含垂直裂解隙PTL介质长波长等效正交各向异性弹性常数

针对PTL介质中存在定向排列的铅垂裂隙系统的组合模型,探讨在长波长情况下其等效正交各向异性弹性常数的计算方法.根据Backus方法并结合Hudson微裂隙理论,推出了PTL与EDA组合之等效正交各向异性弹性常数的计算公式,且在裂隙呈稀疏分布的假设前提下,导出了等效弹性常数的具体计算表达式,并进而用伪谱法对含垂直裂隙PTL介质的弹性波场进行了数值模拟.本文的理论研究及数值计算结果表明:用5个长波长等效PTL弹性常数和3个无量钢的裂隙柔量,就可描述等效正交各向异性介质九个独立的弹性常数.     

多组垂直裂缝诱导各向异性的HTI近似及其特征分析

在裂缝诱导各向异性理论研究中通常使用等效HTI介质来近似多组裂缝所引起的综合效应.由于构造运动的复杂性,多组裂缝普遍存在于地壳与油气储层中.为了研究多组裂缝的地震属性特征,分析常用的等效HTI模型对于多组裂缝近似精度及附加裂缝对介质属性特征的影响,本文利用线性滑移模型进行了多组垂直裂缝的单斜各向异性等效介质理论计算,并利用空间搜索方法求取与其最为接近的HTI介质各向异性弹性参数.重点研究了在两种各向异性介质中纵波速度、快慢横波速度和极化特征及其差异,量化分析附加裂缝对于地震属性如速度、极化方向和走时等的影响,研究对附加裂缝敏感的地震属性.此研究结果和方法为进一步研究多组裂缝的反演及识别方法提供基础,同时对于将高阶对称性各向异性介质中已存在的计算方法应用于低阶对称性时的适用程度、精度分析及相关方法研究具有重要作用.     

裂隙参数对衰减各向异性影响的数值模拟

理论、观测和实验均证实,在地壳和上地幔存在对应力变化敏感的直立裂隙,在整体上呈现方位各向异性.在Hudson裂隙理论基础上,系统全面地数值模拟了裂隙介质几何、物性和弹性波频率等参数对各向异性衰减的影响.结果显示,裂隙密度、裂隙纵横比、泊松比、裂缝填充物、弹性波频率和未破裂岩石母体纵横波速度等对各向异性衰减有着显著影响,...     

岩石物理驱动的储层裂缝参数与物性参数概率地震反演方法

长波长假设条件下,各向同性背景地层中发育一组平行排列的垂直裂缝可等效为具有水平对称轴的横向各向同性（HTI）介质.基于不同观测方位的岩石地震响应特征变化,宽方位地震数据不仅可实现裂缝岩石弹性参数与各向异性参数的预测,同时也蕴含着丰富的孔隙度等储层物性参数信息.本文结合实际地震资料提出了贝叶斯框架下岩石物理驱动的储层裂缝参数与物性参数概率地震联合反演方法,首先基于AVAZ反演裂缝岩石的弹性参数与各向异性参数,并在此基础上通过统计岩石物理模型表征孔隙度、裂缝密度等各向异性介质储层参数与裂缝岩石参数的相互关联,并采用马尔科夫链蒙特卡洛（MCMC）抽样方法进行大量样本的随机模拟,使用期望最大化（EM）算法估计后验条件概率分布,最终寻找最大后验条件概率对应的孔隙度、裂缝密度等HTI裂缝介质储层参数即为反演结果.测井及实际地震数据处理表明,该方法能够稳定合理地从方位地震资料中获取裂缝岩石弹性参数与各向异性参数,并提供了一种较为可靠的孔隙度、裂缝密度等裂缝介质储层参数概率地震反演方法.     

