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Shale transformations and physical properties—Implications for seismic expression of mobile shales
Earth-Science Reviews ( IF 10.8 ) Pub Date : 2021-07-21 , DOI: 10.1016/j.earscirev.2021.103746
Juan I. Soto 1 , Michael R. Hudec 1 , Nazmul H. Mondol 2, 3 , Mahdi Heidari 1
Affiliation  

Seismic interpretation of mobile shales is challenging, mostly because of their unclear seismic expression. Imaging of mobile shales is difficult because of their low seismic-impedance contrast with many sedimentary rocks, spatial variation of their seismic properties, complex geometries of mobile-shales structures, and their complex internal structures. Furthermore, their seismic properties depend strongly on both overpressure and fluid content, which are difficult to predict.

To unravel this problem, we reviewed the physical properties of shales, merging data from in situ determinations of density and sonic velocities with experimental data and modeling results. We analyzed how diagenetic transformations during shale burial modify their physical properties and seismic characteristics. We reviewed conditions for smectite-illite transformation and gas generation (mostly methane) by oil cracking to evaluate how thermal gradient, shale composition, and hydrocarbon content modify the densities, sonic velocities, and seismic expressions of mobile shales. We then incorporated the amount and type of fluids released in shales during diagenesis into a study of seismic reflectivity of mobile shales.

Results derived theoretically for various types of mobile-shale contacts are compared with high-quality seismic examples, including mud volcanoes and a variety of complex shale diapirs. Observed reflectivity and seismic fabrics are discussed to infer clay composition, fluid content and type, and temperature.



中文翻译:

页岩变换和物理性质——对移动页岩地震表达的影响

移动页岩的地震解释具有挑战性,主要是因为它们的地震表达不清楚。由于与许多沉积岩相比,活动页岩的地震阻抗对比度低、地震性质的空间变化、活动页岩结构的几何形状复杂以及内部结构复杂,因此很难对活动页岩进行成像。此外,它们的地震特性在很大程度上取决于超压和流体含量,这很难预测。

为了解决这个问题,我们回顾了页岩的物理特性,将密度和声速的原位测定数据与实验数据和建模结果合并。我们分析了页岩埋藏过程中的成岩转变如何改变其物理性质和地震特征。我们回顾了通过石油裂解进行蒙脱石-伊利石转化和产气(主要是甲烷)的条件,以评估热梯度、页岩成分和碳氢化合物含量如何改变活动页岩的密度、声速和地震表达。然后,我们将成岩过程中页岩中释放的流体的数量和类型纳入了移动页岩地震反射率的研究中。

将各种类型的活动页岩接触的理论推导结果与高质量的地震实例进行了比较,包括泥火山和各种复杂的页岩底辟。讨论了观察到的反射率和地震结构,以推断粘土成分、流体含量和类型以及温度。

更新日期:2021-07-24
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