Geological Heterogeneity of the UKCS Aquifers and its Impact on CO₂ Injection and 4D Seismic Signal

The geological heterogeneity of key CO₂ injection targets in the UKCS is exhibited at various scales. However, due to the size and spatial extent of saline aquifers, usually only the regional scale is modelled to investigate the spatial distribution of CO₂ over time. Time-lapse seismic is a well-established technology used to monitor CCS operations. This study focuses on the different types of small-scale heterogeneity and translating it onto fine-scale 2D reservoir models. We generate multiple heterogeneity scenarios using available literature, build 2D reservoir models based on them, and flow CO₂ across the whole length of the reservoir to simulate progression at the front of the plume. We then utilise Sim2Seis (an ETLP software) to obtain the 4D signal stemming from injection into these heterogeneous reservoirs. As CO₂ is highly mobile, we find that its flow pattern may be hard to predict when faced with heterogeneity. The CO₂ flow pattern differs based on the proximity to the injection site and inherent heterogeneity of the reservoir. The resulting 4D signal is strong and saturation-driven, and the effect of heterogeneity is visible.