Stabilization of rapid frictional slip on a weakening fault by dilatant hardening
Stabilization of rapid frictional slip on a weakening fault by dilatant hardening
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通过膨胀硬化稳定弱化断层上的快速摩擦滑移
DOI：
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发表时间：
1988
期刊：
影响因子：
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通讯作者：
Chao
中科院分区：
文献类型：
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作者：
J. Rudnicki;Chao
摩擦滑移通常伴随着由于在相邻材料上的凸起和微裂纹上滑动而产生的剪胀。如果剪胀发生的速度快于孔隙流体进入新形成空隙的速度，则局部孔隙压力降低，压缩时的有效法向应力增加，倾向于抑制进一步滑移。用一个简单的模型对膨胀硬化进行了分析。板的一个表面受压应力和剪切位移的作用，并与孔隙流体储集层相连，保持恒定压力。另一个边界是一个摩擦表面，假定是在峰值应力下形成的，当滑移从0增加到δ0时，其剪切应力从峰值τp减小到残余值τr。在没有孔隙流体影响的情况下，当剪应力与滑移关系的斜率比周围材料的卸载刚度更负时，就会出现与无界滑移率相对应的失稳。如果储层的孔隙压力足够高，膨胀硬化可以防止这种不稳定性。如果储层压力过低，断层面的压力会降低到孔隙流体体积模量迅速下降的程度，从而消除了稳定作用。当对分析进行修改，包括模拟轴对称压缩试验中的正应力变化时，储层中临界压力的预测与Martin在Westerly花岗岩试验中观察到的结果在2或3倍之内。这些预测也与Martin观察到的油藏临界孔隙压力随有效围应力的增加和名义应变率的降低而降低的趋势相一致。
Frictional slip is often accompanied by dilatancy due to uplift in sliding over asperities and micro-cracking in the adjacent material. If dilatancy occurs more rapidly than pore fluid can flow into the newly created void space, the local pore pressure is reduced and the effective normal stress is increased in compression, tending to inhibit further slip. This dilatant hardening is analyzed for a simple model. One surface of a slab is loaded by compressive stress and shear displacement and connected to a reservoir of pore fluid held at constant pressure. The other boundary is a frictional surface, assumed to have formed at peak stress, on which the shear stress decreases from a peak value τp to a residual value τr as slip increases from zero to δ0. In the absence of pore fluid effects an instability corresponding to an unbounded slip rate occurs when the slope of the shear stress versus slip relation is more negative than the unloading stiffness of the surrounding material. Dilatant hardening prevents this instability provided that the pore pressure in the reservoir is high enough. If the pressure in the reservoir is too low, the pressure at the fault surface can be reduced to the point at which the pore fluid bulk modulus decreases rapidly, eliminating the stabilizing effect. When the analysis is modified to include normal stress changes simulating those in the axisymmetric compression test, the prediction of the critical pressure in the reservoir agrees to within a factor of 2 or 3 with that observed by Martin in tests on Westerly granite. The predictions are also consistent with the trends observed by Martin of decreasing critical reservoir pore pressure with increasing effective confining stress and decreasing nominal strain rate.