A carbon sequestration site has been developed onshore Abu Dhabi in which, for the first time to the authors’ knowledge, 100% of the injected CO2 is to be captured and sequestered in a carbonate saline aquifer. Rock-physics modeling of supercritical CO2 replacing hypersaline water (23% concentration) showed increased seismic detectability compared with injections in oil reservoirs for enhanced oil recovery purposes. A thorough monitoring plan, detailed in the complete paper, was implemented. Minute changes in rock properties caused by CO2 injection in an onshore carbonate saline aquifer can be detected by seismic monitoring using a highly repeatable fiber‑optic-based system.
Method
Changes in elastic rock properties as the result of production in carbonate reservoirs in the Middle East are typically approximately 5%, while the normalized root mean square for repeated land-based surface seismic is typically approximately 30%. Although case-dependent, the large gap between these two numbers explains why 4D seismic largely has been unsuccessful in the Middle East for reservoir monitoring.
The caprock formation is approximately 150 m thick (950–1100 m) and the carbonate saline aquifer is approximately 700 m thick (1100–1800 m). The well was completed with fiber-optic cable cemented in place behind the casing, which terminates 200 m into the injection interval at 1309 m and approximately 50 m above the perforations.
