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arXiv 2103.14367physics.geo-ph
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用混合维流动公式研究水力试验中裂缝的张开

Investigations into the opening of fractures during hydraulic testing using a hybrid-dimensional flow formulation

Patrick Schmidt, Holger Steeb, Jörg Renner

摘要:

我们应用了一个混合维流动模型的压力瞬变过程中记录的泵送实验在Reiche Zeche地下研究实验室进行研究,由于流体注入裂缝的正常打开行为。两种不同类型的压力响应流量步骤进行了识别和数值模拟,使用径向对称的流配方的裂缝,包括一个非线性本构关系的接触力学管理可逆的断裂面相互作用。从传统的压力扩散观点来看,这两组代表径向对称和平面轴对称流态。一个全面的参数研究的敏感性所应用的流体力学模型的特征裂缝参数的变化揭示了裂缝长度和正常的断裂刚度,产生匹配的现场观测和数值计算结果之间的相互关系。断裂刚度值随着相应的断裂长度而增加。将作用正应力分解为与整体裂缝几何形状的变形状态和接触应力相关的应力表明,几何诱导应力的贡献越大,总有效法向应力越低,裂缝越短。分离的贡献的局部接触力学和整体断裂几何断裂法向刚度表明,后者,几何刚度,构成了一个下限的总刚度,其相关性增加,减少断裂长度,太。我们的研究表明,非线性水力机械耦合可以导致截然不同的水力响应,从而提供了一种替代传统的压力扩散分析,需要改变流态,以涵盖整个范围的观察。

英文摘要:

We applied a hybrid-dimensional flow model to pressure transients recorded during pumping experiments conducted at the Reiche Zeche underground research laboratory to study the normal opening behavior of fractures due to fluid injection. Two distinct types of pressure responses to flow-rate steps were identified and numerically modelled using a radial-symmetric flow formulation for a fracture that comprises a non-linear constitutive relation for the contact mechanics governing reversible fracture surface interaction. These two groups represent radial-symmetric and plane-axisymmetric flow regimes from a conventional pressure-diffusion perspective. A comprehensive parameter study into the sensitivity of the applied hydro-mechanical model to changes in characteristic fracture parameters revealed an interrelation between fracture length and normal fracture stiffness that yield a match between field observations and numerical results. Fracture stiffness values increase with corresponding fracture length. Decomposition of the acting normal stresses into a stresses associated with the deformation state of the global fracture geometry and the contact stresses indicates that geometrically induced stresses contribute the more the lower the total effective normal stress and the shorter the fracture. Separating the contributions of the local contact mechanics and the overall fracture geometry to fracture normal stiffness indicates that the latter, the geometrical stiffness, constitutes a lower bound for total stiffness; its relevance increases with decreasing fracture length, too. Our study demonstrates that non-linear hydro-mechanical coupling can lead to vastly different hydraulic responses and thus provides an alternative to conventional pressure-diffusion analysis that requires changes in flow regime to cover the full range of observations.

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