WELL LOGGING METHOD AND APPARATUS PROVIDING MULTIPLE DEPTH INVESTIGATION USING MULTIPLE TRANSMITTERS AND SINGLE RECEIVER PAIR

摘要

An apparatus and method for determining formation resistivity at a plurality of radial distances from an earth borehole uses a single receiver pair (R1, R2) and a plurality of electromagnetic energy transmitters (16, 18, 20) sequentially spaced along the apparatus from the receiver pair, such transmitters being sequentially pulsed at approximately 1-2 MHz each to provide time separation between the pulsing of the plurality of transmitters. The closest spaced transmitter (16) is spaced a predetermined distance from the closer receiver (R1) to make the depth of investigation of the closest trans- mitter (16) essentially independent of formation resistivity. Alterna- tively, a single transmitter is spaced a predetermined distance from the closer receiver to make the depth of investigation of such trans- mitter essentially independent of formation resistivity.