and the magnitudes of the stresses generated around the crack calculated for a variety of loading conditions and crack orientations. Fracture initiation is predicted from the Griffith maximum tensile stress criterion. The location of the maximum tensile stress around the crack is recorded and it is found that for many conditions of applied stresses and crack fluid pressure, the hydraulic shear fracture has a symmetrically developed maximum tensile stress and fracture initiation will occur by growth along the direction of the crack. It is also predicted that fracture initiation will occur when the ratio of fluid pressure to applied least principal stress is considerably less than one. The elastic strain energy fields around elliptical hydraulic flaws have been calculated, and in particular, the change in strain energy upon introduction of a small flaw, and the change in strain energy upon growth of this flaw, have been investigated. The results allow an evaluation of the second part of the Griffith criterion-that fracture growth is accompanied by a decrease in strain energy-for hydraulic fractures. Changes in strain energy with small increases in fluid pressure provide a physical basis for dilatancy hardening and fracture instability. Quasi-static growth from a flaw is modelled by calculating changes in strain energy for unit increases in half length. The distinction between fractures which show an increasing and a decreasing rate of change in strain energy with increasing length, and between fractures which may only extend spontaneously for short distances and those which may show extensive spontaneous growth on the basis of the rate of change of strain energy with length, is made. A gradual drop in crack fluid pressure once the threshold for fracture initiation has been passed may promote the extent to which spontaneous crack growth occurs.The formation of syntectonic veins, particularly in rocks being deformed under low grade metamorphic conditions, is often the most abundant evidence of natural hydraulic fracturing in rocks. Commonly observed geometric features of syntectonic veins-length, simple tapering, symmetric and asymmetric forking, branching, irregular zig-zag traces, en échelon patterns—are discussed primarily with reference to the strain energy model for growth established, and the geometric variation is interpreted in terms of variation in applied stress and fluid pressure conditions and the rate of change of stored strain energy with crack growth. In particular, terminal branching arises when the minimum stress changes from a symmetric to an asymmetric location at the tip of a growing shear fracture, and terminal forking results when there is an increase in the energy release rate during crack growth, and may be symmetric or asymmetric depending on the location of the minimum stress at the crack tip at the time of forking.     

基于3D-ILC含偏心内裂纹半圆弯拉断裂特性研究

断裂力学是各行业的基础学科之一。半圆弯拉(SCB)试验为该领域经典试验,目前含裂纹的SCB研究多为底部切口等表面裂纹或穿透型裂纹研究。内裂纹和内部类裂纹缺陷是材料的固有属性,但是对于SCB内裂纹扩展规律研究较少。基于3D-ILC（三维激光疲劳内裂纹）技术,分析了表面无任何影响的情况下凭空生成任意参数的纯内裂纹,在SCB试样中生成内裂纹,对含内裂纹试样进行SCB试验,分析了裂纹生长过程、应力双折射规律、I-II-III型裂纹扩展面、破坏形态、宏微观断口特征,开展数值模拟,得到裂纹尖端应力强度因子分布规律及扩展路径,与物理试验一致。结果表明：（1）基于3D-ILC的SCB内裂纹及I-II-III型扩展断裂规律明显,3D-ILC为断裂力学中的内裂纹问题研究提供了有力工具;（2）应力云纹在内裂纹处显示应力集中,SCB整体云纹在内裂纹处发生明显变异;（3）SCB试样从预制裂纹处发生压剪型起裂,发生I-II-III型裂纹扩展,分为光滑区和撕裂区,持续生长转变为动态断裂进而破坏,动态断口存在裂纹分叉出现雾化区、羽毛区特征;（4）根据M积分和最大周向应力准则,对试样进行了数值模拟,得到了试样内裂纹尖端应力强度因子分布规律及扩展路径,与试验结果一致。结论与成果对断裂力学领域的SCB试验、内裂纹、I-II-III型断裂问题、裂纹扩展路径模拟问题的研究,具有重要意义。     

