Patent ID: 6331775
Filing Date: 2001-12-18
Classification: G01N,G01V

Abstract:
A nuclear magnetic resonance method for using a borehole tool in a borehole for determining a plurality of parameters of interest of a volume of earth formation in a reservoir adjacent the borehole, the method comprising:(a) using a magnet assembly on the borehole tool 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 sequenceTW.sub.A -90-(t-X-t-echo).sub.j and a second pulse sequence TW.sub.B -90-(t-X-t-echo).sub.j,wherein 90 is a tipping pulse for tipping the nuclear spins at an angle substantially equal to ninety degrees to cause precession thereof, TW.sub.A is a waiting time, TW.sub.B is a second waiting time different from the first waiting 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 signals inaduced by the pulsed RF field in the formation;(d) obtaining a bulk density measurement of the earth formation at the at least one depth; and(e) using a processor for determining a first apparent porosity TPOR.sub.A and a second apparent porosity TPOR.sub.B associated with the first and second pulse sequences respectively from the induced signals at the at least one depth and determining therefrom and from the obtained bulk density the plurality of parameters of interest;wherein said first and second apparent porosities are different from each other and are determined in part from a polarization of the spins produced by the associated pulse sequence.