Patent ID: 6459262
Filing Date: 2002-10-01
Classification: G01N,G01V

Abstract:
An apparatus for determinating a parameter of interest of a subsurface formation in the vicinity of a borehole comprising:(a) a magnet arrangement on a downhole tool for producing a static magnetic field having a substantially uniform field strength in a region of examination in the formation and aligning nuclear spins in said region parallel to a direction of said static magnetic field in said region; (b) a first coil on the downhole tool for transmitting a pulsed radio frequency (RF) magnetic field into said region of examination, said first coil having windings around a first toroidal core having an axis parallel to said axis of the borehole, said first coil windings lying in a plane perpendicular to said axis of the borehole said first toroidal core intensifying the magnetic flux in the first coil, said pulsed RF field substantially perpendicular to said static field and inducing precession of nuclear spins in said region of examination, said first coil further receiving a first component of echo signals from said precessing nuclear spins and producing a first signal; (c) at least one other coil on the downhole tool for receiving a second component of echo signals from the precessing nuclear spins and producing at least one second signal, said second component orthogonal to the first component, and (d) a processor for combining the first signal and the at least one second signal to determine the parameter of interest.