地层压力条件下沁水盆地煤岩动静态弹性参数同步超声实验研究

静态弹性参数对储层压裂改造、应力场及裂缝预测具有重要意义,开展地层压力条件下煤岩动、静态弹性参数实验研究,获得动、静态弹性参数之间的关系,为利用动态弹性参数预测静态弹性参数提供了岩石物理依据.本次研究应用MTS岩石物理参数测试系统完成沁水盆地和顺地区的煤岩样在地层压力条件下的动静态弹性参数同步测试.结果表明:动态杨氏模量随压力的增加而增加,而动态泊松比随压力的变化较为复杂;动、静态杨氏模量之间呈线性关系,且动态杨氏模量大于静态杨氏模量;动、静态泊松比之间的相关性较差,大部分煤样的动态泊松比小于静态泊松比.获得的这些关系为动静弹性参数转换提供了基础,进而为利用地震资料进行静弹性参数预测,获得岩石力学性能参数提供了一种途径.     

Experiment Study and Interpretation on Relation between Modulus of Rock and Strain Amplitude

INTRODUCTIONThe modulus of rock is one of the basic elastic parameters of the earth’s medium. Under theassumption of linear elastic theory and Poisson medium,other parameters can be calculated fromit .But the real earth mediumis nonlinear elastic and has not a simple linear relationship between stressand strain.This causes relatively big differences betweenthe dynamic andthe static modulus of rock.In nonlinear elastic theory,the Young’s modulusEis replaced bythe nonlinear elastic modul…     

Study on anisotropy of Longmaxi shale using hydraulic fracturing experiment

Hydraulic fracturing reservoir reconstruction technology is crucial in the development of shale gas exploitation techniques.Large quantities of high-pressure fluids injected into shale reservoirs significantly alter compressional(P)and shear(S)wave velocities,rock mechanical parameters,and anisotropic characteristics.In this study,differentiated hydraulic fracturing petrophysical experiments were carried out on Longmaxi Formation shale under pseudo-triaxial stress loading conditions.The effects of stress loading methods,and water-rock physical and chemical reactions on P-and S-wave velocities and rock mechanical parameters were compared.The experimental results showed that isotropic stress loading may increase the P-and Swave velocities and Young’s modulus of dry shale kldnsample.Furthermore,it may lead to a weakening of the corresponding anisotropy.In contrast,differential stress loading was able to improve the anisotropy of Young’s modulus and accelerate the decrease in the compressive strength of shale in the vertical bedding direction.The water-rock physical and chemical reactions prompted by hydraulic fracturing was found to"soften"shale samples and reduce Young’s modulus.The influence of this"soften"effect on the compressional and shear wave velocities of shale was negligible,whilst there was a significant decrease in the anisotropy characteristics of Thomsen parameters,Young’s modulus,and Poisson’s ratio.The negative linear relationship between the Poisson’s ratios of the shale samples was also observed to lose sensitivity to stress loading,as a result of the"soften"effect of fracturing fluid on shale.The results of this study provide a reliable reference point and data support for future research on the mechanical properties of Longmaxi shale rocks.     

基于比值均方根的杨氏模量反演方法

杨氏模量和泊松比是表征岩石脆性、评价储层可压性以及描述储层流体特征的重要参数,叠前地震反演是从地震数据中得到此类参数的有效手段.常规的叠前地震反演方法多使用Zeopppritz方程的近似式计算反射系数,近似式的误差影响了反演结果的精度.针对这个问题,推导了比值均方根形式的杨氏模量、泊松比和密度的Zoeppritz方程,并基于广义线性反演构建了杨氏模量和泊松比直接反演方法,有效地避免了使用近似式的局限性,提高了反演的精度.模型测试和实际资料试算结果表明：采用比值均方根形式构建的反演流程稳定,能够从叠前地震数据中获得可信的杨氏模量、泊松比和密度,提供了一种可靠的杨氏模量和泊松比直接反演方法.     

杨氏模量和泊松比反射系数近似方程及叠前地震反演

杨氏模量和泊松比等岩石弹性参数是表征页岩气储集体岩石脆性、评价储层含气特征的重要特征参数,而叠前地震反演是从地震资料中获取此类参数的有效途径.地震波反射系数方程是叠前反演的基础.首先,在平面波入射等假设条件下推导了基于杨氏模量(Y)、泊松比(σ)和密度(D)的纵波反射系数线性近似方程(YPD反射系数近似方程),该方程建立了地震纵波反射系数与杨氏模量反射系数、泊松比反射系数和密度反射系数的线性关系;其次,对该方程的精度和适用条件进行了分析,模型分析表明,在入射角为40°时,该方程具有较高的计算精度;最后,建立了一种稳定获取杨氏模量和泊松比的叠前地震直接反演方法.模型试算和实际资料试处理表明,基于新方程的反演方法能够稳定合理的直接从叠前地震资料中获取杨氏模量和泊松比参数,提供了一种高可靠性的页岩气"甜点"地震识别方法.     

