TEMPERATURE COMPENSATED MAGNETIC CIRCUIT

摘要

An apparatus is disclosed for generating a magnetic field of high field strength, spatial uniformity and minimal drift of magnetic field intensity over a temperature range of about 0 DEG C to 175 DEG C. This apparatus may be used in a standard modular logging tool for direct downhole NMR measurements of various parameters of fluid samples of geologic formations near the walls of a borehole. In one embodiment, the apparatus is composed of two tubular permanent magnets (62 and 66) made of different magnetic materials with different magnetic temperature coefficients to provide temperature compensation. The apparatus preferably also utilizes a pressure barrel (31) that surrounds the magnets (62 and 66) and provides a return path for magnetic flux lines, thereby increasing flux density within the measurement volume.