Fiber optic distributed sensing technology for real-time monitoring water jet tests: Implications for wellbore integrity diagnostics

Distributed fiber optic sensing (DFOS), a rapidly evolving fiber-optic based technology for permanent well-based and geophysical monitoring for CO2 geological storage (CGS) has attracted more attentions to investigate in multiple scales. In this study, two field trial wells were drilled, one well with 300 m depth in Mobara and the other well with 880 m in Ichihara, Japan and DFOS cables were deployed behind well casings. High-pressure water jet tests are performed at constant location of 127 m depth and at changeable jet locations with 1.33 m/min and 0.51 m/min pulling speeds in the 300 m well. Then, this DFOS system was utilized to monitor the water jet along the entire length of the 880 m well with 1.2 m/min descending speed. The temperature profiles induced by water jet could be real-time monitored and analyzed the cementing quality to further evaluate the wellbore integrity. The results show that the temperature abnormal zones have a good reverence with poor cementing in the two wells, which compared well with geophysical well logging data. Therefore, permanently installed DFOS wells will enable an efficient and simpler tool to diagnose the wellbore integrity for the CGS monitoring projects via the field water jet tests.