LOGGING METHOD AND DEVICE USING NUCLEAR-MAGNETIC RESONANCE Russian patent published in 2002 - IPC

FIELD: geophysical method for investigating wells including-nuclear magnetic logging. SUBSTANCE: method includes generation of static magnetic field in close proximity of well by means of permanent magnet saturated in direction perpendicular to magnet axis; generation of radio-frequency field in above-mentioned region in direction perpendicular to both mentioned axis and static magnetic field; reception of nuclear-magnetic resonance signal. In addition, radio- frequency field compensating field is generated in vicinity of magnet made of conducting rare-earth material. Logging device has long magnet saturated perpendicular to its long axis and radio-frequency coil. Coil turns lie in planes parallel to long axis of magnet and to direction of its magnetization. It also has matching device, radio-frequency pulse generator, and nuclear-magnetic resonance signal receiver; starting lead of radio-frequency coil is connected to first input of matching device whose second input is connected to output of radio-frequency pulse generator. Output of matching device is connected to input of nuclear- magnetic resonance signal receiver. Magnet is made of rare-earth conducting material in the form of long parallelepiped magnetized perpendicular to its wide side surface. Magnet width is at least twice as great as that of its narrow side. Radio-frequency coil is wound on cylinder whose diameter is not smaller than sectional-area diagonal of magnet located inside cylinder. Coil turns lie in planes parallel to longitudinal axis of magnet and perpendicular to its narrow side in symmetrical sectors opposing wide side surface of magnet. Magnet is provided with compensating device which is, essentially, either coil whose starting lead is connected to common point of matching device and finishing lead, to that of radio-frequency coil with turn ratio of both coils being equal to ratio of radio-frequency coil diameter to magnet thickness, or it may be made in the form of short-circuited turn manufactured from high-conductivity material. EFFECT: enhanced sensitivity and increased immersion depth of small-diameter investigating probes. 4 cl, 5 dwg