Study on the Progressive Failure Characteristics of Longmaxi Shale under Uniaxial Compression Conditions by X-ray Micro-Computed Tomography

Xiao Li,Shouding Li,Yongting Duan,Runqing Zhou

doi:10.3390/en10030303

Abstract

To investigate the deformation-failure process of Longmaxi shale under uniaxial compression conditions from the mesoscopic and macroscopic points of view, novel X-ray microComputed Tomography (micro-CT) equipment combined with unique loading apparatus was used. Cylindrical shale samples (4 mm in diameter and 8 mm in height) were produced to perform a series of uniaxial compression tests. CT scanning images at different time points during the loading process were obtained to study the characteristics of the progressive failure. In addition, stereograms were reconstructed and vertical slices were selected to explain the failure mechanism. From the results of the testing the low-density area, local per-peak cracks, numerous post-peak cracks and secondary cracks consecutively appeared in the CT images. Vertical and inclined fissures in the samples could be observed from the stereograms’ surfaces and from internal slices. The cracking indicates that the failure process of shale is progressive and the failure mechanism of shale under uniaxial compression is mainly tension destruction or comprehensive tension-shear destruction.

Highlights

Shale gas is one of the most promising unconventional natural gas resources, with huge reserves located around the world [1]
It has been widely recognized that shale gas will play a large role in meeting future worldwide energy demands and become a significant part of the energy policy mix of many countries [2,3,4]
Owing to the geological characteristics of shale in gas reservoirs that generally show low penetrability and remarkable brittleness, large-scale hydraulic fracturing treatments are usually essential in the development of shale gas [5,6,7]

Summary

Introduction

Shale gas is one of the most promising unconventional natural gas resources, with huge reserves located around the world [1]. It has been widely recognized that shale gas will play a large role in meeting future worldwide energy demands and become a significant part of the energy policy mix of many countries [2,3,4]. Owing to the geological characteristics of shale in gas reservoirs that generally show low penetrability and remarkable brittleness, large-scale hydraulic fracturing treatments are usually essential in the development of shale gas [5,6,7]. It is necessary to know about the failure process and the fracture mechanism of shale, which contributes to guiding the fracturing engineering

Results

Discussion

Conclusion