An innovative monitoring system using distributed fiber optical sensing (DFOS) technology based on hybrid Brillouin-Rayleigh backscattering is first proposed to measure small strain profiles from core-scale experiments to field tests. The surface of a sandstone specimen is twined and glued with one single-mode fiber (SMF) as well as four conventional strain gauges. A preliminary laboratory experiment is implemented to testify to the sensing effectiveness of this proposed hybrid DFOS system. Laboratory experiments indicate that the measured strain via SMF along the heterogeneous Tako sandstone core surface coincides well with conventional strain gauges and better tracks injected CO2 fronts. Moreover, this novel DFOS-based optical fiber cable has been deployed behind the well casing for detecting impacted zones along the well depth direction in an actual 300 m-deep field well. Field testing shows that the extent of the deformed zone induced by injected CO2 is successfully monitored and quantified in terms of measured in situ strain profiles. This first-hand hybrid DFOS system and lab-field findings can quantitatively evaluate wellborecaprock integrity by providing real-time in situ strain signals in various Earth geoenergy-related fluids injection, storage, and extraction sites.