• 应用研究 •

### 基于多尺度页岩巴西劈裂试验的岩石强度尺度效应根源研究1)

1. * 西安石油大学陕西省油气井及储层渗流与岩石力学重点实验室,西安 710065;
† 中国石油大学(北京)油气资源与探测国家重点实验室,北京 102249
• 收稿日期:2019-08-13 发布日期:2020-03-13
• 通讯作者: 2) 李帅,硕士研究生,主要研究方向为岩石力学与油气田特种增产技术。E-mail: lishuai_xsy@163.com
• 基金资助:
1) 国家自然科学基金资助项目(51674197,51874239)

### A STUDY ON THE ORIGIN OF SCALE EFFECT OF ROCK STRENGTH BASED ON MULTI-SCALE SHALE BRAZILIAN SPLITTING TEST1)

LI Shuai*, 2), CHEN Junbin*, WANG Hanqing, NIE Xiangrong*, ZHAO Wenjing*, YAO Huanying*

1. * Shaanxi Key Laboratory of Well Stability and Fluid & Rock Mechanics in Oil and Gas Reservoirs, Xi'an Shiyou University, Xi'an 710065, China;
† State Key Laboratory of Petroleum Resources and Exploration, China University of Petroleum (Beijing),Beijing 102249, China
• Received:2019-08-13 Published:2020-03-13

Abstract: In order to explore the scale effect of the shale tensile strength and the origin of the scale effect of the rock strength in general, the outcrop of the continental shale of Chang 7 of Yanchang Formation in Ordos Basin is collected to make rock samples of 50 mm in diameter and 15.32 mm, 20.39 mm, 25.46 mm and 30.28 mm in length for the Brazilian splitting test. On the basis of analyzing the rock tensile strength, a new understanding of the origin of the scale effect is proposed. It is shown that the maximum load on the shale and the number of rupture surfaces increase with the increase of the sample size, while the tensile strength decreases with the increase of the sample size, and the correlation between the fracture time and the sample size is poor. The heterogeneity and the end friction effect are the main causes of the scale effect of the rock strength. The obvious scale effect of the tensile strength in the Brazilian shale splitting test results indicates that the scale effect of the rock strength is not entirely rooted in the end friction between the specimen and the indenter. The scale effect of the rock strength is formed by the interaction of the heterogeneity and the end friction effect. For small scale rock samples, the end friction effect plays the dominant role, and for large scale rock samples, the heterogeneity plays the dominant role. For various types of rocks, the size of rock samples may be neither "small" nor "large". The study of the scale effect and its origin for the rock strength is helpful to improve the accuracy of the rock strength prediction and for revealing the rock failure mechanism.

• TE31