预制横缝条件下水力裂缝的起裂和扩展

针对高角度天然裂缝发育地层中的水平井水力压裂问题,开展了水力裂缝自天然裂缝处起裂扩展的理论和试验研究。尝试将天然裂缝简化为与井筒轴线垂直的横向裂缝,基于线弹性断裂力学理论和最大拉应力准则,给出了水力裂缝起裂压力和扩展过程中应力强度因子的计算方法。利用预制横缝模拟高角度天然裂缝,开展了室内水力压裂试验,对水力裂缝的扩展形态和起裂压力进行了研究。理论计算表明,（1）水力裂缝自预制横缝端部起裂后,扩展距离超过1倍的预制横缝端部半径时可将预制横缝和水力裂缝合并起来,整体视作一条横向裂缝来计算应力强度因子;（2）水力裂缝尖端距井壁处的距离大于4倍的井筒半径时,应力强度因子的计算可忽略井筒的影响,近似采用硬币形裂缝的计算公式。试验研究发现,（1）水力裂缝在预制横缝端部起裂并扩展,形成与井筒轴线垂直的横向裂缝,裂缝的扩展呈现出Ⅰ型断裂的特点,形态近似呈圆形,未发现与井筒轴线平行的纵向裂缝的起裂和扩展;（2）排量对破裂净压力和起裂净压力有重要影响,大排量会导致较高的破裂净压力和起裂净压力,在大、小两种排量下起裂净压力的离散性均较小,计算得到的KⅠ临界断裂值的离散性也较小。研究结果可为改善裂缝发育储层的近井裂缝形态提供指导,也可为煤矿开采中预制横向切槽的水力压裂设计提供参考。     

松辽盆地徐家围子断陷火山岩裂缝形成机理

松辽盆地徐家围子断陷是位于松辽盆地北部深层的半地堑型晚侏罗世-早白垩世伸展断陷,火山岩发育。在已有研究成果的基础上,结合野外露头和岩心观测及镜下研究发现：本区火山岩构造裂缝和溶蚀裂缝都比较发育,具有明显的规律性,多数原生缝被后期的构造应力或溶蚀作用改造成次生缝。本区裂缝形成的控制因素较多,主要有应力、构造、岩性和岩相、溶蚀作用、风化淋滤、构造应力场演化等,其中构造应力场演化、岩性和岩相及风化溶蚀作用是控制裂缝形成的主要因素。构造裂缝以高角度的张扭性和张性缝为主,多为半充填和无充填,具有多期、多方向、组合复杂等特点,是晚侏罗世至新近纪各种地质作用相互叠加的结果。构造通过控制不同构造部位的局部应力场分布来控制裂缝发育程度,沿断裂带存在明显的应力集中,形成裂缝发育带,特别在正断层上升盘、断层端部、背斜轴部等应力集中部位容易形成构造裂缝。有效火山岩油气储层为各类原生孔隙与裂缝的有效组合。由于火山喷发多个旋回叠加,加之风化剥蚀及不整合面的存在,造成裂缝在纵向上发育具有旋回性,溶蚀裂缝主要在不整合面附近发育。在平面上,裂缝主要发育在断裂密集区、断裂交汇部位和背形或向形构造发育的地区。本区处于爆发相和溢流相火山岩的发育区,气孔和裂缝最发育,特别是溢流相的流纹岩中,裂缝和气孔均较为发育,是本区的优质储层最发育区,也是天然气富集区。     

Transformation of two-pyroxene hornblende granulite to garnet granulite involving simultaneous melting and fracturing of the lower crust, Fiordland, New Zealand

Granulite facies gabbroic and dioritic gneisses in the Pembroke Valley, Milford Sound, New Zealand, are cut by vertical and planar garnet reaction zones in rectilinear patterns. In gabbroic gneiss, narrow dykes of anorthositic leucosome are surrounded by fine‐grained garnet granulite that replaced the host two‐pyroxene hornblende granulite at conditions of 750 °C and 14 kbar. Major and trace element whole‐rock geochemical data indicate that recrystallization was mostly isochemical. The anorthositic veins cut contacts between gabbroic gneiss and dioritic gneiss, but change in morphology at the contacts, from the anorthositic vein surrounded by a garnet granulite reaction zone in the gabbroic gneiss, to zones with a septum of coarse‐grained garnet surrounded by anorthositic leucosome in the dioritic gneiss. The dioritic gneiss also contains isolated garnet grains enclosed by leucosome, and short planar trains of garnet grains linked by leucosome. Partial melting of the dioritic gneiss, mostly controlled by hornblende breakdown at water‐undersaturated conditions, is inferred to have generated the leucosomes. The form of the leucosomes is consistent with melt segregation and transport aided by fracture propagation; limited retrogression suggests considerable melt escape. Dyking and melt escape from the dioritic gneiss are inferred to have propagated fractures into the gabbroic gneiss. The migrating melt scavenged water from the surrounding gabbroic gneiss and induced the limited replacement by garnet granulite.     

