Purpose

Thermal fractures initiated under cooling at the surfaces of a 2-D or 3-D structure propagate, arrest and coalesce, leading to its structural failure and material-property changes, while the same processes can happen in the rock mass between parallel hydraulic fractures filled with cold fluid, leading to enhanced fracture connectivity and permeability.

Design/methodology/approach

This study used a 2-D plane strain fracture model for mixed-mode thermal fractures from two parallel cooling surfaces. Fracture propagation was governed by the theory of linear elastic fracture mechanics, while the displacement and temperature fields were discretized using the adaptive finite element method. This model was validated using two numerical benchmarks with strong fracture curvature and then used to simulate the propagation and coalescence of thermal fractures in a long rock mass.

Findings

Modeling results show two regimes: (1) thermal fractures from a cooling surface propagate and arrest by following the theoretical solutions of half-plane fractures before the unfractured portion decreases to 20% rock-mass width and (2) some pairs of fractures from the opposite cooling surfaces tend to eventually coalesce. The fracture coalescence time is in a power law with rock-mass width.

Originality/value

These findings are relevant to both subsurface engineering and material engineering: structure failure is a key concern in the latter, while fracture coalescence can enhance the connectivity of thermal and hydraulic fractures and thus reservoir permeability in the former.

中文翻译：

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平行冷却表面处引发的热裂纹合并

目的

在 2-D 或 3-D 结构表面冷却下引发的热裂缝会传播、停止和聚结，导致其结构失效和材料性能变化，而相同的过程也可能发生在填充的平行水力裂缝之间的岩体中与冷流体一起，导致裂缝连通性和渗透性增强。

设计/方法论/途径

本研究使用二维平面应变断裂模型来模拟两个平行冷却表面的混合模式热断裂。断裂扩展由线弹性断裂力学理论控制，而位移场和温度场则采用自适应有限元方法离散化。该模型使用两个具有强裂缝曲率的数值基准进行了验证，然后用于模拟长岩体中热裂缝的扩展和合并。

发现

模拟结果显示了两种状态：(1) 在未破裂部分减小到 20% 岩体宽度之前，冷却表面的热裂缝按照半平面裂缝的理论解传播和停止；(2) 来自冷却表面的一些裂缝对相反的冷却表面最终会合并。裂缝合并时间与岩体宽度呈幂律关系。

原创性/价值

这些发现与地下工程和材料工程都相关：结构破坏是后者的关键问题，而裂缝合并可以增强热裂缝和水力裂缝的连通性，从而增强前者的储层渗透率。