Abstract：

Rock cohesion strength and internal friction angle are the fundamental and important parameters of borehole stability and hydraulic fracturing research. The conventional method for obtaining the above rock strength properties is triaxial compression test standardized by the International Society of Rock Mechanics (ISRM). The rock mechanics parameters including compressive strength and elastic modulus can be obtained by applying a certain confining pressure to the specimen, and then gradually increasing the axial pressure until shear failure occurs in the rock sample. And because of the advantages of strong adaptability and accurate measurement, triaxial compression experiment method has been widely used. However, this method has high requirements for sample making and which will lead to rock sample breakage, so the sample can’t be reused again. Because it is difficult to make standard samples of complex rock mass, this method is not suitable in complex study. In this paper, based on the mechanical model of rock scratching with sharp and blunt cutters in plastic failure mode, and combined with Mol-coulomb criterion, the mechanical model of rock cohesion strength and internal friction angle were established by using the force of rock breaking with cutters. Then, with the continuous scratch test device, the influence of the order, location and depth of the sharp and blunt cutters on the rock breaking mechanical behavior of the cutters were evaluated, and the scratch parameter setting methods and scratch tests process for accurately obtaining the rock breaking stress curve of the cutters were proposed. The normal stress and shear stress were obtained by cutting the rock sample with sharp and blunt cutters, and then the rock mechanics parameters including cohesion strength and internal friction angle can be obtained by substituting them into the calculation model. Compared with the traditional triaxial compression test, the values of rock mechanical parameters measured by using the continuous scratch methods were consistent with those measured by the traditional triaxial compression test, and there was a certain proportion between them, which proveed that the new method is feasible. The new method requires simple sample preparation specifications, short experimental time, and can test rock strength parameters of complex rock. At the same time, the whole structure of rock sample will not be destroyed in the process of experiment, so the experiment has strong repeatability, which provides a new idea for the test of sample strength parameters before and after water rock interaction, and also provides a new method for the study of hydration.

Key words：strength parameter; continuous scratch test; experimental method; complex rock

Received： 2021-04-15

Corresponding Authors：luyh@cup.edu.cn

Cite this article：刘洪涛, 薄克浩, 金衍, 卢运虎, 朱金智, 张震, 张峰. 基于连续划痕实验确定复杂地层岩石强度参数的方法研究. 石油科学通报, 2022, 04: 532-542 LIU Hongtao, BO Kehao, JIN Yan, LU Yunhu, ZHU Jinzhi, ZHANG Zhen, ZHANG Feng. Determination of rock strength parameters during drilling based on continuous scratch tests. Petroleum Science Bulletin, 2022, 04: 532-542.

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