单轴压缩非贯通节理岩石尖端塑性区及弹塑性断裂模型研究

基于Drucker-Prager（下简称D-P）准则,建立压缩载荷作用下的非贯通节理岩石的弹塑性断裂模型。针对节理岩石小范围屈服翼裂纹尖端塑性区,推导了D-P屈服准则的纯I、纯II及I、II复合型3种翼裂纹无量纲塑性区径长函数,并与Mises准则的塑性区进行对比;结果表明,D-P准则的I型和复合型塑性区较Mises屈服准则的塑性区大,且其II型及I、II复合型塑性区在翼裂纹上下表面不连续。进一步,引入断裂软化因子以表征节理岩石裂隙断裂扩展后的断裂软化规律,考虑非贯通节理岩石复合型断裂软化,是由于节理尖端翼裂纹应变能密度超过最小应变能密度导致其成核扩展引起的,提出用应变能密度的指数函数形式表征断裂软化变量的演化;塑性屈服函数采用Borja等的应力张量3个不变量的硬化/软化函数,反映塑性内变量及应力状态对硬化函数的影响;建立节理岩石的弹塑性断裂本构关系及其数值算法,并用回映隐式积分算法编制了弹塑性断裂模型的程序。以单轴压缩下非贯通节理岩石为例,分析岩石断裂韧度、节理摩擦系数和节理倾角等参数的影响,结果表明,所提出的弹塑性断裂模型与数值和试验结果比较吻合。     

Fracture initiation, growth and effect on stress field: a numerical investigation

A numerical investigation was made of the relationships between fracture initiation, growth, stress field and boundary conditions. Two-dimensional plane strain continuum models were used in which fractures appeared as zones of strain localization developed through application of a strain softening Mohr–Coulomb constitutive model. R and R′ fractures developed first, followed by Y fractures at larger strains. The models showed that equal development of conjugate R and R′ fractures is easily changed to favor one or the other set by minor variations in model initial conditions. Strength loss in fractures caused stress field rotations in regions bounded by fractures, altering the orientation of subsequent fractures. The amount and sense of stress field rotation is dependent on the strength loss during displacement on the fractures, the orientation of fractures, and on the boundary conditions. Y oriented fractures could be explained on the basis of a Mohr–Coulomb failure criterion provided that stress field rotation is accounted for. Monitoring of fracture slip activity showed that, under conditions of constant boundary velocity, slip was discontinuous in time, alternating on fractures throughout the model.     

基于CT-CA的天然裂隙岩石受拉破坏特性研究

岩石内部存在的裂隙、孔洞等天然损伤对岩石的力学性能和破坏过程有重要影响,依据细胞自动机理论结合CT无损识别技术实现了含天然裂隙岩石在劈裂条件下裂纹扩展和贯通全过程及其力学性能变化规律的研究。从裂隙砂岩的真实细观结构出发,构建了天然裂隙岩石的数值计算模型,运用CASRock数值计算软件完成了含不同裂隙倾角的砂岩劈裂破坏的数值试验,分析了裂隙倾角对砂岩的力学特性、裂纹扩展过程及能量演化的影响规律。研究表明：(1)天然裂隙砂岩的抗拉强度与裂隙倾角密切相关,随着裂隙倾角的增加,其抗拉强度呈现先减小后增加的趋势;(2)裂隙起裂于天然裂隙尖端,当裂隙倾角0°≤θ<48°时,岩样的破坏是由错开型裂纹引起,裂纹沿着与天然裂隙近垂直方向扩展;当裂隙倾角48°≤θ<94°时,岩样的破坏是由张开型裂纹引起,裂纹沿着与天然裂隙近平行方向扩展;(3)劈裂过程中裂纹尖端应力场存在拉应力区和压应力区,拉应力造成翼裂纹由天然裂隙尖端沿加载端方向萌生扩展,而压应力则引发次生裂纹沿天然裂隙方向扩展;(4)含天然裂隙砂岩劈裂破坏过程能量演化可划分为4个阶段,随裂隙倾角的增大,峰值点处的总能量密度、弹性能密度先缓...     

