Patent ID: 6392409
Filing Date: 2002-05-21
Classification: G01N,G01R,G01V,Y02A

Abstract:
A method of determining a parameter of interest of a volume of earth formation in a reservoir adjacent a borehole, said parameter of interest including at least one of a longitudinal relaxation time T1 and a transverse relaxation time T2 of a fluid in the reservoir, the method comprising:(a) using a magnet assembly on a borehole tool conveyed in the borehole at at least one depth for producing a static magnetic field in said volume of the formation thereby aligning nuclear spins within said volume parallel to a direction of the static field; (b) producing a radio frequency (RF) magnetic field in said volume of the formation with an antenna on the borehole tool, said RF magnetic field having a direction orthogonal to a direction of the static field, the RF field including a first pulse sequence TWAâˆ’90âˆ’(tâˆ’Xâˆ’tâˆ’echo)j to produce a first echo train and at least one second pulse sequence TWBâˆ’90âˆ’(tâˆ’Xâˆ’tâˆ’echo)j to produce at least a second echo train, wherein 90 is a tipping pulse for tipping the nuclear spins at an angle substantially equal to ninety degrees to cause precession thereof, TWA is a first wait time, TWB is a second wait time, X is a refocusing pulse, and j=1, 2, . . . J, where J is the number of echoes collected in a single sequence of pulses; (c) measuring with the borehole tool the first and at least one second echo train; (d) determining at least one summed signal selected from the group of: (i) a sum of the first echo train, defining a first summation signal, (ii) a sum of the at least one second echo train, defining a second summation signal, (iii) a sum of an average of the first and at least one second echo train, defining a third summation signal, and, (iv) a sum of a difference of the first echo train and the at least one second echo train, giving a fourth summation signal; and (e) determining the parameter of interest from the at least one summed signal.