An empirical evaluation of seals in over 980 reservoirs located in 190 basins worldwide was used to test the validity of the most popular assumptions made when risking hydrocarbon retention. Modern deterministic seal studies have produced a substantial volume of useful information on sealing lithologies, but many have yet to be calibrated with the height of hydrocarbon columns and with the degree in which traps are filled to their maximum capacity. A comprehensive classification, based on the number, type, location and combination of sealing surfaces was developed to better understand the contribution of each sealing surface and to facilitate this calibration process. End-member seal categories are simple top seals, updip lateral fault seals, and lateral stratigraphic seals. Combination types may be top-dominated, fault-dominated, or stratigraphic-dominated. A separate class of miscellaneous or unconventional seals is also considered. Over half of the reservoirs studied are sealed by a combination of surfaces. Assumptions made when using common wisdom for seal risking, followed by an empirical reality check from worldwide reservoir analogs will be discussed.

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