Chemical Tracer for Soil CCS Monitoring Application: Monitoring CO2 Storage in Saline Aquifers Using Advanced Chemical Tracer and Detection Technology

Abstract ADNOC has embarked on a major Carbon Capture and Storage (CCS) project where large quantities of CO2 are injected into deep saline aquifers for permanent storage instead of releasing into the atmosphere. An advanced chemical tracer technology was deployed in the first CCS project in the UAE for continuous CO2 monitoring to ensure permanent and safe CO2 storage. In case of containment breach, the chemical tracer technology can confirm the leakage and identify its source. After CO2 injection for permanent storage, any containment breaching would be detected in the shallow soil monitoring borehole. Few soil monitoring boreholes were excavated across the field in which Capillary Adsorption Tubes (CAT) were inserted for some time and replaced by another according to the sampling frequency plan. The tube is sent to the lab for CO2 leak detection and reporting. The high detection resolution is in the order of 0.1 parts per trillion (ppt). This has a positive impact on the system economics because smaller quantities of chemical tracer material are required. The tracer injection monitoring system is ongoing in the first CO2 storage area of Abu Dhabi. The monitoring includes soil monitoring which are shallow boreholes. The soil monitoring boreholes were excavated close to the CO2 injection well to ensure that there are no well integrity issues developed due to thermal effects by CO2 injection. The soil monitoring boreholes to be verified by surface gas CO2 monitors. Soil monitors were located around the radial storage area, to detect CO2 leakage and to understand CO2 migration to the soil through the cap rock (in case of leakage). The monitoring system for caprock and well integrity will provide: Surface soil monitoring for cap rock integrity, integrity confirmation for legacy wells, integrity confirmation of injection well in the post-injection monitoring period, leakage quantification, leakage origin if multiple injectors. The monitoring system can continue for up to 30 years of the operational period as well as the full post-injection monitoring, measurement and verification horizon. This paper presents a description of a sophisticated CO2 monitoring technology that is being deployed in UAE's first CCS project. CO2 tracer technology is considered as one of the most accurate methods to detect CO2 leakage at surface. Its high-detection resolution allows early leakage identification and early mitigation action. In addition, it proves to be relatively low cost, operationally easy to execute, and requires a small operational footprint.