裂缝介质旋转交错网格正演模拟

油气勘探实践表明, 裂缝是油气的储存空间或运移通道, 裂缝介质地震波场的研究越来越受到关注. 实际地层中裂缝形成受多种因素控制, 物理属性比较复杂, 表现出强烈的各向异性. 由于上覆地层的压力使得水平或低陡倾角裂缝存在较少, 大多数为高陡倾角裂缝, 利用线性滑动裂缝介质的等效理论将高陡倾角裂缝介质等效为横向各向同性介质, 便于实际应用. 本文采用各向异性弹性波旋转交错网格模拟方法对含裂缝介质单炮记录进行模拟与分析. 结果表明: 裂缝的存在相当于人为增加反射界面; 裂缝密度越大, 裂缝纵横比越小, 裂缝充填物与背景介质弹性性质差别越大, 引起的反射波能量变化越大. 本文模拟结果为利用地震数据进行裂缝介质参数反演与储层识别及油气预测提供了依据.      

基于黏弹性Chapman-Kelvin模型的裂缝储层频变AVAZ反演研究

为了在地震资料和裂缝储层特征之间建立联系,对裂缝储层采用了等效介质模型.而传统的等效介质模型未充分考虑非完全弹性介质理论和基于频变各向异性理论的双相或多相流体假设,也不能对实际裂缝储层中的地震波频散和衰减现象提供准确合理的解释,并且储层参数的反演研究对裂缝储层的定性预测和定量描述举足轻重.为此,本文首先根据所提出的黏弹性Chapman-Kelvin动态等效介质模型,该模型考虑了耦合的双相流体假设、黏弹性理论、喷射流以及斑块效应,并在此基础上分析了裂缝储层参数(主要为裂缝密度、裂缝长度、孔隙度和含水饱和度)对地震波频变特征的影响.然后基于黏弹性Chapman-Kelvin模型与Schoenberg和Protazio概括的Zoeppritz方程所计算出的频变反射系数,分析了反射PP波和PS波的频变AVAZ(Amplitude Versus Angle and Azimuth)特性和PP波频变反射系数与裂缝储层参数的关系.同时考虑到发生地震频散时,反射系数和频率产生关系,构建了在角度、方位和时间域内的新型正演方程.最后,基于PP波频变反射系数对裂缝密度、裂缝长度、孔隙度和含水饱和度的变化有较...     

背景为各向异性的含裂缝岩石频散和衰减计算方法研究

裂缝广泛分布于各类储层岩石中,并且会显著提高储层的渗流能力.因此,裂缝的评价和表征对于提高油气产能具有重要意义.由于裂缝与背景介质之间的波致流会显著影响地震波的频散和衰减特性,所以地震勘探是评价裂缝性储层的有效手段.裂缝地震定量表征的前提是要基于含裂缝岩石中波致流对频散和衰减的影响建立含裂缝岩石物理特性与地震性质的关系.然而,目前相关的理论研究大部分基于各向同性背景这一假设,难以有效应用于常见的各向异性储层.本文针对背景为各向异性的含裂缝岩石提出了频散和衰减的计算方法.该方法首先将含裂缝岩石中的各向异性背景介质等效为层状背景介质;然后,通过分析不同频率下层状含裂缝岩石中的流体压力分布,理论计算了两个特定的中间频率并求解得到两个中间频率下的弹性参数;进一步,以计算得到的两个特定中间频率以及高低频极限下的弹性参数为基础,应用数值方法求解得到弛豫函数中的未知参数,最终实现了背景为各向异性含裂缝岩石中频散和衰减的理论模拟.通过将理论预测结果与实验测量和数值模拟结果进行对比,验证了该方法在背景为各向异性含不同分布裂缝岩石中的有效性.本文提出的方法考虑了常见的各向异性背景对含裂缝岩石频散和衰减的影...     

川西新场裂隙储层波场模拟与分析

川西坳陷致密碎屑岩储层虽然地质储量丰富,但是复杂地质条件导致的储层物性差、分布广、层系多、裂隙发育、非均质性强、流体关系复杂的特点加剧了勘探开发的难度。本文针对川西新场探区的复杂性和特殊性,将裂隙储层等效为各向异性储层,进行VTI介质和HTI介质波动方程正演模拟,分析该地区裂隙介质的地震响应特征。波场模拟结果分析表明,裂隙介质的存在,会引起反射波场的振幅和走时变化;另一方面,根据走时的变化,也能估算裂缝发育角度范围。      

