基于流体的潮汐-气压响应特征研究富含页岩含水层的渗流特性

Tidal and barometric water-level responses in wells have been widely used to study the properties of aquifers and, in particular, the response of groundwater to earthquakes. However, the effect of lithology on such responses has not received much attention, especially the influence of shale in the aquifer on the responses has rarely been studied. In this study, based on groundwater observation data, we intend to judge whether horizontal flow or vertical flow occurs in the observed aquifer in tandem with the tidal responses of water-level; while we use the barometric responses of water-level to analyze the confinement and storativity of well aquifer. Here, we compare the tidal and barometric response characteristics of water level for wells with shale or sandstone in the aquifer. We especially focus on the study of different hydraulic response models for different wells with shale or with sandstone in the aquifer, so that to calculate the permeability of aquifer based on different models; and also to detect the influence of increased shale content in the aquifer on the tidal and barometric response characteristics, and then using the response characteristics, we intend to infer whether there is shale in an observed aquifer. In addition, this computational and analytical process might also provide a method to detect and continuously monitor groundwater leakage near the in-situ area of shale gas exploration, where the deep injection of wastewater has been ongoing.

流体的潮汐和气压响应被广泛应用于研究含水层的性质，特别是分析地下流体对地震的响应过程。但含水层岩性对潮汐-气压响应特征的影响目前尚未得到足够的关注，特别是关于页岩的影响研究较少。本申请基于地震地下流体观测资料，拟采用井水位的潮汐响应进行含水层中流体水平向或垂直向流动的判别；采用流体的气压响应分析井含水层的封闭性和井孔的储水性能。从而对比分析砂岩含水层和富含页岩含水层的流体潮汐-气压响应特征，着重研究不同岩性（砂岩、页岩）观测含水层对应井孔的水力响应模型，进而计算含水层的渗透率，探究观测含水层中页岩含量变化对流体潮汐-气压响应的影响规律，期待将响应特征应用于含水层中页岩岩性的识别。此外，页岩气开发过程中产生的大量有毒废水（压裂液）会被注入开发区域附近的地下深部蓄水层，本项目的潜在应用是为有毒废水进行持续性渗流监测提供依据和理论方法支持。

地震和流体的相互加载过程较为复杂，往往存在多种解释，导致较难探知确切的水文物理机理。本项目主要采用实地台站观测 (水位观测、气压观测、地震波记录)，并针对目前含流体多孔介质中地震波传播以及渗透率、裂隙计算的数理模型、计算方法和机理解释方面存在的问题，从4个方面研究不同岩性多孔岩石中的流体运移变化及潮汐响应特征： (1) 申请人揭示了大地震导致的近场和中远场同震流体和体应变变化迥异的耦合机制，阐明了远场同震体应变变化与地壳流体渗透性增强的同步效应机理；(2) 提出了M2+O1波约束的潮汐响应渗漏模型，揭示了致密盖层垂向水力传导系数与气压系数的关联性，为利用流体的潮汐响应监测地壳流体的窜层即垂向渗透性改变提供有效手段，特别是为流体地质封存（废水、CO2等）的渗漏监测提供科学依据；(3) 提出了M2+O1波约束的潮汐响应裂隙方向模型，揭示了地震波驱动的波致流冲刷裂缝淤积、改变裂缝网渗漏走向的物理机理，为利用水位的潮汐响应监测地壳裂缝渗透性走向变化提供有效手段，实现经济、精准且无损的裂隙产状求解；(4) 页岩作为特殊岩性，具有易碎、致密和各向异性的特性，并且由于其极低的孔隙度/渗透率(10-4—10-3mD)，会引起包含页岩和其他岩性岩石的整个岩层的各向异性。申请人研究表明，即使观测含水层中有少量页岩(>=～5%)，整个含水层也可能表现出很强的各向异性和非均质性，从而使得实地观测结果偏离了使用各向同性和均匀假设模型获得的理论解析解；并且发现含水层中页岩含量越高偏差越大。此外，通过COMSOL 数值模拟也验证上述结论。