Time Lapse Compressibility Monitoring for Detection of CO2 Leakage in Brine Aquifers

AbstractThere are several monitoring challenges to demonstrate safe and long term storage of the CO2. In this study a methodology is proposed that uses well known interference well testing for monitoring the Above Zone Monitoring Intervals (AZMI). Advantages of this method are: (1) It helps to distinguish between the brine and CO2 leakage; (2) It can be used to detect low rate/ long term leakages that may not have a noticeable pressure signal as leakage starts and (3) It is designed in a time-lapse form so inherently many uncertain reservoir parameters cancel out in the calculations.Proposed methodology works on the premises of the fact that at any given depth brine and CO2 have different compressibility. This means that in a monitoring zone initially filled with brine any leakage of CO2 will change the total compressibility of the zone. If we assume that the fluids within the area of investigation have not been changed then calculated transmissibility and storativity should remain reasonably constant in repetitive tests. Results based on synthetic simulation models shows that this method can be used to detect CO2 leaks successfully. A generalized equation introduced here that can be used to estimate leak size for any given reservoir. Finally this new method applied to an actual reservoir model and showed that leak size can be determined with ±%15 error