Effect of pore pressure gradient on fracture initiation in fluid saturated porous media: Rock
Effect of pore pressure gradient on fracture initiation in fluid saturated porous media: Rock
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DOI：
10.1016/j.engfracmech.2007.03.028
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发表时间：
2008-05-01
影响因子：
5.4
通讯作者：
Ito, Takatoshi
中科院分区：
文献类型：
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作者：
Ito, Takatoshi
几乎所有的岩石内部都存在着无数的小孔隙，而孔隙的形状和孔隙之间的连通性取决于岩石的类型。孔隙的存在使岩石的力学行为具有不同于其它材料的特殊性。对于在为岩石应力测量而执行的水力压裂中通过将流体注入钻孔中而升高所钻钻孔中的压力的情况，流体从钻孔壁穿过互连孔隙渗透到岩石中，并且流体渗透引起孔隙压力的变化，即，孔隙中的流体压力。所形成的孔隙压力分布在钻孔周围引起压缩的周向应力，其中引起附加应力的力学类似于热应力。孔隙水压力对松动破坏强度的影响遵循太沙基有效应力定律。点应力准则可用于预测在这种复杂条件下发生的岩石拉伸破坏。然后我们应该假设，当最大有效应力达到岩石的抗拉强度时，裂缝开始发生，该点不在钻孔壁上，而是在岩石内部。这种方法使我们能够定量地解释与流体渗透相关的奇怪现象，引起拉伸破坏的临界井眼压力随井眼加压速率的增加而增加。(c)2007爱思唯尔有限公司版权所有。
There are infinite number of small pores at inside of almost rocks, while the pore's shape and the interconnectivity among the pores are dependent on the type of rocks. The existence of such pores brings special feature in mechanical behavior of rocks, different to cases of other materials. For the case when the pressure in a drilled borehole is raised by fluid injection into the borehole in hydraulic fracturing carried out for rock stress measurements, the fluid penetrates through the interconnected pores into a rock from the borehole wall, and the fluid penetration develops the change in pore pressure, i.e., fluid pressure in the pore. The developed pore pressure distribution causes a circumferential stress in compression around the borehole, where the mechanics to cause the additional stress is analogous to thermal stress. Furthermore, the pore pressure affects to loose strength in failure following the Terzaghi effective stress law. The point stress criterion can be applied to predict tensile failure of rock occurring in such complicated conditions. Then we should assume that the fracture initiation occurs when the maximum effective stress reaches the tensile strength of a rock at a point that is not on the borehole wall but is inside the rock. This approach allows us to interpret quantitatively strange phenomena associated with fluid permeation such that breakdown pressure, i.e., a critical borehole pressure to cause the tensile failure, increases with the rate of borehole pressurization. (c) 2007 Elsevier Ltd. All rights reserved.