AN APPARATUS ACCURATELY MEASURING PROPERTIES OF A FORMATION

摘要

A transverse induction logging tool (9) having a transmitter (18) and receiver (19) for downhole sampling of formation properties, the tool having a symmetrical shielded split-coil transmitter coil (30, 32) and a bucking coil (33) interposed between the split transmitter coils (30, 32) to reduce coupling of the transmitter time varying magnetic field into the receiver (19). The tool provides symmetrical shielding of the coils and grounding at either the transmitter or receiver end only to reduce coupling of induced currents into the received signal. The tool provides an insulator between receiver electronics and the conductive receiver housing having contact with conductive wellbore fluid, to reduce parasitic current flowing in a loop formed by the upper housing, feed through pipe, lower housing and wellbore fluid adjacent the probe housing or mandrel. An internal verification loop is provided to track changes in transmitter current in the real and quadrature component of the received data signal. A galvanic electrode (120) is housed in the same mandrel with the induction logging receiver (19) and transmitter (18).