Strain characteristics and permeability evolution of faults under stress disturbance monitoring by fibre bragg grating sensing and pressure pulses

Xu, Lifeng; Li, Qi; Mathias, Simon A.; Tan, Yongsheng; Yang, Duoxing; Fan, Chengkai

Abstract

The sealing and structural stability of faults must be considered in many underground engineering endeavours, such as underground energy extraction and CO2 geological storage. In order to simultaneously study the evolution laws of fault sealing and structural stability evolution law under stress disturbance, the fault samples were first consolidated under previous effective stress (Ppre = 10 MPa) for 62 h to imitate the fault being under the ground stress; then, the effective stress (Pe) was reduced to 0.5 MPa and gradually changed to 20 MPa to imitate the stress disturbance. Permeability and strain were measured throughout the stress disturbance by the pressure pulse method and fibre Bragg grating (FBG) sensors. In particular, high-precision FBG sensors were applied inside the fault to obtain the internal strains. The test results show that: (1) when Pe < Ppre, the permeability rapidly decreased with increasing Pe, and a risk of leakage occurred. Conversely, when Pe > Ppre, fault permeability changed little as Pe increased; but the permeability was still 4.91 times that of the undisturbed state. (2) The internal and external strain monitoring results revealed that the geometric centre of fault showed tensile strain, while other monitoring points showed compressive strain most of the time. The reason for this phenomenon is the end effect, which causes the gouge particles in the middle to move to both ends. (3) The normal deformation of fault gouge not only controls the fault volumetric strain but also controls the evolution of permeability. This study provides technical and theoretical support for the evaluation of fault sealing and structural stability when faults are disturbed in underground engineering development and construction.

Citation

Xu, L., Li, Q., Mathias, S. A., Tan, Y., Yang, D., & Fan, C. (2021). Strain characteristics and permeability evolution of faults under stress disturbance monitoring by fibre bragg grating sensing and pressure pulses. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 7(4), Article 93. https://doi.org/10.1007/s40948-021-00289-8

• Journal Article Type: Article
• Acceptance Date: Aug 23, 2021
• Online Publication Date: Sep 13, 2021
• Publication Date: 2021
• Deposit Date: Nov 1, 2022
• Journal: Geomechanics and Geophysics for Geo-Energy and Geo-Resources
• Print ISSN: 2363-8419
• Electronic ISSN: 2363-8427
• Publisher: Springer
• Peer Reviewed: Peer Reviewed
• Volume: 7
• Issue: 4
• Article Number: 93
• DOI: https://doi.org/10.1007/s40948-021-00289-8
• Public URL: https://durham-repository.worktribe.com/output/1189730