In view of the complex wellbore dynamics associated with liquid/vapor CO2 in the Containment and Monitoring Institute (CaMI) of Carbon Management Canada (CMC) CO2 injection wellbore, a Static Gradient Survey was conducted with the focus on the verification of in-tubing pressures and temperatures at various depths in the wellbore. Specifically, the knowledge sought was to learn about the temperature profile in the regions above and below the gas-liquid interface as well as the temperature profile below the Distributed Temperature Sensing (DTS) fiber termination point in the well, where there is no temperature measurement.

For the static gradient survey, four surveys (passes) were conducted over a span of 6 hours, using tandem pressure/temperature recorders. For the first and second passes, lowering and raising the wireline string in and out of the well at a steady rate was undertaken. The third pass involved stopping the gauges at specified depths for approximately 10 minutes prior to extracting them out of the wellbore. Recognizing that the responses of the gauges to temperature were much slower than to pressure, the duration of the stops varied at different depths, depending on the location of interest. The final pass took place some 6 hours after the initial run.

The location of the liquid level in the well was identified, not only by the change in pressure gradients but also by a change in temperature gradients. At the gas-liquid interface, the liquid was boiling and caused localized cooling around the interface. This cooling event was registered in the DTS data where the temperature departed from the baseline temperature gradient. Another cooling event was observed near the base of the wellbore where the recorded temperature profile cooled before it again approached the normal thermal gradient. We interpreted the cause of this cooling event to be that some of the injected CO2 has migrated up-section into the shallower formation. The corresponding decrease of pressure caused a phase change and evaporation of CO2 which resulted in a reduction in the CO2 temperature.

The temperature anomaly at the base of the injection well is consistent with the geophysical monitoring results from vertical seismic profiles (VSP) and the borehole electrical resistivity tomography (ERT) surveys.

Understanding of the thermal processes related to Geologic Carbon Storage(GCS) is crucial for a successful deployment of projects. Our observations of temperature anomalies within the reservoir will contribute to the feasibility of employing temperature signals as a monitoring tool for the subsurface migration of the CO2 plume.

You can access this article if you purchase or spend a download.