Abstract: A reservoir pressure in an underground formation surrounding a well is analyzed based on a direct measurement of the pressure at the wall of the well using the permeability of mud cake on the wall of the well in the region in which the pressure measurement is made; determining the thickness of mud cake on the well of the well; determining the hydrostatic pressure in the well in the region in which the pressure measurement is made; calculating a pressure decay index from the mud cake permeability and thickness, the hydrostatic pressure and the measured pressure; and using the pressure decay index to analyze the measured pressure to derive the reservoir pressure.

Abstract: A method of analysing a reservoir pressure in an underground formation surrounding a well, comprising: determining the permeability of mud cake on the wall of the well in the region in which the pressure measurement is made; determining the thickness of mud cake on the well of the well in the region in which the pressure measurement is made; determining the hydrostatic pressure in the well in the region in which the pressure measurement is made; measuring the formation pressure at the wall of the well; calculating a pressure decay index from the mud cake permeability and thickness, the hydrostatic pressure and the measured pressure; and using the pressure decay index to analyse the measured pressure to derive the reservoir pressure.