Principal Stress Ratios in Cretaceous Limestones from Texas Gulf Coast
Principal Stress Ratios in Cretaceous Limestones from Texas Gulf Coast
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德克萨斯州墨西哥湾沿岸白垩纪石灰岩的主应力比
DOI：
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发表时间：
1974
期刊：
影响因子：
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通讯作者：
H. C. Heard
中科院分区：
文献类型：
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作者：
M. Friedman;H. C. Heard
对低孔隙度石灰岩岩心中方解石双纹层丰度的研究表明，在20,800英尺取样间隔内，每5,500英尺深度，每毫米的平均纹层数增加10个。在几个不同的应力水平和加载持续时间在适当的围压和温度下，一个代表性的石灰岩蠕变试验确定的条件下的层状形成。结果表明：（1）在均匀围压作用下，试样不会形成孪晶层;（2）孪晶层的丰度随围压差的增大而增大;（3）孪晶层的丰度随加载时间的延长而增大。在1，450 - 5，800 psi的差应力下持续1，000分钟的蠕变试验表明，每毫米的平均层数增加10/510 psi差应力。从这些结果中，我们推断，原位的应力差梯度不可能超过510 psi/5,500 ft的埋藏深度，而且，由于自然界中的时间间隔要长得多，该梯度可能要小得多。假设总垂直应力梯度为1 psi/ft，孔隙压力梯度为0.5 psi/ft，我们得出结论，德克萨斯州墨西哥湾沿岸的垂直有效应力与水平有效应力之比（^sgrv/^sgrh = ^sgr1/^sgr3）可能最大为1.2左右。
Study of calcite twin lamellae abundance in cores of low-porosity limestones indicates that the average number of lamellae per millimeter increases by 10 for every 5,500 ft of depth through the 20,800-ft interval sampled. The conditions of lamellae formation have been determined by creep tests on a representative limestone at several differential stress levels and loading durations at appropriate confining pressures and temperatures. Results show that (1) twin lamellae do not form when the specimens are subjected to a uniform confining pressure alone, (2) the lamellae increase in abundance with increasing differential stress, and (3) the abundance of lamellae increases with the duration of loading. Creep tests at differential stresses of 1,450-5,800 psi over durations of ,000 minutes indicate that the average number of lamellae per millimeter increases by 10/510 psi differential stress. From these results, we infer that the differential stress gradient in situ could not have exceeded about 510 psi/5,500 ft of burial and, because of the much longer time intervals in nature, this gradient probably was much less. Assuming a total vertical stress gradient of 1 psi/ft and a pore-pressure gradient of 0.5 psi/ft, we conclude that the probable maximum ratio of vertical-to-horizontal effective stresses (^sgrv/^sgrh = ^sgr1/^sgr3) in the Texas Gulf Coast is about 1.2.