On the Penetration of Water into Hot Rock
On the Penetration of Water into Hot Rock
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DOI：
10.1111/j.1365-246x.1974.tb05468.x
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发表时间：
1974-12
影响因子：
2.8
通讯作者：
C. Lister
中科院分区：
文献类型：
--
作者：
C. Lister
总结 本文通过考虑最简单的一维模型，发展了水渗透到热岩中的机制理论。裂纹前沿的概念用于将裂纹多孔岩石中的对流状态与其下方的导电边界层分开。随着抗蠕变能力的提高，边界层中的岩石冷却、收缩并产生水平拉应力。当拉应力稍微超过上覆压力时，就会发生裂纹，并导致多边形的近垂直裂纹稳定向下扩展。进一步的冷却收缩使这些裂缝打开，以便水渗透，因此有效体积渗透率是裂缝间距和温度的重要函数。临界裂纹间距是由通过有利裂纹消除应力而扩大图案的竞争过程以及由于与通过裂纹本身冷却相关的径向温度梯度而导致的柱细分的竞争过程决定的。对与原始岩石热收缩相关的瞬态蠕变的初步处理表明，在几公里深度处的开裂温度在 800 至 1000 °K 之间，并且对热激活裂纹扩展的类似处理产生了前沿速度和裂纹间距之间的关系。这允许整个问题的近似解，得出前沿速度的公式，其中 φ 是捏造因子，温度为：TW - 热液，Tφ - 覆盖层消除蠕变应力，T0 - 下沉，T1 - 原始。通过 TW 最大化，可以计算任何给定 Tφ 的 u 和所有相关参数，Tφ 本身接近裂解温度。若Tφ=800°K，则锋面速度为32m/yr，裂缝间距为4.8cm，热液温度约为462°K。对流系统的功率输出约为5 kWm−2。裂纹区域的向下扩展似乎受到应力下柱子静态疲劳失效的限制，柱子位于前部后方一定距离。该模型的定性方面与山脊热流和地震数据总体一致，尽管新地壳表面附近的片状堤坝复合体是通过水循环对每个新堤坝的快速冷却而不是通过与一维模型相当的过程来创建的。随后，更深的水渗透可能会通过类似于模型中描述的过程发生。
Summary This paper develops a theory for the mechanism of penetration of water into hot rock by considering the simplest possible one-dimensional model. The concept of a cracking front is used to separate the convective regime in cracked porous rock from the conductive boundary layer below it. Rock in the boundary layer cools, shrinks and builds up horizontal tensile stress as resistance to creep rises. Cracking occurs when the tensile stress slightly exceeds the overburden pressure and results in the stable downward propagation of a polygonal pattern of sub-vertical cracks. Further cooling shrinkage opens these cracks to the percolation of water so that the effective bulk permeability is a strong function of both crack spacing and temperature. The critical crack spacing is determined by the competing processes of pattern enlargement through stress relief by favoured cracks and the subdivision of columns due to the radial temperature gradients associated with cooling through the cracks themselves. A rudimentary treatment of the transient creep associated with the thermal contraction of virgin rock suggests cracking temperatures between 800 and 1000 °K at depths of several kilometres and a similar treatment of thermally activated crack propagation produces a relationship between front velocity and crack spacing. That permits an approximate solution of the whole problem, resulting in a formula for front velocity where φ is a fudge factor and the temperatures are: TW—hot hydrothermal, Tφ—overburden cancelling creep stress, T0—sink, T1—original. Maximizing through TW permits the calculation of u and all dependent parameters for any given Tφ, itself close to the cracking temperature. If Tφ= 800 °K, the front velocity is 32m/yr, the crack spacing is 4.8cm and the hot hydrothermal temperature is about 462 °K. The power output of the convecting system is about 5 kWm−2. Downward propagation of the cracked region seems to be limited by static fatigue failure of the columns under stress, some distance behind the front. The qualitative aspects of the model are in general agreement with ridge crest heat-flow and seismic data, though the sheeted dike complex near the surface of new crust is created by rapid cooling of each new dike by water circulation rather than by a process comparable to the one-dimensional model. Subsequent, deeper, water penetration may occur by processes similar to those described in the model.