Seismic anisotropy as an indicator of reservoir quality in siliciclastic rocks
Seismic anisotropy as an indicator of reservoir quality in siliciclastic rocks
复制标题
地震各向异性作为硅质碎屑岩储层质量的指标
DOI：
10.1144/sp292.7
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发表时间：
2007
影响因子：
3.9
通讯作者：
W. B. Ismail
中科院分区：
文献类型：
--
作者：
J. Kendall;Q. Fisher;S. Crump;J. Maddock;A. Carter;S. A. Hall;J. Wookey;S. Valcke;M. Casey;G. Lloyd;W. B. Ismail
摘要提高地下成像的精度通常是在地震处理中考虑各向异性影响的主要动机。然而，各向异性本身包含关于岩石性质的有价值的信息，因此，可以被视为地震属性。在这里，我们总结了一个综合项目的结果，探讨了利用地震各向异性观测来解释岩性和流体性质的潜力（SAIL项目）。我们的方法将储集岩的详细岩石组构分析、岩心样品中基于实验室的超声波速度测量和小尺度地震观测联系起来。我们介绍了克莱尔油田的结果，克莱尔油田是苏格兰近海、设得兰群岛西部的一个石炭-泥盆纪油藏。储集岩是成分可变的砂岩，在晶体尺度、颗粒尺度和裂缝尺度上表现出各向异性。我们已经开发了一种方法来评估晶体择优取向（CPO）使用电子背散射衍射（EBSD），X射线织构测角（XRTG）和图像分析的组合。使用定量X射线衍射（QXRD）测量单个矿物的模态比例。这些测量用于计算由于CPO通过Voigt-Reuss-Hill平均的单个晶体弹性和它们的取向的固有各向异性。岩石的内在各向异性受层状硅酸盐含量的控制，在较小程度上受石英和长石的取向的控制;后者可作为古水流指示物。我们的研究结果表明，显着的一致性CPO在整个水库，使我们能够建立一个数学模型的储层各向异性。CPO预测的速度和那些来自实验室测量的超声信号的比较允许估计额外的弹性顺从条款由于晶界相互作用。结果表明，CPO估计是清洁砂岩的内在各向异性的良好替代。更多的云母岩石表现出增强的各向异性，由于页硅酸盐颗粒之间的相互作用。然后，我们比较了实验室规模的预测与地震各向异性，振幅随炮检距和方位角变化（AVOA）分析和非双曲时差的基础上，在实验室规模的测量。该数学模型的建立为精细地震资料解释和复杂储层地质建模提供了基础。所观察到的AVOA信号随深度的增加只能用主要单元边界下方的压裂增加来解释，而不是内在CPO性质的变化。一般而言，Clair油田各向异性的类型和大小似乎是储层质量的指示。
Abstract Improving the accuracy of subsurface imaging is commonly the main incentive for including the effects of anisotropy in seismic processing. However, the anisotropy itself holds valuable information about rock properties and, as such, can be viewed as a seismic attribute. Here we summarize results from an integrated project that explored the potential to use observations of seismic anisotropy to interpret lithological and fluid properties (the SAIL project). Our approach links detailed petrofabric analyses of reservoir rocks, laboratory based measurements of ultrasonic velocities in core samples, and reservoir-scale seismic observations. We present results for the Clair field, a Carboniferous–Devonian reservoir offshore Scotland, west of the Shetland Islands. The reservoir rocks are sandstones that are variable in composition and exhibit anisotropy on three length-scales: the crystal, grain and fracture scale. We have developed a methodology for assessing crystal-preferred-orientation (CPO) using a combination of electron back-scattered diffraction (EBSD), X-ray texture goniometry (XRTG) and image analysis. Modal proportions of individual minerals are measured using quantitative X-ray diffraction (QXRD). These measurements are used to calculate the intrinsic anisotropy due to CPO via Voigt-Reuss-Hill averaging of individual crystal elasticities and their orientations. The intrinsic anisotropy of the rock is controlled by the phyllosilicate content and to a lesser degree the orientation of quartz and feldspar; the latter can serve as a palaeoflow indicator. Our results show remarkable consistency in CPO throughout the reservoir and allow us to construct a mathematical model of reservoir anisotropy. A comparison of CPO-predicted velocities and those derived from laboratory measurements of ultrasonic signals allows the estimation of additional elastic compliance terms due to grain-boundary interactions. The results show that the CPO estimates are good proxies for the intrinsic anisotropy of the clean sandstones. The more micaceous rocks exhibit enhanced anisotropy due to interactions between the phyllosilicate grains. We then compare the lab-scale predictions with reservoir-scale measurements of seismic anisotropy, based on amplitude variation with offset and azimuth (AVOA) analysis and non-hyperbolic moveout. Our mathematical model provides a foundation for interpreting the reservoir-scale seismic data and improving the geological modelling of complex reservoirs. The observed increases in AVOA signal with depth can only be explained with an increase in fracturing beneath the major unit boundaries, rather than a change in intrinsic CPO properties. In general, the style and magnitude of anisotropy in the Clair field appears to be indicative of reservoir quality.