Nuclear magnetism logging tool using high-temperature superconducting squid detectors

摘要

A logging device is disclosed for measuring the nuclear magnetism response of earth formations. The device employs a detector that is capable of detecting sinusoidal and slowly varying changes in magnetic field caused by precession of mobile nuclei about the earth's magnetic field. Such a detector may be one or more laser-pumped helium magnetometers, or one or more high-temperature Superconducting Quantum Interference Devices (SQUID). The invention uses a micro-miniature Joule- Thomson refrigerator to maintain the high-temperature SQUIDs below their superconducting transition point. The SQUIDs are flux coupled in an axial gradiometer configuration to reduce motion-induced magnetic noise.