Retention capacity of seals from hydrocarbon field analogues for appraisal of saline aquifers

Saline aquifers have very large potential as stores for carbon dioxide, but the seals are untested. The effectiveness of typical sealing lithologies can be assessed using natural hydrocarbon reservoirs. The heights of the hydrocarbon columns in many natural reservoirs are limited by a spill point or by the limited thickness of the reservoir; however, amongst the remaining reservoirs the range of calculated limiting porethroat radii correspond with measured literature values worldwide. This suggests that capillary leakage is the limiting factor in the retention of hydrocarbons in many natural accumulations, and is at least potentially the limiting factor in CO2 storage. The distribution of limiting porethroat radii for oil and gas fields of the UK North Sea could be used with caution as a generic input for statistical assessment of a prospective CO2 storage location at an early stage of investigation, before measured site-specific data is available. The calculated limiting porethroat radii show only a weak decrease with burial depth and no correlation to the degree of faulting of the seal. There is a strong correlation with seal lithology; calculated radii for halite seals are significantly smaller than for the majority of shale seals. There is no difference between the calculated limiting porethroat radii for fields with at least some degree of fault sealing, compared to those with no reported fault sealing.