Rotated staggering grid forward modeling in fractured medium
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摘要: 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.Abstract: The practice of oil exploration proves that the fractures are the storage space of oil and gas and channels of them to move, thereby the wave-field of cracked media draws more and more attention. The actual fractured reservoir is influenced by many factors and its physical properties are complex, showing strong anisotropy. There only exist high dip-angle cracks because the pressure in the overlying strata makes only a few of horizontal or low dip angle cracks exist. It will be convenient for the practical application if fracture reservoir is equivalent to HTI medium by linear slip theory. This paper simulated and analyzed two-component records based on the anisotropic elastic wave rotated staggered grid modeling. The result shows that the existence of the crack is equivalent to increase the reflection interface artificially. The larger the crack density is, the smaller the aspect ratio is, the greater the difference between background and fracture fillings is, and the larger the change caused by reflection wave energy is. The result provides a basis for the reservoir identification and prediction when using the seismic data.
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Keywords:
- fracture medium /
- rotated staggering grid /
- fracture density /
- anisotropy /
- linear slip theory
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图 1 裂缝介质等效示意图图中ΔN和ΔT分别为裂缝介质的法向柔度与切向柔度.(a)单缝模型；(b)裂缝组合模型
Figure 1. The sketch of fracture equivalenceΔN denotes the normal weakness， and ΔT denotes the tangential weakness(a)Sigle fracture model;(b)Combination model of fractures
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图 5 不同时刻地震波场示意图.(a)t=0.75 s;(b)t=1.0 s;(c)t=1.6 s
Figure 5. The sketch of seismic wavefield in different moments.(a)t=0.75 s;(b)t=1.0 s;(c)t=1.6 s
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图 6 不同裂缝延伸长度的单道地震记录.(a)PP 波;(b)SS波
Figure 6. Seismic records of single trace in different crack growth.(a)PP wave;(b)SS wave
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图 7 不同裂缝密度(e)正演模拟的地震记录(a)e=0.5条/m;(b)e=1条/m;(c)e=2条/m;(d)e=4条/m;(e)e=5条/m
Figure 7. Seismic records in the media with different fracture densities(a)e=0.5 m-1;(b)e=1 m-1;(c)e=2 m-1;(d)e=4 m-1;(e)e=5 m-1
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图 8 不同裂缝纵横比(a/c)正演模拟的地震记录(a)a/c=1 000;(b)a/c=2 000;(c)a/c=5 000;(d)a/c=7 000;(e)a/c=1 0000
Figure 8. Seismic records in the media with different fracture aspect ratios(a)a/c=1 000;(b)a/c=2 000;(c)a/c=5 000;(d)a/c=7 000;(e)a/c=1 0000
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图 9 不同裂缝充填物正演模拟的地震记录(a)油；(b)水；(c)泥岩
Figure 9. Seismic records in the media with different fracture fillings(a)Oil;(b)Water;(c)Mudstone
表 3 标准交错网格中弹性波场分量和弹性参数的空间位置
Table 3 The positions of elastic wavefield components and elastic parameters in st and ard staggered grid
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表 4 旋转交错网格中弹性波场分量和弹性参数的空间位置
Table 4 The positions of elastic wavefield components and elastic parameters in rotated staggering grid
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何燕. 2008. 正交各向异性弹性波高阶有限差分正演模拟研究[D]. 东营: 中国石油大学(华东)地球资源与信息学院: 55-58. He Y. 2008. High-Order Finite-Difference Forward Modeling of Elastic-Wave in Orthorhombic Anisotropic Media[D]. Dongying: College of Geo-resources and Information, China University of Petroleum: 55-58 (in Chinese).
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