Distributed fiber optic temperature and strain sensing in cementing and water injection: Insights to well integrity monitoring and multisensing optical fiber cable design

In this study, we installed two fiber optic cables with different designs into a new well, a soft-flat cable and a stainless-steel cable, for distributed fiber optic sensing in cementing and water injection. The two fiber cables were cemented behind casing and the soft-flat cable was used for temperature sensing in cementing as well as cement curing period. The high-speed Rayleigh scanning successfully visualized the cement front tracking from the combined effects of temperature and pressure changes by cement pumping. The temperature variations in cement curing reveled the cement volume and have the potential to identify defects in annular cement and formation damage caused by cementing. The water injection test for strain sensing was carried out with increasing injection rate from 100 L/min to 200 L/min. Strain profiles from the two fiber cables suggested that the strain responses reveal alternation of sand and silt, and reservoir heterogeneity. The water injection results showed that the measured strains of the two cables matched fairly well and the stainless-steel cable showed a high strain sensitivity responding to injection pressure (1 mu epsilon/5 kPa). Comparison of strain measurement results of the two cables provided valuable insights for future strain fiber cable design. Strain sensing results also indicated a high capability to capture small pressure changes in the heterogeneous layers. Thus, our results demonstrate the high potential of using strain sensing for leak detection and well integrity monitoring in fluid injections, particularly for the long-term monitoring at CO2 2 storage site.