Viscous creep in room-dried unconsolidated Gulf of Mexico shale (I): Experimental results
Viscous creep in room-dried unconsolidated Gulf of Mexico shale (I): Experimental results
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DOI：
10.1016/j.petrol.2009.08.018
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发表时间：
2009-12
影响因子：
--
通讯作者：
Chandong Chang;M. Zoback
中科院分区：
文献类型：
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作者：
Chandong Chang;M. Zoback
实验室实验表明，南尤金岛油田的室温干燥松散的墨西哥湾页岩在静水压力和三轴压缩应力下都表现出明显的粘性蠕变行为。在所有测试中，页岩在卸载时没有表现出蠕变(和几乎可以忽略的应变恢复)，这表明蠕变应变最好被认为是粘塑性变形。在施加压力或应力阶跃变化后，蠕变压实比瞬时发生的蠕变压实要显著得多，表明页岩压实过程在很大程度上取决于骨架的粘塑性变形。超声速度测量还表明，蠕变对动态特性演化的贡献明显大于增量加载的贡献。动态体积模数与静态模数相似，特别是在气孔和裂纹闭合的高压下。有趣的是，在静水压缩试验中，页岩在围压为~30 Mpa以上和以下的蠕变行为是不同的。在30 Mpa以上，6h内发生的蠕变应变量在等加压步数下基本恒定，表现为线性粘性流变性。当压力低于30 Mpa时，蠕变量随压力的增加呈线性增加，表现为非线性粘性流变性。在不同的应力条件下，也观察到了定性相似的行为。在另一篇论文(Chang和Zoback，本期)中，我们研究了描述粘塑性页岩变形的本构定律。
Laboratory experiments reveal that room-dried unconsolidated Gulf of Mexico (GOM) shale from the South Eugene Island field exhibits pronounced viscous creep behavior under both hydrostatic pressure and triaxial compressive stress. In all tests, the shale exhibits a lack of creep (and nearly negligible strain recovery) when unloaded, suggesting that the creep strain is best considered as viscoplastic deformation. Following application of a step-change in pressure or stress, creep compaction is considerably more significant than that which occurs instantaneously, indicating that the process of shale compaction is largely dependent on the viscoplastic deformation of the frame. Ultrasonic velocity measurements also demonstrate that the contribution of creep to the evolution of dynamic properties is significantly larger than that associated with incremental loading. Dynamic bulk moduli are similar to static moduli especially at high pressures at which pores and cracks are closed. Interestingly, in the hydrostatic compression tests the creep behavior of the shale is different above and below ~30MPa confining pressure. Above 30MPa, the amount of creep strain that occurs in 6h is approximately constant with equal pressurization steps, indicating a linear viscous rheology. Below 30MPa, the amount of creep increases linearly as pressure is raised in constant incremental steps, indicating a nonlinear viscous rheology. A qualitatively analogous behavior was also observed under differential stress conditions. In a companion paper (Chang and Zoback, this issue) we examine constitutive laws that describe the viscoplastic shale deformation.