Monitoring well cementing operations using distributed fibre optic sensing

Abstract

Subsurface resources operations are critically dependent on the behaviour of the well through its lifetime. While the production and injection stages are commonly monitored both at surface and downhole, the monitoring of completion installation, work-overs and decommissioning are performed mostly at surface. Yet, most recently, improvements in distributed fibre optic sensing (DFOS) technology have made downhole monitoring more tractable and enables access to data previously not available. The technology has a very small downhole footprint, low cost and provides high spatial resolution from the surface to the bottom of the well. DFOS has to date been successfully demonstrated for site characterisation via vertical seismic profiling and perforations performances assessment, providing a high-resolution description of the subsurface leading to a better-informed decision. In this work, we focus on illustrating via case studies the benefits of the technology for insights on completion installation and well integrity. Well cementing operations are critical for providing zonal isolation over the life of a well. The deployment of a casing-conveyed fibre optic cable enabled the real-time surveillance of the displacement of mud by cement, the cement equilibration and the cement curing processes. This information allowed the identification of inflow zones and cavities in the well. In another example of cement plug installation, the same technology was used to identify leakage to the formation as well as the timing and depth of the cement plugs at very high spatial resolution.