Side-looking NMR probe for oil well logging

摘要

A side-looking NMR logging tool incorporates a permanent magnet arrangement having a magnetization direction oriented towards a side of the tool and a dipole RF antenna displaced towards the front of the tool. The magnet arrangement produces a shaped region of investigation in front of the tool wherein the magnetic field has a uniform field strength and the RF field has a uniform field strength in a direction orthogonal to the static field. The shaping of the static field is accomplished by the magnet arrangement comprising a plurality of magnets having parallel magnetization or by a single shaped magnet. The antenna arrangement includes a gapped core made of non-ferritic soft material for increasing the antenna efficiency. The magnet arrangement also reduces ringing in the core and the antenna. An optional RF shield is used to reduce NMR signals from borehole fluids.