In recent years, the fiber-optic distributed acoustic sensing (DAS) technology has played an important role in the oil and gas exploration and development. We develop an industrialized ultra-sensitive DAS instrument, named uDAS, which has world-class performances and robust engineering capability. The uDAS achieves the pε/√Hz level strain resolution and broadband frequency response from millihertz (mHz) to 10 kHz. The uDAS system has been widely applied to onshore and offshore vertical seismic profiling (VSP), hydraulic-fracturing monitoring, surface seismic exploration, near-surface structural investigation, and DAS-uphole, with deployments spanning all oilfields of China National Petroleum Corporation (CNPC), and part oilfields of Saudi Aramco and Abu Dhabi National Oil Company (ADNOC). In this paper, we introduce the key technologies of uDAS and its typical applications over the years. These applications demonstrate the uDAS’s ultrahigh sensitivity, broadband frequency response, and high fidelity, enabling near-wellbore fine imaging, high-resolution visualization of downhole fracturing processes, and production optimization. The uDAS is becoming the new generation of all-optical geophones to replace the conventional electronic geophone arrays.

This paper reviews a wide variety of fiber-optic microstructure (FOM) sensors, such as fiber Bragg grating (FBG) sensors, long-period fiber grating (LPFG) sensors, Fabry-Perot interferometer (FPI) sensors, Mach-Zehnder interferometer (MZI) sensors, Michelson interferometer (MI) sensors, and Sagnac interferometer (SI) sensors. Each FOM sensor has been introduced in the terms of structure types, fabrication methods, and their sensing applications. In addition, the sensing characteristics of different structures under the same type of FOM sensor are compared, and the sensing characteristics of the all FOM sensors, including advantages, disadvantages, and main sensing parameters, are summarized. We also discuss the future development of FOM sensors.