Patent ID: 6466013
Filing Date: 2002-10-15
Classification: G01N,G01R,G01V

Abstract:
A method for determining a parameter of interest of a volume of earth formation with a borehole tool conveyed in a borehole within the formation, the method comprising:(a) using a magnet assembly on the borehole tool for producing a static magnetic field having a substantially uniform field strength in said volume of the formation and 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, said RF magnetic field having a direction substantially orthogonal to a direction of the static field, the RF field including a pulse sequence: Wâˆ’Tâˆ’txâˆ’Râˆ’(tcpâˆ’echoâˆ’tcpâˆ’R)j â€ƒwherein W is a wait period, T is a tipping pulse for tipping the nuclear spins at an angle substantially equal to ninety degrees to cause precession thereof, tS is a waiting time, tCP is the Carr-Purcell time, R is a refocusing pulse for having a spin tip angle less a 180Â° pulse, and j=1, 2, . . . J, and J is the number of echoes collected in a single sequence of pulses; (c) measuring with a receiver coil on the borehole tool magnetic resonance signals induced by the pulsed RF field in the formation, said signals having a higher signal-to-noise ratio than a pulse sequence wherein said refocusing pulse is a 180Â° pulse; and (d) processing said measured signals to determine the parameter of interest.