The hazard associated with abnormal formation pressures are of great concern to operating companies in the oil industry worldwide.

As an effort to alleviate mis problem in the Niger Delta, a spread of overpressures as they occur in the basin are shown in a map of the area. The table from which the map was produced contain the values of the top of overpressures obtained from shale resistivity, acoustic and resistivity plots against true vertical depth. The depth to the top of overpressures from the more than 230 wells studied, range from 6,500ft. along the shelf, to 15,000ft. at the middle belt and 16,000ft. at the west-belt of the Niger Delta Basin Complex.

Shale resistivity ratios and shale transit time differences obtained from normal and observed (abnormally high pressured) resistivities and transit times respectively, have been used in conjunction with the fluid pressure gradient, to generate the prediction curves. Comparison is made between the predicted formation pressures using the predicted curves and actual measured pressures. The standard deviation for the resistivity method is +0.626% psi/ft. (or about ±63 psi per 10,000ft.) and the acoustic method is ±2.058% psi/ft. (or about ±200 psi/ft. per 10,000ft.) Using data from previously published papers, correlating equations for predicting formation fluid pressure gradient are presented for some other major producing areas.

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