Compactive Deformation of Sandstone Under Crustal Pressure and Temperature Conditions
Compactive Deformation of Sandstone Under Crustal Pressure and Temperature Conditions
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DOI：
10.1029/2020jb020202
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发表时间：
2021-02
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影响因子：
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通讯作者：
M. Jefferd;N. Brantut;P. Meredith;T. Mitchell;O. Plümper
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作者：
M. Jefferd;N. Brantut;P. Meredith;T. Mitchell;O. Plümper
众所周知，多孔砂岩从宏观脆性变形到宏观延性变形的转变与压力有关，只有在达到显著有效压力时，才会发生压实、延性行为。在地壳内，这种有效压力与埋藏深度在0.5-6公里之间有关，那里的温度可能是35°C-200°C。为了测试这种高温对砂岩强度和变形能力的重要性，在常温或150°C下对三种不同的含水饱和砂岩进行了一系列恒应变速率的三轴变形实验。对于每一种砂岩，都使用了跨越脆性和韧性变形模式的有效压力范围，最高可达120 Mpa。在脆性区，我们观察到屈服应力随温度的降低在8%到17%之间。在延性范围内，我们观察到屈服应力的降幅更大，在9%到37%之间。另一个值得注意的观察是，从膨胀性、脆性行为向紧凑性、延性行为的转变往往发生在较低的有效压力下的高温。在高温下观察到的弱化可以用断裂韧性的降低来解释，数学上表明，这在延性区域引起的削弱比在脆性区域引起的更大。高温下断裂韧性的明显降低可能是表面能降低和亚临界裂纹扩展速率增加共同作用的结果。
The transition from macroscopically brittle to macroscopically ductile deformation in porous sandstones is known to be pressure dependent, with compactive, ductile behavior occurring only once significant effective pressures have been reached. Within the crust, such effective pressures are associated with burial depths in the range 0.5–6 km, where the temperature is likely 35°C–200°C. To test the importance of such elevated temperature on the strength and deformability of sandstone, a series of constant strain rate, triaxial deformation experiments were performed on three different water saturated sandstones at either ambient temperature or 150°C. For each sandstone, an effective pressure range was used which spanned both the brittle and ductile deformation regimes, up to a maximum of 120 MPa. In the brittle regime, we observed a temperature‐dependent lowering of the yield stress of between 8% and 17%. Within the ductile regime, we observed an even greater reduction in the yield stress of between 9% and 37%. A further notable observation is that the transition from dilatant, brittle behavior to compactive, ductile behavior tends to occur at a lower effective pressure at elevated temperature. The weakening observed at elevated temperature can be explained by a reduction in fracture toughness, which is shown mathematically to cause greater weakening in the ductile regime than in the brittle regime. The apparent reduction in fracture toughness at elevated temperature is potentially driven by a combination of a reduction in surface energy and, to a minor extent, an increase in subcritical crack growth rate.