饱和岩石的各向异性及非线性黏弹性响应

在MTS伺服压机上对不同饱和状态的砂岩、大理岩标本进行了垂直层理和平行层理两个方向的正弦波加载试验,研究了饱和岩石的各向异性及非线性黏弹性行为. 在最大载荷低于岩石的屈服点时,获得的衰减、杨氏模量、泊松比、波速都表现出显著的各向异性,同时它们还具有较明显的应变振幅效应和频率效应. 随着应变振幅的增大,衰减近似呈线性增长,杨氏模量和泊松比近似呈线性下降. 在0.005-4Hz频段内除衰减不明显依赖频率以外,杨氏模量、泊松比、波速对频率的依赖性都较强; 当频段扩大到15Hz时,这4个参数都表现出较强的频率效应. 饱和岩石的衰减、杨氏模量、泊松比、波速均随饱和液体的黏滞系数增大而增大.     

应变能积累在地震安全性评价中的应用探讨

理论及实验研究显示,震源区的位置和最大震级不仅可能与构造和历史有关,更重要的是与应力状态包括其方向、大小、增加速率、集中位置等以及岩体自身性质,包括其强度、杨氏模量、应变大小及增长速率、裂缝(断层)大小和数量等有关,同时与作用方式有关.综合考虑各种因素,探讨了利用应变能积累确定强震位置和震级的方法:首先对利用形变空间特征变化判断强震震源区位置的方法进行了讨论;接着着重提出估算应变能的初步方法:一是由地表裂缝最大错距和裂缝(断层)长度比估算地震释放能量;二是由新构造运动分区块体体积、年平均应变速率及杨氏模量估算块体应变能积累;进而依据能量估算地震震级;最后以实例论述了应变能积累过程及特点对地震安全性评价的重要作用.     

具有割缝的大理岩试件破坏过程的有限元模拟

本文使用应变软化的弹塑性本构模型,用有限元方法对具有中心斜割缝的岩石试件在轴压下的破坏过程进行了数值模拟。得到了与实验观察相当一致的结果:在割线端部附近,首先发生张破裂,裂纹的扩张是逐渐地弯向试件的轴线方向,并变为稳定的。随着轴向压力增加,在张裂纹的相反方向上出现共轭的剪破裂。这些现象与割缝顶端附近材料的应变软化性质有关。说明所采用的有限元方法是研究岩石材料破裂过程的一种可行的方法。     

State ofin-situ stress in different rocks

According to the regression analysis of measured stress data in magmatite, sedimentary and metamorphic rock all over the world, it is found that the stress state in the three rocks is different and closely related to its formation. The relationships among the stress and depth and the Young’s modulus of rock are also discussed and the results show that stress can increase with the Young’s modulus.     

State of in-situ stress in different rocks

According to the regression analysis of measured stress data in magmatite, sedimentary and metamorphic rock all over the world, it is found that the stress state in the three rocks is different and closely related to its formation. The relationships among the stress and depth and the Young’s modulus of rock are also discussed and the results show that stress can increase with the Young’s modulus.     

页岩气储层纵横波叠前联合反演方法

杨氏模量与密度乘积(Eρ)能够突显页岩气储层的异常特征,泊松比能够指示储层的含流体性.与常规叠前弹性参数反演相比,基于Eρ、泊松比和密度的叠前纵横波联合反演可以获得更加精确的弹性参数,为页岩气储层识别和流体预测提供可靠的依据.首先,推导了基于Eρ、泊松比和密度的纵波和转换波反射系数近似方程,利用典型模型对新推导的反射系数方程做精度分析,当入射角小于30°时,新推导的反射系数公式具有较高的精度;其次,充分利用纵波和转换波的信息,在贝叶斯的框架下,建立叠前纵横波联合反演流程,进行Eρ、泊松比和密度的直接反演,避免了间接反演带来的累积误差;最后,利用实际工区井模型数据进行算法测试,结果表明,该反演方法所获得的Eρ、泊松比和密度的估计值与真实值吻合较好,满足精细地震反演的精度要求.     

