With the oil and gas industry growing rapidly, increasing the yield and profit require advances in technology for cost-effective production in key areas of reservoir exploration and in oil-well production-management. In this paper we review our group’s research into fiber Bragg gratings (FBGs) and their applications in the oil industry, especially in the well-logging field. FBG sensors used for seismic exploration in the oil and gas industry need to be capable of measuring multiple physical parameters such as temperature, pressure, and acoustic waves in a hostile environment. This application requires that the FBG sensors display high sensitivity over the broad vibration frequency range of 5 Hz to 2.5 kHz, which contains the important geological information. We report the incorporation of mechanical transducers in the FBG sensors to enable enhance the sensors’ amplitude and frequency response. Whenever the FBG sensors are working within a well, they must withstand high temperatures and high pressures, up to 175 °C and 40 Mpa or more. We use femtosecond laser side-illumination to ensure that the FBGs themselves have the high temperature resistance up to 1100 °C. Using FBG sensors combined with suitable metal transducers, we have experimentally realized high- temperature and pressure measurements up to 400 °C and 100 Mpa. We introduce a novel technology of ultrasonic imaging of seismic physical models using FBG sensors, which is superior to conventional seismic exploration methods. Compared with piezoelectric transducers, FBG ultrasonic sensors demonstrate superior sensitivity, more compact structure, improved spatial resolution, high stability and immunity to electromagnetic interference (EMI). In the last section, we present a case study of a well-logging field to demonstrate the utility of FBG sensors in the oil and gas industry.

A microfiber-optics interferometer was proposed, and the theoretical analysis and experimental demonstration were characterized in detail. The device comprised a Fabry-Perot interference (FPI) structure with an open-cavity, whereby a hollow core fiber (HCF), spliced to the single mode fiber (SMF), was collapsed and swelled into a thin-wall air bubble by multiple discharge operations. The closed bubble was then partially opened by using a micromachining technology, i.e. the focused femtosecond laser was utilized to ensure that the removed portion of the wall was precisely positioned over the cavity. The remaining wall was acted as a support beam that was easy to deform by external pressure. The smooth inside surfaces of the opened air cavity reflected light backwards to the leading-in SMF, resulting in a well-defined interference spectrum. For exerting the micropressure on the top of the open cavity and making the support beam bend, the proposed sensor shows a high resolution of 0.42 μm for the detection of displacement by simply monitoring the interference wavelength shift.

A fiber-optic gas refractometer based on a slotted photonic crystal fiber (PCF) is developed for gas refractive index (GRI) measurement. The sensor consists of a six-air-hole grapefruit PCF sandwiched between two single-mode fibers, which forms a Mach–Zehnder interferometer by a slight offset splicing at the lead-in junction. One air hole of the PCF is open and exposed to external gas sample via two micro slots by femtosecond laser micromachining. Due to a large overlapping of the mode field and gas sample, a high GRI sensitivity of −827.94-dB/refractive index unit is obtained. Temperature change only shifts the interference wavelength and the cross-sensitivity of fiber deformation is also negligible. The proposed sensor with a good mechanical strength can be a promising candidate for highly sensitive GRI measurement by simple intensity interrogation.