水平井多段压裂应力场计算新模型

为了准确认识水平井多段压裂过程中井筒周围应力场变化,指导裂缝起裂和延伸机制研究,综合考虑井筒内压、地应力、压裂液渗流、热应力、射孔和先压开裂缝等因素的影响,根据应力叠加原理,建立了水平井多段压裂应力场计算模型。该模型利用位移不连续法,重点考虑了先压开裂缝在水平井筒周围水平面上产生的诱导应力大小,克服了裂缝诱导应力解析模型只能计算裂缝高度平面诱导应力大小的局限。结果表明,通过应力场模型进行的破裂压力预测与实际破裂压力值吻合度较高,验证了建立模型的准确性;人工裂缝形成后会对水平井筒周围应力场造成很大影响,在裂缝尖端出现应力集中,造成应力分量降低,在裂缝周围一定区域造成应力分量有较大的升高;多段压裂压开人工裂缝越多,应力之间干扰越严重,水平井筒周围应力分布越复杂。该研究对认识多段压裂存在先压裂缝干扰下后续裂缝的起裂和延伸机制,指导压裂施工具有一定意义。     

基于离心试验的反倾层状岩质边坡内非贯通性裂缝变形特性分析

坡体内不同部位结构面间岩桥断裂扩展导致了反倾层状岩坡的破坏。为研究坡体内非贯通性裂缝断裂扩展对坡体演化的控制作用,以苗尾水电站右坝肩倾倒变形体为地质原型,开展含多组非贯通性裂缝的反倾层状岩质边坡离心模型试验,分析反倾层状岩质边坡内非贯通性裂缝变形特性。结果表明：（1）坡体内含非贯通性裂缝的岩层断裂最终呈现为裂缝间岩桥贯通、缓倾裂缝与上岩层贯通、陡倾裂缝与下岩层贯通、陡倾裂缝与缓倾裂缝端口处贯通及非裂缝处岩层发生断裂等5类裂缝断裂模式,并以裂缝间岩桥贯通为主要断裂模式;（2）基于断裂力学并结合裂缝断裂叠加原理,主折断面处岩层的不稳定系数在坡高1/3处最小,并向坡脚和坡顶两侧逐渐变大,而应力强度因子由坡高1/3处向坡脚和坡顶处逐渐变小;（3）裂缝的断裂扩展控制着坡体演化,并受裂纹率及裂缝周围的尖端应力场影响较大。在坡体演化初期,以坡体后缘压缩沉降和局部岩层裂缝压剪破坏为主,岩层倾角发生较大变化,呈现由坡体上部往下逐级变大的趋势;演化中期,坡体后缘裂缝扩展形成主折断面,坡体中上部岩层角度变化较大,裂缝断裂数目的继续增加;演化末期,裂缝断裂数目保持平稳,主要以断裂岩层的位置重分布为主要变形特征...     

赫兹破裂：一种被忽视的构造

赫兹破裂在工程和材料领域一直备受关注,但其在地质学领域的应用还很少,远未像里德尔破裂那样熟知。从微观尺度到露头尺度,从板块尺度到行星尺度,赫兹破裂在自然界都广泛存在。赫兹破裂作为一种点接触破裂区别于常见的里德尔剪切破裂。它们均是自然界中特殊而又普遍发育的破裂形式,代表了不同的边界和应力条件。典型的赫兹破裂属于弹性变形范畴,由于点接触而在三维空间中形成特征的锥形破裂,在平面上则表现为放射状及环状破裂。在剖面上锥形破裂一般会出现一定角度的拐折,下段破裂与接触面的角度变大,是锥形破裂的典型特征之一。在地质学领域,赫兹破裂有着重要的指示意义,可以表征物质的韧性（toughness）、解释环状和放射状构造、解释锥状以及弧形破裂成因与样式、判断冰川以及断层的运动学特征、区分不同破裂机制形成的新月形构造等,也可以应用于恢复沉积环境以及判断成岩过程中或者构造变形过程中的古应力及其方向。板块碰撞过程中,在特定环境下也可形成赫兹破裂,因此该类型破裂将会有助于我们理解一些断层的成因、发展以及大陆的变形,同时为类地行星（卫星）表层的构造提供解释方案。     

