Reliable high sensitivity FBG geophone for low frequency seismic acquisition

Abstract

A fiber Bragg grating (FBG) based geophone is designed for low-frequency signal detection. It has high acceleration response of about 60 dB re pm/g in a low frequency range of 5–60 Hz. However, the basic sensing principle of stretching FBG requires much more delicate and reliable packaging design and technology. Especially the high sensitivity at low frequency challenges the reliability in packaging, transportation and installation of sensor. To guarantee normal operation in field test and practical application, an acceleration amplitude restriction is added in the mechanical design of the FBG geophone. Then a series of environmental and reliability tests have been proceeded with online or offline monitoring of its working performance, including high & low temperature test, vibration test, shock test and tensile test, strictly according to National standard and Oil & Gas Industry Standard. The experimental results indicate that our FBG geophone meet the criterion of oil and gas industry product and is capable of field application. Finally, in the filed blasting tests, the seismic cross-section profile was obtained by use of FBG geophone array which shows the advantage in low frequency signal acquisition compared to conventional move-coil geophone.