Gas chimneys are geological features that are associated with seal bypass systems. Knowledge of the capacity of the seal is important for the evaluation of the petroleum systems and Carbon Capture and Storage (CCS) studies. The seal is breached when the capillary pressure threshold is exceeded by the underlying buoyancy pressure. The chaotic seismic character that is generally associated with the gas chimneys has been studied previously to evaluate the origin and geometry of the chimneys. Seismic attributes have also been used to determine the character of the gas chimneys and the potential association of hydrocarbon fields. However, it is important to evaluate the sealing potential of the cap rock in the vicinity of the gas chimney. This paper demonstrates that the chimney can be used as a calibration point and, with the use of seismic attributes, variations of sealing capacity can be evaluated. Out of many existing seismic attributes, understanding the shale structure is crucial to narrow the search criteria for the right class of attributes. Using the most useful stream of seismic attributes, the average sealing potential of the Lakes Entrance Formation is estimated. The sealing capacity map across the field is then shown to help evaluate the prospectivity of the area of study and may upgrade subsequent play fairway maps.