The Hydro-Mechanical Properties of Fracture Intersections: Pressure-Dependant Permeability and Effective Stress Law
The Hydro-Mechanical Properties of Fracture Intersections: Pressure-Dependant Permeability and Effective Stress Law
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裂缝相交处的水力力学特性：压力相关渗透率和有效应力定律
DOI：
10.1029/2022jb025516
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发表时间：
2023
期刊：
影响因子：
3.4
通讯作者：
Stanton-Yonge A
中科院分区：
文献类型：
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作者：
Stanton-Yonge A
通过脆性地壳的流体流动主要受裂隙网络为流体输送提供通道的能力控制。裂隙岩体中的主导渗透率方向一直与裂隙交点的发育相关联；在中区域尺度上也进行了观察。尽管裂缝交汇处在促进流体流动方面很重要，但它们对裂隙岩石渗透率的增强程度尚未量化。在这里，我们通过使用巴西测试设备产生两个由两个单独的载荷产生的正交拉伸裂缝，并测量它们的渗透率作为静水压力的函数，来表征Seljadalur玄武岩样品中交叉点的流体力学特性。我们观察到，相交的两个裂缝明显比两个独立的宏观裂缝更具渗透性，而顺应性更差。通过添加两个独立裂缝和一个管状空腔的贡献，我们建立了裂缝交汇处渗透率随压力的函数模型，管状空腔的有效弹性压缩系数由其几何形状决定。循环加载过程中的渗透率测量可以确定裂缝和交点渗透率的有效应力系数(αinpe=pc−αpp)。我们观察到α交叉值相对于α裂缝有降低的趋势，这表明相对于独立的裂缝，控制流体流动的通道具有更高的纵横比(更具管状)。研究结果表明，裂缝交汇处对深层渗透率的维持起着至关重要的作用，这对于裂缝渗透率的定量化和油藏尺度模拟具有重要意义。
Fluid flow through the brittle crust is primarily controlled by the capability of fracture networks to provide pathways for fluid transport. The dominant permeability orientation within fractured rock masses has been consistently correlated with the development of fracture intersections; an observation also made at the meso‐regional scale. Despite the importance attributed to fracture intersections in promoting fluid flow, the magnitude of their enhancement of fractured rock permeability has not yet been quantified. Here, we characterize the hydro‐mechanical properties of intersections in samples of Seljadalur Basalt by generating two orthogonal, tensile fractures produced by two separate loadings using a Brazilian test apparatus, and measuring their permeability as a function of hydrostatic pressure. We observe that intersecting fractures are significantly more permeable and less compliant than two independent macro‐fractures. We formulate a model for fracture intersection permeability as a function of pressure by adding the contributions of two independent fractures plus a tube‐like cavity with an effective elastic compressibility determined by its geometry. Permeability measurements during cyclic loading allowed determination of the effective stress coefficient (αinpe=pc−αpp) for fracture and intersection permeability. We observe a trend of lowerαintersectionvalues with respect toαfracture, which suggests that the channels controlling fluid flow have a higher aspect ratio (are more tubular) for the intersections relative to independent fractures. Our results suggest that fracture intersections play a critical role in maintaining permeability at depth, which has significant implications for the quantification and upscaling of fracture permeability toward reservoir‐scale simulations.