含垂直裂解隙PTL介质长波长等效正各向异性弹性常数

针对PTL介质中存在定向排列的铅垂裂隙系统的组合模型，探讨在长波长情况下其等效正交各向异性弹性常数的计算方法。根据Backus方法并结合Hudson微裂隙理论，推出了PTL与EDA组合之等效正交各向异性弹性常数的计算公式，且在裂隙呈稀疏分布的假设前提下，导出了等效弹性常数的具体计算表达式，并进而用伪谱法对含垂直裂隙PTL介质的弹性波场进行了数值模拟。本文的理论研究及数值计算结果表明：用5个长波长等效PTL弹性常数和3个无量钢的裂隙柔量，就可描述等效正交各向异性介质力个独立的弹性常数。     

煤储层双相EDA介质的地震波场模拟

基于二维-二分量弹性波方程交错网格高阶有限差分法数值模拟,对各向同性介质模型、高裂隙密度含干裂隙和饱和水裂隙煤层各向异性介质和双相介质的二维层状模型进行了弹性波场数值模拟.结果表明:双相EDA介质中存在第二类纵波(慢纵波).各向异性理论和双相介质理论比单相理论要好,单相理论存在衰减问题.各向异性和双相理论在含气情况下比...     

基于各向异性梯度的裂缝密度反演

裂缝密度是评价裂缝性储层的重要参数. 本文提出一种利用各向异性梯度计算裂缝密度的新方法,即运用裂缝介质等效理论将高陡倾角裂缝介质等效为横向各向同性介质,得到裂缝介质AVO响应特征,从而得到裂缝介质的各向异性梯度,之后由该梯度与裂缝密度的关系得到裂缝介质的裂缝密度. 实际处理中可以根据地震数据直接求取裂缝介质的各向异性梯度,最后求取裂缝介质的裂缝密度. 模型试算表明, 该方法能得到裂缝介质准确的裂缝密度. 反演结果与初始模型基本一致验证了该方法的正确性; 另外地震记录添加一定的信噪比后也能反演得到准确的裂缝密度,证明了该方法的稳定性.      

Effective velocities in fractured media: a numerical study using the rotated staggered finite‐difference grid

The modelling of elastic waves in fractured media with an explicit finite‐difference scheme causes instability problems on a staggered grid when the medium possesses high‐contrast discontinuities (strong heterogeneities). For the present study we apply the rotated staggered grid. Using this modified grid it is possible to simulate the propagation of elastic waves in a 2D or 3D medium containing cracks, pores or free surfaces without hard‐coded boundary conditions. Therefore it allows an efficient and precise numerical study of effective velocities in fractured structures. We model the propagation of plane waves through a set of different, randomly cracked media. In these numerical experiments we vary the wavelength of the plane waves, the crack porosity and the crack density. The synthetic results are compared with several static theories that predict the effective P‐ and S‐wave velocities in fractured materials in the long wavelength limit. For randomly distributed and randomly orientated, rectilinear, non‐intersecting, thin, dry cracks, the numerical simulations of velocities of P‐, SV‐ and SH‐waves are in excellent agreement with the results of the modified (or differential) self‐consistent theory. On the other hand for intersecting cracks, the critical crack‐density (porosity) concept must be taken into account. To describe the wave velocities in media with intersecting cracks, we propose introducing the critical crack‐density concept into the modified self‐consistent theory. Numerical simulations show that this new formulation predicts effective elastic properties accurately for such a case.     

具有离散裂缝空间分布的二维固体中地震波传播的有限差分模拟

结合有限差分方法和等效介质理论,模拟了离散分布裂缝介质中地震波的传播. 基于等效介质理论,利用二维有限差分实现封闭裂缝的离散分布;裂缝可以处理成固体岩石中的高度柔性界面,并可以用线性滑动或者位移间断模型进行裂缝的物理描述. 对于含有多组裂隙的破裂固体,其有效柔度可以认为是固体骨架背景柔度和裂缝附加柔度之和. 在一阶近似条件下,固体骨架和裂缝参数可以通过有效各向异性系数联系起来,有效各向异性系数决定了各向异性（裂缝效应）对于地震波传播的影响. 通过与射线理论方法的对比检验,说明本文提出的模拟方法的有效性,并通过几个数值算例说明本方法可有效模拟不同的裂缝分布效应. 结果表明,即使在裂缝密度很小的情况下,具有相同裂缝密度的不同的空间分布可以产生不同的波场特征. 同时,也验证了不同裂缝尺度对波长的不同影响,以及裂缝尺度具有幂率分布（分形）时,尺度对波场的影响. 最后得出结论：在运用建立在等效介质理论基础上的地震各向异性概念来描述裂缝固体的特征时,要倍加小心,等效介质理论中尚未合理处理的裂缝尺度和空间分布对波的传播特征具有重要的影响.     