岩石模量与应变振幅关系的实验研究及理论解释

地球介质的非线性弹性造成了岩石动态和静态弹性模量在数值上的差异。本文用超声波速度测量得到岩石的动模量，用含有小循环的加卸载实验得到小循环模量，用大循环的应力、应变曲线斜率得到静模量，用测点的应力、应变之比得到杨氏模量。通过改变小循环的应变振幅来研究模量与应变振幅的关系，进而比较用不同测量方法得到的模量值的差异。结果表明，动模量值最大，小循环模量值次之，大循环静模量值再次之，而杨氏模量最小。岩石非线性模量既是所受应变水平的函数，也是应变振幅的函数，模量随应变振幅的增加以指数形式下降，随应变水平增加以指数形式上升。最后简要介绍了P-M模型的基本概念，用岩石中微裂缝具有不同的分布密度，不同的打开和关闭压力来解释模量与应变振幅的关系。     

Burial stress and elastic strain of carbonate rocks

Burial stress on a sediment or sedimentary rock is relevant for predicting compaction or failure caused by changes in, e.g., pore pressure in the subsurface. For this purpose, the stress is conventionally expressed in terms of its effect: “the effective stress” defined as the consequent elastic strain multiplied by the rock frame modulus. We cannot measure the strain directly in the subsurface, but from the data on bulk density and P‐wave velocity, we can estimate the rock frame modulus and Biot's coefficient and then calculate the “effective vertical stress” as the total vertical stress minus the product of pore pressure and Biot's coefficient. We can now calculate the elastic strain by dividing “effective stress” with the rock frame modulus. By this procedure, the degree of elastic deformation at a given time and depth can be directly expressed. This facilitates the discussion of the deformation mechanisms. The principle is illustrated by comparing carbonate sediments and sedimentary rocks from the North Sea Basin and three oceanic settings: a relatively shallow water setting dominated by coarse carbonate packstones and grainstones and two deep water settings dominated by fine‐grained carbonate mudstones and wackestones.     

Buckling of a pervasively faulted lithosphere

We investigated the buckling response of a faulted elastic plate under horizontal compression using the finite element technique to better understand the effect of faults on the elastic behavior of a plate. We studied the effect of changes in fault spacing, depth and dip on the effective Young's modulus, buckling stress and wavelength. Our model consists of a thick elastic plate whose entire upper surface is cut by evenly spaced faults. We impose either an initial sinusoidal deformation with a fixed wavelength or a random deformation to the grid. A fault is represented as a free surface with no resolved shear stress and is allowed to slip in a specified direction using the method of slippery nodes. With the assumption of free slip on the faults, our model results represent an end member case in which the buckling wavelength and buckling stress are minimized by the presence of the faults.In our models, fault depth was varied from 0 to 75% of the plate thickness. As strain increases, the grid deforms by antisymmetric flexural folding and the initial imposed wavelength of deformation is modified such that the new buckling wavelength emerges. Our results show that the effective Young's modulus is a decreasing function of fault depth and an increasing function of fault spacing. In addition, buckling of the plate occurs at a lower stress for greater fault depths. Buckling wavelength is independent of the initial deformation wavelength however, it is modified by the presence of faults. For a plate with closely spaced faults extending through at least 75% of the plate, buckling occurs at a wavelength one half as large as that for a continuous plate. Buckling stress is not independent of the intial deformation wavelength, rather it increases slightly with increasing difference between the initial deformation wavelength and the buckling wavelength.Analytical models that approximate or ignore the effect of faulting can have large errors in calculation of the buckling stress. More importantly, modeling the observed wavelength of deformation in a faulted region with analytical solutions for continuous plates may result in a significant underestimate of elastic thickness. Fault dip does not strongly affect either the effective Young's modulus or the buckling wavelength. Thus, the buckling response should be the same for a plate cut by a low angle fault or a high angle fault.     

岩石损伤模量分析

从能量的角度出发定义损伤变量,通过应力-应变曲线卸载段有效应力与总应力之间的假定关系,确定损伤模量的计算方法。在单轴和三轴条件下,对岩石损伤相关参数进行统计研究,重点对损伤模量进行计算和对比分析。结果表明,单轴及低围压下损伤模量基本呈逐渐减小的趋势,而随着围压的增大,损伤模量呈先减小后保持动态稳定的趋势。损伤变量的计算充分考虑到围压的影响,可进一步增进对岩石损伤的认识。     

饱和砂岩的黏弹行为的实验研究

通过Metravib热机械分析仪,用正弦波进行加载,实验时固定静载为100 N,正弦波动载荷恒为60 N,将总载荷控制在屈服点以下;在温度为-50～125℃,升温速率为1℃/min,频率为5～1000 Hz的条件下,对泵油饱和长石砂岩、彭山砂岩样品进行单轴循环加载实验,求取泵油饱和长石砂岩和彭山砂岩的衰减、耗散角、模量...     

