METHOD AND APPARATUS FOR WELL LOGGING COMBINING RESISTIVITY BY ELECTROMAGNETIC INDUCTION AND NUCLEAR MAGNETIC RESONANCE

摘要

Instrument to measure the induction resistivity and the nuclear magnetic resonance properties of earth formations crossed by a wellbore. The instrument 10 comprises a magnet 8 for inducing a static magnetic field in the formations, a TX transmitting antenna positioned close to the magnet and having a main magnetic axis substantially perpendicular to the main direction of the magnetic field of the magnet. The instrument includes receiving antennas RX1, RX2 positioned at spaced locations relative to the transmitting antenna, a circuit for generating radio frequency power pulses which is selectively connected to the transmitting antenna, and circuits for measuring the induced voltages both in the transmitting antenna and in the receiving antennas. The measurement circuit is suitable for measuring the voltages in the receiving antennas during radio frequency power pulses, when the voltages are induced in the receiving antennas by electromagnetic induction. The measurement circuit is also suitable for measuring the voltages induced in the transmitting antenna between successive power pulses, when the voltages are induced by nuclear magnetic resonance.