Experimental verification of effective anisotropic crack theories in variable crack aspect ratio medium

Physical modelling of cracked/fractured media using downscaled laboratory experiments has been used with great success as a useful alternative for understanding the effect of anisotropy in the hydrocarbon reservoir characterization and in the crustal and mantle seismology. The main goal of this work was to experimentally verify the predictions of effective elastic parameters in anisotropic cracked media by Hudson and Eshelby–Cheng's effective medium models. For this purpose, we carried out ultrasonic measurements on synthetic anisotropic samples with low crack densities and different aspect ratios. Twelve samples were prepared with two different crack densities, 5% and 8%. Three samples for each crack density presented cracks with only one crack aspect ratio, whereas other three samples for each crack density presented cracks with three different aspect ratios in their composition. It results in samples with aspect ratio values varying from 0.13 to 0.26. All the cracked samples were simulated by penny‐shaped rubber inclusions in a homogeneous isotropic matrix made with epoxy resin. Moreover, an isotropic sample for reference was constructed with epoxy resin only. Regarding velocity predictions performed by the theoretical models, Eshelby–Cheng shows a better fit when compared with the experimental results for samples with single and mix crack aspect ratio (for both crack densities). From velocity values, our comparisons were also performed in terms of the ε, γ, and δ parameters (Thomsen parameters). The results show that Eshelby–Cheng effective medium model fits better with the measurements of ε and γ parameters for crack samples with only one type of crack aspect ratio.     

Effective elastic properties of randomly fractured soils: 3D numerical experiments

This paper is concerned with numerical tests of several rock physical relationships. The focus is on effective velocities and scattering attenuation in 3D fractured media. We apply the so‐called rotated staggered finite‐difference grid (RSG) technique for numerical experiments. Using this modified grid, it is possible to simulate the propagation of elastic waves in a 3D medium containing cracks, pores or free surfaces without applying explicit boundary conditions and without averaging the elastic moduli. We simulate the propagation of plane waves through a set of randomly cracked 3D media. In these numerical experiments we vary the number and the distribution of cracks. The synthetic results are compared with several (most popular) theories predicting the effective elastic properties of fractured materials. We find that, for randomly distributed and randomly orientated non‐intersecting thin penny‐shaped dry cracks, the numerical simulations of P‐ and S‐wave velocities are in good agreement with the predictions of the self‐consistent approximation. We observe similar results for fluid‐filled cracks. The standard Gassmann equation cannot be applied to our 3D fractured media, although we have very low porosity in our models. This is explained by the absence of a connected porosity. There is only a slight difference in effective velocities between the cases of intersecting and non‐intersecting cracks. This can be clearly demonstrated up to a crack density that is close to the connectivity percolation threshold. For crack densities beyond this threshold, we observe that the differential effective‐medium (DEM) theory gives the best fit with numerical results for intersecting cracks. Additionally, it is shown that the scattering attenuation coefficient (of the mean field) predicted by the classical Hudson approach is in excellent agreement with our numerical results.     

裂缝型储层流体识别方法

裂缝型储层的描述包括预测裂缝分布特征和识别裂隙充填物.依据等效介质理论计算的纵波速度随裂缝密度的增大而减小.正演地震记录显示,裂缝介质含气时反射振幅最大,且变化程度比含油或含水时大.叠前方位AVO反演所得的各向异性梯度Bani与裂缝密度成正比,可用于描述有效裂缝发育强度.对于不同的裂缝密度,各向异性梯度Bani与各向同性梯度Biso的比值I(1)fluid近似为常数,且对流体敏感.经裂缝纵横比和背景介质拉梅常数修正后,流体因子Ifluid既不随纵横比变化,又不受背景介质的影响,是裂缝型储层敏感的流体识别因子.在塔里木盆地塔北哈拉哈塘地区热瓦普区块碳酸盐岩储层裂缝发育区域,运用该参数在井点处的流体识别效果与钻井结果一致.     

