Patent ID: 6710596
Filing Date: 2004-03-23
Classification: G01N,G01R,G01V

Abstract:
A method of measuring formation pressure of an earth formation utilizing at least one nuclear magnetic resonance (NMR) tool placed in a wellbore in the formation, the wellbore being at a wellbore pressure and having an annular mudcake at a pressure between the NMR tool and the formation, the method comprising:measuring the pressure of the wellbore as a function of time; inducing fluid to flow; applying a static magnetic field from the NMR tool to a volume of the formation, the static magnetic field polarizing a substantial portion of the formation that is subject to the static magnetic field; applying an oscillating magnetic field to a specific part of the polarized portion to induce the production of measurable signals, the oscillating magnetic field being applied in accordance with field maps BO and B1 to produce a resonance region having a thin, long cylindrical shell-shape that is sensitive to radial flow; measuring the induced signals; deriving a horizontal component of flow velocity from the measured signals; monitoring the derived flow velocity while varying wellbore pressure until a zero velocity condition is obtained; and providing the wellbore pressure when zero velocity occurred as the measure of formation pressure.