Theoretical model for the elastic properties of cracked fluid-saturated rocks considering the crack connectivity

IF 2.8 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Geophysical Journal International Pub Date : 2024-09-13 DOI:10.1093/gji/ggae330
Pu Wang, Yi-an Cui, Jingye Li, Jianxin Liu
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Abstract

Summary Cracks are a common rock microstructure and have a large effect on elastic properties during wave propagation. The fluid flow between a crack and its adjacent pore space can cause wave attenuation and dispersion. In this work, we introduce a crack connectivity parameter which is meant to improve the expression of local flow by weighting the contributions of fully connected and isolated cracks. We then update the analytical expression for frequency-dependent moduli by modifying the boundary conditions of the linearized Navier-Stokes equation and mass conservation equation. The proposed model contains the effect of cracks and stiff pores, in which the attenuation and dispersion are determined by squirt-flow and stiff-pore relaxations. The resulting model shows the squirt-flow relaxation frequency depends on not only the crack aspect ratio but also the crack connectivity. However, their contributions are different. The crack connectivity has little effect on the attenuation amplitude of shear modulus, but affects the attenuation amplitude of bulk modulus when multiple sets of cracks exist in the rock. The attenuation frequency band is also affected by the crack connectivity. As the crack connectivity deteriorates, the attenuation peak moves to low frequencies. In addition, by comparing the crack connectivity with the fluid viscosity coefficient, it is observed that the crack connectivity only affects the attenuation frequency band of cracks, whereas the fluid viscosity coefficient affects the attenuation frequency bands of cracks and stiff pores simultaneously. Thus, the introduction of crack connectivity is a supplement to the theoretical model of cracked fluid-saturated rocks. It helps understand the local fluid flow induced by seismic waves and provides a reasonable variation analysis of moduli and attenuation, especially for tight reservoirs.
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考虑裂缝连通性的裂缝流体饱和岩石弹性特性理论模型
摘要 裂缝是一种常见的岩石微结构,在波传播过程中对弹性特性有很大影响。裂缝及其相邻孔隙空间之间的流体流动会导致波的衰减和分散。在这项工作中,我们引入了一个裂缝连通性参数,旨在通过加权完全连通和孤立裂缝的贡献来改进局部流动的表达。然后,我们通过修改线性化纳维-斯托克斯方程和质量守恒方程的边界条件,更新了频率相关模量的分析表达式。所提议的模型包含裂缝和僵硬孔隙的影响,其中衰减和弥散由喷流和僵硬孔隙松弛决定。由此得出的模型表明,喷流弛豫频率不仅取决于裂纹长宽比,还取决于裂纹连通性。然而,它们的贡献是不同的。裂缝连通性对剪切模量的衰减幅度影响不大,但当岩石中存在多组裂缝时,裂缝连通性会影响体积模量的衰减幅度。衰减频带也受裂缝连通性的影响。随着裂缝连通性的恶化,衰减峰值会向低频移动。此外,通过比较裂缝连通性和流体粘度系数,可以发现裂缝连通性只影响裂缝的衰减频带,而流体粘度系数会同时影响裂缝和僵硬孔隙的衰减频带。因此,裂缝连通性的引入是对裂缝流体饱和岩石理论模型的补充。它有助于理解地震波诱发的局部流体流动,并提供合理的模量和衰减变化分析,尤其适用于致密储层。
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来源期刊
Geophysical Journal International
Geophysical Journal International 地学-地球化学与地球物理
CiteScore
5.40
自引率
10.70%
发文量
436
审稿时长
3.3 months
期刊介绍: Geophysical Journal International publishes top quality research papers, express letters, invited review papers and book reviews on all aspects of theoretical, computational, applied and observational geophysics.
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