Effect of stress interactions on anisotropic P-SV-wave dispersion and attenuation for closely spaced cracks in saturated porous media

Generally, local stress induced by individual crack hardly disturbs their neighbours for small crack densities, which, however, could not be neglected as the crack density increases. The disturbance becomes rather complex in saturated porous rocks due to the wave-induced diffusion of fluid pressures. The problem is addressed in this study by the comparison of two solutions: the analytical solution without stress interactions and the numerical method with stress interactions. The resultant difference of effective properties can be used to estimate the effect of stress interactions quantitatively. Numerical experiments demonstrate that the spatial distribution pattern of cracks strongly affects stress interactions. For regularly distributed cracks, the resulting stress interaction (shielding or amplification) shows strong anisotropy, depending on the arrangement and density of cracks. It has an important role in the estimation of effective anisotropic parameters as well as the incident-angle-dependency of P- and SV-wave velocities. Contrarily, randomly distributed cracks with a relative small crack density generally lead to a strong cancellation of stress interactions across cracks, where both the numerical and analytical solutions show a good agreement for the estimation of effective parameters. However, for a higher crack density, the incomplete cancellation of stress interactions is expected, exhibiting an incidence-angle dependency, slightly affecting effective parameters, and differentiating the numerical and analytical solutions.     

Seismoelectric numerical simulation in 2D vertical transverse isotropic poroelastic medium

Seismoelectric coupling in an electric isotropic and elastic anisotropic medium is developed using a primary–secondary formulation. The anisotropy is of vertical transverse isotropic type and concerns only the poroelastic parameters. Based on our finite difference time domain algorithm, we solve the seismoelectric response to an explosive source. The seismic wavefields are computed as the primary field. The electric field is then obtained as a secondary field by solving the Poisson equation for the electric potential. To test our numerical algorithm, we compared our seismoelectric numerical results with analytical results obtained from Pride's equation. The comparison shows that the numerical solution gives a good approximation to the analytical solution. We then simulate the seismoelectric wavefields in different models. Simulated results show that four types of seismic waves are generated in anisotropic poroelastic medium. These are the fast and slow longitudinal waves and two separable transverse waves. All of these seismic waves generate coseismic electric fields in a homogenous anisotropic poroelastic medium. The tortuosity has an effect on the propagation of the slow longitudinal wave. The snapshot of the slow longitudinal wave has an oval shape when the tortuosity is anisotropic, whereas it has a circular shape when the tortuosity is isotropic. In terms of the Thomsen parameters, the radiation anisotropy of the fast longitudinal wave is more sensitive to the value of ε, while the radiation anisotropy of the transverse wave is more sensitive to the value of δ.     

基于改进BISQ机制的双相HTI介质波传播伪谱法模拟与特征分析

改进BISQ(Biot-Squirt)机制在不引入特征喷流长度的情况下,将含流体孔隙介质中Biot流动和喷射流动两种重要的力学机制有机地结合起来,且各相关参数具有明确物理意义和可实现性.本文将改进BISQ机制一维孔隙流体压力公式推广到三维具有水平对称轴横向各向同性介质(HTI介质)情况,结合裂缝各向异性理论,给出了基于改进BISQ机制的双相HTI介质模型及其二维三分量波传播方程,采用伪谱法求解该方程,进行了不同相界、不同频率以及双层地质结构情况下该类介质中波场的数值模拟与特征分析.数值模拟结果表明:伪谱法模拟精度高,压制网格频散效果好,可以得到高精度的波场快照和合成记录;基于改进BISQ机制的双相HTI介质模型兼具裂缝各向异性特征和孔隙弹性特征,其为从双相各向异性理论角度深入研究裂缝性储层的地震响应奠定了理论基础.