A Simplified Numerical Approach for the Prediction of Rainfall-Induced Retrogressive Landslides

Retrogressive landslides are common geological phenomena in mountainous areas and on onshore and offshore slopes. The impact of retrogressive landslides is different from that of other landslide types due to the phenomenon of retrogression. The hazards caused by retrogressive landslides may be increased because retrogressive landslides usually affect housing, facilities, and infrastructure located far from the original slopes. Additionally, substantial geomorphic evidence shows that the abundant supply of loose sediment in the source area of a debris flow is usually provided by retrogressive landslides that are triggered by the undercutting of water. Moreover, according to historic case studies, some large landslides are the evolution result of retrogressive landslides. Hence the ability to understand and predict the evolution of retrogressive landslides is crucial for the purpose of hazard mitigation. This paper discusses the phenomenon of a retrogressive landslide by using a model experiment and suggests a reasonably simplified numerical approach for the prediction of rainfall-induced retrogressive landslides. The simplified numerical approach, which combines the finite element method for seepage analysis, the shear strength reduction finite element method, and the analysis criterion for the retrogression and accumulation effect, is presented and used to predict the characteristics of a retrogressive landslide. The results show that this numerical approach is capable of reasonably predicting the characteristics of retrogressive landslides under rainfall infiltration, particularly the magnitude of each landslide, the position of the slip surface, and the development processes of the retrogressive landslide. Therefore, this approach is expected to be a practical method for the mitigation of damage caused by rainfall-induced retrogressive landslides.     

Early phases of Caledonian deformation in the Dalradian of the Ballachulish district,Argyll

Two early phases of deformation preceded the development of the major NE-SW-trending folds, including the Appin Fold. The earliest recognized structures include small folds, lineations and inclusion trails in garnet porphyroblasts. The dominant schistosity and mineral lineation was developed during the second phase of deformation, associated with the formation of similar folds and tectonic banding, under garnet grade conditions over much of the area. The later-formed major folds are associated with low grade retrogressive metamorphism and crenulation and fracture cleavage formation. These folds are concentric folds and have associated tectonic slides producing low grade cataclastic schists. On the basis of fold style and sequence and metamorphic grade there is a great similarity between the structures in the Dalradian rocks of the Ballappel Foundation and those of the Iltay Nappe.     

Early fracture evolution within the Eye-Dashwa Lakes pluton,Atikokan, Ontario,Canada

The fracture history of part of the Eye-Dashwa Lakes pluton near Atikokan, Ontario was investigated from drill core and surface fracture data. The earliest fractures contain aplite and compose less than 5% of the population. They developed during the initial stages of plutonic cooling and contraction, in response to local magma-related pressures. Internal pressures decreased as the pluton cooled. Subsequent fractures, comprising more than 90% of the population, formed soon afterwards under the influence of a regional subhorizontal NW-SE compression. Statistical analysis and field evidence indicate that subhorizontal and moderately dipping dip-slip fractures are filled mainly with epidote. These were followed by formation of steeply dipping to subvertical strike-slip fractures that are filled mainly with chlorite. The resulting fracture framework was well established by the end of the Archaean. Minor stress changes since then have rejuvenated the old fracture zones rather than creating new zones.     

