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Seismic characterisation of fault damage in 3D using mechanical and seismic modelling

机译：使用机械和地震模型对3D断层破坏进行地震表征

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Although typically interpreted as 2D surfaces, faults are 3D narrow zones of highly and heterogeneously deformed rocks with petrophysical properties differing from the host rock. Fault zones have been extensively studied in outcrop, but in the subsurface they are barely explored, mainly because they are at the limit of seismic resolution and are rarely drilled and cored. We present a 3D synthetic workflow to assess the potential of seismic data for imaging and characterising fault damage and properties. The workflow is based on forward modelling techniques. First, we run a 3D discrete element model to simulate faulting and associated deformation. Then, we use simple relationships to modify the initial elastic properties of the model based on its volumetric strain. From this reflectivity cube, we apply a ray based, pre-stack depth migration simulator. Finally, from the resultant seismic image, we use seismic attributes to characterise the fault volume. We illustrate the workflow for a large displacement normal fault in a sandstone-shale sequence for two cases, one with constant fault displacement and another with linearly variable displacement along strike. Seismic cubes of these models for a homogeneous overburden and several wave frequencies are generated. High frequencies show the impact of the fault on the offset and folding of the reflectors. In the variable fault slip model, the fault has less impact as the displacement decreases, and the fault tipline can be interpreted. We extract the fault geobody using three combined seismic attributes: dip, semblance and tensor. The geobody for the constant fault displacement model corresponds to an inner high-deformation area within the fault zone, while in the variable fault slip model the geobody captures better the entire fault zone. Cross plotting of amplitudes and strains shows that the geobody contains all range of strains, but almost all high strain values are within the geobody. This allows a direct comparison between the fault zone identified on the seismic image and that in the mechanical model. (C) 2016 Elsevier Ltd. All rights reserved.
机译：尽管断层通常被解释为2D曲面，但断层是岩石变形性质与主体岩石不同的高度且非均质变形岩石的3D狭窄区域。在露头对断层带进行了广泛的研究，但在地下却很少进行勘探，这主要是因为它们处于地震分辨率的极限，并且很少钻探和取芯。我们提出了一种3D综合工作流程，以评估地震数据用于成像和表征断层破坏和性质的潜力。该工作流基于正向建模技术。首先，我们运行3D离散元素模型来模拟断层和相关变形。然后，我们使用简单的关系根据其体积应变修改模型的初始弹性特性。从这个反射率立方体，我们应用基于射线的叠前深度偏移模拟器。最后，从合成的地震图像中，我们使用地震属性来表征断层体积。我们以两种情况说明了砂岩-页岩层序中的大位移法向断层的工作流程，一种是断层位移恒定，另一种是沿走向线性位移。这些模型的地震立方产生了均匀的覆盖层，并生成了多个波频率。高频显示故障对反射器的偏移和折叠的影响。在可变断层滑动模型中，随着位移的减小，断层的影响较小，并且可以解释断层的尖端。我们使用三个组合的地震属性（倾角，相似度和张量）提取断层地物。恒定断层位移模型的土工体对应于断层带内的内部高变形区域，而在可变断层滑动模型中，土工体更好地捕获了整个断层带。振幅和应变的交叉图显示，土体包含所有应变范围，但是几乎所有高应变值都在土体内。这允许在地震图像上识别的断层带和力学模型中的断层带之间进行直接比较。 （C）2016 Elsevier Ltd.保留所有权利。

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