Testing Technology of fiber Bragg grating in the shale damage experiments under uniaxial compression conditions

Since serious environmental pollution problems are caused by the continuous development of fossil energy industry and releasing huge combustion products, shale gas is gradually becoming the key element of the green revolution. The Longmaxi shale formations in the Sichuan basin are the main mining layers of shale gas in China. In the process of exploiting shale gas, monitoring the stress and strain of the shale gas reservoir is helpful to guide programs in exploitation of shale gas and provide management of security risk and other works. Fiber Bragg grating (FBG) strain sensor system is a widely-used advanced technique to monitor real-time strain in recent years. In this paper, the FBG system was employed to measure the strain of shale surface in uniaxial compression tests using the MTS 815 machine. The results show that the strain variation of shale surface was well recorded by FBG, and axial strain transferring was more effective than that of the radial strain. It is found that the strains measured by FBG sensors were superior to those from strain gage rosettes, but the axial strain variation was susceptible to the development of surface cracks, resulting in lower strain transmission efficiency. The strain transfer ratio was mainly influenced by the grating itself, the properties and thickness of the bonding layer. According to experimental results from two kinds of epoxy resins, it can be seen that the new 555 viscose was better than DP100. © 2017, Science Press. All right reserved.