Exploring safe disposal of CO2 and wastewater in saline aquifers

Abstract

Process safety has taken the spotlight in recent years for both carbon sequestration and wastewater disposal operations. We present a systematic approach to monitoring injection-well performance in saline aquifers for both wastewater disposal and CO2 injection with required well surveillance and injection data. Uncertainty assessment formed the cornerstone of understanding the fundamental variables impacting the injection performance with numerical modeling. Among the variables studied, aquifer heterogeneity and injection parameters, rock compressibility, and fracture gradient have a significant influence on total cumulative injection and safe-volume injection.The modified-Hall analysis turned out to be the critical diagnostic tool for identifying the abnormal injection behavior and real-time disposal process for both fluids. We estimated the safe pore-volume injection for disposal of wastewater and CO2 to be 1.6% and 1.5%, respectively, in saline aquifers at 80% probability. Of the CO2 trapping mechanisms studied here, critical gas saturation turned out to be the most dominant in residual trapping mechanism, whereas porosity and brine salinity appeared dominant in solubility trapping mechanism.