水压致裂测量地应力的断裂力学方法

本文提出了一个水压致裂测量地应力的新的断裂力学方法.该方法改进了 Abou-Sayed 等人（1 978）提出的断裂力学方法.因为当裂隙长度小于某一临界值时,岩石的断裂韧度 K1 c与裂隙长度相关.另外,精确地确定岩石中原生裂隙长度 L 是非常困难的。因此,在计算最大水平主应力时,用一个新参数 U(U=K1 cπ1/2L)代替 K1 c和 L,将显著地提高最大水平主应力的精确度.此外,这个参数可以通过一个简单的空心圆柱破裂实验直接来测定.基于岩石断裂韧度最近的实验结果,当裂隙长度小于某一临界值时,新参数 U 近似为岩石材料常量.同时,参量21/2U 可以取做为含有随机分布较小裂隙的岩石抗拉强度.

Fracture Mechanics Approach for In-situ Stress Determination by Hydra- Fracturing

A new fracture mechanics approach for in-situ stress determination by hydra-fracturing is proposed. It improves the fracture mechanics method as presented by Abou-Sayed etc. (1978). The accuracy of determination of the maximum horizontal stress (σHmax) is considerably enhanced by replacing fracture toughness of rock, K1c, and preexisting crack length L in rock by a new parameter U(U=K1c/√2) . The reason is that K1c is related to crack length L when crack length is smaller than a critical value and to determine the length of preexisting crack in rock as accurate as possible is very difficult. In addition the parameter U can be directly measured through a simple hollow-cylinder burst test. Based on recent experimental tests of fracture toughness of rock the new parameter U appears to be a constant when crack lengths are smaller than a certain critical value . The parameter √2 U may be taken also as a tensile strength of rock which contains small randomly distributed preexisting cracks.