红河断裂带断层泥基本力学性质的初步研究

本文对红河断裂带断层泥的某些基本力学性质进行了实验研究,得到红河断层泥的体积压缩模量为104巴的量级,杨氏模量为102—103巴的量级,泊松比为0.3—0.4,单轴抗压强度由数巴至数十巴,单轴抗剪强度为数巴,粘滞系数为1010—1011泊的量级,弹性波速为1.5—2.2公里/秒。对比红河断裂带南北两段断层泥的力学性质,看出南段断层泥的体积压缩模量,杨氏模量、抗压强度、粘滞系数和弹性波速比北段断层泥高。此外,南段断层泥弹性波速基本上各向同性而北段断层泥弹性波速显示出各向异性。      

引潮力作用下饱和地质岩体的力学响应

本文应用孔隙弹性理论,探讨了引潮力作用下饱和地质岩体的力学响应.首先通过引潮力作用下饱和岩体的自由能表达式,得到岩体孔压与应力、应力与应变之间的关系;然后从引潮力作用下饱和岩体的平衡微分方程出发,结合流-固耦合理论,分析了饱水岩体应变与引潮位之间的关系;最后推导出饱和岩体的两大力学物理量--孔压和潮汐应力(平均应力)与引潮位之间的物理关系.模型表明:饱和岩体孔压与引潮位成反比,平均潮汐应力与引潮位成正比;比例系数不仅与岩体骨架的Lame系数有关,而且与Biot模量有关.将模型应用于会理川-18井水位变化分析,估计出水位响应系数D,并以此为基础,求得岩体孔压、潮汐应力与引潮位的相关系数(A和C)及Skempton系数B.最后对比分析了耦合条件下与不考虑耦合时得到的各参数之间的差异,分析表明:对饱和地质岩体而言,应力、孔压对引潮力的响应是流-固耦合作用的产物;研究其力学响应时必须充分考虑耦合效应.模型的建立,为研究引潮力作用下井-承压含水层系统力学、水动力学、与地震有关的断层力学以及引潮力触发机制的定量研究提供了基础.     

Effects of pore fluids on quasi-static shear modulus caused by pore-scale interfacial phenomena

It is evident from the laboratory experiments that shear moduli of different porous isotropic rocks may show softening behaviour upon saturation. The shear softening means that the shear modulus of dry samples is higher than of saturated samples. Shear softening was observed both at low (seismic) frequencies and high (ultrasonic) frequencies. Shear softening is stronger at seismic frequencies than at ultrasonic frequencies, where the softening is compensated by hardening due to unrelaxed squirt flow. It contradicts to Gassmann's theory suggesting that the relaxed shear modulus of isotropic rock should not depend upon fluid saturation, provided that no chemical reaction between the solid frame and the pore fluid. Several researchers demonstrated that the shear softening effect is reversible during re-saturation of rock samples, suggesting no permanent chemical reaction between the solid frame and the pore fluid. Therefore, it is extremely difficult to explain this fluid–rock interaction mechanism theoretically, because it does not contradict to the assumptions of Gassmann's theory, but contradicts to its conclusions. We argue that the observed shear softening of partially saturated rocks by different pore fluids is related to pore-scale interfacial phenomena effects, typically neglected by the rock physics models. These interface phenomena effects are dependent on surface tension between immiscible fluids, rock wettability, aperture distribution of microcracks, compressibility of microcracks, porosity of microcracks, elastic properties of rock mineral, fluid saturation, effective stress and wave amplitude. Derived equations allow to estimate effects of pore fluids and saturation on the shear modulus and mechanical strength of rocks.     

中国及邻区现代构造应力场的数值模拟

我国及邻区的现代构造应力场作为一平面应力问题用有限单元法进行了计算。将本区地壳看成是一不均匀的弹性板,根据各地区杨氏模量E、泊松比v和地壳厚度T的不同,组成12种材料区。全区被分成288个三角形单元。考虑了五种应力和位移边界条件,这些边界条件分别反映了印度洋板块、太平洋板块及菲律宾海板块对我国及邻区施加应力的相对大小。将计算得到的最大剪应力值与强震分布进行对比,将最大主压应力方向与震源机制解的最大主压应力方向进行对比,选择一种和实际符合得最好的边界条件作为可取的模式。结果表明:来自印度洋板块的作用力最大,大约是来自太平洋板块和菲律宾海板块作用力的两倍。