Patent ID: 6650114
Filing Date: 2003-11-18
Classification: G01R,G01V

Abstract:
A method for determining a parameter of interest of a volume of earth formation surrounding a borehole with a Nuclear Magnetic Resonance (NMR) logging tool conveyed in the borehole, the method comprising:(a) using a magnet assembly on the NMR logging tool to produce a static magnetic field in said volume of the formation said static magnetic field having a substantially time-invariant gradient; (b) producing a radio frequency (RF) magnetic field in said volume of the formation with an antenna on the NMR logging tool, said RF magnetic field having a component in a direction orthogonal to a direction of the static field, the RE field including at least one pulse sequence comprising a tipping pulse and at least four refocusing pulses, each refocusing pulse producing at least one corresponding spin echo signal, and (c) measuring with the NMR logging tool spin echo signals induced by the RE field in the formation; wherein earlier successive ones of said at least four refocusing pulses of a single one of said at least one pulse sequence have a first time interval therebetween and at least three later successive ones of said at least four refocusing pulses of said at least one pulse sequence have a second time interval therebetween, said second time interval greater than the first time interval.