Innovation and instrumentation in CO2 monitoring wells for reservoir surveillance and advanced diagnostics

In 2015, CO2CRC Ltd embarked on an ambitious plan to field test innovative technologies to monitor a CO2 plume injected into a saline aquifer with a view to address many of the economic and environmental concerns frequently associated with commercial carbon capture and storage project’s long-term monitoring programs (Jenkins et al. 2017). It was called the Otway Stage 3 Project and it was focused on testing the technologies of seismic and downhole pressures applied in unique ways to monitor an injected plume of approximately 15 000 tonnes as it developed and migrated in the subsurface. To achieve this goal, five new wells were drilled at CO2CRC’s Otway International Test Centre – one dedicated to injection (drilled in 2017) and the remaining four wells (drilled in 2019) were used for monitoring purposes. Each monitoring well and the gas injection well, were outfitted with fibre optic systems installed and cemented outside the casing (specifically for seismic monitoring) and with pressure gauges installed at the reservoir depth. The challenge of the installation was to install fibre optics outside of the casing, cement them in place securely and to perforate the wells without damaging the fragile TEF bundles. While the installation of the pressure gauges in the injection well was a conventional in-tubing gauge mandrel, the installation in the monitoring wells, which were to be used for water injection as well as pressure monitoring, used a less conventional deployment method, where the gauges were instead installed using a more economic and flexible approach by suspending the gauges from the wellhead via a hanger system. This not only ensured continuous offline monitoring of the downhole well pressures and temperatures, but also facilitated future well operations by simple wireline retrieval and deployment of the gauge, forgoing the need for a workover rig. The various systems were commissioned over the period of March–June 2020 and were in full operation in the second half of 2020 – all successfully operating and acquiring baseline data remotely as designed. The Stage 3 Project commenced gas injection operations in December 2020 and data acquisition using the innovative systems have commenced successfully.