Characterizing Tracer Transport Behavior in Two‐Phase Flow System: Implications for CO₂ Geosequestration

Abstract

Tracers are used to tag the injected carbon dioxide (CO 2) for verification of the storage performance and containment in geosequestration. Yet the characterization of the transport behavior of a chemical tracer in two-phase flow system has not been fully investigated. We present experimental observations together with numerical results for both homogeneous and heterogeneous media from core scale to field scale. The key features of the breakthrough curves (BTCs) that include the tracer arrival time, peak concentration, and tailing pattern were examined. We identify distinct differences in BTCs depending on whether the formation was previously swept by CO 2. When the tracer is released before CO 2 sweeps the formation, the tracer transports at the front of gas-liquid interfaces with a narrow tracer plume distribution and the BTCs reflect the effect of local heterogeneity. Furthermore, a series of tracer pulse can be used to identify whether new pathways have been developed during CO 2 injection. Plain Language Summary Geologic storage of carbon dioxide (CO 2) has become an attractive climate change mitigation option, and ensuring the containment of injected CO 2 is of prime importance for successful geological storage. Tracers are an effective means of tracking injected CO 2 and verifying containment within the storage formation. Here we show that distinctive features in observed tracer data are highly related to whether or not the storage formation was previously swept by CO 2. When the tracer is released at the beginning of CO 2 injection, the tracer moves with narrow distribution and is advantageous for the tracer data to reflect multiple pathways. By contrast, once the CO 2 sweeps the formation, the tracer moves much faster with a wider dispersion pattern.