考虑卸荷作用的底板突水破坏机制研究

在依据摩尔图解及断裂力学理论对底板卸荷突水破坏分析的基础上,运用损伤断裂力学并结合统一强度理论,建立了考虑渗透水压作用下分支裂纹端部形成的塑性区范围计算方程与岩体发生贯穿破坏时的损伤阀值。将裂纹扩展过程与岩体损伤耦合起来,确定了裂纹的损伤断裂能量计算公式并分析了其影响因素。结果表明：侧压系数 0.5时,最大主应力完全卸荷状态下裂纹端部应力强度因子比双轴应力状态下大,岩体易发生破坏。考虑了裂纹端部塑性区的影响,裂纹损伤断裂能量相比于不考虑其影响时偏大,增大了煤层底板突水的危险性。裂纹损伤断裂能量 与裂纹半长 、裂纹面连通面积与总面积之比 、裂纹面渗透水压 及最小主应力 呈正相关,与裂纹面摩擦系数 及岩体的弹性模量 呈负相关。分析结果为底板突水破坏机制研究提供了一定的参考依据。     

层流—紊流共存流场中岩溶裂隙网络演化过程的数值模拟方法

研究岩溶水系统的演化过程对许多资源与环境问题有着重要意义。岩溶地区水资源、油气资源的预测与开发、水土流失成因及防治等课题都与此密切相关。岩溶管道是地下水对裂隙的逐渐溶蚀扩展形成的,岩溶演化初期,所有裂隙宽度不大,流场整体成层流状态。随着溶蚀的进行,一部分裂隙优先扩大使其中的水流进入紊流状态,而另一部分裂隙中水流仍呈层流状态。文章提出一种数值方法,能够模拟层流-紊流共存流场的岩溶演化过程。利用蒙特卡洛(Monte-Carlo)方法模拟初始裂隙网络,通过非连续介质方法模拟裂隙网络中的渗流。裂隙扩展的速度通过岩石表面溶蚀速度经验公式计算,使用迭代方法求解层流-紊流共存条件下的水头非线性方程。构建了能够利用解析法求解的模型,把数值解和解析解的结果进行对比,验证了本研究的数值法及软件的可行性。      

从断裂带内部结构出发评价断层垂向封闭性的方法

脆性断层和塑性断层断裂带内部结构存在差异: 脆性断层断裂带由以断层岩和伴生裂缝为特征的破碎带和诱导裂缝带2部分组成; 塑性断层断裂带表现为几条充填断层泥大裂缝的组合, 诱导裂缝带不发育.破碎带内部伴生裂缝、无粘结力断层岩带和诱导裂缝带都可能成为油气运移的通道, 只有这3种通道均封闭, 脆性断层垂向才是封闭的.只要伴生裂缝封闭, 塑性断层就是封闭的.基于这种封闭机理, 分析了3种通道封闭的条件: 无粘结力断层岩带是否封闭取决于断层泥含量大小; 破碎带内部伴生裂缝的封闭性取决于断面压力和断层泥塑性强度关系; 诱导裂缝带封闭程度受控于后期成岩充填的程度.提出了利用断面压力、断层泥的含量和塑性强度、后期成岩程度综合判定不同性质断层垂向封闭性评价方法.并利用该方法对克拉2构造F₁断层垂向封闭性进行了评价, 结果表明F₁断层垂向封闭性具有分段性: ①和③段均表现为脆性, 但①段因诱导裂缝没有被充填不封闭, ③段是封闭的; ②段是塑性断层, 垂向封闭性好.这是克拉2构造有大规模天然气聚集成藏的关键因素之一.      

压剪应力状态下岩石复合型断裂判据的研究

考虑岩石闭合裂纹壁面间存在的摩擦力对裂纹尖端应力场的影响,应用最大周向应力理论得到压剪复合裂纹的断裂角。在此基础上,依据岩石裂纹尖端双向受力时的破坏特征,结合最大周向应力准则与修正的格里菲斯（Griffith）强度理论,建立了考虑摩擦效应的闭合裂纹失稳扩展的岩石压剪断裂判据。研究结果表明：断裂角受裂纹和荷载方向的夹角、裂纹壁面之间的摩擦系数、侧压力系数的影响;当压剪裂纹的断裂角是某个定值时,纯II型裂纹的断裂韧度与纯I型裂纹的断裂韧度的比值只与岩石裂纹表面的摩擦系数取值有关,而与其他岩石力学参数无关。此研究成果可为压剪应力作用下裂隙岩体的失稳破坏提供参考。