NMR LOGGING IN THE EARTH'S MAGNETIC FIELD

摘要

An apparatus (Figure 1) and a method for measurement of NMR relaxation parameters of earth formation (25) uses a coil (13) on a logging tool (11) t o substantially polarize nuclear spins within a volume of earth (25). The polarizing pulses then switch off adiabatically. The magnetization of the spins then processes around earth's magnetic field (21) at a Larmor frequenc y corresponding to the earth's field (21). A second coil (15) on the logging tool (11) is pulsed with a carrier signal having this frequency and modulate d by CPMG sequence to obtain spin echo signals. The spin echo signals may be received by the same coil (13) or by a second coil (15). Alternatively, beem steering of two coils (13 and 15) on the tool (11) may be carried out to ensure a resultant field that has a significant component transverse to the earth's field (21) for carrying out the spin echo measurements.