Detection of CO2 Distribution by Seismic Pulse Width Analysis using Mollifier Functions

The relative contribution of buoyancy to dissipative forces that characterise CO2 flow can significantly impact the capacity of a geological storage site. For example, a smaller contribution of the buoyancy forces due to limited density variation with depth will cause the plume to spread out more laterally. With CO2 being injected in supercritical thermodynamic conditions, close to the critical point, thermodynamic models support that its diffusion within the formation will create a plume with acoustical properties that vary gradually. Such impedance profiles (not limited to linear ramps) generate so-called transitional reflection responses. We describe a method to detect and analyse such transitional reflections based on the analysis of reflection pulse width performed using basis functions called mollifiers. This method performs well on a synthetic dataset. When we apply this technique on the Sleipner data it detects anomalies at locations where previous publications have observed or inferred CO2 chimneys. This study introduces a novel approach to identifying transitional reflection responses in CO2 storage sites, demonstrating its effectiveness in detecting anomalies that were previously observed or inferred, thus providing a new tool for monitoring and assessing geological storage sites.