With the objective in mind to estimate the possible hydrocarbon columns, a statistical analysis has been made of 160 reservoirs in structural traps in several basins. Care was taken to assemble data in those areas where hydrocarbon charge is so abundant that underfilled structures imply seal deficiency. Likewise faulted anticlines and doubtful traps were avoided.

A multivariate statistical analysis was made by defining the dependent variable to be the differential pressure that the hydrocarbon column exerts at the culmination of the trap. This allowed the simultaneous analysis of data comprising oil, gas, and combined columns at different depths. Columns in reservoirs full to spillpoint were considered to indicate minimum (censored) values for the differential pressures. Other situations led to maximum values for the trapping efficiency, while in only a minority of places a column was believed to be in equilibrium with the sealing capacity and hence providing a real (uncensored) observation.

A special regression program that allows censored observations for the dependent variable has been used to relate differential pressure to a set of independent geologic parameters (X-variables). The important X-variables considered here are seal lithology, thickness, and depth of reservoir.

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Significant statistical results support the idea that lithology of seal is of considerable importance. Sealing capacity is also correlated with seal thickness and depth.

These statistical results have been helpful in creating a quantitative assessment of hydrocarbon retention expectation for exploration prospect appraisals.

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