1. Anisotropy and Heterogeneity Induced by Shale in Aquifer lithology—Influence of Aquifer Shale on the Leaky Model With Tidal Response Analysis.
- Author
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Zhang, Yan, Fu, Li‐Yun, Zhu, Aiyu, Zhao, Lianfeng, Qi, Shengwen, Huang, Tianming, Ma, Yuchuan, and Zhang, Wang
- Subjects
AQUIFERS ,PETROLOGY ,SHALE ,ANISOTROPY ,HETEROGENEITY ,LARGE deviations (Mathematics) - Abstract
Tidal and barometric water‐level responses in wells have been widely used to calculate the hydraulic properties of aquifer systems. The effect of anisotropy induced by shale content on such responses has not received significant attention. In this study, we examine how the presence of shale (anisotropy, extremely low porosity/permeability; approximately 10−4 to 10−3 mD), which occurs as interlayers in aquifers, affects the tidal responses of the leaky model. Our findings show that the number of wells with shale in the screened section of the study aquifer is limited. Here, we focus on the study of the limited number of wells in the North China Platform to ensure a similar geological background for each well. Calculations indicate that wells, even with a small amount of shale (≥∼5%) in the observation aquifer, may exhibit strong anisotropy and heterogeneity, deviating from the theoretical analytical solutions obtained using isotropic and homogeneous assumption models. Generally, the higher the shale content in aquifer lithology, the greater the phase shifts deviated. Thus, theoretical ideal models with isotropic and homogeneous assumptions may only obtain a rough estimation for wells with shale in aquifer lithology, suggesting that we avoid setting observation aquifers onto shale layers. Plain Language Summary: As special lithology, shale is fragile, compact, and anisotropic, and because of its extremely low porosity/permeability (10−4 to 10−3 mD), it will also induce the heterogeneity of the whole layer containing both shale and other lithology rocks. Therefore, aquifers containing shale might exhibit unique characteristics. However, there is mostly no previous research on this topic in the hydro‐geophysics region, perhaps because the number of wells with shale in aquifer lithology is very limited. Key Points: Well aquifers, even with little amount of shale (∼5%), might have strong anisotropy and heterogeneity and deviate from the ideal modelsThe more shale content in the aquifer lithology the larger the deviation occursFurther call for us to avoid setting the observation aquifers onto the shale (low permeability, friability, and anisotropy) layers [ABSTRACT FROM AUTHOR]
- Published
- 2023
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