US 2002/0153887 A1 · NMR logging in the earth's magnetic field

Abstract

An apparatus and a method for measurement of NMR relaxation parameters of earth formations uses a coil on a logging tool to substantially polarize nuclear spins within a volume of earth. The polarizing pulse then switched off adiabatically. The magnetization of the spins then precesses around earth's magnetic field at a Larmor frequency corresponding to the earth's field. A second coil on the logging tool is pulsed with a carrier signal having this frequency and modulated by a CPMG sequence to obtain spin echo signals. The spin echo signals may be received by the same coil or by a second coil. Alternatively, beam steering of two coils on the tool may be carried out to ensure a resultant field that has a significant component transverse to the earth's field for carrying out the spin echo measurements.

Claims30

Dependent claims

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) pulsing a first coil on the borehole tool with a polarizing signal and aligning nuclear spins within said volume substantially parallel to a direction of a magnetic field produced thereby in said volume;
(b) adiabatically discontinuing the polarizing signal and allowing said nuclear spins to reorient towards a direction parallel to a magnetic field of the earth;
(c) pulsing a second coil on the borehole tool with a sequence of pulses for exciting nuclei within said volume;
and
(d) detecting nuclear magnetic resonance spin echo signals from said excited nuclei.
(e) providing in response to said signals an output indicative of said parameter of interest of the volume of earth formation.

3 more elements

Dependencies are inferred from the claim text.

NMR logging in the earth's magnetic field

Life of this patent

NMR logging in the earth's magnetic field

Life of this patent

Abstract

Claims30